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

[Nate Laverdure]

I'll have a hard time answering these but I'll give it a shot; my ability to converse intelligently about programming is very limited.

Originally Posted by Ether

1) what was your driver interface? e.g. did you just give the driver direct access to the 3 degrees of freedom (fwd/rev, strafe R/L, rotate), or did you put a layer on top of that to abstract it to a more intuitive level? one mode or several? etc

Just two modes:
Robot-centric control allowed the the driver to adjust the setpoint of the PID loops for the 3 DOFs you listed.
Field-centric control added a layer of abstraction: the translation DOFs became north/south and east/west.

My understanding is that teams attempt these kind of field-centric control schemes all the time, but the drift in FRC-grade gyros often makes them unusable after ~10 seconds. Our original intent was to counteract this by integrating the data from multiple gyros with robust "sensor fusion."

Originally Posted by Ether

2) Did you derive the inverse kinematics from first principles, or did you refer to available papers on this topic?

I made sure the literature was provided, but I'm fairly certain my programming student derived everything from scratch. I believe he also threw out a couple of the WPI libraries and rewrote them. The often-spotlighted Matt Kline quote comes to mind: "A good programmer can look at a library, decide he hates it, and code everything from scratch. An amazing programmer can look at a library, decide he hates it, but realize the time it will save him and learn to use it." I hope to work on this with him next year.

Originally Posted by Ether

3) Why was field-centric problematic? Were you having gyro drift problems, or did you encounter difficulties with the programming?

I believe even the KOP gyro was fairly stable. Two main problems stick out in my memory:
-- Issues with communicating with the IMUs via any of the available protocols. One of the IMUs had an on-board microprocessor that supposedly provided built-in sensor integration, but we were never able to get access to this predigested data. We lost ~2 weeks on this. We ended up duplicating this capability by building a Kalman filter that ran on the cRio, ready to recieve the raw input from multiple sensors. I don't quite remember the rest of the story, but in the end we were using only the KOP gyro.
-- Whatever this was. We lost another 1.5 weeks on this.