The Project
In my quest to build cheap bots, I wanted a cheaper switch. Sure I could use a Link...but no. The Finger Tech switches are fine, but can cost $7-$15 and they seem to explode on impact. Joseph Betz makes a nice little switch, but it is really best suited for Fairies and still runs $5.
Design Goals
- Cheap - should cost around $1 to make
- Light - should weight around 2g to be on par with a Finger Tech switch
- Ant Weight current - should be able to handle the current that any ant weight will throw at it.
- Shatter Proof - should not explode on impact.
Things needed
- TPU shell - flexy and shatter proof.
- Brass or aluminum screws for good conductivity
- Brass or aluminum nuts for good conductivity
- A way to load test the switches to get an accurate current threshold
- A temp sensor to monitor the switch under load
The Story
My first thought was to get two aluminum nuts, solder wires to them, then put them in a TPU body that would keep them separated. Then a screw would thread between them completing the ciruit.
I prototyped this with some zinc coated nuts and it worked well. So i ordered some aluminum nuts. However, I didn't take into account how hard it would be solder to aluminum. It turns out I'd need special solder or flux to make it work because aluminum oxidizes sooooo quickly.
The new plan is to use some brass nuts with and an aluminum screw.
The Results
In the prototype, I used general zinc coated steel hardware. I found that I could get the switch down to 2.6g, a cost of around 30¢ and it could handle 10A for 3min with the switch reaching a temp of 85ºC. I suspect with brass & aluminum hardware it will cost around 50¢ but should have a higher current capacity and weigh a little less.
Next Steps
- Solder up a version using brass nuts and aluminum screw
- Load test brass/al version
- Improve my load tester
