Keeping the main breaker from tripping

[metalthorn]

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?

[cgmv123]

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.)

[AllenGregoryIV]

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.

[TikiTech]

Originally Posted by metalthorn

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?

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!

[Chadfrom308]

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.

[magnets]

Originally Posted by TikiTech

Cooling by using canned air in a non approved method isn't safe. More than likely the trick will be illegal soon..

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.

[Cory]

Originally Posted by magnets

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.

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.

[Mark Sheridan]

Originally Posted by magnets

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.

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.

[brycen66]

Originally Posted by magnets

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.

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.

[Ether]

Originally Posted by brycen66

I made one last year in twenty minutes with parts that cost 3-4 dollars.

Please post details?

[brycen66]

Originally Posted by Ether

Please post details?

Place a steel washer or ring(any ferrous metal works) around one of your main wires. Then cut a slot in a steel washer and place a linear hall sensor in the slot. We epoxied ours in to keep it intact. The hall sensor outputs voltage which is directly related to the total robot current, and it can be plugged directly into the analog breakout. This is the system we have implemented into our practice robot and the results so far look good.
http://www.jameco.com/webapp/wcs/sto...001_1915940_-1

[Ether]

Originally Posted by brycen66

This is the system we have implemented into our practice robot and the results so far look good.

Have you compared the readings to a precision ammeter to determine the accuracy over the current range?

[brycen66]

Originally Posted by Ether

Have you compared the readings to a precision ammeter to determine the accuracy over the current range?

No, we compared it to the voltage drop data

[GeeTwo]

Originally Posted by brycen66

Place a steel washer or ring(any ferrous metal works) around one of your main wires. Then cut a slot in a steel washer and place a linear hall sensor in the slot. We epoxied ours in to keep it intact. The hall sensor outputs voltage which is directly related to the total robot current, and it can be plugged directly into the analog breakout. This is the system we have implemented into our practice robot and the results so far look good.
http://www.jameco.com/webapp/wcs/sto...001_1915940_-1

For anyone trying to implement this --the voltage produced by the ring (which merely needs to be conductive, not ferrous) is directly related to the RATE OF CHANGE of the current. You will need to keep a running total of the voltage to get a good value for current draw. I don't see how you're going to keep from having significant drift in a practice session unless you pause and recalibrate regularly, though perhaps over the duration of an FRC match it wouldn't be too bad. This trick works well for A/C meters because the current is constantly changing (and adds up to zero), so that the average voltage induced over a 1/60 sec cycle is proportional to the RMS current flow. For DC, no such luck - if you draw a steady curent, whether 1A or 110A, the voltage will be zero after it stabilizes.

[Alan Anderson]

Originally Posted by GeeTwo

For anyone trying to implement this --the voltage produced by the ring (which merely needs to be conductive, not ferrous) is directly related to the RATE OF CHANGE of the current....

That might be true if using an inductive sensor, but a Hall effect transducer responds to magnetic flux directly. The ring is not acting as a transformer element, but as a flux concentrator, and does need to be ferrous.