Abstract:
A miniature universal dynamometer for use in teaching and measuring horsepower of scaled down electronic vehicles and DC generators is provided. The miniature universal dynamometer relates generally to electro-mechanical vehicles that use DC energy and DC generators that produce electrical power. This miniature universal dynamometer relates specifically to vehicles that easily and quickly demonstrate to students and auto workers the design and horsepower used by the electronic vehicles in moving vehicles on various roadways. The device also utilizes a switch which allows the device to measure horsepower required to produce electrical power from a DC generator.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is based on U.S. provisional application No. 61/616,482 filed on Mar. 28, 2012, currently co-pending, the entire contents of which are incorporated by reference. Applicant claims the priority benefit of the 61/616,482 application. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Electric motor/generator dynamometers are a specialized type of adjustable-speed drive or roller used for measuring force, moment of force (torque), or power. For example, the power produced by an engine, motor or other rotating prime mover can be calculated by simultaneously measuring torque and rotational speed (RPM). 
         [0003]    An absorption/driver roller may be driven by, for example, either an alternating current (AC) motor or a direct current (DC) motor. Either an AC motor or a DC motor may operate as a generator which drives the engine being tested. When equipped with appropriate control features, electric motor/generator dynamometers may be configured as universal dynamometers. More specifically, in engine testing, a universal dynamometer may not only absorb and measure the power of the engine, but it may also drive the engine for measuring friction, pumping losses and other factors. 
         [0004]    The present device relates to a miniature dynamometer which may easily and quickly demonstrate to students, auto-builders and others the techniques used in measuring engine forces and horsepower. The present device is especially suitable for testing the force of a miniature car and then scaling the results to determine an approximate force for a full sized vehicle. The present dynamometer utilizes DC motors/generators on each end of a roller upon which car tires rotate to drive the roller. In an alternative embodiment, the universal dynamometer may be aided by the roller motor/generators to simulate up and down hill conditions. The motor/generator bearings of the device may also act as the roller bearings. The revolutions per minute (RPM) and circumference of the roller may then be used to, for example, calculate the actual miles per hour of a miniature car driving on the roller. The car is scaled down to match the miniature size of the present dynamometer. The miles per hour displayed on the meter may then be multiplied up to emulate actual miles per hour of a full-sized car. 
         [0005]    The present universal dynamometer utilizes a beam of light sent to a receiving unit which in turn measures the light intensity of the beam and produces an electrical output proportional to the intensity of the light beam. A rotating roller of the device is designed to block or reflect the beam of light which, in turn, produces a pulse train which may be used to later calculate the RPM of the roller. More specifically, the rotating roller produces pulses at a frequency which is ultimately converted into an actual miles per hour of the miniature car. 
         [0006]    A light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting. Introduced as a practical electronic component in 1962, early LEDs emitted low-intensity red light, but modern versions are available across the visible, ultraviolet and infrared wavelengths, with very high brightness. 
         [0007]    The present miniature universal dynamometer educational tool allows for a safe and fun teaching device for students and industrial engine designers. The device may be used to study engine design and horsepower without the dangers often associated with working with full-sized vehicles and dynamometers. 
         [0008]    There are mechanical products to measure horsepower such as dyno systems which include bike dynes, rolling road dynes (auto, kart, motorcycle or truck), and sled track-dynos. However, these devices are used to measure actual full-sized vehicles. Some teaching aids currently being sold which emulate the complex interactions of forces in the real world by electric motors are large, expensive, and dangerous. Diagrams, videos and teaching aids are also available which explain horsepower measurements in a virtual environment, but these devices typically lack the physical interaction with real variables such as wind resistance, uphill, downhill, and battery drain. To completely understand the complexity of an electric engine powered vehicle, a teaching aid is required which emulates the mixing of road conditions and drain on engine power source. The present device utilizes hardware along with software (virtual) test equipment to allow a student to fully grasp real life engine principles. The students learn by acquiring measurements obtained in the present system and may alter the system to test for various elements, such as, unique environmental and road conditions. 
