Main breaker tripping, dead CIM

[jeremylee]

I think you could be geared a little fast. If its not too hard to swap, a 50:24 gearkit and some 14T or 13T pinions would fix it, though you lose some top speed. Checkout WCP website for ratio options.

[Oblarg]

Originally Posted by jeremylee

I think you could be geared a little fast. If its not too hard to swap, a 50:24 gearkit and some 14T or 13T pinions would fix it, though you lose some top speed. Checkout WCP website for ratio options.

The problem is that doing this on a KOP chassis is about 2-3 hours of work. We might go this route if we don't think any other option will suffice, but it's not a particularly favorable option.

[m1506m]

Does anyone have any advice (other than ditching a bunch of weight and cleaning out the gearboxes) for ensuring we're not tripping our breaker at worlds?[/quote]


Pull one cim off each side and replace them with mini cims. Making a 2cim/1mini cim gear box on each side.

[mman1506]

Originally Posted by Ian Curtis

I was always under the impression that once a main breaker had tripped you should replace it since it took less energy for subsequent trips. Is that actually true?

It seems to be true in our case. Switching out the breaker solved almost all our problems. We also copied the poofs and used a upside down can of compressed air to freeze the main breaker before a match.

[MrRoboSteve]

Originally Posted by m1506m

Does anyone have any advice (other than ditching a bunch of weight and cleaning out the gearboxes) for ensuring we're not tripping our breaker at worlds?

Programming options:

1: easy: set a maximum current flow lower than 100%
2: more challenging: limit current to CIMs at a gearbox when it is not turning and you've been at high power for a bit. This requires distinguishing "starting at rest" from "been pushing for a while".
3: more challenging: like 2, but turn off other motors/compressor on robot when in pushing situations
4: more challenging: like 2, but implement this as a "current budget" where you estimate current flows and heat dissipation, with the latter decaying over time.
5: easy: like 1, exception implement a driver controlled "pushing mode" on your robot, that lowers maximum current levels
6: more challenging: like 2, but only when driver selects "pushing mode"

Next year's control system should open up some interesting options in this scenario.

[Pat Fairbank]

Originally Posted by Ian Curtis

I was always under the impression that once a main breaker had tripped you should replace it since it took less energy for subsequent trips. Is that actually true?

We've observed this on multiple occasions, and my understanding is that the tripping action is caused by the bending of a bimetal strip inside the breaker. I imagine that the strip could be subject to plastic deformation near the trip point and wouldn't have the same characteristics afterwards.

Whenever we trip a main breaker in competition (twice so far this year) it gets thrown into the nearest trash can and a new one goes on the robot. As Marcus said, between matches with tight turnaround we cool it down with compressed air.

[NotInControl]

Originally Posted by Ryan Dognaux

You could try implementing a voltage ramp in software. We did this in-between Central Illinois & St. Louis and never had another issue.

We did some testing on our practice drive at our school and found we were able to force the robot's radio or CRIO to reboot using 6 full sized CIMs geared similarly to what you described. Once we implemented the voltage ramp the problem was solved and we couldn't re-create the symptoms.

+1 for voltage ramp. Doing this will lower the probability of all of your motors drawing peak current. We too do this on all of our 6-cim robots.

What language do you use? I am sure many teams on here can provide an example for the implementation in your programming language.

Originally Posted by Pat Fairbank

Whenever we trip a main breaker in competition (twice so far this year) it gets thrown into the nearest trash can and a new one goes on the robot. As Marcus said, between matches with tight turnaround we cool it down with compressed air.

I know im side tracking here, but I am curious, do you know what was causing you to trip the main breaker?

[Pat Fairbank]

Originally Posted by NotInControl

I know im side tracking here, but I am curious, do you know what was causing you to trip the main breaker?

Usually it's stalling a six-CIM drivetrain while trying to get out of a pin or T-bone, sometimes exacerbated by having had another match right before for the breaker to heat up.

