We're doing something very similar for Butter Side Down (12lb): couple layers of PCB that create a screw bridge (Allen/hex) across a custom main board. Some observations: first is that we use 3d printed housings to cover any exposed contact points and create a guide for the on/off wrench. This reduces accidental shorts during hard hits or creating one on a damaged bot while trying to disable/service Second thing is that each on/off creates a spark, which I'm sure is worse on a bigger bot, but principle is the same: each action blasts away a little bit of PCB copper until the contacts are shot. For us (6s) that's maybe 15-50 actuations. This bit us in a finals when it literally just turned off after a big hit. After the match it was clear everything except the switch was in perfect condition. Solution: use two in parallel, and have the first one channel through a current limiting resistor so there's no spark. If you're already designing PCBs for 150g I bet you could incorporate the parallel pair, housing, SMD resistor in a couple layers so it only uses one screw to pass through two different "stages" and guarantee you've got a good connection :)

An incorporated LED would be handy for these switches :)

Another idea involving two boards. Board 1 has a ring on the surface around the hole (or just pads) but the hole is not plated or threaded. Board 2's hole has thick plating and is threaded. This should avoid any soldering and you don't need to line up threads. Basically the same principle as the botbitz ant switch but you replace the nut with a PCB which you don't have to solder.

I would suggest threaded inserts to the p c b itself with a short piece of braided wire soldered to the circuit, Also don't cut the third tab off the rocker switch, instead Attach a green LED to designate Safe mode and then store with a battery unplugged. Red LED means hot, green LED means cold. That way even if the red L E D fails you will know if it's safe

RE the first concept: the problem with trying to thread a plated thru hole using a regular tap is that the tap is designed to cut into the material. that's why it has the flutes, they form a sharp cutting edge that efficiently removes solid metal from a hole, but in this case, it just cuts through the (very thin) plating. I'm surprised it's working as well as it is, but you'd probably get better results with a forming tap, which is a special type of tap that doesn't have flutes, and instead deforms the material to create the threads. but those are expensive, so a cheaper option could be to just use a screw as a makeshift "forming tap" and just force it through the hole. you'd need to experiment to find the exact diameter where you get the best thread engagement without risk of tearing the hole plating; maybe start with the 50% engagement diameter for the screw and iterate from there. you're right that the annular ring size can help improve reliability, there's more surface area of material bonded to the PCB surface, so it can better resist delamination (as well as provide some extra margin in the event of some tearing does happen). if you want to have your outer contacts near the hole and this limits your annular ring, you could use a copper pour to create a non-circular "annular ring", where it's still narrow where it needs to be but then reaches further out where there's space available. also, you can put a series of vias around the hole as well so that if the plating in the hole is ever fully severed, you don't lose connectivity between the top and bottom halves of that (plus the vias can help stop tears from spreading) this is incompatible with the previous advice, but, instead of 2 pads 180 degrees apart, why not try just have a continuous ring around the hole? then you don't need to worry about where the low spot is

Modifying a toggle switch seems like a good idea. I think, with a "big enough" switch, it could possibly work for a beetle. I'm quite sure it'll be less bulky and maybe lighter than the screw switch I made for The Unmaker. That just used a pair of hacked M6 captive nuts for contact points, divided by a polycarbonate ring, and it was screwed together in a small hand-billeted HDPE block. Great vid as usual, Ben! 👍

You should look into press nuts and do something similar to Seth with just cuz

The nice thing about the 1lb switch is that it would be very simple to have a 'safe-to-handle' light using the unused switch terminal. Might be useful for loan bots?

Ben, we had the same problem with our beetleweight AntiDozer, initially used a toggle switch and big hits would occasionally flick it off. We moved to a Fingertech type design - 3D printed a small block that would hold two M3 nuts with a small hole drilled though each and the power wires looped through and soldered and used a M3 grub screw to make the connection. No problem since. Though it has to be said there isn't much room on a M3 nut to drill a hole big enough to feed the wire through..........

The smaller single boards could be held apart in a "E" shape bracket which they could slide into which would be even lighter again than the 3D printed spacer.

I made a little box with a hole through it and 2 compartments, each holds a nut, then I soldered the wires to the nuts and put a screw through them.

Tapping would be easier with a printed guide where the pcb sits at the bottom of long hole so the tap is forced straight

I like the two-threaded-hole (fingertech style) version better than version #1 or #2. If that one starts to get loose, it will still make decent contact, while the other ones will be intermittent or lose contact almost immediately. Taking 3-5 turns of the screw to disconnect will be a lot more reliable than .5 turns. It also seems like it will wear less.

Ben, I'm not Combat robot builder, but I'd be weary of the "1 pound" switch. I especially fear that the glue would crack and fail under a big shock, and that the spring would force the new cover away. Or you'd need to ensure the "switch part" stays in place even if the glue fails. For the first ones, wouldn't it make sens to print them "vertically" instead of horizontally, so that you can slide the two parts into "5 side constrained" slots ? I guess a .4 "sidewall" would be enough to help keep the pcb in place and at least partly increase the electric insulation of the switch

possibly dumb question, but if the resistance of the 150g switch is similar to the 1lb one, then they should be fine for 1lb bots? if you have enough spare, and a test power supply, it'd be interesting to see what sort of current the 150g switches can take and see if they'd actually be okay for larger bots. Or stick one into a 1lb bot and do the most current-abusive things you can think of and see if they get hot. A thin (lock) nut soldered to the board (probably on the back) would make a far more sturdy connection and avoid the plated hole tearing out issue entirely, and should work with either v1 or v2 of the ant weight switches given the other contact is on the opposite side of the pcb. It might also be worth looking at the sort screw-clips that as used on cars for some trim retainers, they're stamped steel so should be conductive and reasonably strong, but also cheap and light. Just maybe not quite as compact. edit: google "speed clips" for this style of clip.

You couldn’t need to even tap it, you can ptpbably just screw it directly into the pcb

Personally I would be worried that it would come loose and you'd lose main power

Looks similar in concept to the Just cuz robotics PCB switch, interesting to see the development and how they function nonetheless

Maybe you can make a version out of a single dual-layer PCB with two thin nuts (ideally copper) soldered on either side? No issues with tapping or plating, and the nuts will work great for wear and robustness.

The fingertech switches are nice, but i worry about the current carying capacity of them. Aluminum or Copper screws would be much better than steel ones, and moving the two "bars" closer would also be a good idea. A shorter, thicker screw would also be better, while still being the same weight.

I don't understand how brits and australians have the patience to work with 150g bots and all the components that are smaller than their fingernails. Me and my fat fingers would lose my mind.