         [0009]    Attempts have been made to produce an efficient universal dynamometer, as demonstrated in U.S. Pat. No. 6,247,357 to Yamamoto which provides for a “test apparatus in the form of dynamometers which is widely used for testing motor vehicles in place. Since the test vehicles are not moving over a road bed, the dynamometer must simulate certain forces normally associated with actual vehicle operation. These parameters include forces associated with inertia (related to the mass or weight of the vehicle) and road load forces (related to the velocity of the vehicle). The vehicle engine (or its braking system) must overcome inertial forces in order to accelerate or decelerate the vehicle. In addition, the engine must overcome breakaway frictional and rolling frictional forces (i.e., road/tire friction) as well as windage forces (i.e., drag forces caused by air passing over the vehicle). These latter forces are commonly referred to as road load (RL) forces and may be represented by a formula:” 
         [0010]    Attempts have also been made to utilize a USB computer connection to determine force as provided by in U.S. Pat. No. 6,282,469 to Rogers which provides “a multi-point serial link protocol, such as USB, is used to transfer vehicle diagnostic information back and forth between vehicle diagnostic sensors and a host computer. Multiple distinct vehicle servicing applications may be added to or removed from the service bay without requiring substantial software changes or revisions. The amount of vehicle diagnostic hardware is also minimized. The multi-point serial link may originate in the vehicle&#39;s on-board computer, allowing the vehicle itself to function as a data hub for the diagnostic automotive service sensors.” 
         [0011]    Further, U.S. Pat. No. 6,457,351, also to Yamamoto, demonstrates the measuring of the force of electric motor vehicles wherein “a hybrid electric vehicle is placed in a running condition on a chassis dynamometer, a vehicle-end data is acquired by access to sensors in the vehicle, a dynamometer-end data is acquired by measurements at the chassis dynamometer, and the vehicle-end data and the dynamometer-end data are analyzed for inspections of drive and control systems of the vehicle. 
         [0012]    These devices and patents fail to disclose a miniature dynamometer education tool and system which may easily, quickly and safely act as a teaching tool for students, auto-designers and others to learn and test simulated real world forces through the use of miniature or scaled down vehicles. Further, these devices and patents fail to disclose a device and system which has road load forces which may be used to test scaled-down vehicles and which may be used to demonstrate the workings of a fully electric miniature vehicle under various real world conditions. 
       SUMMARY OF THE INVENTION 
       [0013]    A miniature universal dynamometer (MUD) educational tool and system for using the same is provided. The present MUD generally relates to an electro-mechanical systems with mechanical structures which produce electrical signals and switching systems similar to that of an actual full-sized car dynamometer used to measure engine characteristics and horsepower. This MUD relates specifically to structures that easily and quickly demonstrate to students and auto designers the loads and power sources used by an electric vehicle in travel through environmental conditions such as wind and uneven terrain. The device utilizes a beam of light sent through a rotating roller, which supports the driving wheels of a scaled down vehicle, to a receiving unit which produces a pulse train which is later converted to revolutions per minute and analyzed on a computer monitor to determine the speed of the vehicle. 
         [0014]    A safe electro-mechanical system is provided which easily demonstrates the principles of power consumption in the miniature vehicle and emulates a real world fully electric vehicle. A computerized software system is also provided which demonstrates how to measure and maximize mileage from electric powered vehicles. This simulated system also allows for adding environmental conditions such as uneven terrain and wind resistance. Software in the system further allows the system hardware to make adjustments to keep speed and power levels accurate for measurements of horsepower. Test points are further included to allow for educational investigation. 
         [0015]    There are many different ways to measure the horsepower of a vehicle. Gross horsepower is the measurement of engine output without the engine installed in a vehicle. Since the engine has no load on it, all of its energy can be used for making horsepower. 
