Center to Center with belts

[MetalJacket]

Originally Posted by DampRobot

Not necessarily true. The maximum torque that can be put on a belt varies proportionally to its width. If you're right on the edge in terms of how much torque that can be on the belt, the switch from 15mm to 9mm definitely makes a difference in whether it will ratchet or not. If you want to be sure, check the Gates website. They should have some nice tables that give all of the relevant torque and speed information.

Just keep in mind that for FRC, your FoS or duty rating will probably be much lower than 1 (i.e., it can take more torque than what's on the table). Those belts are designed for hundreds of thousands of cycles, something they'll never see in FRC, so we can probably get away with more torque than they were designed for. Adam Heard probably has a more exact number, as he's built a lot of belts drivetrains before.

OK thanks, I'll check out the Gates website to try to get some more exact numbers.

[jspatz1]

We've always had perfect results by simply laying out the belt in a CAD sketch. Draw the pitch diameter circles of your pulleys, connect them with tangent lines, trim the inner portion of the circles, then measure the loop length. Adjust the C to C until the loop length matches the available belt pitch length.

[chmorroni]

We haven't tried to do the C-C in our CAD until this year, but I am going to use this calculator to do it. It should get you pretty close, if not dead on a good tension. If it isn't exactly how you want it, you should be able to make small tension changes if you are using COTS gearboxes.

[Chris is me]

Originally Posted by MetalJacket

Just to clarify for my own knowledge, there should be little to no performance issues using 9mm wide belts compared to using 15mm wide belts (like those in this year's KoP) assuming they both have the same tooth profile? I'm currently working on a practice sheet metal chassis using belts and I'm trying to make the wheel wells as thin as possible but I don't want to compromise performance for space. Thanks,
Jesse

Look at the Gates spec, though know that their numbers are *very* conservative. In my team's experience, if you are using a smaller pulley (such as to fit in a small space height wise) you'll want 15mm GT2 and if you're using a larger pulley then 9mm is just fine. Since you're doing sheet metal, you probably have enough room to use 2.5"+ diameter pulleys and can step down to 9mm.

[MetalJacket]

Originally Posted by Chris is me

Look at the Gates spec, though know that their numbers are *very* conservative. In my team's experience, if you are using a smaller pulley (such as to fit in a small space height wise) you'll want 15mm GT2 and if you're using a larger pulley then 9mm is just fine. Since you're doing sheet metal, you probably have enough room to use 2.5"+ diameter pulleys and can step down to 9mm.

The design I'm working on would be using the 42 tooth HTD pulleys from AndyMark for convenience sake so I wanted to see if I could get away with the 9mm belts so that I could fit two belts on a single pulley, which would save a significant amount of space.

[AdamHeard]

Originally Posted by MetalJacket

The design I'm working on would be using the 42 tooth HTD pulleys from AndyMark for convenience sake so I wanted to see if I could get away with the 9mm belts so that I could fit two belts on a single pulley, which would save a significant amount of space.

You're likely fine with 9mm belts. What wheel size, wheel type, and overall ratio are you running?

[MetalJacket]

Originally Posted by AdamHeard

You're likely fine with 9mm belts. What wheel size, wheel type, and overall ratio are you running?

I'm actually working on two designs right now - one for an offseason project that will actually be built and another that is just for practice.
The Real One -
6WD with 8" pneumatic wheels
4 cim motors with a 6.67:1 reduction on a custom gearbox, center wheel direct driven off the gearbox with the other two wheels being powered by belts (using the 42 tooth AM pulleys)
(I know it's going to be ridiculously fast but it's for a t-shirt cannon that needs to be able to cross a football field in a reasonable amount of time)

The Practice One -
6WD with 4" plaction wheels
6 cim motors with a 6:1 reduction using a VEXPro single stage gearbox
external reduction of 1.08:1 (AM 39 tooth to AM 42 tooth)

[Chris Fultz]

We had very good results using the belt length and pulley C-C calculator on the Gates website.