GregT - you need to go back and look at the Team 578...physics lesson photo again.

yes we slowed the turning part of our V-turn down enough to stay closed looped with the gyro

and we beat you to the wall

anytime you use feedback you must run 'slower' than the systems top speed - otherwise you have no room / margin for making corrections.

We could have made our auton mode even faster if we wanted to. We had the bot going back to the center of the field before making its 45° turn - and we also had the motors running at less than half speed while going backwards AND while turning.

We didnt have a full sized ramp to practice on, and we couldnt get enough carpet time at the events to adjust it any finer. If we had added a wheel revolution counter then we could have backed up until we barely cleared the ramp side wall, then turned just enough to start going forwards, continuing to turn as we climbed the ramp.

Feedback is like magic in engineering. You can take a sloppy, loose system and make it as fast, accurate and precise as you want by using feedback. MUCH easier to do than to try to build a system (bot) that is accurate and precise all by itself and let it run blind (open loop).

I forgot to mention:

DO NOT SHOCK MOUNT YOUR GYRO!

you dont want it padded from the frame - you want it firmly mounted so it moves exactly as the frame moves. If the gyro is wobbling around or is acting like its mounted on springs, then your feedback system is going to be wacked out!

also make sure you mount it on the most solid part of your frame, not anyplace that bends or twists when the bot is in use.

the gyro already has an internal bandwidth limit (filtering) so random impacts and vibrations will be averaged out over time - if something hits your bot so hard that it accelerates faster than 75°/S then you need to put bumpers on your ROBOT! - not on your gyro :c)

An extension to that:

Mount the gyro as low as possible to the ground to reduce jitter (vibrations are more exaggerated on taller superstructures).

I got the gyro hooked up, but I'm having a slight problem; when the robot is sitting still, the gyro reads 129 or 130...not 127...

Is there any way to "reset" it?

It is sitting at a slight angle because the robot itself is angled...would this cause the problem?

the gyro will only change its output when you turn on its axis of rotation

so when its sitting still, whatever it puts out is 'zero'

I suggest you have your SW read the gyro when the robot is first powered up, and use that reading (whatever it is) as your zero

also, you might want to code in a dead band, to ignore zero-1, zero, zero+1 when you are integrating the output

then the compass heading you are creating will not drift when the bot is not turning.

This is normal, and no there's not a way to reset it. Every gyro that we've examined here has it's own "normal" center value. I've also been told that some teams have seen the gyro have a different center value each time it's powered up, although I didn't see this myself.

To combat this problem, we had our custom circuit take 256 samples from the gyro on powerup and average them to determine it's center value. Worked perfectly. One word of caution if you try this: when the gyro first receives power, it's output will be all over the place for a few seconds, so you don't want to take these samples right away when your robot is powered up. Our custom circuit had a 4 second delay before reading the gyro and it worked great.

How did you guys find out the sampling rate of the RC? I'll trust that it is in fact 26 ms, but is there a data sheet somewhere, or does it depend on the size of the main loop of the program?
Thank you
-Bobby Sakurai

It's stated in the kickoff presentation by Bob Mimlitch on the FIRST website under Team Resources & Kickoff Workshop Archive.

I believe it's based on the radio packet transmission rate and is imposed by the IFI implementation of the Robot Controller, not the Basic Stamp itself.