         [0016]    Wheel-driven horsepower, by comparison, is a measurement taken at the driven wheels of a vehicle on what&#39;s called a dynamometer. This is done by placing the vehicle&#39;s driven wheels on a large roller and accelerating the wheels up to a set condition. The vehicle&#39;s ability to turn this roller is measured and calculated to come up with a figure that represents how much horsepower is actually available to move the vehicle around—or real-world horsepower. Because a frictional loss between the engine and the driven wheels is unavoidable, wheel-driven horsepower will almost always be less than gross horsepower. One exception would be a steep and long downward slope that would add horsepower to the wheels. 
         [0017]    The present device and system are especially suitable for giving an educator, student, or engineer a tool which not only closely emulates a real electric vehicle, but which does so in a safe manner designed to protect the user from harm and allows for investigation of the scaled down vehicle components. Different energy sources such as alkaline or lithium batteries may be added in this system to study maximum distance and power versus battery type. Actual working scaled down models of some real cars may even be used to further enhance the emulation. 
         [0018]    Software of the system emulates a display panel which would be similar to a real display present on a full scale dynamometer. On this panel, the actual voltage and current being used by the electric motor is displayed. The actual revolutions per minute of the roller is displayed and used to calculate distance traveled. Actual miles per hour is calculated and displayed, then multiplied and displayed to emulate real world conditions for a full sized car. The horsepower is also calculated using a roller mass related to car weight and actual mph. A DC input is provided to allow external power sources to drive the car and not use batteries. By eliminating the use of disposable batteries, this invention also follows the principles required to reduce pollution. 
         [0019]    An advantage of the present Miniature Universal Dynamometer (MUD) and system for using the same is that the present MUD provides a realistic simulator for an actual full-sized dynamometer which is used on vehicles which are sold to a final consumer. 
         [0020]    Another advantage of the present Miniature Universal Dynamometer (MUD) and system is that the present MUD provides an economical way of teaching students and auto technicians how a typical electric vehicle works. 
         [0021]    Yet another advantage of the present Miniature Universal Dynamometer (MUD) and system is that the MUD provides a safe way to test electric vehicles on a small scale. 
         [0022]    Still another advantage of the present Miniature Universal Dynamometer (MUD) and system is that the present MUD provides a computer connection and software package to measure the horsepower and other performance factors of an electric vehicle which may then be compared to real world full-size vehicles. 
         [0023]    And yet another advantage of the present Miniature Universal Dynamometer (MUD) and system is that the present device and system provide for a portable device which is easy for a student or auto designer to test and learn about electric vehicle systems. 
         [0024]    For a more complete understanding of the above listed features and advantages of the smart miniature universal dynamometer (MUD), reference should be made to the following detailed description of the preferred embodiments and to the accompanying drawings. Further, additional features and advantages of the invention are described in, and will be apparent from, the detailed description of the preferred embodiments and from the drawings. 
     
    
     
       BRIEF DESCRIPTION OF FIGURES 
         [0025]    The accompanying Figures illustrate the following: 
           [0026]      FIG. 1  illustrates a perspective view of the Miniature Universal Dynamometer wherein numerous electrical and non-electrical components are secured to the same and wherein a scaled down fully electrical vehicle is being inserted on the Miniature Universal Dynamometer. 
           [0027]      FIG. 2  illustrates a view of a computer screen with a display showing: voltage at the engine, current used by engine, acceleration control, a graph of engine horsepower versus horsepower at the wheels, roller revolutions per minute, roller assist control, vehicle speed, vehicle weight, actual vehicle miles per hour and miles per hour for scaled up vehicle. 
           [0028]      FIG. 3  Shows a cutaway view of a permanent-magnet DC electrical motor/generator. 
           [0029]      FIG. 4  illustrates a schematic of the wiring of the Miniature Universal Dynamometer simulator and scaled down vehicle. 
           [0030]      FIG. 5  illustrates a block diagram for using the Miniature Universal Dynamometer in the absorption mode to measure horsepower at the motor of an electronic vehicle and horsepower at the wheels of that vehicle. 
