Re: pic: Manually machinable one-speed gearbox
 

That's an interesting idea for sure. Main problem I see with it really is that 2 18T VexPro COTS sprockets can't fit inside 2x1. It would require either the custom machining of a double 18t sprocket or shaving down the COTS 18t sprockets. (unless there's a thinner double 18t sprocket on the market that I'm unaware of)

A .1" drop should be plenty, at least by my observations. I've seen teams run 3/32 without a problem.

A nicer way to do it might be to run 17t sprockets on the center wheel and 16t on the corners. You also get almost exactly an 1/8" drop then. But at that point, you might as well run all 17t sprockets with drop center, since that gets more teeth meshing with chain.

Re: pic: Manually machinable one-speed gearbox
 

Would there be a problem if you ran the outer wheels slightly faster than the middle wheels?

Re: pic: Manually machinable one-speed gearbox
 

One solution, if a drop center is really desired, is to cut a pocket on the bottom of the center of the tube for the middle sprocket. IMHO, that's kind of defeating the point of chain in then.

Re: pic: Manually machinable one-speed gearbox
 

The outer wheels would be shaved down to 3.75" diameter to ensure equal linear speeds on all wheels.

What 118 currently does as far as I know is use all 17t sprockets and use smaller diameter wheels on the corner, causing their larger diameter wheels to have greater linear speeds than the outer wheels. Jack's idea is a possibility to fix that problem without having to implement a drop center.

Re: pic: Manually machinable one-speed gearbox
 

Is that a problem? Teams have been running uneven diameters for a long time.

Your wheels are slipping in one way or another in any motion other than going straight anyway.

The normal force is highest on the inner (larger diam) wheels as well.

Re: pic: Manually machinable one-speed gearbox
 

So what you are saying is that some one could run sprockets with 16t-17t-16t all on the same wheel size?

Re: pic: Manually machinable one-speed gearbox
 

I agree that it's not an issue. Game permitting I'd be surprised if we didn't run a setup very similar to 118's 2014 bot this upcoming season. The idea I presented would give an ideal set of linear speeds, but would likely lead to a few other issues down the line. For example, your center-to-center distances would no longer be nice easy numbers.

The width of the vexpro sprockets can easily be solved by shaving them down a little. Beware of the 16t sprockets, however, as we found that the chain would grind on the bearings, as Mason pointed out earlier.

All in all, 118 has it figured out. Their system is the easiest Texas Tube I've seen so far, no need to reinvent the wheel.

Re: pic: Manually machinable one-speed gearbox
 

To anyone who has run with "Texas Tube" in the past: How do you account for the stretching of the chain over the course of the season? There doesn't appear to be a lot of room for tensioners. Is this even a concern with the lengths of chain that are being used?

Re: pic: Manually machinable one-speed gearbox
 

This season we built our system with no tensioners and never had to touch it. It ran very smoothly through three regionals and champs. I belive others have had similar success.

Re: pic: Manually machinable one-speed gearbox
 

Alright, that's good to know! Now, since this is an awesome thread and I'm learning a lot from it, I'm going to ask another question.

Has anyone every thought about using timing belts instead of chain? Fitting it into a 2x1 box probably wouldn't be possible, but what about a 2x2 box. I'd imagine it would be even more of a "set it and forget it" scenario because a timing belt would be less likely to break than a chain.

Re: pic: Manually machinable one-speed gearbox
 

That's a lot of weight you're gaining though (~2-4lbs depending on drivetrain), and you would have to settle for 1/8" wall probably. If teams say the chain doesn't break, then it doesn't break. That might be okay if you have the space and weight and mounting issues solved, because then you get a decent efficiency bonus.

Re: pic: Manually machinable one-speed gearbox
 

This season, 1477 used a Texas Tube style chassis. On a 4WD with all omni wheels, we used VexPro 16t #25 sprockets. We had tensioners on both our practice bot and our competition bot, and never used them on either robot. We had no issues with the 16t sprockets, and our chain runs were more than 200 links long. Game permitting, we will likely be running a Texas Tube style drive chassis again. Our experience with #25 chain in 2x1 tube has been outstanding thus far.

This is something I've been thinking about a lot lately. If using 1/16th wall 2x1 tube, it is theoretically possible to run 24t pulleys and 9mm belts from VexPro inside the 2x1. This could result in an extremely lightweight and efficient drive, at the cost of some structural integrity in the drive chassis. In my experience, #25 chain is less likely to break than 9mm timing belts, but is heavier and less efficient, assuming both the belt/pulley and chain/sprocket are assembled correctly.

http://www.chiefdelphi.com/forums/sh...ad.php?t=94701

Here is a picture of 2791 running timing belts inside tube extrusion.

Re: pic: Manually machinable one-speed gearbox
 

2791 has continued iterating on their belt-in-tube drive since then. Chris Picone would be the guy to talk to about that.

Re: pic: Manually machinable one-speed gearbox
 

192 has also used belt in tube for the past three years. 15mm wide GT2 in 2x2 .125 wall. With our set up and access points it's incredibly fast to assemble and tear down even though you'll never need to.

It is possible to run 15mm wide belts in 2x1.5 but you'd have to bore out the pulleys around the bearings or move the bearings out. I wouldn't recommend 9mm belt in the DT unless you had a proper tensioning system like 971 and even then they have had issues breaking belts.

Re: pic: Manually machinable one-speed gearbox
 

How are your access points for belt in tube set up? How is it assembled?