Re: 9 mm Wide Belts
 

That's very interesting. I've never heard of problems on correctly tensioned belts in a drive. Were you using GT2? HTD is better rated for rapid direction change, though it really shouldn't matter.

Re: 9 mm Wide Belts
 

GT2. I know of plenty of teams experiencing ratcheting with 9mm wide belt. Once you go up to 15mm ratcheting only happens in extreme cases, but then you're much wider than running #25 chain

Re: 9 mm Wide Belts
 

We ran 9mm wide GT2 belts last year, and didn't have any ratcheting. We had some wear, but it was what you would expect for a device running outside the rated specifications. 1 set of belts lasted the entire season (2 competitions, 1 offseason, and lots of practice.) Ratcheting occurs when your belts are under-tensioned, which means that your belts were under tensioned. You can look at the failed belt to figure out what was wrong. For comparison, we had a 24 tooth pulley with a 3.5" diameter wheel.

Re: 9 mm Wide Belts
 

We're using the small 18 tooth pulleys (9 teeth in contact). We will have the means to tension the belts.

I suppose that in the worst case scenario, we'll switch back to 25 chain. Now were are we going to get the weight for that...?

- Mr. Van
Coach, Robodox

Re: 9 mm Wide Belts
 

We experienced ratcheting problems with 9mm belts. Our experience mirrors Sean's. We now use 15mm belts and 24T pulleys for our 6 CIM WCD.

I would be very hesitant to take risks with belt sizing, unless you have a good reason. Looking pretty is not.

Re: 9 mm Wide Belts
 

This will likely be an issue.

Re: 9 mm Wide Belts
 

Worth taking a look at this document Adam threw together. Lots of great input from tons of teams on their experience incorporating belts into their custom drivetrains. We referred to this when throwing our off-season WCD belt drive together.

-Mike

Re: 9 mm Wide Belts
 

Thanks Mike and Adam! Very good information (if not entirely encouraging) - better know now than later!

- Mr. Van
Coach, Robodox

Re: 9 mm Wide Belts
 

We've used 9mm HTD belts for the last 8 years no problem. GT2 might give you a few problems. Small pulleys will do the same. I believe we run 36t pulleys for all of our wheels. We've used them for our standard 6" wheels, and 8" wheels as well. HTD is better for the quick change in direction. HTD is High Torque Drive.

Try using SDP-SI's belt distance calculator. It'll give you pretty good numbers to run with. We also pull all of our pulley files from SDP-SI for our CAD.
http://www.sdp-si.com/cd/default.htm

Re: 9 mm Wide Belts
 

For avoiding belt slippage, HTD is the way to go. I've had mixed experience running 9mm. A long time ago, we made our own pulleys (around 20t) out of aluminum, and we had the center to center distance very accurate, and it worked very well. Later, using an off the shelf pulley and a not as super rigid frame with a not super accurate (but still within 0.002") center to center, we experience some slip.

I'd go with the 15mm if possible. If you can't, you'll survive with 9mm, but you could have some slipping. Slipping isn't that bad (apart from belt wear).

Re: 9 mm Wide Belts
 

Thanks for all the advice. We will be running a 6 Cim drive train (maybe shifting if VEX gets them in stock) with 8WD and it would be 9mm HTD belts from VEX with their 42 tooth versa pulleys. All 4 wheels would be powered on either side. Also, when I said it makes the CAD pretty, all I meant was that it would make my life easier my not having to change all of my mounting plates :rolleyes: .

What about having one 15mm belt on the inside part but then 2 9 mm belts on the outside? We might try that to save some space but still have the advantages of 15mm wide pulley on the 4 dropped drive wheels.