           [0031]      FIG. 6  illustrates a flow chart of the system used to measure and compare engine horsepower with load by using voltage and current at the electronic vehicle engine under load, versus vehicle horsepower using force through distance method of calculation at the wheels of the electronic vehicle. 
           [0032]      FIG. 7  illustrates a block diagram for using the Miniature Universal Dynamometer in the driving mode to measure horsepower required to drive a DC generator unloaded and loaded. 
           [0033]      FIG. 8  illustrates a flow chart of the system used to measure and compare power required to drive a DC generator with and without a load. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0034]    The present device generally relates to a miniature universal dynamometer for use in connection with electro-mechanical cars with fully electrical engines. The present device may be used to determine the approximate force of scaled-up full-size all electrical automobiles. The present miniature universal dynamometer allows for easy and quick demonstrations for students and automobile engineers and designers of the architecture and power requirements used by fully electrically powered vehicles. The device utilizes a generally transparent spinning roller which is driven by the tested vehicle and a light source aimed at a receiving unit wherein the light source is sent through the generally transparent spinning roller. When the light source is interrupted by an opaque area on the generally transparent spinning roller while traveling to a receiving unit, the light source produces a square wave which is later converted to revolutions per minute (rpm) which may then be used to calculate the distance the wheels of the vehicle have transversed in a given time period (mph) and ultimately the work done by the vehicle or horsepower at the wheels to turn the roller. 
         [0035]    The present miniature universal dynamometer uses a scaled down vehicle in both size and weight. The scaling factor for size is the ratio of the vehicle wheel diameter on the miniature model to the real world vehicle wheel size that the model emulates. This ratio is used to compare actual miles per hour to a scaled up miles per hour in the real world and a factor of twenty-eight (28) was therein used in this system. Miles per hour is defined as the ratio of the distance traveled (in miles) to the time spent traveling (in hours). The scaling factor for weight is also required when comparing the miniature vehicle horsepower to the horsepower of a real world vehicle being emulated. This ratio can be calculated by using the weight of the miniature vehicle, approximately 185 grams with batteries, and the weight of the, for example, Chevy Volt (3520 lbs) electric car which equals a ratio of approximately 8,650:1. 
         [0036]    An inertial test consists of accelerating an engine which has been connected to an inertial wheel or roller in the range of revolutions to be studied. The quality of the results depends mainly on the inertia of the roller. As the engine accelerates, it consumes part of the energy which is available to provide accelerating its own rolling elements (gears, toothed wheel, wheels, and bearings) which also have their own inertia. It is desired that the inertia of the roller be greater then equivalent inertia of the rolling parts of the vehicle. Another desired condition is that the inertia of the roller may be controled by a DC motor breaking force. In this miniature universal dynamometer, the power is trasmitted to the inertial mass of the roller by traction of the tire on the same roller. Using the above conditions a calculation of vehicle power at the wheels of the vehicle can be expressed as: 
         [0000]        P=W /( t   2   −t   1 ) where;       P=power in Watts   W=work done in time period (t 2 −t 1 ) in joules   t 1 =start time   t 2 =stop time         
         [0000]        W=W   1 (inertia of roller)+ W   2 (drag due to roller motors) 
         [0000]        W   1 =½ Iω   2   2   −Iω   1   2  where;
       W 1 =work done in time period (t 2 −t 1 ) in joules   I=roller inertia in kg·m 2      ω 1 =speed of roller at time 1 in rad/sec   ω 2 =speed of roller at time 2 in rad/sec       
 
         [0000]        W   2 =( E   avg   ×I   avg )×( t   2   −   t   1 ) in joules.
 
         [0045]    E avg =Average voltage on roller moters during time t 2 −t 1    
         [0046]    I avg =Average current to roller moters during time t 2 −t 1    
         [0047]    Referring now to  FIG. 1 , the miniature universal dynamometer  100  may have a top  102 , a bottom  103 , a first side  104 , a second side  105 , a front  106  and a back  107 . In an embodiment, the miniature universal dynamometer  100  may be generally the size of, for example, a notebook computer. The miniature universal dynamometer of the present application is generally illustrated in a rectangular manner in the drawings; however, the miniature universal dynamometer  100  may take any suitable shape capable of supporting a scaled down vehicle  190 . 
