# The Development of Data Acquisition System of Formula SAE Race Car Based on CAN Bus Communication Interface and Closed-Loop Design of Racing Car

Authors: Zhonghao Li; Da Wang; Qiao Kang
Journal: Wireless Communications and Mobile Computing
 (2021)

---

## Abstract

This paper is mainly based on the college formula race car, through the application of CAN bus communication interface settings, the layout and adjustment of the car sensors, and then carry out the data collection and analysis of the car. CAN bus is the local area network of controller and is one of the field bus which is put forward by German Bosch company and applied most widely in the world. The development of the data analysis system is mainly based on the MoTeC i2 data analysis software. MoTeC i2 data analysis software has been developed for many years under the continuous research of professional teams all over the world. According to the data analysis requirement of FSAE undergraduate Formula 1 teams, this paper introduces a series of data analysis methods closely related to FSAE, mainly including data channel research. This paper expounds the reliability, suspension, tire temperature, steering, and braking data analysis, respectively. Based on the data analysis template created by Motec i2, this paper conducts analysis and basic application according to the data of the real car, so as to meet the requirements of verifying design made by simulation model and tuning the real car scientifically. By means of wheel speed sensor, acceleration sensor, displacement sensor, multichannel temperature sensor, and so on, we conduct a series of tests on 2020 season car, including endurance test, linear acceleration experiment, steady rotation, etc., evaluate the data collected, and then carry on a reasonable set-up of racing, ultimately improving lap speed.


---

## Body

## 1. Introduction

Formula SAE (FSAE) was first proposed by an American factory in 1978. This race is held for college students to collect small formula cars with creative design and scientific ideas. These cars are stable and durable in all aspects of performance. Compared with foreign countries, our domestic college student formula racing started late. The first Formula Student China (FSC) competition was held at the Shanghai International Circuit in 2010. Formula Student of China (“China FSC”) is a car design and manufacturing competition organized by students majoring in automotive engineering or automotive related in universities. Each participating team in accordance with the rules of the race and racing car manufacturing standards, in one year’s time to design and manufacture a small single-seat recreational racing car in the acceleration, braking, handling, and other aspects of excellent performance, can successfully complete all or part of the race links. China FSC is committed to building a public platform for the training and selection of outstanding domestic automotive talents, and through general assessments to improve students’ comprehensive capabilities in five aspects, including design, manufacturing, cost control, commercial marketing, communication, and coordination. In order to improve the comprehensive quality of automotive students, make long-term talent accumulation for the development of China’s automotive industry, and promote the strategic direction of China’s automotive industry from a “manufacturing country” to an “industrial power” [1]. Gspeed Electric Racing Team of Jilin University has participated in the FSC series for 5 consecutive years. In 2019, it went to Japan to participate in the Formula Student Japan and won the second prize of design project many times. In 2018, it won the first prize of the FSC. GspeedE-2019 and GspeedE-2020 race cars are shown in Figures 1 and 2, respectively. When we design a racing car, we often fail to make a reasonable design for some parameters of each system, and the rough design fails to support and prove the completed design with data. Therefore, we installed a data acquisition system on our race car, that is, the sensors we need and the wiring harnesses which connect them to a low-voltage electrical system and panel. Then, we used MoTec i2 to deal with the data we collected. Due to the large proportion of engineering design events and dynamic events in Formula Student [2], data analysis of race cars, which plays an important role in verifying design, guiding tuning, and further contributing to future design, do show its important value. Therefore, we do research on analysis methods of race cars and put it into practice by using MoTec i2 templates and math channels, which quickly analyze the large amount of data generated by each test. In this way, we obtain the direction of tuning and improve the performance of our car.Figure 1
GspeedE-2019 racecar.Figure 2
GspeedE-2020 racecar.At the same time, the data acquisition and analysis system of the whole car is a feedback system for driver training and making suggestions for tuning [3]. Through scientific road test and data analysis, the whole process can form a closed-loop design. In addition, the driving habits and styles of different drivers can be summed up by recording and analyzing the same project they conduct. In this way, different car set-up methods can be matched for different drivers. Figure 3 shows the flow chart of data collection and analysis of the race car.Figure 3
Flow chart of data collection and analysis for racing car.The sensor interface setup and connection of the vehicle are based on CAN bus communication protocol, among which, the car has three CAN communication networks:(1)
Motor control network, connecting the vehicle controller with the motor controller, to realize the function of sending the torque instruction of the drive system and obtaining the working state of the motor of the drive system(2)
The conventional information communication network realizes the information transmission between the vehicle controller and the battery management system, instrument panel, sensors, and other equipment(3)
In order to charge the communication network, the experimental information transmission between the battery management system and the chargerUsing the MoTeC C125 racing digital instrument, ECU uses CAN-B to collect and record training data for improved vehicle performance.Figure4 shows the CAN bus network of the whole vehicle.Figure 4
Vehicle CAN network.


## 2. Reliability Data Analysis

As we know, one of the most important functions of the data acquisition system is to find the potential faults of race car by monitoring the reliability data, which determines whether the car can run normally or not. So we should make obtaining and checking reliability data a top priority. Once anything abnormal is found, stop the car immediately and troubleshoot the fault. For Formula E racing, the important reliability data consist of high voltage battery voltage, high voltage battery temperature, motor output power, low voltage battery voltage, etc. Second, there are some reliability indicators, such as tire pressure, and brake pressure. Figure5 is the reliability data template.Figure 5
Reliability data template.To check the reliability data, the first step is to observe the maximum and average values of each channel, and the second step is to examine its changing trend. The observation of maximum value can determine whether the data is within safe range, while the observation of variation trend can determine whether the car is running normally during the whole process and can predict the state of the car when running continuously. Especially in endurance test, the data of battery temperature and power usually change linearly.In order to know the condition of reliability parameters during each run, we set up an alarm mechanism on the car instrument panel. In the endurance race, it is one of the key factors to detect abnormal reliability parameters in advance and make a right decision.Similarly, an alarm mechanism can be set in the data analysis software to find out the problematic channel data in the first time.If the voltage provided by the power battery is found to be too low, it is considered that the power supply system of the battery box body has poor contact and the battery module bolts have loosened. At this time, the battery box should be inspected and the battery management system (BMS) should be used for fault detection.


## 3. Suspension System Data Analysis

The suspension system of this season’s Gspeed formula E racing car is an independent suspension of unequal length, with a third spring system and a T-shaped anti-roll bar.This part includes the calculation of roll gradient and roll stiffness, load transfer, and the analysis of shock absorber.The purpose of suspension data analysis is to verify the design and guide the adjustment through the compilation and processing of the data. Detailed tuning projects consist of tire pressure, shock absorber gear, antiroll bar stiffness, load distribution of front and rear tires, adjusting four-wheel positioning parameters, and carrying out the corresponding fault troubleshooting.


