Serious Problem of Unknown Origin

[Al Skierkiewicz]

If the RC is switching to the backup battery to stay alive, all PWM outputs are disabled. Replace or recharge the main battery.

[Team865]

Thanks everybody for the suggestion, we are going to try them tomorrow when our teacher is here to provide us with a fully charged gray battery/battery charger.

Mr. Anderson - We meant that reverting back to the default code did not resolve the problem. By "behaved like before" we mean that the motors still spun at a very low rate.

[Team865]

Yes, we have tried resetting.

[matt91]

Ok well in that case what I would do is run the programing, and test your voltage everywhere in between the IFI board and the power source and the motors. Maybe the trouble is in the motors... have you driven the robot yet? Maybe there burned out?

[TubaMorg]

In addition to what everyone else has been saying (charge your battery or swap it out for a freshly charged battery), your OI should report battery voltage > 12.4 volts for a nice happy robot. Once you get there, make sure your Victors are calibrated. Neutral is orange, max in one direction should produce a green led (at the Victor), max in the other direction should produce a red led (at the Victor).

[Team865]

Thank you for your suggestions so far.

Currently we are charging one of our 'big greys' and will see what happens when we try again with it.

[Team865]

We've just tested our robot with a new battery, and the problem is resolved! The motors are now spinning at their normal speed. Thank you everybody for your prompt replies and "gracious professionalism".

[MrForbes]

I'm glad to be of help!

Do you understand why the robot behaved as it did when the battery was discharged? It might take some thinking to figure this out, but if you develop an understanding of how batteries work, specifically how the available voltage changes with charge state and current load, it should make sense.

[JesseK]

Do not ever set your battery on concrete.

I don't understand the chemistry/physics behind it, nor do I ever intend to delve into the science of why it happens but something about rebarb, concrete and long half-life radiation drains your battery if it's in close proximity to concrete. I saw it happen repeatedly at the VA State Fair with our robot and rather than trying to understand why I'll just accept the fact that it happens for now.

What we saw was that the charger would say our battery was fully charged. We'd then transfer the battery to the robot and place it on the field. At the start of the match, the bot would move extremely slowly, and the OI would indicated ~7V on the battery. About 15 seconds into the match, the voltage would go UP and the robot would act normally. Who knows why ? What I do know is, we do not place batteries on concrete any more and we haven't seen the problem since.

If you thought your batteries were charged and then you get these results, perhaps this is why.

[MrForbes]

The battery on concrete thing likely has to do with temperature, since colder temperatures slow down the chemical reaction that releases electricity (that's my incomplete understanding of it)

[Kevin Sevcik]

Originally Posted by JesseK

Do not ever set your battery on concrete.

I don't understand the chemistry/physics behind it, nor do I ever intend to delve into the science of why it happens but something about rebarb, concrete and long half-life radiation drains your battery if it's in close proximity to concrete. I saw it happen repeatedly at the VA State Fair with our robot and rather than trying to understand why I'll just accept the fact that it happens for now.

What we saw was that the charger would say our battery was fully charged. We'd then transfer the battery to the robot and place it on the field. At the start of the match, the bot would move extremely slowly, and the OI would indicated ~7V on the battery. About 15 seconds into the match, the voltage would go UP and the robot would act normally. Who knows why ? What I do know is, we do not place batteries on concrete any more and we haven't seen the problem since.

If you thought your batteries were charged and then you get these results, perhaps this is why.

I'm highly skeptical of this. In olden times before plastic cases for batteries, this was true as slightly porous casing materials could would become moist on a damp concrete floor and let some current flow, draining the battery, but those days are a rather long way behind us. There simply isn't any possible way for batteries to self-discharge faster than normal just because they're on the floor.

If your robot was moving slowly for the first 15 seconds of a match, I think it's much much more likely that there was a programming error in your autonomous mode that was causing some of your motors to fight each other and put a large load on the battery. Autonomous mode IS 15 seconds long, after all.

[JesseK]

Originally Posted by Kevin Sevcik

I'm highly skeptical of this. In olden times before plastic cases for batteries, this was true as slightly porous casing materials could would become moist on a damp concrete floor and let some current flow, draining the battery, but those days are a rather long way behind us. There simply isn't any possible way for batteries to self-discharge faster than normal just because they're on the floor.

If your robot was moving slowly for the first 15 seconds of a match, I think it's much much more likely that there was a programming error in your autonomous mode that was causing some of your motors to fight each other and put a large load on the battery. Autonomous mode IS 15 seconds long, after all.

No, it was 15 seconds of teleoperated period (sorry for being unclear) and we'd literally see the OI Voltage Indictor go from 7 on up to 9, then trickle up to 12.

It was wierd and unexplicable by everyone except our team lead, who said it was because we placed the batteries on concrete. We stopped putting the batteries on the ground, and the wierdness stopped happening. Who knows.

[Al Skierkiewicz]

Jessie,
This more likely from a dirty contact on the battery than anything else. There is no explanation other than extreme low temperature for the battery voltage rising during play. It is also possible that there was some veryhigh friction in the drive train that worked itself out during the match. Loose hardware is a good example. If one of the motors is running near stall the terminal voltage on the battery will read low. The battery internal impedance is .011 ohms. Using Ohm's Law and fudging a current draw of 200 amps you would expect to see 2.2 volts dropped just across the battery. However, the RC stops functioning when that battery voltage falls below 8 volts, so I think the 7 volt display you saw was in error.
The battery on concrete was an issue long ago with car batteries and the case material and the fact that the battery was not sealed. Sneak paths through leaking electrolyte, minute caracks in the case and the concrete would serve to discharge a battery left in contact with the floor. A simple insulator like carboard usually prevented the discharge, which took several weeks. Our battery does not suffer from any of these issues. In fact most modern batteries have no problem sitting on concrete or steel for that matter.

[wilsonmw04]

Originally Posted by JesseK

Do not ever set your battery on concrete.

I don't understand the chemistry/physics behind it, nor do I ever intend to delve into the science of why it happens but something about rebarb, concrete and long half-life radiation drains your battery if it's in close proximity to concrete. I saw it happen repeatedly at the VA State Fair with our robot and rather than trying to understand why I'll just accept the fact that it happens for now.

What we saw was that the charger would say our battery was fully charged. We'd then transfer the battery to the robot and place it on the field. At the start of the match, the bot would move extremely slowly, and the OI would indicated ~7V on the battery. About 15 seconds into the match, the voltage would go UP and the robot would act normally. Who knows why ? What I do know is, we do not place batteries on concrete any more and we haven't seen the problem since.

If you thought your batteries were charged and then you get these results, perhaps this is why.

From my limited understanding of Physics and Chemistry, concrete should not affect the charge of the batteries in any way. It doesn't seem logical. Squirrel is probably correct about the temp, but the building at the VA fair is more likely hot than cold.

[Kevin Sevcik]

Originally Posted by wilsonmw04

From my limited understanding of Physics and Chemistry, concrete should not affect the charge of the batteries in any way. It doesn't seem logical. Squirrel is probably correct about the temp, but the building at the VA fair is more likely hot than cold.

Temp has some affect on batteries, but I don't think it's THAT great. I've got a panasonic SLA spec sheet pulled up that indicates you'd lose less than 20% capacity between 30C and 0C. Since as far as I know, all Regionals are held indoors or at least somewhere comfortably above freezing, I don't think you'd be likely to lose even that much capacity.