         [0048]    The miniature universal dynamometer  100  may have a circuit board  110  which forms a main base portion. The circuit board  110  may have a top  111 , a bottom  112 , a first side  115 , a second side  116 , a front  113  and a back  114 . The circuit board  110  of the present miniature universal dynamometer  100  may be largely planar and may have a height  117 . Further, the circuit board  110  may be strong enough so as to support numerous components (as discussed below) which may be secured and/or may rest on the top  111  of the circuit board  110 . In addition, the circuit board  110  of the miniature universal dynamometer  100  may have electrically conductive and electrically non-conductive components (as discussed below). 
         [0049]    Mounted on the top  111  of the circuit board  110  of the miniature universal dynamometer  100  may be a generally transparent spinning roller  120  (or “inertial roller”) which rotates along a center rotational axis. The generally transparent spinning roller  120  may be rotated by, for example, two permanent magnet DC motors/generators  121 ,  122  which, in turn, rotate two drive shafts  123 ,  305  which are located on each end of the generally transparent spinning roller  120 . The permanent magnet DC motors/generators  121 ,  122  may be mounted and attached to circuit board  110  by, for example, two motor mounting brackets  124 ,  125  located on opposite ends of the generally transparent spinning roller  120 . 
         [0050]    An LED  126  may be secured to the top  111  of the circuit board  110  of the device  1 . The LED  126  may be aimed at the generally transparent spinning roller  120  so that light which exits the LED  126  moves toward the generally transparent spinning roller  120 . In an embodiment, the generally transparent spinning roller  120  is substantially transparent so as to allow light radiated from the LED  126  to pass through the transparent portions of the spinning roller  120  wherein the light is then detected on the other side of the generally transparent spinning roller  120  by a photo transistor  127  which is also secured to the top  111  of the circuit board  120 . More specifically, the generally transparent spinning roller  120  may be located between the LED  126  and the photo transistor  127  such that light from the LED  126  cannot reach the photo transistor  127  without passing through the generally transparent spinning roller  120 . 
         [0051]    An opaque piece of material  128  may be mounted on or in the generally transparent spinning roller  120 . The opaque piece of material  128  may be generally rectangular in shape and may block the light from LED  126  from reaching the photo-transistor  127  twice per revolution. In an embodiment, the generally transparent spinning roller  120  may be hollow and capable of holding a balanced mass  129 , to increase the moment of inertia of the generally transparent spinning roller  120 . 
         [0052]    The device  100  may utilize a fully electronic miniature vehicle  190  having a female plug  191  which securely mates with a male plug  130  on the miniature universal dynamometer  100 . The fully electronic miniature vehicle  190  may have front and rear wheels  192 , wherein the real wheels  192  rest at top dead center of generally transparent spinning roller  120 . The connection of the female plug  191  and male plug  130  may create an electrical communication between the miniature vehicle  190  and the miniature universal dynamometer  100  which in turn allows a user to control and measure electrical parameters of the miniature vehicle  190 . Data obtained from running the miniature vehicle  190  on the generally transparent spinning roller  120  may then be transferred through an interface device  131  and cable  132  to a computer with appropriate software to display the data. 
