We built a 6-CIM Kiwi Drive. Criticisms please!

[Nate Laverdure]

Originally Posted by Andrew Schreiber

What sort of control set up did you have? Feedback?

We used a 250-count US Digital encoder on each gearbox. Using this sensor data we had PID control over each velocity component, although I believe we typically only used the P and I terms.

We experimented with a few different IMUs, gyros, and accelerometers in a 4-week-long effort to develop true field-centric control:
-- Adafruit 10-DOF IMU (p/n 1604)
-- DIYDrones ArduIMU+ V3 (Sparkfun p/n DEV-11055)
-- KOP Analog Devices gyro & accelerometer (AndyMark p/n am-2067)

In the end, however, we decided to use the KOP gyro only and limit field-centric control to autonomous only. During teleop we used robot-centric control.

Originally Posted by Andrew Schreiber

Did the 6CIM help with acceleration?

I didn't really make any scientific comparisons between the actual performances of the 3-CIM prototype and the 6-CIM final design. I really missed a learning opportunity there.

Intuitively, doubling the CIM count cut the per-motor current draw in half. In situations where we drive the fully-loaded robot straight into the wall at full voltage, this draw (sometimes called the "pushing match current") reduced from 101 A to 52 A.

However, there was also a non-technical reason that we chose to dedicate 6 CIMs to the drive system: in 2012 and 2013 we fielded robots with only 2 CIMs on the drivetrain! As you might have guessed from the 5-sided chassis, with this year's design we wanted to make major changes from our past behavior in as many ways as possible.