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):

http://img.photobucket.com/albums/v1...o/IMG_8105.jpghttp://img.photobucket.com/albums/v1...o/IMG_8104.jpg
Pulley straight from the manufacturer, with a notch cut in it.

http://img.photobucket.com/albums/v1...o/IMG_8108.jpg
http://img.photobucket.com/albums/v1...o/IMG_8112.jpghttp://img.photobucket.com/albums/v1...o/IMG_8114.jpg
Removing the majority of the pulley's flanges to better fit within the bulkhead (the pulley is pinned to that shaft).

http://img.photobucket.com/albums/v1...o/IMG_8119.jpg
Removal of the pulley hub using a bimetal hole saw with a 1/4" drill bit in the arbor.

http://img.photobucket.com/albums/v1...o/IMG_8130.jpg
Checking fitment of pulley inner diameter to outer diameter of diff cup.

http://img.photobucket.com/albums/v1...o/IMG_8126.jpg
I purchased a plastic Losi spur gear for the steel insert it comes with, and used the (modified) steel insert as a diff backplate.

http://img.photobucket.com/albums/v1...o/IMG_8127.jpg
The adapter plate to bolt the pulley to the diff.

http://img.photobucket.com/albums/v1...o/IMG_8131.jpg
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!

Thanks! Just wait 'til you see the rest...

My original goal was a custom scratch-built buggy but this would be a very difficult feat. Integrating suspension and pulleys while maintaining belt clearance and keeping debris out are the primary goals for such a project, everything else is easy. I met it halfway by using the XTM front end and designing a new rear end based on the XTM parts.

Oh how easy life would be with a plastic injection moulder. :angel:

Don't forget the 5-axis CNC mill to make the molds. :smile:

...Or the lathe to turn custom turnbuckles!

Scratch-built doesn't mean the entire thing needs to be custom designed and built! I would simply use a proven suspension design off of another car and develop new parts around those suspension pieces, and integrate belt-drive stuff. Much easier that way :yes:.

Yeah, I figure I'll use a-arms, shocks, wheel shafts, and steering parts off of a kit.

Finally, what many have been waiting for! It's still not done and has a fair bit more work required, but the rest is pretty easy and should go quick once I start. But much of the remainder is dependent upon the proper length front belt, which I just ordered and probably won't be here for another week... Anyways:

Lower belt guide:
http://img.photobucket.com/albums/v1...o/IMG_8166.jpg
http://img.photobucket.com/albums/v1...o/IMG_8170.jpg

Inside front diff case:
http://img.photobucket.com/albums/v1...o/IMG_8171.jpg

Upper belt guide:
http://img.photobucket.com/albums/v1...o/IMG_8176.jpg

Belt clearance with lower arm mount (note there is actually less clearance when the belt isn't lifted up):
http://img.photobucket.com/albums/v1...o/IMG_8178.jpg

Complete front end:
http://img.photobucket.com/albums/v1...o/IMG_8180.jpg

Belt protrusion below front bulkhead:
http://img.photobucket.com/albums/v1...o/IMG_8184.jpg

Mounted front end:
http://img.photobucket.com/albums/v1...o/IMG_8188.jpg

Rear end gear reduction:
http://img.photobucket.com/albums/v1...o/IMG_8191.jpg

Bottom of rear end (minus suspension plate):
http://img.photobucket.com/albums/v1...o/IMG_8201.jpg

Lower suspension mount:
http://img.photobucket.com/albums/v1...o/IMG_8202.jpg

Back of rear end showing sway bar mounting:
http://img.photobucket.com/albums/v1...o/IMG_8207.jpg

Front of rear end:
http://img.photobucket.com/albums/v1...o/IMG_8209.jpg

Bottom of rear end:
http://img.photobucket.com/albums/v1...o/IMG_8212.jpg

Rear end mounted:
http://img.photobucket.com/albums/v1...o/IMG_8216.jpg

Check out all those screws holding the rear end on! Normally only 4 screws have that job...
http://img.photobucket.com/albums/v1...o/IMG_8217.jpg

And of course the motor/reduction unit:
http://img.photobucket.com/albums/v1...o/IMG_8220.jpg

Positioning:
http://img.photobucket.com/albums/v1...o/IMG_8224.jpg
http://img.photobucket.com/albums/v1...o/IMG_8226.jpg

The pics of the center unit are older, it will actually have the polycarbonate mounting piece directly behind the motor (and the gear will be behind it) so that the entire unit will fit on the chassis.

:surprised: wow... That's quite a build man... I can't wait to see the completed thing. Please keep the pictures coming.

Alien

Amazing work. Can't wait to see it finished! :yes: :great:

sweet!

I want to see that in person. Can I tempt you with a ride in a certain car? LOL

When the time comes :wink: (wow that was awkward)

My God this is amazing work. This has got to go in the record book, folks... just.. wow! It all is put together to well, quite a feat in itself to make it look like it was made that way from the factory. Ingenious ideas here.

wow, thats turning out to be very complex

Thanks guys! :yes:

Hi, pardon my ignorance but what is there a benefit for a belt driven off roader, or is this just one of those projects where the main reason behind it is "because I can" (something I have done plenty of times :)). Just curious is all.

Well done, your workmanship is top shelf.

I Love your projects MMan. I thought the CORR truck was amazing but I didn't expect to see yet another sweet project none the less an extremely ingenuitive one. This is what the true meaning of this hobby is. This is like seeing the first electric conversions, it just awed me.... I can't wait to see how this turns out. I only wish I could make things as awe inspiring as you can make em.

After that rant I must point out my user name has nothing to do with you, thankfully. :eyes: I am referring to the music genre of metal, and that I like to listen to it. :smile: I made it up long before I joined this site... :wink:

I'm curious to see how the belt holds up. I would hope there would be no diff problems. I would expect this to be a more efficient drivetrain also.

Dunno about benefits at this point, but I do know that this truck won't experience any torque twist like ALL shaft driven vehicles do. Also, if the belt layout were optimized it would be possible to place the motor and battery directly on the centerline of the chassis which would improve handling considerably. My current layout isn't the best, unfortunately.

The main point behind this project is because I can, and because it's never been done before. Most of my projects are unique :neutral:

My username also has to do with the music I listen to, but we probably listen to different genres of metal. I also got my big start in RC by working with aluminum so that helped too.

Thanks for the comments guys!

hey i think it time for an update!

It is... still waiting for another front belt to come in, and for my homework load to lessen. And I've been working on the final project for my Solidworks class:

http://img.photobucket.com/albums/v1...it_sldwrks.jpg

A digital representation of the belt drive Mammoth ST Pro! Figured I would start with the center motor unit. Just a quick note: the motor actually rotates JUST like in real life, as do the pulley and gear on its shaft. The other shaft and its gear and pulley also rotate. However, I don't know how to link up the rotation of the two gears (so that the motor spinning causes the other shaft to spin). Anyone know how to do that?

Nice work, u did all the machining urself? what tool do u use if so?

great CG, Looks strong.

I'm not familiar with Solidworks. How did you go about "syncing" the other components? On that interface, can you select the direction of rotation and add a ratio between the first and second axles, then sync the second gear/pulley set to that second axle?

Looks good.

Have you checked out the mechanical mates in solidworks? There is an easy option for gearing. You should be able to work it out.