[Tristan Lall]

I've got a couple suggestions (based on using 3-motor gearboxes for the last three years).

SDP/SI is a good choice for gears--their service is fast and they stock many sizes and materials; however, I know for a fact that they carry 32 pitch, 20° pressure angle gears which will mesh properly with the F-P--why choose to use the approx. 36.29 pitch gears (i.e. 0.7 module) instead? Is it because of compactness? Consider choosing the right gears from their catalogue, and modifying the design to accomodate both the 0.7 (for the drill) and the 32 (for the F-P)--you can also match rotational speeds better this way.

Which 24 pitch gears are you using? Consider the hardened steel ones that SDP/SI sells--they worked nicely for us last year. By all accounts, they're fantastically strong. For a low-speed, high-torque gear, I'd be wary of regular steel gears, and would absolutely rule out aluminum, brass or plastic (again, experience...we chewed up some rather expensive aluminum gears last year, and they were only in the middle of the gearbox). Edit: To clarify, in terms of 24 pitch gears, I'd be careful about regular steel gears. Regular, un-hardened steel 20 pitch gears will be fine--that's what we use for the gears beside the shifter, though having them hardened wouldn't be a bad idea.

You're welding some of the gears, I see. I'm not a fan of welding, because it can make disassembly a great pain. I'd recommend keyways if possible. (Consider adapting the design for keyways; despite the initial difficulty of putting them in, if you lack a broach, they're very precise and easy to work with.) If you do weld, make sure that the materials are compatible!

Finally, I'm always a little concerned about those drill motors being held on by a pair of 10-32 or M5 screws alone (in holes with very little thread). While teams have definitely had success using this method, I've always preferred to use an aluminum collar around the drill motor. (As it happens, the last two years, I've used a "belt and suspenders" approach by using both the collar and the mounting holes--but this may not be suitable, depending on how quickly you want to be able to change a drill motor.)

With any luck, I'll be posting some specs for an uprated version of 188's 2004 gearbox (3-motor, two-speed dog shifting) in the near future...as a matter of fact, the design is done, and I'm working on the drawings now.