### 3.1. Roll Gradient (RG) Analysis

In vehicle dynamics, roll gradient refers to the roll angle of a vehicle per unit lateral acceleration.Equation (1) is the definition formula of roll gradient RG.
(1)RG=αrollGlat.In the above formula,αroll is roll angle (deg); Glat is lateral acceleration (g).Therefore, in order to calculate the roll gradient, the first parameter we need to get is the roll angle. The following is the mathematical channel formula of the front and rear suspension roll angleαF andαR and the total suspension roll angle α. In order to get the roll angle of the vehicle, the left and right suspension displacements should be calculated, and the trigonometric function formula should be used to solve the problem. Table 1 shows the vehicle parameters required by formulas (2)–(4).
(2)αF=ArcTanxSuspLF−xSuspRFMRFTF·180π,(3)αR=ArcTanxSuspLR−xSuspRRMRRTR·180π,(4)α=ArcTanxSuspLF−xSuspRFMRF+xSuspLR−xSuspRRMRRTF+TR·180π.Table 1
Parameters in formulas (2)–(4).
ParameterDescriptionxSuspLFLeft front suspension displacementxSuspRFRight front suspension displacementxSuspLRLeft rear suspension displacementxSuspRRRight rear suspension displacementMRFFront suspension motion ratioMRRRear suspension motion ratioTFFront track widthTRRear track widthAmong these parameters, suspension displacement is what we should detect. It can be obtained by measuring the displacement of the shock absorber with the traditional linear displacement sensor. And when the suspension arrangement style is not suitable for using displacement sensor (for instance, a decoupling suspension with single spring mounted between two rockarms), we can use angular displacement sensor to get suspension displacement indirectly by measuring rockarm rotation angle. The angle and the suspension displacement usually have high linearity, whose linear coefficient can be fitted by means of parallel wheel jump simulation in Adams-Car [2]. After this work, what we need to do is to set up math channel in MoTec i2. Figure 6 shows the template of suspension system roll angle data.Figure 6
Template of suspension system roll angle data.It should be noted that the roll angle calculated from the suspension displacement is only the roll angle caused by the lateral transfer of sprung mass, that is, the suspension roll angle. Therefore, the following calculation is also the roll gradient of the suspension system using the roll angle of the suspension.Then, we create a scatter graph with the vertical axis as roll angle and the horizontal axis as lateral acceleration and obtain the trend line equation, whose slope is the roll gradient of the suspension system. Figure7 is the roll gradient diagram of GspeedE-2019 in a test. From the equations in the lower left corner of each template in the figure, it can be seen that the roll gradients of front suspension, rear suspension, and total suspension are 0.552°/G, 0.557°/G, and 0.555°/G, respectively.Figure 7
Roll gradient data template.


### 3.2. Roll Stiffness

The roll stiffness of suspension refers to the total elastic recovery couple moment given by the suspension system to the carriage under the unit carriage rotation angle when the vehicle rolls (the wheels remain on the ground). The roll stiffness of the suspension will affect the lateral load transfer of the car during steering and then affect the wheel load of the inside and outside wheels as well as the front and rear wheels. The difference of wheel load will lead to the difference of the slip angle of the tires and then affect the steering characteristics [4]. According to the above roll gradient analyzed by MoTec i2 software and the vehicle parameters provided in Table 2, the roll stiffness of the suspension system and its components can be further calculated. Among them, the collection and analysis result of the roll gradient is RGF=0.552°/GRGR=0.557°/G RG=0.555°/G .Table 2
Basic parameters of racing car.
ParameterDescriptionValue : frontRearTotalWTTotal mass (kg)134.2170.8305WUUnsprung mass (kg)212344WSSprung mass (kg)113.2147.8261hHeight of mass center (m)0.28ZHeight of roll center (m)0.030.04RTire load radius (m)0.2350.235TTrack width (m)1.2661.241LWheel base (m)1.575aSSprung mass distribution on the front suspension (%)45We can obtain the following parameters by taking the torque on the ground:Height of sprung mass centerhS:
(5)hS=WTh−WUFRF−WURRRWS.Roll moment lever armhRM:
(6)hRM≅hS−ZF+ZR−ZF1−aS=0.252m.Roll moment per lateral accelerationMϕ:
(7)Mϕ=WShRM.Then, the total suspension roll stiffnessKϕ is
(8)Kϕ=MϕRG=1161.379N·m/∘.According to the distribution of front and rear roll stiffness, the front and rear suspension roll stiffnessKϕF and KϕR can be calculated as follows:
(9)KϕF=Kϕ·RGRRGF+RGR=583.308N⋅m/∘,(10)KϕR=Kϕ−KϕF=578.072N⋅m/∘.Because in many cases, the roll stiffness provided by the spring cannot meet the requirement, so the antiroll bar mechanism is added. Therefore, suspension roll stiffness is the sum of the roll stiffness provided by spring and antiroll bar. Table3 shows the vehicle parameters required by formulas (11) and (12).
(11)KϕF=KSpringF+KARBF,(12)KϕR=KSpringR+KARBR.Table 3
Parameters in formulas (11) and (12).
ParameterDescriptionKSpringFRoll rate of the front springKSpringRRoll rate of the rear springKARBFRoll rate of the front antiroll barKARBRRoll rate of the rear antiroll barIn the above formula,KSpringF (N·m/∘) is the roll rate of the front spring; KSpringR (N·m/∘) is the roll rate of the rear spring; KARBF (N·m/∘) is the roll rate of the front antiroll bar; KARBR(N·m/∘) is the roll rate of the rear antiroll bar.After calculating the roll stiffness of the spring through the known number of spring pounds, the roll stiffness of the antiroll bar can be further calculated [5].By comparing the roll gradient and roll stiffness with the design objective, the gap between the actual race car and the simulation design can be obtained. If there is a large error, it is necessary to examine the specific cause of the error (for example, processing or assembly problem of parts) and solve it in time. In the test and tuning of real vehicle, after the ideal tuning strategy is obtained, the corresponding roll gradient can be used as the reference aim of the next season.


### 3.3. Dynamic Vertical Load of Tires

The vertical load directly affects the grip performance of the tire, while the load distribution between front and rear affects the steering characteristics of the car. In addition, the amount of tire load transfer can also affect the aerodynamic performance of the car. Therefore, knowing the tire dynamic vertical load is beneficial to evaluating the balance of a racing car, as well as the choice of tire pressure and analysis of tire surface temperature. By optimizing the four-wheel positioning parameters and other tuning methods, the tire load transfer of the racing car can be reduced and balanced as far as possible, and the ultimate performance of race car can be further improved.In order to calculate the dynamic vertical load of each wheel, it is necessary to understand the various parameters and influencing factors involved. And Figure8 shows each component of wheel load.Figure 8
Each component of wheel load.The vertical load on each wheel is the sum of the components listed above. The detailed analysis and calculation are as follows.


#### 3.3.1. Static Wheel Load

We can measure the static load of each wheel when the car is in the ready state (that is, the car with fully equipped driver). Figure9 shows static wheel load measured by loadometer.Figure 9
Static wheel load measurement.


