pic: 2012 frc971 transmission

[Brandon Holley]

Originally Posted by Cory

Weight is an obvious reason. Pulleys are all aluminum and belt is vastly lighter than chain.

To go along with this- we ran our belts without tensioners at all this year, dead center to center distance and that was it. Zero issues all year.

You also don't have to 'make' chains to certain lengths, you can just buy the belt and design around it. This usually saves at least a few hours later in the build season. I know once we had all our components in, the assembly of our drive system took less than an hour.


Damp- would you mind sharing your W.O.T.? I'm just curious to see what metrics you value versus my own.

-Brando

[MichaelBick]

After realizing that your gearbox had two reductions instead of three(that was really nice designing by the way, as expected from 971), it became clear why the belt drive had some really nice advantages over the chain. I really thought that you were running a three stage gearbox for a second, which really threw me off.

Thanks for the great explanation of your drivetrain. It was fantastic that you emphasized building to a team's strengths, and I think that is one of the most, if not the most, important lessons for all the new teams.

[DampRobot]

Originally Posted by Brandon Holley

Damp- would you mind sharing your W.O.T.? I'm just curious to see what metrics you value versus my own.

-Brando

Sure thing. I've always designed belt setups just like chain, with a tensioner/sliding endpoint, so this effected my WOT:


Category Weight Chain Belt
Availability: 4 4/16 3/12
Weight: 4 3/12 4/16
Manufac.
Speed: 3 4/12 4/12
Total: 11/40 11/40

The thread I was referring to in terms of efficiency can be found here: http://www.chiefdelphi.com/forums/showthread.php?t=76964&highlight=belt+chain+effici ency. I believe their methods were quite scientific and methodical, and they concluded that belt was 6% "faster" then chain over a given distance.

6% used to seem small compared to the difficulty of obtaining belts that can only be used for one application. I suppose that not having to do sliding tensioning blocks would be a plus for chain, but I'm really not that sure. Although teams certainly have been successful with it, center distance design with belt or chain has always seemed like a technique that could tend to cause problems when you actually try to put it together.

[AdamHeard]

Originally Posted by DampRobot

Sure thing. I've always designed belt setups just like chain, with a tensioner/sliding endpoint, so this effected my WOT:


Category Weight Chain Belt
Availability: 4 4/16 3/12
Weight: 4 3/12 4/16
Manufac.
Speed: 3 4/12 4/12
Total: 11/40 11/40

The thread I was referring to in terms of efficiency can be found here: http://www.chiefdelphi.com/forums/showthread.php?t=76964&highlight=belt+chain+effici ency. I believe their methods were quite scientific and methodical, and they concluded that belt was 6% "faster" then chain over a given distance.

6% used to seem small compared to the difficulty of obtaining belts that can only be used for one application. I suppose that not having to do sliding tensioning blocks would be a plus for chain, but I'm really not that sure. Although teams certainly have been successful with it, center distance design with belt or chain has always seemed like a technique that could tend to cause problems when you actually try to put it together.

6% is substantial when teams are operating on fixed power.

The argument that the lead time of belts is a disadvantage isn't really the entire story there. Do teams really build their entire robots with no parts that have a lead time? We have several suppliers of belts, and we KNOW that we can get any given belt we need in reasonable time. We also make sure to design around belts that exist and are in stock, which is trivially more effort than designing around a chain spacing you know.

[scottandme]

For those who are using/have used belts in their drivetrain, what belt/pulley combinations have worked well? I'm assuming everyone is using the 5mm GT2 profile, but I've seen a good amount of variance in belt width and pulley diameter.

We're currently working on a drivetrain based around 15mm wide 5mm GT2 belts, and 20T pulleys. The gates website has a lot of information regarding the rated load capacity of different profiles/belt/pulley combinations, and it looks like 20T pulleys should be sufficient, but some real world experience would be helpful.

[Jared Russell]

Originally Posted by scottandme

For those who are using/have used belts in their drivetrain, what belt/pulley combinations have worked well? I'm assuming everyone is using the 5mm GT2 profile, but I've seen a good amount of variance in belt width and pulley diameter.

We're currently working on a drivetrain based around 15mm wide 5mm GT2 belts, and 20T pulleys. The gates website has a lot of information regarding the rated load capacity of different profiles/belt/pulley combinations, and it looks like 20T pulleys should be sufficient, but some real world experience would be helpful.

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.

[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