Perhaps it's time for FIRST to consider distributing a higher-amperage breaker in the Kit of Parts? With all the motor power available to teams now, this seems like a pitfall that a lot of teams are falling into.

[Travis Schuh]

Originally Posted by Pat Fairbank

Perhaps it's time for FIRST to consider distributing a higher-amperage breaker in the Kit of Parts? With all the motor power available to teams now, this seems like a pitfall that a lot of teams are falling into.

Or perhaps it is time for teams to back down on the number of motors they stall at the same time. Our experience with 6 CIM drive in 2013 was that we lost more matches due to blowing the main breaker than we won by having that little extra in our drive train. We went back to 4 CIMs in the 2013 off season and this year and have been very happy with the results (IE no blown breakers, just fine pushing and speed). The extra 2 CIMS in the drive isn't really adding 50% more performance. I would be interested to see some testing/analysis (which is on our todo list) of how much of a difference 6 CIMs vs 4 CIMs makes on performance given the limitations of the battery.

[Mr V]

Originally Posted by Pat Fairbank

Usually it's stalling a six-CIM drivetrain while trying to get out of a pin or T-bone, sometimes exacerbated by having had another match right before for the breaker to heat up.

Perhaps it's time for FIRST to consider distributing a higher-amperage breaker in the Kit of Parts? With all the motor power available to teams now, this seems like a pitfall that a lot of teams are falling into.

But to allow a higher amperage breaker would mean requiring larger gauge wire, higher capacity Anderson Connectors and a battery that could sustain a higher continuous current. I'm sure many teams would be upset as some have a rather significant investment in the current batteries and associated pieces.

[Oblarg]

The crucial bit we noticed is that at our gearing, our breaker is fine unless we stall the CIMs, i.e. while slipping the wheels we have no problem, and the CIMs do not stall on a fully topped-up battery if the compressor is not running.

So, it seems our short-term options (barring changing our gear ratio - if anyone thinks this is really our best solution even with the 2-3 hour investment to get it done, please let me know) are to not turn on our compressor if we are going to be playing defense and to make sure our batteries are in absolute top shape before going out on the field.

Does anyone know if there's a reliable way to test if batteries are actually charged? We have all new batteries this year, but the charge indicator on the charger can be misleading.

(As a side note, I'm wary about swapping two of our CIMs for mini-CIMs, as this could have the opposite of the desired effect by making it absolutely impossible for us to slip our wheels in a pushing match.)

[Ether]

Originally Posted by Oblarg

The crucial bit we noticed is that at our gearing, our breaker is fine unless we stall the CIMs,

Here's a possible software solution:

Measure the voltage drop across the main breaker with an analog input. Sample it and square each sample. Run the squared samples through a low-pass filter (a simple IIR would probably suffice). If the filtered value exceeds some experimentally-determined threshold, reduce the commands to the drive motors until the filtered value drops below the threshold.

[Oblarg]

Originally Posted by Ether

Here's a possible software solution:

Measure the voltage drop across the main breaker with an analog input. Sample it and square each sample. Run the squared samples through a low-pass filter (a simple IIR would probably suffice). If the filtered value exceeds some experimentally-determined threshold, reduce the commands to the drive motors until the filtered value drops below the threshold.

This certainly sounds like it's worth trying. Unfortunately, I'm a mechanical mentor, and am not sure how to implement this; what would be the best way to actually wire that, and what sort of low-pass filter code would you recommend (I know how to do simple exponential smoothing, but that's about it)?

[Ether]

Perhaps something like this.

[Oblarg]

Originally Posted by Ether

Perhaps something like this.

Amusingly, that's essentially exactly what my naive approach would have been, software-wise. Thanks.

I'm still partially leaning towards swapping out our gearkit to 7:1 or 8:1; we've got two spare gearboxes which should expedite the process greatly (much easier to switch out the whole gearbox than to change the gearkits of the ones on the bot). We can probably absorb the hit in top speed without too much trouble, as our defensive strategy is very much based on positioning and pushing.