So, more of a joke project... but I motorized a beer cooler with some surplus hoverboard wheels and made a build video. hope you all find it humorous!

@motsu · edit-2 23 days ago

So, more of a joke project... but I motorized a beer cooler with some surplus hoverboard wheels and made a build video. hope you all find it humorous!

@motsu · 23 days ago

oh, thats a good point on the heat issue with solder… i mean the BMS and fuse should save it, but i hadn’t thought of that. Do you have recomendations for how to attach the main bus wires coming off the battery in a non soldered way? cause with flat top 18650 based batteries, you have to spot weld nickel strips, and soldering the main wire to the strip before spot welding is the only thing i can think of. If you go with something like headway lifepo4, they are screw top, so you could fab a contact plate that the wire crimps into, then screws to the battery, but yeah - no idea how to do something like that with flat top batteries.

@[email protected] · edit-2 23 days ago

I’m not an expert with building battery packs, but I think solder isn’t a problem for connecting the nickel strips, so long as it’s only a fraction of the whole pack. And if it’s encased within the battery housing, spall won’t be as bad of a problem. The highest currents would be where the “strings” are aggregated together in parallel, and that’s usually when heavy gauge copper is used.

I recall that Aging Wheels has done videos on cell replacement, and I think maybe there was some sort of copper/brass busbar which aggregated the various nickel strips and then had large screw-down terminations for attaching external cables.

Rewatching your video again, do I understand that your emergency cut-off is inline with the full battery voltage? If your design had a smaller auxiliary 12v battery for powering the electronics, you could have a low-voltage control signal that closes a normally-open contactor that connects the main battery. Your emergency cut-off would be in-series of the control signal, so that loss of the signal immediately cuts off main battery voltage.

The same signal wire could be routed around to other safety sensors to isolate the main battery if something is wrong. In the most extreme case, the wire could be routed so that severe structural damage would automatically sever the wire.

This would also reduce the amount of heavy wire to only where it’s needed, with some weight savings. Air conditioner condensers do this same trick, so that the safety sensors don’t have to be rated for full 240 VAC.

@motsu · 23 days ago

yeah, the emergency kill switch had the full power going through it. I did something similar with relays on the back with the initial esp32 control, where if the relays were powered but no signal was sent to the relays, it would close the brake pins on the cheaper ESC’s as another safety feature.

it was kinda cool, a little kid (like, elementary school aged) came up and was asking about the project, with his dad right behind him. the kids questions were all pretty much around how he could potentially make something similar. I answered them in an age understandable way, but also walked through all the different potential failures and how it related to saftey, and how I added things like the relays, battery fuse, and cut off switch to mitigate the risks. basically saying “yeah, making something like this is dangerous, but you shouldn’t let that get in the way of making your ideas a reality - its just important to walk through those risks and mitigate them as best as you can, and think if you can reach an acceptable risk before you spend money and time”. The dad didn’t say anything, but i could tell he was beaming since the kid was realizing all the safety stuff, and realizing that thinking through that stuff is very important. about 1/2 way through, the kid was just asking more safety related questions haha

@[email protected] · 23 days ago

That’s wonderful that children are interested in the project. This and related projects would be great to showcase at Open Sauce. I certainly enjoyed this year’s displays.

@motsu · 23 days ago

yeah, i went the past 2 years. sadly driving a project down wasn’t in the cards. Both times i brought a body mounted project though. First year it was a 3d printed cat treat dispenser that would track the distance my cat runs on a cat wheel, then gives him a single treat after he runs a certain amount. I had a mini version mounted on my chest. This past year, i brought some arm mounted EDF’s that I plan on using to propel myself on skiis in the snow. I plan on making videos about both eventually, but im trying to space out larger projects like those (and the cooler kart) with smaller ones :)