#### 3.3.2. Lateral Load Transfer

We can measure the force of the suspension push rod through the pull pressure sensor, and then we can get the curve of tire load change with time. After that, by using the mechanical formula to calculate the other force elements of the suspension system, we can get the value of the downward pressure produced by the aerodynamic package on the race car, which is conducive to the design of the aerodynamic package on the racing car. Figure10 shows the data collected by the pressure sensor.
(i)
Lateral load transfer of the unsprung massΔWu(13)ΔWuF=WuF·Glat·RFTF,(14)ΔWuR=WuR·Glat·RRTR.Figure 10
Data acquisition by pressure sensor.It should be noted that in the early design, we used the tire load radius as an approximate value of unsprung mass center height. After the design work is completed, the height of wheel carrier mass center can be calculated in the 3D modeling software, which can be used as a more accurate value of unsprung mass center height.(ii)
Lateral geometric load transferΔWg(15)ΔWgF=WsF·Glat·ZF·S/LTF,(16)ΔWgR=WsR·Glat·ZR·1−S/LTR.In the above formula,S is the distance (m) from the geometric center of rear axle to the sprung mass center in the side view. The calculation formula is as follows:
(17)S=L·WSFWS.It should be noted that the unsprung mass and the geometric load transfer cannot be measured by pull pressure sensor and displacement sensor. Except lateral acceleration, other parameters are in Table1, considered as theoretical value.
(iii)
Lateral load transfer of the sprung massΔWs(18)ΔWsF=Ws·Glat·hRMTF·q,(19)ΔWsR=Ws·Glat·hRMTR·1−q.The definition ofq is
(20)q=K∅FK∅F+K∅R=RGRRGF+RGR.From the above equations, we can see the importance of calculating roll gradient. The roll gradient can not only be used to further calculate the roll stiffness, verify whether the real car reaches the preliminary design expectation, and guide the adjustment of spring pounds and antiroll bar stiffness but also reflect the proportion of the lateral sprung mass transfer on front and rear suspension compared with total amount and then calculate respective values.


#### 3.3.3. Total Longitudinal Load TransferΔWLong

(21)ΔWLong=W·GLong·hL.To sum up, we can find that a large part of the calculation of load transfer is to calculate the value of mechanical concepts such as the mass center height, the roll center height, and the roll moment lever arm, while the lateral and longitudinal accelerations are obtained by the digital acquisition equipment.


#### 3.3.4. Influence of Track Slope

Since FSAE racing venues are usually well paved, this effect is ignored here. For example, the 2020 season was held at the Da’an Automotive Testing Center in Xiangyang, Hubei Province, which is authorized by the National Automobile Testing Ground. As a result, road conditions can be guaranteed.


#### 3.3.5. Aerodynamic Effect

The aerodynamic effect on car can be measured with relevant sensors. When all components are known, the total vertical load on each wheel can be calculated. Figure11 is the dynamic load data of the tire in a skidpad track event (the skidpad track consists of two pairs of concentric circles in a figure of eight pattern) [3].Figure 11
Tire dynamic load template.According to the average value in the upper right corner of the tire load graph above, the load transfer in the skidpad test is distributed as the front 48% and the rear 52%. Theoretically, neutral steering occurs when the distribution of load transfer is equal to the distribution of axle load [1]. Since the axle load distribution of the real car is the front 45% and the rear 55%, it can be concluded that the steering characteristics of the car are very close to the neutral steering.According to the tire dynamic load, we can also choose more appropriate tire pressure according to the tire file provided by manufacturer. In FSAE, the straight line acceleration, skidpad event, and autocross event are performed in cold tire conditions [3], so in these events, the tire pressure can be directly selected according to the tire load that required lateral and longitudinal acceleration determine, without extra consideration of the tire temperature influence. The collection and calculation processes of tire load are shown in Figure 12.Figure 12
Tire load collection and calculation process.


### 3.4. Damper Analysis Study

For the data acquisition and analysis system, the analysis of the shock absorber is mainly to analyze its velocity through the displacement sensor. Equation (22) is the relation between the damper force and its velocity.
(22)Fdam=C·vdam.In the above formula,Fdam is the force generated by shock absorber, C is the damper coefficient, and vdam is the velocity of the shock absorber.To get the velocity, we can take derivative of the shock absorber displacement signal.(23)vdam=ddtsdam.And Figure13 shows the displacement and velocity data acquisition diagram of shock absorber.Figure 13
Displacement and velocity data acquisition diagram of shock absorber.In part 2.1 we have discussed, the shock absorber can be measured by linear displacement sensor directly or calculated through rockarm rotation angle.The velocity interval of the shock absorber is mainly divided into three parts:(i)
The First Interval (<5 mm/s). The velocity in this area is mainly caused by friction in the suspension system(ii)
The Second Interval (5-25 mm/s) (Low-Speed Damping Interval). This area is the main area where the shock absorber responds to chassis motion of the car and is also an important area for driver to perceive the car(iii)
The Third Interval (25-200 mm/s) (High Speed Damping Interval). The velocity of shock absorber in this area is mainly caused by road excitation. The impact of road shoulder usually allows the velocity to exceed 200 mm/sIn order to make the time ratio of shock absorber velocity in each interval more intuitive, damping velocity histogram, an important tool for damper analysis and adjustment, is presented here. The damping velocity histogram is a graph that describes the time proportion of damping in each velocity interval [6]. By observing the shape of the histogram, we can roughly analyze the “soft” and “hard” of the suspension. The establishment method of this histogram template is as follows: create a new workbench in MoTec i2, select the histogram template, and choose the time and proportion in horizontal and vertical coordinates, respectively. Finally, add the digital channel of the linear displacement sensor of the shock absorber, import the data, and then generate the template [7]. Figure 14 shows the damping velocity histogram of the car after an endurance test.Figure 14
Damping velocity histogram data acquisition graph.In order to improve the tire grip performance and maintain a certain contact between tire and ground, the damping adjustment should make the histogram conform to the normal distribution as far as possible, and the histogram shape of the four wheels should be consistent with each other, as well as the difference between peak values should be as small as possible [2].