         [0053]    Referring now to  FIG. 2 , the data gathered by the miniature universal dynamometer  100  may be displayed on a computer screen  200  using an RPM (Revolutions per Minute) pointer meter  201  with digital readout  207 , actual miles per hour digital display  202 , scaled up to full vehicle size miles per hour being emulated on a miles per hour pointer display  203 , digital display of voltage at engine  204 , digital display of current being used by engine  205 , a pointer display of electrical motor power  206 , frequency in cycles per second of inertial roller  208 , and a graph of Horsepower  209  for both engine  210  and at wheels  211 . A throttle control  212  to adjust the voltage on the vehicle&#39;s  190  electronic engine is also displayed on the computer display  200 . An input box  213  for the weight of the vehicle  190  is available and data entered into said input box  213  is used to calculate the wheel horsepower  211  displayed on the graph  209 . A digital display  214  of the milli-horsepower at the wheels is also provided. Horsepower data can be recorded in the Table  216  display be clicking the Record Button  217 . Table  216  data can be cleared by clicking the Clear Table button  218  or stored in a computer file by clicking the Save button  219 . A roller control  215  is also provided which drives motors  121 ,  122  and can be used to emulate down hill or up hill conditions. 
         [0054]      FIG. 3  shows a sectional view of the DC motors  300 ,  121 ,  122  which support the generally transparent spinning roller  120  on each end by pressure fitting the motor shaft  305 ,  123  through roller end caps  133 ,  134  along the spinning roller&#39;s  120  rotation axis. Said motor shaft  305  is supported by ballbearings  306  which provide minimum friction at maximum support. The DC motor  300  uses brushes  302 , permanent magnets  301 ,  307 , a winding  303  and a commutator  304  which allows the motor  300  to generate a DC voltage when rotated by an external force. Switch SM  401 ,  138  is a double pole double throw switch in  FIG. 4  showing the two motors  121 ,  122  in parallel to drive the generally transparent spinning roller  120 . Flipping switch SM  401 ,  138  will break the parallel connection and place the leads from motor M2  402  on test points TM1  403  and TM2  404 . In this case the motor M2  402 ,  122  is driven by motor M1  405 ,  121  and connecting roller  120 . The present device may be used in association with software as a universal dynamometer as a result of being able to be used as both an absorption dynamometer with a switch SM  401 ,  138  as shown in  FIG. 4  or as a driven dynamometer when switch SM  401 ,  138  is flipped. 
         [0055]    Referring to  FIG. 4  a schematic view for the electronic vehicle  190 , is shown in Section A  490 . Power to the electronic vehicle  190  may be controlled and supplied through the female connector  406 ,  191  which mates with the corresponding male connector  407 ,  130 . Section B  491  may be used to control and measure the engine power of the electronic vehicle  190 . Section C  492  of  FIG. 4  is a schematic showing how Power Plug  408 ,  139  may provide external power to the device or how the battery  409  located in the electronic vehicle  190 ,  409  may be used when switch S2  410 ,  137  is in position shown. 
         [0056]    If S2  410  and S1 411  are in the opposite position as shown in  FIG. 4 , then external power at plug J1  408 ,  139  will be sent to power roller motors  121 ,  405 ,  122 ,  402  and associated circuits shown in Section D  493 , Section E  494 , and Section F  495 . When switch S1  411 ,  136  is in position shown in  FIG. 4 , power for roller motors  121 ,  405 ,  122 ,  402  and associated circuits shown in Section D  493 , Section E  494 , and Section F  495  will come from USB cable  132  and interface module  131 . In this embodiment, the RPM of the generally transparent spinning roller  120 ,  412  may be measured by transmitting light from an LED  413 ,  126  through the generally transparent spinning roller  120 ,  412  and sensing the light on the other side of the spinning roller  120 ,  412  with the photo-transistor  414 ,  127 . As mentioned above, an opaque piece of material  128  (such as an opaque tape)  415 ,  128  may be placed inside the generally transparent spinning roller  120 ,  412  so as to block the light twice per revolution. In this manner the associated circuitry in Section F  495  produces a train of pulses that can be used to calculate the RPM of the generally transparent spinning roller  120 ,  412 . 
         [0057]    In an embodiment, the opaque piece of material  128  may also be made from a reflective material and may be placed on the outside of a non-transparent spinning roller reflecting the transmitted light from LED  413 ,  126  once each revolution to a photo-transistor  414 ,  127  placed on the same side as the LED  120 ,  412 . Section E  494  circuitry uses the voltage at P4 to control the direction of rotation of roller  120 ,  412 . Section D  493  circuitry uses the voltage at P4 to control the speed of roller  120 ,  412 . 
