I'm crafting a small 3 speed "gearbox" for a project of mine and I'm aiming for simplicity in the first place since I'll have to create it myself and I'm not particularly gifted when it comes to using my hands.
Initially the idea was to buy proper cogs but when I discovered how their prices go I resorted to using bicycle sprockets from a cassette like this one which go for ~$10.
Basically I'll take it apart and have 2 shafts with sprockets on both sides matching my calculated gear ratios, one side will be on bearings, all 3 pairs, respectively for my 3 gears, connected with a chain piece of their own and I'll have selectors sliding on the bearing side engaging different gears - pretty close to how a conventional gearbox works just a poor man's version.
My problem is I can't figure out what type of chain goes on a typical mountain bike you would see sold commonly in any casual bike store. There are a bunch of different claims I found which lead me to believe that it's either 25H or T8F but I couldn't determine with enough confidence to order.
The maximum force that will need to be exerted in order to propel my vehicle on the steepest hill I've designed it for is about 650N, which multiplied by wheel size comes out to about 150Nm on the output shaft. That's roughly about 60kg I'm assuming the chain and sprockets will have no problem handling that.