pic: 2012 frc971 transmission

[scottandme]

Originally Posted by Jared341

Having a number of teeth that is evenly divisible by 3 lets you hold a pulley with a standard 3-jaw chuck more easily, just in case you want to do something to the bore.

The tentative CAD design for now has us running a 6WD Franken-WCD with the two 15mm belts running inside a 2"x2"x0.125" tube. Not really ideal from a maintenance standpoint, but I'm hoping the belts will reliable enough.

I'm also fond of the divisible by 3 trick, but I think the 18T is the minimum Gates recommends for the 5mm profile, and bigger pulleys have higher load capacity. The 20T is about the biggest pulley size that fits comfortably inside the side rail tube, accounting for the center drop. The next pulley divisible by 3 is the 24T, which is too big. Setting up the 4-jaw isn't too big of a hassle, but I would probably just make a fixture plate for 8 pulleys, probe the existing bores and have the mill drill the bores to 0.5" before broaching them.

[AdamHeard]

Originally Posted by scottandme

The tentative CAD design for now has us running a 6WD Franken-WCD with the two 15mm belts running inside a 2"x2"x0.125" tube. Not really ideal from a maintenance standpoint, but I'm hoping the belts will reliable enough.

I'm also fond of the divisible by 3 trick, but I think the 18T is the minimum Gates recommends for the 5mm profile, and bigger pulleys have higher load capacity. The 20T is about the biggest pulley size that fits comfortably inside the side rail tube, accounting for the center drop. The next pulley divisible by 3 is the 24T, which is too big. Setting up the 4-jaw isn't too big of a hassle, but I would probably just make a fixture plate for 8 pulleys, probe the existing bores and have the mill drill the bores to 0.5" before broaching them.

You get a little more freedom if you aren't set on running the belts internal. That would let you pick a lighter profile tubing for your frame as well.

[scottandme]

Originally Posted by AdamHeard

You get a little more freedom if you aren't set on running the belts internal. That would let you pick a lighter profile tubing for your frame as well.

That's true, I think it'll be the pulley diameter needed that dictates that decision more than the weight gain/loss. 2x1x0.125 is 0.8085 lb/ft vs 1.036 lb/ft for 2x2x0.125, so it's only ~1.3 lbs lighter all said and done. Probably figure some weight added when you push the gearbox further inside the chassis to accommodate the ~1.25" of belt.

It's been hard to find enough detail from some CD research, but here are some I found.

1625 ran 2x1 frame with 9mm wide belt http://www.chiefdelphi.com/forums/sh...ad.php?t=86668

2791 looks like they used 2x1 with a single 9mm belt in 2011, but I think they mentioned ratcheting going full fwd to reverse. Also needs idlers to maintain proper wrap, I would rather avoid that. (http://www.chiefdelphi.com/forums/sh...ad.php?t=94701)

2791's 2012 chassis looks like 4x2 tubing with two 15mm belts. (http://www.chiefdelphi.com/forums/sh....php?t=101454). More weight, and requires >4" wheels, but solves the belt problem at least.

[Chris is me]

Originally Posted by scottandme

The tentative CAD design for now has us running a 6WD Franken-WCD with the two 15mm belts running inside a 2"x2"x0.125" tube. Not really ideal from a maintenance standpoint, but I'm hoping the belts will reliable enough.

We've run a very similar setup for two years, but we used 3x1.5" tube. The extra inch lets you get a bigger pulley in the tube and a little more room for installation, which makes the drive stronger and less likely to ratchet with quick direction changes.

Our drivetrain was literally maintenance free since we first set it up in week 4. Not a thing needed to be maintained. It was wonderful.

[Brandon Holley]

I'd guess we're venturing into a thread takeover at this point...We utilized 5mm, 15mm width HTD belts with great success this year. We ran these on 24tooth pulleys.

-Brando