Optifuse main breaker issue

At the Las Vegas regional, our robot’s main breaker failed as we were setting up for a quals match, causing us to be bypassed for the match.


Ouch! Sorry that you missed a match.
At the North Carolina DCMP I was inspecting, and followed an experienced CSA into the pit of a robot that had been playing well then mysteriously powered down mid-match. Might have been 4561?

The CSA noticed that the breaker was by Optifuse, then I think ohmed it out. He immediately got the team a Bussman main breaker from Spare Parts. The removed Optifuse braker had a suspicious rattling sound when shaken.
Just another data point.


Optifuse breakers are not fit for robot consumption competitive robotics use.

As a CSA and RI, I always recommend the teams I work with to swap to a Bussman breaker as soon as they get home from their event.

Here’s a non-exhaustive list of failure modes for the Optifuse breakers that aren’t frequently reported with Bussman breakers:

  • Attaching them to something with bolts shatters the black housing (without any excessive forces)

    • I’ve personally broken two by simply attaching them to a robot, and I know of at least one other team that has had this failure.
  • The housing can crack from non-direct impacts (like bumper-to-bumper contact)

  • The internal mechanism for the red “off” button can break, causing the breaker to “fail closed” (fail while turned on and become impossible to turn off), which is exceptionally dangerous

    • IMG_2602
  • As seen in OP’s image, the red “on” lever can break off, rendering them inoperable

    • This one is new to me, and seems to be related to the brittleness of the black plastic
  • The breaker can “fail open” where the “on” lever won’t stay engaged and the breaker won’t supply power

It’s a shame that these were included in the KOP this year, and in FC last year. Several people have been ringing the alarm bell on Optifuse breakers, so I hope FIRST finally gets the message that they need to be banned.

If you have Optifuse breakers, get rid of them. Don’t relegate them to a testbed, because someone is bound to rip it off and put it on the robot when they can’t find a Bussman one, or end up accidentally donating them to an unsuspecting rookie team.


Yep… let’s remove these from being legal please?


I think I also remember reading that these have a worse trip time than the Bussmann one, but I couldn’t find the thread to cite it.

These were likely made legal because since the pandemic the Bussmann ones have, at times, been impossible to source in volume, but AndyMark is committed to only selling Bussmann brand 120A breakers.


Just to clarify, by worse do you mean faster or slower trip time?


Trips faster for a given amperage.

Worse for pushing the limits :wink:

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For those that already order from PowerWerx for other reasons, it might make sense to pick your breakers up there instead. The price is substantially lower, and they offer volume discounts (20%-40% cheaper than AndyMark). They offer the newly legal CB285-120 model, but not the classic CB185-120. (AndyMark sells both SKUs, but may substitute the CB285 if you order the CB185). https://powerwerx.com/bussmann-cb285-120-circuit-breaker-surface

I like the CB285 because it uses M6 studs instead of 1/4-28 (like the classic CB185), so I don’t have to have any 1/4-28 nuts floating around our shop and getting mixed with the 1/4-20s. The size and hole pattern of the CB285 is a drop-in replacement for the CB185, so no need to re-3d-print breaker covers and whatnot.


That right there is a reason for us not to use them. We have removed as many metric tools out of our toolbox as possible to keep the students from using metric allen wrenches and combination wrenches on all the standard hardware on the robot. 99% of the hardware we typically use SAE and not metric. So with that being 6mm It’ll probably take a 13mm wrench which will then be used on a half inch hex head. The bigger problem will be when a student drops one of the nuts and can’t find it then goes and takes a nut off an old breaker they’ll just send it. Screwing up the threads on the stud as well as the nut. Sorry for the rant but I’ve seen this scenario play out too many times


Pick your poison. Labeled metric wrenches in your toolbox, or unlabeled 1/4-28 nuts in your 1/4-20 nuts bin. :person_shrugging:. Just as likely someone grabs a 1/4-20 nut and puts it on the 1/4-28 breaker stud and wrecks it. Maybe even more likely…


we definitely learned the hard way about the 1/4-28 stud today :')


M6 nuts in the 1/4-20 nut bin. The only way that gets spotted is they don’t fit all that well… but a 1/4-20 nut can gum up an M6 stud.

(I work in a shop that’s mixed-systems. It gets interesting sometimes. M5s in the #10s. M8s in the 5/16-18s. And vice versa.)

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We keep the 1/4-28 locknuts in the pneumatics bin since many cylinders use that thread size as well. That keeps them far enough away from the normal hardware that it hasn’t been much of a problem.


Not really since the only place there are 1/4-28 nuts is on the breakers and the breakers stay in the electrical cabinet. The biggest problem we’ve had with nuts and bolts getting mixed up came from the old head coach buying and using 10-24 hardware to use everywhere on the robots. I finally convinced the new head coach to buy all new 10-32 hardware and remove the 10-24 from use. This year was perfect for it since we only had 1 returning build student that was used to using the 10-24 hardware.

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Oh boy. I fought this battle last year too. FIRST should ban 10-24 hardware alongside the Optifuse breaker ban :joy:


Another thing here that we weren’t aware of until we had to carry the robot off the field:

Once these breakers are tripped once, they’re toast. We tripped ours once at the very beginning of the season before we current-limited everything, and fast-forward a couple months to a qual, the robot turns off mid-match, with the lever STILL PRESSED IN. We turned the bot off and back on, and it worked.

Apparently, once these are tripped once, the current they trip at is lowered to a different value. The best guess of the CSAs on site was that we did something (i.e. hit a specific patch of carpet with a specific amt of fuzz in a wheel at a specific angle) that just exceeded that lowered limit, tripping the breaker, with the lever not displaying this trip because our breaker was bad.

So PSA: Replace your breakers if you trip them at all! Or just don’t use Optifuse

This is all of the breakers on an FRC robot. Internally to these breakers, there is a piece of metal that deforms as it heats up… it heats up under load (when current is passing through it). The amount of time it takes to deform (derived from the temperature it is at for an amount of current being passed through it for that time) is the “trip time”.

Anyway… that metal, like pretty much all metal, has “memory” and once it deforms likes to keep on being deformed so every single breaker on an FRC robot, once tripped, will keep on lowering the value at which it trips. There is, in theory, an asymptotic relationship here and there is some lower bound to it but… if you’re a team pushing on the main breaker then you’ll be pushing it ever lower.

We had one brand new optimax breaker mixed in with our bussman yesterday when i looked. I removed it and thew it out. When the lead build mentor saw me do it and asked why i informed him of being junk and unreliable. There have been so many parts i have thrown out in the last couple years that were being kept that were questionable wheter they were good or bad including 2 drive station controllers that had major drift and could be used in a pinch. Found out about those at one comp when one was used in a match accidentally and it cost us the match. What made me mad about the controller is the one mentor took it out of the trash and said we will just label it. So i went over took it, and cut the cord off of it and threw it out again. Some things are worth keeping to use if they are questionable but not many.

Interesting…thanks for the info! 6672 requested us to make this knowledge more public because it seems like very few teams have knowledge of it.

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