[OCCRA]: REALLY weird robot behavior

Ok, so the second match that we competed in (against chief and whoever they had blocking for them) I did a LOT of pushing. I put quite a bit of strain on the motors, because I was blocking easily half of the time. In the last quarter of the match, the bot just stopped dead, and wouldn’t respond to any control input.

At first, I thought I had blown a fuse, but when we turned it off, took it back to the pit, and turned in on a again, everything worked fine, and we proceeded to run another match without any issues without touching anything. Fuses don’t heal themselves, so it had to be something else.

Are there any circut breakers or something of the like in the bot’s electrical innards? Has something similar ever happened to any other teams?

Sounds like you had a radio problem. Did you happen to look at the lights on the O/I during this odd behavoir? (We actually dedicate one of our drive team as a status montior.) If your No Data/Radio light went Red, your robot would have appeared to ‘died’, simply because you don’t have control anymore. There are a number of reasons for loss in Radio connection, some of which are unexplained (-shudder- Anapolis Regional 2006 (yeah, yeah, this is OCCRA, not FRC) … I was on Team 181 paired with a couple of other awesome teams… what are the odds that TWO radios on the same alliance drop out during the same match for -no apparent reason-??), but this sounds like the most likely behavior.

Another possibility are a loose battery connection that got reconnected after you jostled the bot around when picking it up. Do you remember if the there was power to the bot when you went out to the field to retreive it?

My FRC 2 cents where it probably doesnt belong :stuck_out_tongue: ,
Jacob

Most people protect their drive motors with the 35Amp slow-blow circuit-breakers. These will kick out if you draw too much current and will later come back on once they have had a few seconds to cool.

The battery is in there quite tightly, and it did still have power when we took it off the field. In retrospect, I should have checked the board, but I just watched the match when I realised I couldn’t control the bot.

In any case, a loss of radio sounds relatively consistent with what happened – the bot stayed on, but was dead to input. Only problem though is that that conclusion doesn’t entirely make sense, considering that it just went out and wouldn’t come back on, and it was near the center of the field, so it clearly wasn’t out of range.

This seems quite a bit more plausible, except I wasn’t entirely sure even slow-blow fuses worked like that. I’ll look into that tomorrow I guess.

I don’t know what control system OCCRA uses, but with the FIRST control system this has happened to me a few times. Check to see whether the 120Amp main breaker is tripped. That’s usually what did it for us. Stalling the drive motors too much while pushing was more than the little guy could take sometimes.

Based on the story you documented - I would agree entirely with Mr Mac. That is exactly how it is suppose to work to protect the rest of the system.

If you pull too much current, it will shut down the entire system. Not all fuses or circuit breakers require replacement, when they fail. It is best to know which ones do, and which ones don’t.

Usually a single short circuit on an individual line will blow one of the fuses and the rest of the motor driven actuators will remain alive.

If you pull too much current, the main circuit breaker will shut down the entire machine - once the current draw is removed and either time or temperature requirements are met - it will reset itself automatically.
That is what sounds like happened when you were in a pushing match.

That’s the answer I was looking for, I just wasn’t certian there was such a circut breaker on the bot.

So, if it’s tripping the main breaker, there’s no way to avoid that aside from not pushing the bot as hard, right?

I am going to repeat what Mr. Aubry and Mr. Mac said. Last year team 47 had this issue for the entire 1st competition. We could not figure out what was going on and the robot would just turn off about 20 to 30 seconds into the match. We were in 2nd gear on the drive motors and we were kicking out the breakers the entire time. We moved to first gear for the next competition and had no problems what so ever and so we stayed in first all season. This year as far as I know team 47 tried 2nd gear agian and it did the same thing so they moved to first and I guess it was better, but I don’t know if they stayed in first or not. Just try switching to 1st gear if you are in 2nd and see what happens. There is a trade-off though, you will lose speed but it will be tougher to push you around and your machine may run flawlessly.:slight_smile:

Josh is right we had the same problem the first match of the competition last week. We kept losing the control of our drive motors and they would not respond to our commands. We did shift to first gear after that match and it fixed all of our problems. Tripping the breakers did make us shift to first and cause us to lose speed but there are other ways you can get your speed back similar to what we have done and others will see come thursday.

But wouldn’t the two 35s blow (with a combined 70A being drawn) before the 120 blows? Plus, we were using the 30A accidentally instead of the 35A. We weren’t drawing any other current at the time except for the robot controller. How could the 120 possibly trip?

surferacf -
First of all, In this particular case, the answer is NO! The individual fuses won’t “blow” before the circuit breaker cuts out.

The fuses protect certain things and the circuit breaker protects other things -whenever conditions occur that could result from shorts and high current draws.

Second, You really don’t know what amount of current is being drawn because when you stall the motors (which is what occurs in a pushing match or very inefficient drive systems) - the current goes very high, very fast!

Hope this helps,
Mike Aubry

Well, from the information given, we know that the 120 Amp breaker didn’t trip (he said that the bot was still on when they went to retrieve it.)

As far as the “slow-blow” self resetting breakers, once those trip, they will try to reset themselves after a second or two. The likelyhood that both of these tripped at once, and continued to trip over and over again is unlikely.

I’m sticking with a control problem. Even if it wasn’t radio, maybe your program found somewhere it shouldn’t be and got caught in a loop somewhere. This would be consistent with the robot working fine after a reset, because the program would start over and not be stuck in the loop (who know the conditions that could have caused the processor to get lost.)

Jacob

I watched the match you talked about - I am one of the refs.

They were tripping the breakers on the drive motors trying to push. The drivers kept full throttle and the breakers could not re-set. Stalling the Dewalt motors (NOT USED IN FRC) will draw enough current to keep them dead.

If this happens leave the joy sticks alone for a few seconds then ease the power on.

The real answer is to look at your drive gear ratio and solve that problem…consider the size of your wheels also.

[mini-rant] Or, if you were still able to obtain IFI’s breaker panel, write a bit of code to automatically detect when these are getting tripped consistantly and automatically stop applying power to the motors for a second or two… [/mini-rant]

What Mike said is completley consistant with what was going on. If you were stalling out the motors (which are capable of drawing too much current), then you wouldn’t have ‘control’ anymore (because the motors are disabled).

I completly agree with Mike; redesign your system so that pushing won’t cause stalling. It sounds like stalling your De-Walt motors will cause problems.

Jacob

We’re in first gear and have a ridiculous amount of mechanical advantage in the driveline. I’m sure you saw us push 47 around. If anyone should be reconsidering their gearing, I’m sure it’s not us. In any case, I guess that’s the answer I was looking for. We replaced the 30 amp fuses with 35’s, and I’ll try not to put that much strain on the bot. Moreover, if just not touching the controls for a second fixes things, then that’s perfect.

We should be good, thanks alot everyone.