## 3.1. Roll Gradient (RG) Analysis

In vehicle dynamics, roll gradient refers to the roll angle of a vehicle per unit lateral acceleration.Equation (1) is the definition formula of roll gradient RG.
(1)RG=αrollGlat.In the above formula,αroll is roll angle (deg); Glat is lateral acceleration (g).Therefore, in order to calculate the roll gradient, the first parameter we need to get is the roll angle. The following is the mathematical channel formula of the front and rear suspension roll angleαF andαR and the total suspension roll angle α. In order to get the roll angle of the vehicle, the left and right suspension displacements should be calculated, and the trigonometric function formula should be used to solve the problem. Table 1 shows the vehicle parameters required by formulas (2)–(4).
(2)αF=ArcTanxSuspLF−xSuspRFMRFTF·180π,(3)αR=ArcTanxSuspLR−xSuspRRMRRTR·180π,(4)α=ArcTanxSuspLF−xSuspRFMRF+xSuspLR−xSuspRRMRRTF+TR·180π.Table 1
Parameters in formulas (2)–(4).
ParameterDescriptionxSuspLFLeft front suspension displacementxSuspRFRight front suspension displacementxSuspLRLeft rear suspension displacementxSuspRRRight rear suspension displacementMRFFront suspension motion ratioMRRRear suspension motion ratioTFFront track widthTRRear track widthAmong these parameters, suspension displacement is what we should detect. It can be obtained by measuring the displacement of the shock absorber with the traditional linear displacement sensor. And when the suspension arrangement style is not suitable for using displacement sensor (for instance, a decoupling suspension with single spring mounted between two rockarms), we can use angular displacement sensor to get suspension displacement indirectly by measuring rockarm rotation angle. The angle and the suspension displacement usually have high linearity, whose linear coefficient can be fitted by means of parallel wheel jump simulation in Adams-Car [2]. After this work, what we need to do is to set up math channel in MoTec i2. Figure 6 shows the template of suspension system roll angle data.Figure 6
Template of suspension system roll angle data.It should be noted that the roll angle calculated from the suspension displacement is only the roll angle caused by the lateral transfer of sprung mass, that is, the suspension roll angle. Therefore, the following calculation is also the roll gradient of the suspension system using the roll angle of the suspension.Then, we create a scatter graph with the vertical axis as roll angle and the horizontal axis as lateral acceleration and obtain the trend line equation, whose slope is the roll gradient of the suspension system. Figure7 is the roll gradient diagram of GspeedE-2019 in a test. From the equations in the lower left corner of each template in the figure, it can be seen that the roll gradients of front suspension, rear suspension, and total suspension are 0.552°/G, 0.557°/G, and 0.555°/G, respectively.Figure 7
Roll gradient data template.


## 3.2. Roll Stiffness

The roll stiffness of suspension refers to the total elastic recovery couple moment given by the suspension system to the carriage under the unit carriage rotation angle when the vehicle rolls (the wheels remain on the ground). The roll stiffness of the suspension will affect the lateral load transfer of the car during steering and then affect the wheel load of the inside and outside wheels as well as the front and rear wheels. The difference of wheel load will lead to the difference of the slip angle of the tires and then affect the steering characteristics [4]. According to the above roll gradient analyzed by MoTec i2 software and the vehicle parameters provided in Table 2, the roll stiffness of the suspension system and its components can be further calculated. Among them, the collection and analysis result of the roll gradient is RGF=0.552°/GRGR=0.557°/G RG=0.555°/G .Table 2
Basic parameters of racing car.
ParameterDescriptionValue : frontRearTotalWTTotal mass (kg)134.2170.8305WUUnsprung mass (kg)212344WSSprung mass (kg)113.2147.8261hHeight of mass center (m)0.28ZHeight of roll center (m)0.030.04RTire load radius (m)0.2350.235TTrack width (m)1.2661.241LWheel base (m)1.575aSSprung mass distribution on the front suspension (%)45We can obtain the following parameters by taking the torque on the ground:Height of sprung mass centerhS:
(5)hS=WTh−WUFRF−WURRRWS.Roll moment lever armhRM:
(6)hRM≅hS−ZF+ZR−ZF1−aS=0.252m.Roll moment per lateral accelerationMϕ:
(7)Mϕ=WShRM.Then, the total suspension roll stiffnessKϕ is
(8)Kϕ=MϕRG=1161.379N·m/∘.According to the distribution of front and rear roll stiffness, the front and rear suspension roll stiffnessKϕF and KϕR can be calculated as follows:
(9)KϕF=Kϕ·RGRRGF+RGR=583.308N⋅m/∘,(10)KϕR=Kϕ−KϕF=578.072N⋅m/∘.Because in many cases, the roll stiffness provided by the spring cannot meet the requirement, so the antiroll bar mechanism is added. Therefore, suspension roll stiffness is the sum of the roll stiffness provided by spring and antiroll bar. Table3 shows the vehicle parameters required by formulas (11) and (12).
(11)KϕF=KSpringF+KARBF,(12)KϕR=KSpringR+KARBR.Table 3
Parameters in formulas (11) and (12).
ParameterDescriptionKSpringFRoll rate of the front springKSpringRRoll rate of the rear springKARBFRoll rate of the front antiroll barKARBRRoll rate of the rear antiroll barIn the above formula,KSpringF (N·m/∘) is the roll rate of the front spring; KSpringR (N·m/∘) is the roll rate of the rear spring; KARBF (N·m/∘) is the roll rate of the front antiroll bar; KARBR(N·m/∘) is the roll rate of the rear antiroll bar.After calculating the roll stiffness of the spring through the known number of spring pounds, the roll stiffness of the antiroll bar can be further calculated [5].By comparing the roll gradient and roll stiffness with the design objective, the gap between the actual race car and the simulation design can be obtained. If there is a large error, it is necessary to examine the specific cause of the error (for example, processing or assembly problem of parts) and solve it in time. In the test and tuning of real vehicle, after the ideal tuning strategy is obtained, the corresponding roll gradient can be used as the reference aim of the next season.


## 3.3. Dynamic Vertical Load of Tires

The vertical load directly affects the grip performance of the tire, while the load distribution between front and rear affects the steering characteristics of the car. In addition, the amount of tire load transfer can also affect the aerodynamic performance of the car. Therefore, knowing the tire dynamic vertical load is beneficial to evaluating the balance of a racing car, as well as the choice of tire pressure and analysis of tire surface temperature. By optimizing the four-wheel positioning parameters and other tuning methods, the tire load transfer of the racing car can be reduced and balanced as far as possible, and the ultimate performance of race car can be further improved.In order to calculate the dynamic vertical load of each wheel, it is necessary to understand the various parameters and influencing factors involved. And Figure8 shows each component of wheel load.Figure 8
Each component of wheel load.The vertical load on each wheel is the sum of the components listed above. The detailed analysis and calculation are as follows.


### 3.3.1. Static Wheel Load

We can measure the static load of each wheel when the car is in the ready state (that is, the car with fully equipped driver). Figure9 shows static wheel load measured by loadometer.Figure 9
Static wheel load measurement.


### 3.3.2. Lateral Load Transfer

We can measure the force of the suspension push rod through the pull pressure sensor, and then we can get the curve of tire load change with time. After that, by using the mechanical formula to calculate the other force elements of the suspension system, we can get the value of the downward pressure produced by the aerodynamic package on the race car, which is conducive to the design of the aerodynamic package on the racing car. Figure10 shows the data collected by the pressure sensor.
(i)
Lateral load transfer of the unsprung massΔWu(13)ΔWuF=WuF·Glat·RFTF,(14)ΔWuR=WuR·Glat·RRTR.Figure 10
Data acquisition by pressure sensor.It should be noted that in the early design, we used the tire load radius as an approximate value of unsprung mass center height. After the design work is completed, the height of wheel carrier mass center can be calculated in the 3D modeling software, which can be used as a more accurate value of unsprung mass center height.(ii)
Lateral geometric load transferΔWg(15)ΔWgF=WsF·Glat·ZF·S/LTF,(16)ΔWgR=WsR·Glat·ZR·1−S/LTR.In the above formula,S is the distance (m) from the geometric center of rear axle to the sprung mass center in the side view. The calculation formula is as follows:
(17)S=L·WSFWS.It should be noted that the unsprung mass and the geometric load transfer cannot be measured by pull pressure sensor and displacement sensor. Except lateral acceleration, other parameters are in Table1, considered as theoretical value.
(iii)
Lateral load transfer of the sprung massΔWs(18)ΔWsF=Ws·Glat·hRMTF·q,(19)ΔWsR=Ws·Glat·hRMTR·1−q.The definition ofq is
(20)q=K∅FK∅F+K∅R=RGRRGF+RGR.From the above equations, we can see the importance of calculating roll gradient. The roll gradient can not only be used to further calculate the roll stiffness, verify whether the real car reaches the preliminary design expectation, and guide the adjustment of spring pounds and antiroll bar stiffness but also reflect the proportion of the lateral sprung mass transfer on front and rear suspension compared with total amount and then calculate respective values.


