Keeping the main breaker from tripping
 

We have purchased the 3 CIM vex pro ball shifters. We used them last year but only with 2 CIMs because we tripped the main breaker multiple time. We want to go back to three but we need some tricks to stop the main breaker, we know about the canned air flipped upside down, do you guys have tricks or recommendations?

Re: Keeping the main breaker from tripping
 

Monitor current in code using the new PDB and adjust outputs accordingly. I'm sure multiple teams will post example codes of how to do this. (For all we know, multiple beta teams have code that does this, but they can't share them yet.)

Re: Keeping the main breaker from tripping
 

There isn't any one solution. We ran 6 CIMs, & 2 MiniCIMs through 7 events this past year counting off-season events and never tripped the main breaker.

We were running a butterfly type drive so we were mostly on 4 omni-wheels which means we have minimal wheel scrub.

Wire management is also important. Ensure that you have the shortest possible wire path from your battery to your drive train motors. This means your battery wires to PD board/panel should be short, your wires from speed controllers to PD panel should be short, and the wires from speed controllers to motors need to be short as well. This takes a lot of pre-planning to do well.

We also used a single reduction gearbox that made it very efficient compared to more complicated gear boxes and we also ensured that our wheels would slip before we ever stalled the drive train motors.

On our practice robot we ran fans over the motors to keep things cool during long sessions and we will likely look at adding fans over our motors and our main breaker on next year's robot.

Re: Keeping the main breaker from tripping
 

We ran the WCP 3CIM DS transmissions last year without any issues at all.

The biggest trick - Make sure you set up the gearing correctly for your load.
Most of the problems I have seen were based on trying to run too high of a FPS. Also USE the low gear range. I have also seen a lot of these dual speed transmissions running generally as a single speed.

We have been very pleased with these DS transmission. It just take some research to get it right.. Making sure that you are not stalling your motor for a long period of time is key.

Cooling by using canned air in a non approved method isn't safe. More than likely the trick will be illegal soon..
Perhaps adding a fan that helps cool the breaker could help, we run one for the compressor as it is..

Designing the robot with this in mind is a much better approach.

I understand using this process in a pinch but this should not be the standard solution to the issue.

Good luck this season,

Aloha!

Re: Keeping the main breaker from tripping
 

We ran ~2.1kW on our drivetrain. That's 4 big CIMS and 4 Mini CIMS on our drivetrain (1 CIM and 1 Mini CIM per wheel). We never tripped the breaker. We also had mecanum wheels which helped us reduce the load because they slipped a little.

Re: Keeping the main breaker from tripping
 

Excellent point. FIRST goes bananas about safety. There is a safety animation, a safety award, a safety manual, safety inspectors, and tons of safety rules on the robot. I understand the need for safety, but FIRST should be consistent with how they make calls like this. Why should canned air, used in an unrecommended situation be considered perfectly fine, while using an air compressor or a flap grinder in its recommended configuration be considered too dangerous for use in a pit?

It's not unreasonable to think that a safety inspector would call this out. FIRST seems to have given the okay on this for now since Einstein teams were visibly misusing the canned air to cool their breakers on the field, but I agree that the trick will be illegal very soon.

Re: Keeping the main breaker from tripping
 

Teams have been using air dusters to cool motors/breakers since I joined FIRST in 2001. It probably happened before then too. You'd have to be a complete idiot to endanger yourself or anyone else while using it. Clearly a properly used air grinder is exponentially more dangerous than spraying an air duster upside down.

Re: Keeping the main breaker from tripping
 

There is a version of air duster specific for cooling electronics. so they are ok to cool circuit breakers. also the air duster I buy actually says its ok to use upside down, it just warns about freezing liquid coming out and to not contact that liquid. This may be specific to the stuff I use, I don't know other air dusters.

Re: Keeping the main breaker from tripping
 

That would be me, and I disagree.

Using canned air to cool the main breaker is actually very effective and not unsafe or misuse. If they do make it illegal it will not be because of the unsafe nature of spraying canned air but instead because of the possible unprotected surges of current. I think it is much more likely that the use of a fan on the breaker will be made illegal.

That all being said the most effective way to prevent a breaker tripping is having a properly trained driver or having automatic shifting. I say this because often the breaker will trip when the drive train motors are both stalled in high gear. A driver who downshifts before a collision and does not rapidly change from moving forward to backward will not trip the main breaker. I would be wary of the current sensing limiting the driver train because it takes control away from a driver and has a high chance of failing.

That being said if you are going to sense current, you should make your own sensor instead of using the built in sensors in the power distribution panel. This is because from my understanding the power distribution panel only has current sensing on the outputs and not the input. You should put the current sensor on the main pole of the battery, it should also be inductive instead of resistive. I made one last year in twenty minutes with parts that cost 3-4 dollars.

Re: Keeping the main breaker from tripping
 

Please post details?

Re: Keeping the main breaker from tripping
 

Why not just sum the currents at the outputs to get the current at the input?

Re: Keeping the main breaker from tripping
 

One team will come up with a clever way to keep the breaker's temperature super cold for the duration of the match, then FIRST will likely ban these sorts of modifications. In my opinion, the freeze spray is totally illegal from two rules. FIRST knows that teams are doing this, and although they haven't said anything about it last season, I wouldn't be too surprised to see an addition disallowing methods to change the temperature of breakers.

The first is G3. Deliberately freezing a safety device so it does not operate as intended seems like it may qualify as an unsafe modification in the eyes of some inspectors. It also seems to violate R64, because it can easily be considered to be tampering, modifying, or adjusting. It's clear that they don't want you changing the "performance and specifications of the device".


Also, could you clarify about the input/output comment for the current sensor? You should be able to sum all the drive/big motors up, and everything else should only end up being a few amps in total.

Re: Keeping the main breaker from tripping
 

By cooling the breaker you merely restore it to its rated current level. You don't get "bonus" current. You just aren't de-rating it due to it being hot (since it is a thermal switch).

By extension, you are against fans on motors?

Re: Keeping the main breaker from tripping
 

What is tampering, modifying or adjusting about it? The breaker spec sheet lists it's operation characteristics to -50F, and that it's designed to operate down to -25F. It is still operating completely within its design, performance and specifications. Freezing the breaker does not physically change the way it works, it just changes the operating temperature at the start of the match. There's nothing inherently unsafe about operating the breaker within it's design range.

I personally would not want to rely on freezing my breaker as a primary method to keep my robot alive during a match, but under previous FIRST rules, I don't believe it was illegal.

Re: Keeping the main breaker from tripping
 

To all teams running six or more cims on their bot and say that they have zero breaker issues, what speeds were you running?
Because there are only miniscule gains from running six cims on anything under 15 fps according to my drivetrain calculator. Maybe a few extra inches out of ten feet if you go from four to six cims.
Why do you run such low speeds on six cims?

On freezing the breaker, I don't really like it if it's before a match. After a match, okay. But before a match I feel like it defeats some of the purpose of having a main breaker. If it is to limit power, then why are you allowed to give yourself more power like that?

To asnwer OP's question:
Current sensing. Autoshift to low gear when you hit a certain amount of current for an extended period of time.