Monster Beetle Wheel judder under power

[fakiee]

Hey,  just build my Monster Beetle with a alloy gear box, carbon plates and a MIP diff.

 

I was expecting a super smooth drive train but when testing it judders like a tractor with the wheels on.

 

Under power it resonates and judders like crazy, if I find a good power band it smooths out, but then goes back to juddering.

Any advice on this?  Diff feels smooth and doesn't happen when wheels removed.

 

Video for the issue Monster Beetle Wheel Judder

[Saito2]

The suspension is in full droop in that running video. Try compressing the rear suspension (both trailing arms) to level out the driveshafts and re-test to see if the juddering diminishes. The dogbone end of the universal shafts might be close to pulling out of the diff outdrive cap at full extension. Also, the Monster Beetle shafts were not made properly either, being 90 degrees out of phase which caused vibrations (though yours appears extreme). Tamiya rectified the issue with the later Blackfoot re-release which uses the same chassis. Just some things to start with.

[ADRay1000]

idk man, looks pretty smooth for a MB driveline. 

might want to check the action on the diff if the wheels are up and not rotating at the same speed. 
 

 

[fakiee]

Thanks for the insights Saito2 and ADRay1000 

Your right the driveshafts do rub when the suspension is fully extended, and I tired what you suggested by compressing the suspensions, straightening the drive shafts and the issue still persists. 

I need to limit shock travel but I don't think that's the issue.

I've stripped the gearbox now to rebuild the diff as I received it built, as ADRay1000 says it could be unbalanced.

[markbt73]

Blackfoot and Monster Beetle wheels/tires are also notorious for being slightly out of round and out of balance. That could be what you're seeing, especially if the axles run smoothly with the wheels removed. It probably won't really affect running much.

[Kol__]

@fakiee, see this thread which details the issue with the MB UJ's that @Saito2 referenced above. Page 2 @OoALEJOoO describes the issue in detail, on page 3 you can also see my confirmation of the issue and solution with fitting the BF UJ's👍

Looking at your video, the above is 100% the solution to your problem.