### 3.3.3. Total Longitudinal Load TransferΔWLong

(21)ΔWLong=W·GLong·hL.To sum up, we can find that a large part of the calculation of load transfer is to calculate the value of mechanical concepts such as the mass center height, the roll center height, and the roll moment lever arm, while the lateral and longitudinal accelerations are obtained by the digital acquisition equipment.


### 3.3.4. Influence of Track Slope

Since FSAE racing venues are usually well paved, this effect is ignored here. For example, the 2020 season was held at the Da’an Automotive Testing Center in Xiangyang, Hubei Province, which is authorized by the National Automobile Testing Ground. As a result, road conditions can be guaranteed.


### 3.3.5. Aerodynamic Effect

The aerodynamic effect on car can be measured with relevant sensors. When all components are known, the total vertical load on each wheel can be calculated. Figure11 is the dynamic load data of the tire in a skidpad track event (the skidpad track consists of two pairs of concentric circles in a figure of eight pattern) [3].Figure 11
Tire dynamic load template.According to the average value in the upper right corner of the tire load graph above, the load transfer in the skidpad test is distributed as the front 48% and the rear 52%. Theoretically, neutral steering occurs when the distribution of load transfer is equal to the distribution of axle load [1]. Since the axle load distribution of the real car is the front 45% and the rear 55%, it can be concluded that the steering characteristics of the car are very close to the neutral steering.According to the tire dynamic load, we can also choose more appropriate tire pressure according to the tire file provided by manufacturer. In FSAE, the straight line acceleration, skidpad event, and autocross event are performed in cold tire conditions [3], so in these events, the tire pressure can be directly selected according to the tire load that required lateral and longitudinal acceleration determine, without extra consideration of the tire temperature influence. The collection and calculation processes of tire load are shown in Figure 12.Figure 12
Tire load collection and calculation process.


## 3.3.1. Static Wheel Load

We can measure the static load of each wheel when the car is in the ready state (that is, the car with fully equipped driver). Figure9 shows static wheel load measured by loadometer.Figure 9
Static wheel load measurement.


## 3.3.2. Lateral Load Transfer

We can measure the force of the suspension push rod through the pull pressure sensor, and then we can get the curve of tire load change with time. After that, by using the mechanical formula to calculate the other force elements of the suspension system, we can get the value of the downward pressure produced by the aerodynamic package on the race car, which is conducive to the design of the aerodynamic package on the racing car. Figure10 shows the data collected by the pressure sensor.
(i)
Lateral load transfer of the unsprung massΔWu(13)ΔWuF=WuF·Glat·RFTF,(14)ΔWuR=WuR·Glat·RRTR.Figure 10
Data acquisition by pressure sensor.It should be noted that in the early design, we used the tire load radius as an approximate value of unsprung mass center height. After the design work is completed, the height of wheel carrier mass center can be calculated in the 3D modeling software, which can be used as a more accurate value of unsprung mass center height.(ii)
Lateral geometric load transferΔWg(15)ΔWgF=WsF·Glat·ZF·S/LTF,(16)ΔWgR=WsR·Glat·ZR·1−S/LTR.In the above formula,S is the distance (m) from the geometric center of rear axle to the sprung mass center in the side view. The calculation formula is as follows:
(17)S=L·WSFWS.It should be noted that the unsprung mass and the geometric load transfer cannot be measured by pull pressure sensor and displacement sensor. Except lateral acceleration, other parameters are in Table1, considered as theoretical value.
(iii)
Lateral load transfer of the sprung massΔWs(18)ΔWsF=Ws·Glat·hRMTF·q,(19)ΔWsR=Ws·Glat·hRMTR·1−q.The definition ofq is
(20)q=K∅FK∅F+K∅R=RGRRGF+RGR.From the above equations, we can see the importance of calculating roll gradient. The roll gradient can not only be used to further calculate the roll stiffness, verify whether the real car reaches the preliminary design expectation, and guide the adjustment of spring pounds and antiroll bar stiffness but also reflect the proportion of the lateral sprung mass transfer on front and rear suspension compared with total amount and then calculate respective values.


## 3.3.3. Total Longitudinal Load TransferΔWLong

(21)ΔWLong=W·GLong·hL.To sum up, we can find that a large part of the calculation of load transfer is to calculate the value of mechanical concepts such as the mass center height, the roll center height, and the roll moment lever arm, while the lateral and longitudinal accelerations are obtained by the digital acquisition equipment.


## 3.3.4. Influence of Track Slope

Since FSAE racing venues are usually well paved, this effect is ignored here. For example, the 2020 season was held at the Da’an Automotive Testing Center in Xiangyang, Hubei Province, which is authorized by the National Automobile Testing Ground. As a result, road conditions can be guaranteed.


## 3.3.5. Aerodynamic Effect

The aerodynamic effect on car can be measured with relevant sensors. When all components are known, the total vertical load on each wheel can be calculated. Figure11 is the dynamic load data of the tire in a skidpad track event (the skidpad track consists of two pairs of concentric circles in a figure of eight pattern) [3].Figure 11
Tire dynamic load template.According to the average value in the upper right corner of the tire load graph above, the load transfer in the skidpad test is distributed as the front 48% and the rear 52%. Theoretically, neutral steering occurs when the distribution of load transfer is equal to the distribution of axle load [1]. Since the axle load distribution of the real car is the front 45% and the rear 55%, it can be concluded that the steering characteristics of the car are very close to the neutral steering.According to the tire dynamic load, we can also choose more appropriate tire pressure according to the tire file provided by manufacturer. In FSAE, the straight line acceleration, skidpad event, and autocross event are performed in cold tire conditions [3], so in these events, the tire pressure can be directly selected according to the tire load that required lateral and longitudinal acceleration determine, without extra consideration of the tire temperature influence. The collection and calculation processes of tire load are shown in Figure 12.Figure 12
Tire load collection and calculation process.


