serious problem found - robot controller resets when jarred!

[KenWittlief]

EDIT: DID SOME MORE TESTING IN OUR LAB - THE PROBLEM WE HAD IS NOT DUE TO THE BREAKERS RESETTING THE ROBOT CONTROLLER -

SEE MY POST ON PAGE TWO THAT BEGINS WITH THE LINE:

"OK I did some more testing in my lab."




the subject line is a little misleading. The 20A breakers open when jarred causing the robot cotroller to lose power for an instant, and reset!

At the buckeye regional team 578 observed, in two matches, our robot restarted automode halfway through the 15 second period - both times after the robot was smacked.

We discovered the 20A and 30A circuit breakers open for an instant when jarred. You can try this for yourself - put a continiuty meter across a 20A breaker, then flick it with your finger, or tap it on the table - the circuit will open briefly.

These breakers are not defective, its a characteristic of the way they work - Bimetal strips that act as springs, and bend (pop) the other way when too much current heats them up.

This is what causes it to open on impact - it is esentailly a switch held closed with a small spring. When the impact force overcome the pressure of the 'spring' the breaker opens. The breakers look like a fat pizza box. We took one apart - the switch opens and closes in the same direction as if you were opening a pizza box.

What this means is, the robot controller power can be interrupted if the robot is hit, hits a wall, bounces hard on the ramp... when the power is interruped like this the controller resets, and if it happens in the 1st fifteen seconds, your auton mode code starts over from the beginning (we tested it - the controller does reset).

We emailed FIRST about this, and recommended all teams be allowed to use a 20A fuse (like the ones in the spikes) in the fusebox for the robot controller power. Its ok if your motors and other devices glitch for an instant when hit, so only the robot controller needs a fuse instead of a breaker.

if your bot is smacked at any point during the 2 minutes, and it resets, it will cost you several seconds of dead time, as the controller restarts and renegotiates the communication link - its more serious during auton mode because the automode sequence of events you programmed your bot to follow will start over from the beginning.

if FIRST wont let us use fuses instead of the breakers for the robot controller circuit, the one thing you can do is make sure your fuse panel is oriented, screwed to a vertical surface in the bot, so the 'pizza box' shape is flat in the robot. This will lessen the susceptability to impacts in the X and Y planes, and put it on the Z plane - so if your bot is dropped (gets lots of air) then the breaker will be most likely to open, and less likely to open from a front/back or side impact.

another solution is to shock mount your breaker panel.

The fuses that are in the spikes are 20Amp (and they are supplied by FIRST). The fuse is simply a strip of metal that melts when too much currrent flow (it gets hot). The fuse cannot reset. There is no logical reason why you should not be able to use a fuse for the robot controller. There is no condition in which the controller should be drawing more than 20 amps (unless you have loose metal bounceing around inside your robot.

I have not heard anything back from FIRST yet on the Q&A section in the robot rules section - they have not even posted the question yet. If you dont see a respose from FIRST on the Q&A forum then raise the issue yourself with the judges/inspectors at your next event - advocate a fuse be allowed in that circuit (for all teams) - or at least orient your fuze panel so the breakers are flat.

If you are trying to achieve king of the hill in the last seconds of your final match for the regional trophy, and you are smacked at the top of the ramp, breaker opens and your controller resets for several seconds

it will be all over.


-Ken Wittlief sparkie engineer team 578 'Blue Lightning'
NASA/Gleason/Fairport - see you in Toronto!