[Joe Johnson]

What teams used wheel encoders this year?

CD8 had encoders.


How did you build it or did you buy a shaft encoder?

We had home brew encoders. We used IR based sensors from Digi-Key with interrupters mounted on the motor shaft (4 pulses per rev of the motor).


What was its resolution?

EXTREME resolution. We had 2 encoders per motor (mounted 90 degrees out of phase with eachother) to give direction and distance.

In low gear we had 60 pulses per inch of robot travel. In high gear we had about 20 per inch. We had surprisingly little slip on the ground and (once we found a MAJOR bug in our auxiliary STAMP2 code) very consistant results.


Did you use them only for autonomous or for the whole match?

Autonomous only. if we had been more reliable earlier, we would have probably used the sensors to drive the robot always (i.e always have the robot wheels in feedback mode just like we do with our arm joints). But they weren't so we didn't.


How did they work for you?

Once we got the motors mounted robustly (i.e. fixed the problems FIRST created with their motor mount kits) and the interrupter's robustly mounted (20,000 RPM can shake things loose pretty easily) and the sensors mounted robustly (these things need to be designed in from the start -- eyeballing it after the fact is asking for trouble), the system worked like a charm.

Note that we had not just a the sensors but sensors (2 per motor) PLUS up/down counter circuits to count the fast pulses PLUS shift registers to take a snapshot of the counter while we read them PLUS an auxiliary STAMP2 to read the shift registers and do some processing for us (calculating distance traveled by the robot CG and the orientation of the robot).

It turned out to be a very complicated little setup. AND for all its cleverness, in the elimination rounds, it fail us do to an a connection becoming partially unplugged when we climbed up on another robot in the last round of the qualifying rounds.


Do you plan to use it next year?

I think yes, if the game needed it. But... ...it was not an easy thing. We would also put the sensors and the electronics box in a little more protected location and make sure the connectors are a bit more robust, but generally speaking, it worked pretty well.

Joe J.