• Sajiv Shah

Initial Electronics Setup - VSA Jumping Leg

A crucial part of our variable stiffness leg is the electronics. Electronics is going to be the entire system that will allow us to gather data and automate sequences to analyze the benefits of our simplistic VSA design.

The basic electronics that are required for our project are two motors, one to move the actuator further from the joint, and the other to rotate the joint, as well as an encoder at the joint. Additionally, in order to control the two motors, we would need some sort of additional position tracking encoder. This however would require more complex code and would make motor control far more difficult, which is why we leaned towards stepper or servo motors. Stepper motors are controlled by phases and small steps that they take, making it easy to know their relative position. However, they have low torque and can easily "skip steps" meaning we would lose track of the position of the motor. They also do not utilize an absolute encoder, meaning we would need some sort of homing sequence to know the initial position of the motor. Servo motors, on the other hand, have absolute encoders and built in motor controllers, making them super easy to use. One can send a basic position command and the motor will move to that position at a relatively constant speed. The major downside is it becomes difficult to control the velocity of the servo motor, but there are some methods to do so.

For our application, a servo motor makes the most sense. Because of the high torque necessary to hold the springs extended, we would need to use servos that are slightly more powerful than standard 9-gram hobby servos, so I found some 25 Kg-cm servos on amazon that looked promising.

For the encoder, we needed an absolute encoder that was reliable and easy to use. The first two that came to mind were ones that we had used in robotics, the hex through bore encoder from REV robotics and the MA3 absolute encoder from USDigital. Not only are these good encoders, but I also happened to have a couple laying around from other projects making them cost-effective to test with and use.

The last major piece of the puzzle is the actual controller. Our application demands decently fast processing to run all the different sequences, so something more powerful than an Arduino is necessary. The ESP series is a great entry-level board that is cheap and easy to code as it can be used with the Arduino IDE but has MUCH MUCH higher processing speed and other things such as wifi which will be of benefit to us.