## 3.4. Damper Analysis Study

For the data acquisition and analysis system, the analysis of the shock absorber is mainly to analyze its velocity through the displacement sensor. Equation (22) is the relation between the damper force and its velocity.
(22)Fdam=C·vdam.In the above formula,Fdam is the force generated by shock absorber, C is the damper coefficient, and vdam is the velocity of the shock absorber.To get the velocity, we can take derivative of the shock absorber displacement signal.(23)vdam=ddtsdam.And Figure13 shows the displacement and velocity data acquisition diagram of shock absorber.Figure 13
Displacement and velocity data acquisition diagram of shock absorber.In part 2.1 we have discussed, the shock absorber can be measured by linear displacement sensor directly or calculated through rockarm rotation angle.The velocity interval of the shock absorber is mainly divided into three parts:(i)
The First Interval (<5 mm/s). The velocity in this area is mainly caused by friction in the suspension system(ii)
The Second Interval (5-25 mm/s) (Low-Speed Damping Interval). This area is the main area where the shock absorber responds to chassis motion of the car and is also an important area for driver to perceive the car(iii)
The Third Interval (25-200 mm/s) (High Speed Damping Interval). The velocity of shock absorber in this area is mainly caused by road excitation. The impact of road shoulder usually allows the velocity to exceed 200 mm/sIn order to make the time ratio of shock absorber velocity in each interval more intuitive, damping velocity histogram, an important tool for damper analysis and adjustment, is presented here. The damping velocity histogram is a graph that describes the time proportion of damping in each velocity interval [6]. By observing the shape of the histogram, we can roughly analyze the “soft” and “hard” of the suspension. The establishment method of this histogram template is as follows: create a new workbench in MoTec i2, select the histogram template, and choose the time and proportion in horizontal and vertical coordinates, respectively. Finally, add the digital channel of the linear displacement sensor of the shock absorber, import the data, and then generate the template [7]. Figure 14 shows the damping velocity histogram of the car after an endurance test.Figure 14
Damping velocity histogram data acquisition graph.In order to improve the tire grip performance and maintain a certain contact between tire and ground, the damping adjustment should make the histogram conform to the normal distribution as far as possible, and the histogram shape of the four wheels should be consistent with each other, as well as the difference between peak values should be as small as possible [2].


## 4. Tire Temperature Analysis

As we know, tire surface temperature is an external indication of how well the tire works during testing. By analyzing the tire surface temperature and considering various factors of suspension kinematics and dynamics, the ideal working temperature range of the tire can be obtained, and the adjustment trend of tire camber can be deduced, as well as the real-time state of tire pressure in the test. By adding a tire temperature sensor, real-time tire temperature distribution and temperature rise data during running can be obtained conveniently, and the relationship between tire temperature and damping ratio can be established to guide the racing car set-up [8].


### 4.1. Evaluate Wheel Camber from Tire Temperature

As the car runs, the camber of wheels determines the position in which the tires are in contact with the ground, and the surface temperature of tires provides the desired position. When the car corners, for the outside wheels, by observing the color contrast diagram of tire temperature distribution, we can conclude that if the temperature distribution is uniform, then the camber angle is appropriate [9]. If the outer temperature of the outside wheel is significantly higher than that of the inner, it means that the camber angle is too small, otherwise, the camber angle is too large. For the inside wheel, if the temperature in the inner or middle of the wheel rises too fast, it means that the camber angle is too large; otherwise, it is too small. Since the outside wheels provide most of the lateral force when cornering, the camber of the outside wheels is of more concern. We can characterize the camber state by the temperature difference between the inside and outside of the tire [10]. Equation (24) is the calculation formula of temperature difference between inside and outside tire surface:
(24)ΔTti=Ttiin−Ttiout.In the above formula,i is LF (left front wheel), RF (right front wheel), LR (left rear wheel), RR (right rear wheel), Ttiin is the temperature of the inside of the tire (°C), and Ttiout is the temperature of the outside of the tire (°C).However, it is not in line with scientific principles to make a final judgment on the data of a few specific corners, so it is necessary to evaluate the data of the whole lap comprehensively [11]. By equipping multichannel tire temperature sensors, we can obtain real-time tire temperature distribution and temperature rise data during running conveniently. Therefore, the proper camber angle can be determined by observing the average tire surface temperature difference throughout the lap [12]. Figure 15 shows the layout of tire temperature sensor on our car.Figure 15
Position of tire temperature sensor.


### 4.2. Examine Tire Pressure from Temperature Analysis

Except evaluating whether the camber angle is appropriate, we also use the tire temperature to analyze the tire pressure when the car is running [13]. Comparing the temperature of the inner and outer part of the tire with the middle, we can find that when the tire pressure is too low, the inner and outer tire temperature will be higher than that of the middle part, while when the tire pressure is too high, the situation will be opposite. Therefore, the tire pressure can be evaluated by the difference between the middle and the average inner and outer tire temperature [14]. This difference is denoted as ΔTpi.
(25)ΔTpi=Ttimid−Ttiin+Ttiout2.In the above formula,Ttimid is the tire middle temperature (° C), Ttiin is the tire inside temperature (° C), and Ttiout is the tire outside temperature (°C). When the result ΔTpi is positive, it indicates that the tire pressure is too high, vice versa. The following figure shows the tire temperature data collected in the first 20 seconds of a linear acceleration event. Through observation, it can be seen that the temperature in the middle part of the tire is higher and the temperature on both sides is lower. It can be preliminarily concluded that the tire pressure is too high and should be lowered. Figure 16 shows the tire temperature data acquisition graph.Figure 16
Tire temperature data acquisition graph.


## 4.1. Evaluate Wheel Camber from Tire Temperature

As the car runs, the camber of wheels determines the position in which the tires are in contact with the ground, and the surface temperature of tires provides the desired position. When the car corners, for the outside wheels, by observing the color contrast diagram of tire temperature distribution, we can conclude that if the temperature distribution is uniform, then the camber angle is appropriate [9]. If the outer temperature of the outside wheel is significantly higher than that of the inner, it means that the camber angle is too small, otherwise, the camber angle is too large. For the inside wheel, if the temperature in the inner or middle of the wheel rises too fast, it means that the camber angle is too large; otherwise, it is too small. Since the outside wheels provide most of the lateral force when cornering, the camber of the outside wheels is of more concern. We can characterize the camber state by the temperature difference between the inside and outside of the tire [10]. Equation (24) is the calculation formula of temperature difference between inside and outside tire surface:
(24)ΔTti=Ttiin−Ttiout.In the above formula,i is LF (left front wheel), RF (right front wheel), LR (left rear wheel), RR (right rear wheel), Ttiin is the temperature of the inside of the tire (°C), and Ttiout is the temperature of the outside of the tire (°C).However, it is not in line with scientific principles to make a final judgment on the data of a few specific corners, so it is necessary to evaluate the data of the whole lap comprehensively [11]. By equipping multichannel tire temperature sensors, we can obtain real-time tire temperature distribution and temperature rise data during running conveniently. Therefore, the proper camber angle can be determined by observing the average tire surface temperature difference throughout the lap [12]. Figure 15 shows the layout of tire temperature sensor on our car.Figure 15
Position of tire temperature sensor.


