Re: pic: Gear Drive Concept
 

Just raise the outer wheels 1/16th and drop the middle wheels 1/16th to make it fit. A design like that one based on 3x1 is much better.

Re: pic: Gear Drive Concept
 

Another iteration:

http://i.imgur.com/YQCeY48.jpg?1

60t gears running down the whole length. A stock vexpro 2-stage 2 cim ball shifter can be face mounted to any of the hex bearings depending on space and or orientation needs. 10wd/6wd 1/8in drop center - flip the chassis upside down for 8wd 1/8in drop center. All of the gears are installed via reciprocal slots in the tube.

Stock ratios: 3.61:1 High, 8.33:1 Low. JVN Calc says that on 3.25 wheels, its a 16.6fps / 7.3fps split.

Re: pic: Gear Drive Concept
 

I'm curious, what size wheels are you using now, and what are the dimensions of the frame? This is starting to look more and more like our robot this year...

Re: pic: Gear Drive Concept
 

3.5" Colsons, though I'm also toying with 3.25 Versa DT's.

What were your impressions on gear drive this year?

Re: pic: Gear Drive Concept
 

It worked great for us, our drive system was zero maintenance all season. Aside from the bit of gunk we had to clean off after our last event, the gears still looked brand new, no chipping or anything.

Our system used 50t gears on the wheels and idlers which allowed us to mount the gearbox either direct drive or to an idler without having to modify any ratios (we did end up using direct drive though). The spacing between the gears also worked nicely this way and it guaranteed virtually every part was interchangeable so it meant we didn't need to bring as many spares to events (though it turned out we didn't end up needing any spares at all).

We used 4in VexPro Traction wheels in a 1.5in wide configuration with traction tread. We mounted the wheels on a 32 foot arc pattern, which gave a good offset for basically zero-scrub turning, but also helped in pushing matches by keeping partial contact on the other wheels.

Re: pic: Gear Drive Concept
 

You might want to look into using onlinemetals if you end up buying some 3x1 tubing (or for most material, really). Our team buys all of our tubing there and while I can't comment on tolerances, other than to say it has always worked like we expect it to, they are definitely cheaper than McMaster - about $60 for a 6' length of 3x1 from McMaster, about $30 for the same length from onlinemetals.