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.

[Ernst]

why are your wheels so big and not custom?

[Greg Woelki]

Originally Posted by Ernst

why are your wheels so big and not custom?

I tried, but our freshmen lost enthusiasm about filing the blocks of aluminum I gave them into Andymark Performance Wheels after only a few hours!

[asid61]

Very nice... I love what you've done with the double first stage belts. The weight came out really nicely it looks like too. Given the price of waterjetting, this could be a great way to make the DT as fast as possible early in the season. Are you planning on releasing CAD for this?
Seconding the notion about the massive wheels. If it's not under 2", it's definitely too big.

Seriously though, what is it with you people and not using buttonheads?

EDIT: Given the space between plates, this could be a good candidate for 15mm wide belts.

[marshall]

With this drivetrain and some roughtop tread we can tear up twice as much field carpet. Thanks!

[Greg Woelki]

Originally Posted by asid61

Very nice... I love what you've done with the double first stage belts.
Seconding the notion about the massive wheels. If it's not under 2", it's definitely too big.

Seriously though, what is it with you people and not using buttonheads?

Thanks!

Unless I need them because of clearance issues, I prefer to avoid using button heads. The smaller hex size is much easier to strip and doesn't allow for as high tightening and loosening torque. Additionally, button heads are weaker (compare alloy steel button heads and socket head cap screws on McMaster Carr, minimum tensile strength of 120ksi for button heads, 170ksi for socket head cap screws).

Edit:

Originally Posted by asid61

Are you planning on releasing CAD for this?

Sure, I'll upload both of them to GrabCAD.

[Zac]

Originally Posted by asid61

Seriously though, what is it with you people and not using buttonheads?
.

In my experience button heads typically have a shallower hex, as well as a smaller hex size. With overzealous wench operators (common in these parts) this leads to stripped heads, stripped Allen wrenches, or both.

~Zac

[RoboChair]

Originally Posted by Zac

In my experience button heads typically have a shallower hex, as well as a smaller hex size. With overzealous wench operators (common in these parts) this leads to stripped heads, stripped Allen wrenches, or both.

~Zac

And sometimes even the fabled "handled" bolt

[Greg Woelki]

Originally Posted by RoboChair

And sometimes even the fabled "handled" bolt

And sometimes even my 3/32" allen wrench being snapped in half by one of our members at champs...

[pwnageNick]

Originally Posted by Greg Woelki

Unless I need them because of clearance issues, I prefer to avoid using button heads. The smaller hex size is much easier to strip and doesn't allow for as high tightening and loosening torque. Additionally, button heads are weaker (compare alloy steel button heads and socket head cap screws on McMaster Carr, minimum tensile strength of 120ksi for button heads, 170ksi for socket head cap screws).

Yeah I generally only use button head or counter-sunk if I have to. However on the outisde of your drive I would have used button head since that's the very outside of the drive. It would make dealing with the bumper a bit easier.

[Greg Woelki]

Originally Posted by Greg Woelki

Sure, I'll upload both of them to GrabCAD.

I lied. Here are Google Drive download links.

Two-Speed
Single-Speed

Originally Posted by pwnageNick

Yeah I generally only use button head or counter-sunk if I have to. However on the outisde of your drive I would have used button head since that's the very outside of the drive. It would make dealing with the bumper a bit easier.

Yeah, if I were actually building this with the reality of bumper rules I'd probably just bite the bullet and countersink them all.

[BrendanB]

Originally Posted by pwnageNick

Yeah I generally only use button head or counter-sunk if I have to. However on the outisde of your drive I would have used button head since that's the very outside of the drive. It would make dealing with the bumper a bit easier.

^+1

I'm a big fan of the following combo on a robot which is what we used:

1/4-20 countersunk
1/4-20 button head
10-32 socket head

We had a few T handle 5/32 allen keys so when combined with riv nuts most of the robot came apart with one tool. On our wheels we used 1/4-20 socket heads and 5/16-18 button heads for our axles and wheel hubs. This meant we could use a 3/16 allen T handle for both as well.

Nice drive Greg!

[dirtbikerxz]

IF you are tired and sick of having 775-pros lying around everywhere, than we will buy some from you!