Billfred's Very Silly Gift Card Main Breaker Shield

I’m wired a certain way. I buy a lot of gift cards under advantageous terms (either money off or getting more credit card points than I’d normally get going straight with the company), but I’ve never loved the waste factor. I keep a container of empty ones for tasks–spreading glues, scraping stuff that doesn’t need a razor blade, things like that–and at my last job I chopped up many to make really cheap battery interrupters (and I’d happily put mine against the COTS ones).

In 2022, we put on an AndyMark printed breaker guard. At SCRAP 2022, an errant intake from an opponent smashed it and hit the breaker hard enough to halt the robot for the last bit of the match. Ironically, I didn’t have a gift card handy–but we had gaffer tape and our lead teacher’s EMT credential, and that got us through the day.

Now that I’m the owner of my own 3D printer, I decided to give myself a task.

Design objectives:

  • Minimize filament usage–beat the AndyMark shield and Nick Aarested’s excellent shroud, probably by using gift cards to bridge spaces.
  • Provide a reasonable amount of protection against the button being bumped, assuming a frame member is close enough by to absorb the worst of most hits. (I’m not expecting any printed shield to survive the whack we took at SCRAP 2022.)

I’m hardly a master designer (teams I’ve been on have won two events in 20 years playing offense), so it took a few rounds to get happy with it:

The first round was a complete spitball. I guessed at the sizes needed to accommodate a standard credit card, and the result was much too tight. In the process, I also snapped some of the legs.

Generation 2 gave me the card notch size I’ve used since, and I started playing with gussets to strengthen the posts on the sides that don’t get cards. Generation 3 was another version of that, using the space from the bottom of the breaker to the bottom of the stud to tie them together.

The last generation was when I realized the long sides really didn’t need to be straight at all. I also shortened the posts holding the cards, since they weren’t really doing much at the top, and I sent Onshape’s Lighten feature script after the bottom plate.

The result of all this? On my Bambu P1P on Extra Draft settings (and Random seam position) with a 0.4mm nozzle, BambuStudio reports:

  • AndyMark breaker shield: 40.42 grams of filament, 1h5m print time
  • Nick Aarested’s Shroud: 19.18 grams of filament, 36m12s print time
  • Mine: 11.99 grams, 35m8s print time. (My shipping scale reads 18-20 grams with two gift cards thrown on, but that’s on the very low end of its reading range so I don’t trust the number for much.)

Will this cure the world? Nah. Does it use less filament and get one more use out of waste plastic? Yeah. Baby steps.

Here’s the Onshape document, if you’d like to play with it. It’s designed to mount like the AndyMark mount, with bolts holding the breaker to the mount and a larger plate below.

The cards are fairly comfortable in the slots, but I’d put a drop of CA glue on the cards once installed before competing with it.

If you make it, let me know what you think!


Would you recommend the Optifuse main breaker for anything other than using as a model?

We used the optifuse this past year, had no issues, also didn’t see any difference compared to the “standard” breaker.

I’ve heard of zero advantages and a few horror stories, so why mess with the brand we’ve known for 20 years?


Ours failed after a single event and left me feeling like it could fail closed instead of open as ours did. There isn’t a whole lot in FRC that will make me exclaim “safety!” but the optifuse breaker is in the list. I wouldn’t use it again and it terrifies me.


From a comp I was at:

The same team had a second one fail too. There were several more reports in the CSA slack. The Optifuse has much more brittle plastic and seems less well assembled, in my opinion they shouldn’t be legal and including them in the kit hurts teams.


Billfred, have you gotten to do any impact testing with this design? Or will you all be running it at SCRIW?

First, really cool shield idea Billfred, especially using the old gift cards. I’ll definitely be showing this to the team for next year’s robot.

Second, why did they switch the KoP to the Optifuse breakers? What was wrong with the old Bussman breakers? Those things are practically bulletproof. Goodness knows we’ve had them take serious hits and come through undamaged (though they have been switched off a couple of times, thus my warm feelings for Billfred’s fine work.) We didn’t switch last season because we’d done all the opt-outs and we have several brand new in-box Bussmans still sitting around the shop. Did no one do durability testing on the Optifuses at FIRST HQ before they sent them out in the KoP?

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I haven’t gotten runtime on it yet, but I tried to bust the cards by bending them toward the inside and wasn’t able to apply a force that actuated the breaker’s trip button. The (unglued) cards actually popped out of their channels first before any of the print failed, and the transparent part of that Starbucks card in the pictures shows some fatigue marks from me trying to bend it. Having the cards so close to the sides of the breaker seems to help here, since they don’t have room to do anything too silly. I wouldn’t run it on the very exterior of a robot, but then I think you’re tempting fate mounting main breakers to the very exterior of a robot no matter what shielding you’re running. As protection against a stray part or game piece inside a robot, I think it’ll please a lot of folks.

Assuming we have the people available to field the robot at SCRIW on top of our hosting duties, our main breaker needs a relocation anyway (the SCRAP rebuild took away the easy access angle, and we didn’t notice that until SCRAP). I’ll work that into the plan.


Huh, that’s unfortunate, good to know.

Yeah, this breaker sucks. Glad to see this post bring some awareness to issues teams are seeing. Shield is neat tho!


How should an inspector determine the fair market value of a gift card?


Call the number on the back


You can get them for free. So $0.

Usually, it says on the back of the gift card how they aren’t worth anything (a hundredth of a cent, if I recall correctly). I really hope that’s below the limit.


If it’s a Visa gift card, send me the number, the three digits on the back, and the expiration month and year and I can make sure the card’s value is low enough.


Or have memories from the hotels and use the key cards from places your team has stayed :rofl:

For Sure! Cabin door card from my post about the Danube of last week’s weekly wins. Drive the robot up the gangplank and the boat says Welcome Aboard the Viking Jarl Mr. Thomas. (Non-slip, cleated gangplank will remind the robot of StrongHold - shudder!)