Cim breakers tripping?

[Hazmatt]

Hello. My team was having a little trouble at the West Michigan regional with the main CIM motor's breakers tripping towards the end of the match. My mentor tried to explain that as the victors heated up, resistance would rise causing a higher current draw, but that seems backwards to me.

My thought was that maybe 2 victors weren't enough to push our bot and the CIMs were being over-taxed. The bot weighs 119.2 pounds(without batteries) We are using a two wheel center drive system, 1 motor per wheel using standard toughboxes with direct drive to the wheel (no further reduction after the toughboxes). Would adding another CIM to each wheel remedy this situation? Thanks alot!

[Chuck Glick]

One motor : ONE victor.

What are you using on the ends of the bot for wheels? (casters, omnis, static wheels)

[Hazmatt]

Originally Posted by Chuck Glick

One motor : ONE victor.

Elaborate... Each motor is being driven by ONE victor. The ends of the robot have castors on them.

[chris31]

Originally Posted by Hazmatt

Elaborate... Each motor is being driven by ONE victor. The ends of the robot have castors on them.

He is saying that your cant use more than one Victor per motor. What are your center wheels?

[Hazmatt]

The center wheels are treaded 6" wheels.

[Gocho]

[quote= Would adding another victor to each wheel remedy this situation? [/QUOTE]

Each motor should only be powered by one victor, period. You can't add another one per the rules and adding one in the circuit would most likely not fix your problem. Make sure that the fans are running on the victors because they can and will over heat with extended use. The fact that it is happening at the end of the match rules out a short unless it is just bad luck...

[Hazmatt]

Sorry, what I meant to say was "would adding 2 more cim motors remedy this situation"

[jee7s]

Assuming you are in complaince with the rules (it's hard to not be given inspections) you should only have 2 CIM motors if you are only using 2 speed controllers. Each speed controller is protected by (at most) a 40A breaker. You can't drive a (single) motor with more than one victor under the rules (this also presents some coordination problems), and the victors can handle more than the 40 A (or so) that the breakers blow at.

Keep in mind that using two CIMs as drive motors gives you half the power of using 4 CIMs. This presents a possible solution, but it is too much weight given your margin.

Since you are only using two CIM motors, you have a limit to the force they produce as well. This depends on the reduction, but if the motors are loaded too much, they will draw excess current, and thus blow the breaker.

If these problems occur late in matches, look for something heating up or binding which would present mechanical resistance. Also, look for ways to eliminate friction within the drivetrain.

However, I would suggest you see if it is merely the time of the match that coincides with the breaker blowing. Consider what the robot was doing at the time. If it was pushing into a robot (or a wall) and you have high traction wheels, this would easily cause a breaker to blow.

EDIT: Almost forgot...

If a victor overheats, its internal resistance increases. However, increased resistance would cause less current draw. If the victor was overheating, you'd have a wonderful burnt plastic smell in the vacinity of your robot. Also, you would see decreased power at the motor without the breakers tripping. If it were to overheat too much, you'll melt the transistor packages, then cause all sorts of thermal effects that would alter the doping of each transistor, rendering it unusable. (but you'd probably stop before this when you saw the smoke and (potentially) fire.)

Part of what the rules do is prevent this. FIRST knows that a properly cooled victor handling 40 A, as expected in a match, would most likely not overheat. Safety is built into the rules

[ShaneP]

How hot are the motors getting? 120lbs. robot, one CIM per side, direct drive off of tough box. Sounds to me like the two CIMs are having to work too hard. After they heat up, they do draw more current, and could be causing your breakers to trip.

[Gocho]

I have seen teams get into pushing matches with only two CIMs and no gear down and do fine and not blow breakers. Check for shorts and make sure that the connections on the power distribution block are tight because they come loose easily. Did it happen at the same time during every match? Did you ever regain power to that motor? and was it both motors or just one?

[Hazmatt]

I really have nothing to compare the heat of the motors to, being on a rookie team and all, but The CIM's were hot. If adding more motors is a necessity, we can always shave a bit off of our 30 lb counterweight.

[Hazmatt]

Originally Posted by Gocho

I have seen teams get into pushing matches with only two CIMs and no gear down and do fine and not blow breakers. Check for shorts and make sure that the connections on the power distribution block are tight because they come loose easily. Did it happen at the same time during every match? Did you ever regain power to that motor? and was it both motors or just one?

It seemed like both motors, and I suspected breakers because if I let the robot idle for a few seconds, it would regain full power. The breakers seemed to trip always towards the middle to the end of the match.

[EricVanWyk]

A 40 Amp breaker doesn't magically break at exactly 40 Amps; the trip time is an imperfect function of its internal heating, which is a function of current. When the metal strips inside reach a certain temperature, they bend and push away from each other.

CIMs can draw upwards of ~120Amps if you stall them. At that draw, the breakers should pop within a few seconds. But you aren't stalling them, you are simply asking a lot of them. It is very possible you are drawing 60-80 amps many times a match.

The first time you do this, your breakers won't trip because they are cold. Each time after that, you run an increasing risk of popping as they heat up.

Adding two more CIMs will definitely help the situation. In the mean time, you can reduce the load on your motors by reducing any friction you may have in the transmission.

[Hazmatt]

Okay. Thank you.

[Uberbots]

You sure its the breakers tripping and not the robot simply resetting due to a lack of battery power? keep your batteries in order

I cant imagine that you would have the motors under so much stress that their breakers would pop in a 2 minute match... im thinking something else is wrong. did this ever happen in practice?