V-Electronics and Software

This portion of the project is yet to be implemented. Initially I attempted a direct drive of the prototype, but the motor I had on hand did not have sufficient torque to get through the entire motion path of the mechanism. The crank was able to spin up until the "foot" would have to lift off the flat part of the trajectory. Early in this upcoming week, I plan on implementing a geared mechanism to provide the motor with a mechanical advantage to overcome the torque deficiency. Nonetheless, I was ready with my arduino platform setup using Sparkfun's TB6612FNG motor driver and a 5V power supply. I wanted to be able to control the position of the motor to allow me to check and compare the simulations done previously at different crank positions. Hence, I had coded my arduino program to take the input from a potentiometer as feedback on the motor's angle. From there, I would have been able to measure angles or at least validate the simulation by roughly comparing the position in the gait of the mechanism.

The code for this motor drive system can be found in the appendix. Its operation is rather simple and proves to be a rudimentary closed loop controller. Essentially, a desired angle is given to the arduino, which translates the angle to a value from 0 to 1023 (the operating range of the potentiometer's analog feedback). Based on the designated value, the arduino determines whether the motor is above or below the desired position and moves in the necessary direction until it deems motion in the opposite direction necessary. This loops through several times until the motor is in an acceptable range of the desired angle (2° here) and then stops. I 3D printed a sleeve that allowed me to connect a flathead bit from my screwdriver set to the motor's shaft to verify the system's functionality. However, with the need to now use gears, I will not be able to directly connect to the motor's shaft for position control. I think I will opt to simply operate the motor at a set speed using PWM, so that the motion of the mechanism is smooth.

Update 5/10:

With Texas Invention Works reopened, I was able to laser cut additional gears giving an additional gear ratio of 6:1 to the motor's output shaft. Additionally, a thicker 3D printed shaft was made to fit a key hole in the main gear and link for translating the torque effectively to the mechanism. These modifications made the difference, and the video below demonstrates the completed electrified Bionic Bevo!

Original links (left) updated links with key hole on crank input arm (right):

Shaft: