pic: Offseason Gearbox

[Joey Milia]

Originally Posted by rponmalai

http://imgur.com/a/n6cZ8
One of the things I was playing around with in this design was running the timing belts through the tubing of the drive base. I have an access hole for putting the belts through that can easily fit the bearing. The entire shaft would be held together with snap rings. The grooves for those snap rings are on either end of the output shaft.

That answers the bearing questions. What's the belt set up you were thinking about? Pulley tooth count and belt size?

[rponmalai]

Originally Posted by Joey Milia

That answers the bearing questions. What's the belt set up you were thinking about? Pulley tooth count and belt size?

I have a Vex 18T pulley for 5mm HTD timing belts. The pulley thickness is for a 15mm belt.

[R.C.]

Originally Posted by rponmalai

I have a Vex 18T pulley for 5mm HTD timing belts. The pulley thickness is for a 15mm belt.

I would recommend at least 24t or larger if your using HTD.

[Chris is me]

Originally Posted by rponmalai

I have a Vex 18T pulley for 5mm HTD timing belts. The pulley thickness is for a 15mm belt.

You really can't get away with less than 24T 15mm wide on a drive belt. 24T belt-in-tube generally works best in a 3" tall drive tube, though it could probably be made to work in a 2.5" tall tube as well. So going belt in tube generally costs you a little bit of weight.

When doing a gearbox in the back like this rather than the middle, keep in mind that belt connecting the back wheel to the middle wheel will always see the full load of the drive base. So it's extra important to use a properly sized pulley.

[rponmalai]

Am I correct in assuming that you need a larger pulley to keep the belt from slipping off of the pulley?
The more I hear about this I am starting to lean towards chain drive to run through the tubes. My only draw back is keeping the chain tensioned. What would be the best way to keep the chain tight while it is in the tube?

[Abhishek R]

Originally Posted by rponmalai

Am I correct in assuming that you need a larger pulley to keep the belt from slipping off of the pulley?
The more I hear about this I am starting to lean towards chain drive to run through the tubes. My only draw back is keeping the chain tensioned. What would be the best way to keep the chain tight while it is in the tube?

If it's nice and tight properly upon installation, you shouldn't need any form of tensioning for the chains.

[Knufire]

Originally Posted by rponmalai

Am I correct in assuming that you need a larger pulley to keep the belt from slipping off of the pulley?
The more I hear about this I am starting to lean towards chain drive to run through the tubes. My only draw back is keeping the chain tensioned. What would be the best way to keep the chain tight while it is in the tube?

FRC runs belt some belt very close to it's max load. Both a wider belt and a bigger pulley reduce load on the belt.

If you have the proper center-to-center distance on the chain, it should stay tensioned. 5188 did the calculated center-to-center + 0.018" this past year, and the chain stayed perfectly tensioned all season. This was based on Paul Copioli's recommendation and further coborrated by the testing done in this thread. However, with the chain in tube, remember that a tigher chain is more difficult to install, and there isn't anywhere for the chain to go, so the added distance may not be necessary.

[Chris is me]

Originally Posted by rponmalai

Am I correct in assuming that you need a larger pulley to keep the belt from slipping off of the pulley?
The more I hear about this I am starting to lean towards chain drive to run through the tubes. My only draw back is keeping the chain tensioned. What would be the best way to keep the chain tight while it is in the tube?

Slipping off, no, ratcheting or failing, yes.

That said, you never have to tension a properly dead spaced belt in tube drive. It has its pluses. It's just not

If you have the proper center-to-center distance on the chain, it should stay tensioned.

Maybe in certain applications depending on load, chain length, etc, but this just isn't a blanket statement you can make. Both chain stretch and sprocket wear are very real phenomena that shouldn't be ignored. The 118 solution does an unconventional but effective job at containing this chain stretch to prevent failure, but in most cases you're going to want a tensioner. Optionally, you could replace the chain once it's stretched to the point of giving you problems.

For a very extreme example, our chain elevator this year had a nice 13 foot long loop that was dead spaced, and it stretched noticeably over the course of a few hours of low to no load testing. It is a function of sprocket diameter, chain length, and several other factors. At the size of sprockets used in west coast drives, it's a factor.

Originally Posted by Abhishek R

If it's nice and tight properly upon installation, you shouldn't need any form of tensioning for the chains.

The other important caveat here is that your chain and sprocket should be constrained by the tube itself for this to work (very close to inner walls of tubing). One of the reasons chain in tube seems to work so well is that there is nowhere for the chain to go when it does stretch, preventing the jumping problems found with looser chains.

[MichaelBick]

Originally Posted by Chris is me

24T belt-in-tube generally works best in a 3" tall drive tube, though it could probably be made to work in a 2.5" tall tube as well. So going belt in tube generally costs you a little bit of weight.

We found out this year that Coast Aluminum in California actually has 2" x 2" x 1/16" tube (its not in their catalog) which is really useful material. One of the things I have been considering is doing a belt in tube drive with this stock, which compared to the 2" x 1" x 1/8" tube we use right now in our WCD we'd actually be taking a weight savings.

[Abhishek R]

Originally Posted by Chris is me

The other important caveat here is that your chain and sprocket should be constrained by the tube itself for this to work (very close to inner walls of tubing). One of the reasons chain in tube seems to work so well is that there is nowhere for the chain to go when it does stretch, preventing the jumping problems found with looser chains.

Yeah, that's pretty much a requirement too, thanks for clarifying. There's literally nowhere for the chain to go, so as long as it doesn't break you're good.

[rponmalai]

Originally Posted by MichaelBick

We found out this year that Coast Aluminum in California actually has 2" x 2" x 1/16" tube (its not in their catalog) which is really useful material. One of the things I have been considering is doing a belt in tube drive with this stock, which compared to the 2" x 1" x 1/8" tube we use right now in our WCD we'd actually be taking a weight savings.

Is 1/16th strong enough for a drivebase?

[MichaelBick]

Originally Posted by rponmalai

Is 1/16th strong enough for a drivebase?

I know people do it all the time with sheet construction, but they may also be running taller drive plates. Sheet drives however also have to trade off material strength because 5052 is weaker than 6061. Its going to be something we have to test out