8x 775pro, 2-speeds

[Greg Woelki]

If you're like most of us, the first thing you thought upon seeing Nick's 6 775pro drivetrain was, "But what do I do with the rest of my 775pros???"
Fear not.
If you're tired of having 775pros lying around everywhere and fed up with having available 40A circuits on your PDP, then this is the drivetrain for you!

2-Speed Version:



Specs:

8x 775pro
Adjusted theoretical speeds of 8.6 ft/s and 15.2 ft/s
22.8:1 and 12.9:1 reduction
1.5"x1.5" 1/16" wall 6061 square tubes for front and back crossmembers
1/8" diamond-cut aluminum bellypan with 1/4" wide strands
6x 3" x 0.875" wheels
#25 chain on 17t sprockets
9.9 lbs per module
23.3 lbs total


Single Speed Version:



Specs:

8x 775pro
Adjusted theoretical speed of 10.3 ft/s
19.0:1 reduction
1.5"x1.5" 1/16" wall 6061 square tubes for front and back crossmembers
1/8" diamond-cut aluminum bellypan with 1/4" wide strands
6x 3" x 1.5" wheels
#25 chain on 17t sprockets
9.8 lbs per module
23.0 lbs total

Note that the weight differences from shifting are essentially canceled out by my use of wider wheels on the single speed version.

I think that the belt wrap on the 775 pulleys would be just fine (it's only a little worse than what 971 used all over the place this year),
but obviously I'd test it out before actually making something like this.

To fixture for welding, the inner plates and crossmembers are assembled using 610's roll pin and threaded rod method and the bellypan is riveted to the crossmembers.
After welding, the threaded rods can be removed if one so desires, but I'd imagine you wouldn't want to assemble with significant preload if you intend to remove them.

Apologies for the huge images.