         [0058]      FIG. 5  shows the steps necessary to use the miniature universal dynamometer  100  in the absorption mode to measure the power coming from a scaled down electronic vehicle  190 . The first block  501  describes how to mount the electronic vehicle  190  to the dynamometer  100 . The next block  502  describes connection of the dynamometer  100  to a computer. Block three  503  gives instructions on switch setup and the control process to turn on the electronic vehicle  190  from the computer. Block four  504  describes how to record data to a file on the computer. Block five  505  describes how open road conditions, such as uphill or downhill, can be emulated using the computer. The final block  506  describes the horsepower data being displayed in a graph on the computer screen. 
         [0059]    The flow chart in  FIG. 6  shows the computer software procedure used to calculate the electronic vehicle  190  horsepower. When the throttle  601 ,  212  is increased the vehicle  190  motor  602  voltage is increased. The motor  602  turns the gear box and wheels  609  which in turn drives the roller  120 ,  412 ,  603 . A counter  604  is used to read the cycle per second of the roller  120 ,  412 ,  603  and this information is passed to the MPH section  605  which calculates the actual MPH  606 ,  202  of the vehicle  190 . The measured MPH  606 ,  202  is multiplied by the weight of the vehicle  610 ,  213  to get the horsepower at the wheels of the vehicle  214  and display it in a graph  611 ,  211 . When the inertia of the roller  120 ,  412 ,  603  is equal to the weight of the vehicle  190 ,  213 ,  610  the horsepower calculated from force times distance will be accurate. The horsepower at the vehicle  190  motor is calculated in the Watts Section  612  of the program and divided by 1000 to get milli-horsepower. This number is then sent to the graph  611 ,  209  and displayed as engine horsepower  210 . 
         [0060]      FIG. 7  shows the steps necessary to use the miniature universal dynamometer  100  in the driving mode to measure the power needed to drive a DC generator. The first block  701  describes connection of the dynamometer  100  to a computer. The next block  702  gives instructions on switch setup. Switch SM  401 ,  138  converts motor M2  402 ,  122  into a DC generator by transferring motor leads for this motor to test pins TM1  403  and TM2  404 . Block three  703  describes how to drive the DC generator M2  402 ,  122  and record the unloaded voltage at M2  402 ,  122  output leads. Block 4 704  describes storing data in chart  216  and loading the generator  402 ,  122  for next reading. Block five  705  describes how to calculate power at the load and store data in a file. The final block describes what is graphed on the computer graph display  209 . 
         [0061]    The flow chart in  FIG. 8  shows the computer software procedure used to calculate generator efficiency. When the assist  801 ,  215  is increased the M1 motor  802 ,  121 ,  405  voltage is increased and turns the roller  803 ,  120 ,  412  which in turn drives the generator  804 ,  402 ,  122 . A counter  805  is used to read the cycle per second of the roller  120 ,  412 ,  803  and this information is passed to the MPH section  806  which calculates the actual speed in MPH  807 ,  202  of the roller  120 ,  412 ,  803 . The speed  807  and inertia of the roller  808  is multiplied to get the horsepower at the generator shaft  123  and display on a graph  811 ,  211 . When the generator  804  is placed under load by placing a resistor from TM1  810  to TM2  809  speed of the roller  120 ,  412 ,  803  will drop as horsepower is transferred to the load. The difference in power should be the power delivered to the load and can be verified by squaring the voltage on the load and dividing by the load resistance value. Again the watts produced by the generator should be slightly less than the power calculated from force times distance. 
         [0062]    Although embodiments of the miniature universal dynamometer for use in teaching and measuring horsepower of scaled down electronic vehicles and DC generators are shown and described therein, it should be understood that various changes and modifications to the presently preferred embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the device for increasing its educational value without diminishing its attendant advantages. It is, therefore, intended that such changes and modifications be covered by the forthcoming claims.