BELT Drive Conversion - XTM Mammoth ST Pro
 

Building a 1/8 off-road vehicle with belt drive has been a dream project of mine for some time now. At first the idea was a buggy with a custom CF chassis (which I would lay myself), but later it turned out it would be a truggy - a conversion of the XTM Mammoth ST Pro.

This truggy kit went on sale at Hobby People for clearance and was priced at $100, a deal which no mortal human being in my position should pass on :yipi:. The box sat in my garage for a while until I realized the front/rear bulkheads on my XTM XLB (the Mammoth ST's buggy-sister) would be optimum for fitment of pulleys/belts.

For a random guy like myself, this is a huge undertaking considering a restrictive budget (prototype=production). To achieve the project goals, anything which requires customization or special fitment has to be done by my two hands.
To put things into perspective: there are NO belts/pulleys designed for 1/8 off-road, so wherever there is a pulley on my truck keep in mind that it had to be specially selected and designed around or modified for the intended purpose.

For starters here is what it takes to turn a specially-selected standard pulley to fit a regular 1/8 off-road diff (a Jammin' diff in this case):

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Pulley straight from the manufacturer, with a notch cut in it.

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Removing the majority of the pulley's flanges to better fit within the bulkhead (the pulley is pinned to that shaft).

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Removal of the pulley hub using a bimetal hole saw with a 1/4" drill bit in the arbor.

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Checking fitment of pulley inner diameter to outer diameter of diff cup.

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I purchased a plastic Losi spur gear for the steel insert it comes with, and used the (modified) steel insert as a diff backplate.

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The adapter plate to bolt the pulley to the diff.

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All assembled minus the internals, and also filled with epoxy to act as a bushing between the pulley and diff cup. There is grease between the diff cup and epoxy so that the epoxy bushing/pulley can slide off the diff cup for easy maintenance.

There's much more progress to report, but that's enough for now :angel:
However, I will say that a shipment of belts and pulleys arrived today :yes:

wow, definately a neat project, cant wait to see more

Looks good MM, can't wait to see more...

There will be more, working on it as I type :intello:
Hoping to have something worthy of showing off come time for RCX on Sunday.

I'll be watching.

looks like a cool project and it sounds like you are on the right track

Looks cool...look forward to your progress

Looks like realy interesting project.
But, how would those belts stay on pulleys as you removed flanges?

He didn't remove all the flange and he might use some sort of tensioner/guide AKA flanged ball bearing to keep the belt in place.

That's right, there is still some of the flange left. But I won't rely on that, there will be flanged bearings to help guide the belt onto that pulley.

Made a good amount of progress on the rear end (completely redesigned bulkheads and suspension mounting), but still nothing picture-worthy. And this will be a pretty hectic school week, so it seems progress won't be as much as any of us would like :neutral:

take your time, do it right

BUMP

I wanna see this

I know, I know... Aside from school (last midterm is tomorrow, Tuesday!) the rest of the wait on this project is due to shipping. It took 3 separate orders to SDP-SI for me to finally select the right belt lengths and gearing combination, and now I'm waiting on a sheet of aluminum so I can finish up the center motor/reduction unit. SDP-SI is in New York, so I've been selecting UPS 3-Day shipping, which has already added up to almost $50 to ship 3 small boxes. The price of prototyping...

Much progress has been made, though. The front belt is now completely routed around the front diff and free of drag (rolling on bearings), the center unit is complete aside from the top/bottom pieces, and the rear end is all together. Once the center unit is mounted and the belts are properly tensioned I can create an enclosure to keep debris out of the belts/pulleys. So once progress continues it should go quick!

I plan to do something like this with a completely custom truggy built from scratch. Your integrated diff into the gear is very cool!