# Analysis and Design of a Minimalist Step Climbing Robot
## 5 Proof of Concept Model  
By using design analysis, it was found that robots with fixed center distance between the front and rear wheels fail to carry a load with a high center of gravity while climbing a stair. In order to realize the phenomenon, a scale-down prototype is developed and experiments are performed on steps. In Figure 15, an image of the model is shown. Table 8 describes different parts of the model. The prototype consists of two front wheels and a rear wheel. The rear wheel is connected to the body by a link termed as the connecting link. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{4}{c}{**Normal Reaction (N)**} \\ \cline{2-5}  & **Step 1** & **Step 2** & **Step 3** & **Step 4** \\ \hline Mean & \(-128.93\) & \(-277.34\) & \(-453.69\) & \(-676.34\) \\ \hline Std. Dev. & 42.09 & 84.94 & 131.98 & 188.12 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Statistical analysis of variation in difference of normal reaction at the rear wheel during the controlled and uncontrolled conditions with respect to center of gravity of load. Figure 14: Variation of normal reaction on rear wheel with respect to change in height of the center of gravity of the load. Figure 13: Variation of inclination angle of the robot with change in height of step during the act of climbing down the stairs. The electronic components used to develop the prototype are shown in Figure16a. In the prototype, an Arduino Uno microcontroller is used as the brain of the robot. All the wheels are driven by continuous servo motors. In order to control the inclination angle, another servo motor is used which drives the connecting link of the robot. The prototype is powered by a 6V battery source. Three toggle switches are used in the robot. Switch 1 is used to connect the power source to the four motors of the robot. The power supply to the microcontroller is connected through switch 2. Switch 3 is responsible for toggling between the operating conditions of the prototype, i.e., operating with or without control. MPU 6050 is used to sense the inclination angle of the model. The sensor consists of three Gyroscopes and three accelerometers for sensing three degrees of rotation and three dimensional spatial motions, respectively. The inclination angle of the robot is communicated to the monitor by using a wireless module. Experiments are performed for ascendance and descendance of the robot on the stairs. Figures 17-20 show the snapshots of the videos of the experiment. In order to remotely monitor the change in inclination angle of the prototype, a wifi module is used. \begin{table}
\begin{tabular}{c l l l} \hline \hline
**Sl. No.** & **Description** & & \\ \hline
1 & MPU 6050 (IMU sensor) & 7 & Front Wheel (\(\phi\) 67 mm) \\  & (Gyroscope range: \(\pm\)2000 deg/s) & 8 & Load (\(\phi\) 37 \(\times\) 72.75 mm; \\  & (Accelerometer range: \(\pm\) 16 g) & & 600 gm) \\
2 & 6V Power Supply & 9 & Body (126 \(\times\) 101 \(\times\) 62 mm) \\
3 & Arduino Uno (\(\upmu\)C) & 10 & Weight of robot \\
4 & Wireless Module (nRF24 LO1) & & (1.34 kg (without load)) \\
5 & Rear Wheel (\(\phi\) 67 mm) & 11 & Rise of step (15 mm) \\
6 & Servo Motor (RDS3115 MG) & 12 & Run of step (33 mm) \\  & (Max. torque: 17.0 kgf-cm) & 13 & Number of steps (11 mm) \\  & (Max. operating angle: 180\({}^{\circ}\)) & 14 & Connecting link (152 mm) \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Parts of the robot Model. Figure 16: (**a**) Electronics components diagram; (**b**) block diagram of the controller. Figure 15: Model of the proposed robot; (**a**) Isometric view; (**b**) Front view; (**c**) Side view. Figure 16b shows the flow chart of the control system that is used to maintain the inclination angle of the proposed robot. The inclination angle sensed by the inertial measurement unit (IMU) is processed by the microcontroller. Depending upon the deviation of the current inclination angle of the robot from the desired value, the microcontroller sends the actuation signals to the actuator for rotating the connecting link.