Were might a guy buy some treads, or tread assemblies (with the wheels, etc)

I've just started on a design project, and the guy wants tank treads on his invention. Something along these lines:
http://library.thinkquest.org/03oct/00114/images/tread.jpg
The point here being the treads and motors - what's on top is the novel part of the invention, and proprietary.
The thing is, I'm wondering if it's possible to buy treads - imagine that in the picture in the link above, the carriage (or whatever you call it) is about 3' long and about 2' wide, and the treads are, say, 4"-6" wide.
Is there anyplace to buy suitable belting material or something, or do I have to invent something from scratch, design new molds, and pay somebody $50,000.00 for first item? =:-O
Where do the guys that do those battlebot thingies get their treads?
This isn't going to be a robot - the closest thing to smarts will be the operator guiding it by a handle that has a "forward/reverse" knob.
The client didn't think about turning, but that's no problem - I'll just have side-to-side motion of the handle drive the treads differentially.
I'd also like to see if I can find some ideas on building the idlers and undercarriage and so on such that it's sand-proof. =:-O
Thanks, Rich
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    --Check out snow blowers.
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"Steamboat Ed" Haas : Why do weekend projects
Hacking the Trailing Edge! : always last a month??
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Rich Grise wrote:

In that size range, the cheap options are few. Smaller, and you can use Tamiya model tank tracks. Larger, and you can use the track assembly from a Bobcat. But there are many commercial robots in that scale, from iRobot and others.
Here's a low-end tracked base in that scale:
    http://www.themachinelab.com/MMP-40.html
                John Nagle
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I offer smaller all-rubber tank treads and matching idlers/sprockets at Budget Robotics. Might be handy for a small prototype. For larger, Lynxmotion sells some that are about 2" wide, which is about as wide as you will find right now for amateur/educational robotics or controlled vehicles. You can always gang several parallel if you need wider still.
If you are looking for very rugged treads for an all-terrain vehicle, the snowblower tracks Ed mentioned, as well as snowmobile treads, are probably the best for metal. You'll have to order by model number, so look at some replacement parts catalogs so you know what to order.
-- Gordon
Rich Grise wrote:

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One option for the treads is tabletop conveyor chain. Rexnord makes many sizes and types in plastic and metal, and there are usually some available on ebay for a reasonable price, though the widest I've seen there was 3.5 inches. You would need sprockets too, of course, which I have never seen on ebay.
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