## 4.2. Examine Tire Pressure from Temperature Analysis

Except evaluating whether the camber angle is appropriate, we also use the tire temperature to analyze the tire pressure when the car is running [13]. Comparing the temperature of the inner and outer part of the tire with the middle, we can find that when the tire pressure is too low, the inner and outer tire temperature will be higher than that of the middle part, while when the tire pressure is too high, the situation will be opposite. Therefore, the tire pressure can be evaluated by the difference between the middle and the average inner and outer tire temperature [14]. This difference is denoted as ΔTpi.
(25)ΔTpi=Ttimid−Ttiin+Ttiout2.In the above formula,Ttimid is the tire middle temperature (° C), Ttiin is the tire inside temperature (° C), and Ttiout is the tire outside temperature (°C). When the result ΔTpi is positive, it indicates that the tire pressure is too high, vice versa. The following figure shows the tire temperature data collected in the first 20 seconds of a linear acceleration event. Through observation, it can be seen that the temperature in the middle part of the tire is higher and the temperature on both sides is lower. It can be preliminarily concluded that the tire pressure is too high and should be lowered. Figure 16 shows the tire temperature data acquisition graph.Figure 16
Tire temperature data acquisition graph.


## 5. Steering System Data Analysis

The design of the steering system is based on Ackerman steering geometry and takes the slip angle of tire into account. In the analysis of steering data, the steering characteristic of the race car is mainly studied. In addition, the steering design of Formula One should not only reduce tire wear and prolong the service life of tires but also have good steering stability [7]. The racing car mostly uses the broken steering trapezoid, the steering torque on the steering wheel from the transmission mechanism to the gear of the steering machine, and then driven by the gear and rack movement. Both ends of the steering rod are, respectively, connected with the steering rack and the steering knuckle arm. Under the action of the pull rod thrust and tension, the steering knuckle arm drives the tire to rotate, so as to achieve steering. A reasonable steering trapezoid structure should make the four steering wheels roll as far as possible without sideslipping, that is, the instant center of the four steering wheels’ speed intersects at the same point. When the rear wheels of the race car do not steer, the steering center of the race car should be on the rear wheel axle line. This steering relationship is the ideal Ackermann turning angle relationship, as shown in Figure 17. For this reason, the concepts of understeer angle and attitude angular velocity are presented in this section to evaluate the steering characteristic of race cars [4]. Figure 18 shows the data acquisition of steering wheel angle and lateral acceleration data scatter diagram [15].Figure 17
Ideal Ackermann angle.Figure 18
Data acquisition of steering wheel angle and lateral acceleration data scatter diagram.


### 5.1. Understeering Angle

According to the definition of steering characteristic in Race Car Vehicle Dynamics [5], when the actual wheel steering angle is equal to Ackerman steering angle, the vehicle will have neutral steering. When the steering angle is larger than Ackerman steering angle, the vehicle understeers. Oversteer on the other hand. Therefore, the difference between the absolute value of the actual wheel steering angle θ and Ackerman steering angle θAck can be defined as the understeering angle θu. The formula is as follows
(26)θu=θ‐θAck,(27)θ=θswi,(28)θAck=L·GlaV2.Table4 shows the vehicle parameters required by formulas (26)–(28).Table 4
Parameters in formulas (26)–(28).
ParameterDescriptionθswActual steering angleiSteering ratioLLateral accelerationGlaRoll rate of the rear antiroll barVVehicle speedAccording to formula (26), the following conclusions can be drawn:
(29)θu<0,oversteer,=0,neutralsteer,>0,understeer.By calculating the understeering angle, we can understand the steering characteristics at various stages of the corner. In order to study the overall steering characteristics of the car, the average understeering angle of the car can be obtained through the steady-state rotation test, and the overall steering characteristic of the car can be evaluated [13]. Figure 19 shows the actual steering angles of the car collected by MoTec i2 analysis.Figure 19
Actual steering angle data acquisition chart.


### 5.2. Attitude Velocity Analysis

In addition to the understeering angle, the vehicle steering characteristics can be characterized by the difference between the absolute value of the actual yaw rate and the theoretical yaw rate, that is, the attitude angular velocity [16]. The following is the definition formula of attitude angular velocity ωa.
(30)ωa=ωyaw−ωt,(31)ω=GlatV.In the above formula,ωyaw is the actual yaw rate of the vehicle (°/s), and ωt is the theoretical yaw rate of the vehicle (°/s). Figure 20 shows the yaw rate data collected.Figure 20
Yaw rate data acquisition graph.Through the analysis, the following conclusions can be drawn:(32)ωa<0,oversteer,=0,neutralsteer,>0,understeer.


## 5.1. Understeering Angle

According to the definition of steering characteristic in Race Car Vehicle Dynamics [5], when the actual wheel steering angle is equal to Ackerman steering angle, the vehicle will have neutral steering. When the steering angle is larger than Ackerman steering angle, the vehicle understeers. Oversteer on the other hand. Therefore, the difference between the absolute value of the actual wheel steering angle θ and Ackerman steering angle θAck can be defined as the understeering angle θu. The formula is as follows
(26)θu=θ‐θAck,(27)θ=θswi,(28)θAck=L·GlaV2.Table4 shows the vehicle parameters required by formulas (26)–(28).Table 4
Parameters in formulas (26)–(28).
ParameterDescriptionθswActual steering angleiSteering ratioLLateral accelerationGlaRoll rate of the rear antiroll barVVehicle speedAccording to formula (26), the following conclusions can be drawn:
(29)θu<0,oversteer,=0,neutralsteer,>0,understeer.By calculating the understeering angle, we can understand the steering characteristics at various stages of the corner. In order to study the overall steering characteristics of the car, the average understeering angle of the car can be obtained through the steady-state rotation test, and the overall steering characteristic of the car can be evaluated [13]. Figure 19 shows the actual steering angles of the car collected by MoTec i2 analysis.Figure 19
Actual steering angle data acquisition chart.


## 5.2. Attitude Velocity Analysis

In addition to the understeering angle, the vehicle steering characteristics can be characterized by the difference between the absolute value of the actual yaw rate and the theoretical yaw rate, that is, the attitude angular velocity [16]. The following is the definition formula of attitude angular velocity ωa.
(30)ωa=ωyaw−ωt,(31)ω=GlatV.In the above formula,ωyaw is the actual yaw rate of the vehicle (°/s), and ωt is the theoretical yaw rate of the vehicle (°/s). Figure 20 shows the yaw rate data collected.Figure 20
Yaw rate data acquisition graph.Through the analysis, the following conclusions can be drawn:(32)ωa<0,oversteer,=0,neutralsteer,>0,understeer.


## 6. Braking System Data Analysis

In race car competition, we know that if you spend less time slowing down, you spend more time accelerating and you can improve your lap speed. As for the braking system, the important analysis data include vehicle speed, wheel speed, longitudinal acceleration, front and rear brake pressure, and front brake ratio.


### 6.1. Braking Force

The real braking force data can be collected through the brake oil pressure sensor, and the maximum longitudinal deceleration obtained in the running test corresponds to the maximum braking force of the car. The maximum braking force is one of the evaluation parameters of car braking performance, and usually, the maximum longitudinal deceleration of the car should be about 95% of the maximum lateral acceleration [5]. Figure 21 shows the braking force data collected in a race car running test, and Figure 22 shows the actual braking force distribution obtained from data collection. We performed a dynamic test on the car. Figure 23 shows the picture taken during the test [17].Figure 21
Braking force data collection in race car running test.Figure 22
Actual braking force distribution obtained from data collection.Figure 23
Race car running test.


### 6.2. Braking Lock

The braking lock can be directly observed through the curve of wheel speed data. When decelerating, the wheel speed will drop in a straight line, when the tire is locked, the wheel speed will drop rapidly; when the driver senses that the tire is locked, he releases the brake slightly, and the wheel speed returns to its original straight line, forming a small trough, as shown in the wheel speed curve in Figure24. The braking lock will cause the tire to lose grip performance, which should be avoided as far as possible.Figure 24
Brake data analysis template.


### 6.3. Braking Pressure Distribution

Braking pressure distribution is the ratio of the front braking pressure to the total braking pressure, and equation (30) is the math channel formula of it:
(33)BF=BrakePFBrakePF+BrakePR·100%.In the equation,BrakePF is the front brake pressure (MPa), BrakePR is the rear brake pressure (MPa). Figure 25 shows the wheel speed data.Figure 25
Wheel speed data.Braking pressure distribution affects the maximum braking force in the pure braking condition and the steering characteristics in the cornering condition with braking. Too much distribution of brake pressure on one axle will result in the corresponding tire lock. In the corner with braking, too much braking pressure to the front axle will lead to understeer, and too much to the rear axle will lead to oversteer. Therefore, according to the track characteristics and driver’s feedback, and combined with data collection, we can improve the performance of our car by tuning braking pressure distribution properly.


### 6.4. Set the ABS

We analyze information obtained by data acquisition, concluding that in the process of race, the braking intensity is usually small and medium-sized. In the traditional brake system design, in order to make the front wheel lock first and achieve stable condition, the traditional design always matches a large synchronous adhesion coefficient to achieve this goal, so that will make the rear wheels have larger attachment loss. The inability to provide greater longitudinal adhesion of rear wheels results in the lack of lateral adhesion of the front wheels, which is very detrimental in the process of cornering and cannot guarantee the speed and stability of the car. Therefore, the ABS system is set to ensure that the front and rear wheels do not lock, lose steering ability, or slip, and at the same time, the braking force distribution of the rear wheels is improved then the speed of cornering is improved. At the beginning of design, we use Simulink and Carsim cosimulation to establish the corresponding model, to judge its feasibility, and whether it can reduce the braking distance. Figure26 shows the ABS/EBD simulation result, and Figure 27 shows the comparison of simulation under open road conditions [18].Figure 26
ABS simulation result.Figure 27
Comparison of simulation under open road conditions (the figure on the left does not include ABS braking, and the figure on the right includes ABS braking).


## 6.1. Braking Force

The real braking force data can be collected through the brake oil pressure sensor, and the maximum longitudinal deceleration obtained in the running test corresponds to the maximum braking force of the car. The maximum braking force is one of the evaluation parameters of car braking performance, and usually, the maximum longitudinal deceleration of the car should be about 95% of the maximum lateral acceleration [5]. Figure 21 shows the braking force data collected in a race car running test, and Figure 22 shows the actual braking force distribution obtained from data collection. We performed a dynamic test on the car. Figure 23 shows the picture taken during the test [17].Figure 21
Braking force data collection in race car running test.Figure 22
Actual braking force distribution obtained from data collection.Figure 23
Race car running test.


## 6.2. Braking Lock

The braking lock can be directly observed through the curve of wheel speed data. When decelerating, the wheel speed will drop in a straight line, when the tire is locked, the wheel speed will drop rapidly; when the driver senses that the tire is locked, he releases the brake slightly, and the wheel speed returns to its original straight line, forming a small trough, as shown in the wheel speed curve in Figure24. The braking lock will cause the tire to lose grip performance, which should be avoided as far as possible.Figure 24
Brake data analysis template.


## 6.3. Braking Pressure Distribution

Braking pressure distribution is the ratio of the front braking pressure to the total braking pressure, and equation (30) is the math channel formula of it:
(33)BF=BrakePFBrakePF+BrakePR·100%.In the equation,BrakePF is the front brake pressure (MPa), BrakePR is the rear brake pressure (MPa). Figure 25 shows the wheel speed data.Figure 25
Wheel speed data.Braking pressure distribution affects the maximum braking force in the pure braking condition and the steering characteristics in the cornering condition with braking. Too much distribution of brake pressure on one axle will result in the corresponding tire lock. In the corner with braking, too much braking pressure to the front axle will lead to understeer, and too much to the rear axle will lead to oversteer. Therefore, according to the track characteristics and driver’s feedback, and combined with data collection, we can improve the performance of our car by tuning braking pressure distribution properly.


## 6.4. Set the ABS

We analyze information obtained by data acquisition, concluding that in the process of race, the braking intensity is usually small and medium-sized. In the traditional brake system design, in order to make the front wheel lock first and achieve stable condition, the traditional design always matches a large synchronous adhesion coefficient to achieve this goal, so that will make the rear wheels have larger attachment loss. The inability to provide greater longitudinal adhesion of rear wheels results in the lack of lateral adhesion of the front wheels, which is very detrimental in the process of cornering and cannot guarantee the speed and stability of the car. Therefore, the ABS system is set to ensure that the front and rear wheels do not lock, lose steering ability, or slip, and at the same time, the braking force distribution of the rear wheels is improved then the speed of cornering is improved. At the beginning of design, we use Simulink and Carsim cosimulation to establish the corresponding model, to judge its feasibility, and whether it can reduce the braking distance. Figure26 shows the ABS/EBD simulation result, and Figure 27 shows the comparison of simulation under open road conditions [18].Figure 26
ABS simulation result.Figure 27
Comparison of simulation under open road conditions (the figure on the left does not include ABS braking, and the figure on the right includes ABS braking).


## 7. Conclusion

This paper introduces the important mathematical channels for FSAE racecar data collection of the five types: reliability, suspension, tire, steering, and braking, as well as the corresponding calculation formula and the analysis template used in data analysis. Based on the MoTec i2 data processing platform, the paper carries out data analysis and post-processing for formula student. In addition, we use CAN bus communication to layout and design the vehicle sensor and wiring harness system.In the sensor fault diagnosis, for CAN bus signal, we use interrupt counter counting method to diagnose the loss of signal frame or signal line disconnection and other faults.As for reliability data, we analyze the safety and reliability of race cars by collecting battery voltage, battery temperature and motor power, so as to troubleshoot potential faults.As for suspension system, we mainly analyzed the data collected by linear displacement sensor and studied the roll gradient, roll stiffness, tire load transfer, and shock absorber, so as to verify our design and tune the suspension to an appropriate state.As for tires, we studied whether the corresponding four-wheel positioning parameters and tire pressure were appropriate and whether the utmost performance of tires could be exerted through the data collected from the multichannel tire temperature sensor.As for the steering system, we obtained steering angle and lateral acceleration scatter diagram and change rate of steering angle and yaw velocity, to judge the steering characteristics of race car and make corresponding adjustments.As for the braking system, we analyzed maximum braking force, braking pressure distribution, and checked wheel speed data to deal with brake lock. Furthermore, we do some research on the ABS/EBD system.Due to our limited knowledge, the data analysis we have done is relatively basic, but for FSAE teams, it has been an effective and systematic approach. We will continue to improve our data analysis method to make it more standardized in the future.



---

*Source: 4211010-2021-08-26.xml*