Weird "chugging" in reverse?

[Shadow Fox]

Where to begin...well whenever I go to reverse my truck "chugs" as if I'm pushing the throttle on and off at a consistent rate....and it only does this in reverse....it "chugs" hard enough sometimes that it rolls off a slope when in reverse. (It's roughly a 5-6Lb Truck)

I'm running a stock Axial SCX-10 Chassis and tranny, Tekin FXR ESC and 35t Tekin motor with a CC BEC and a Traxxas 2075 servo...and a 3s LiPo


any reason why it'd be doing this?

I searched the forum, and couldn't really find anything.

[Trubble]

What radio are you using?
ABS turned off?

[rangair94]

I had the same problem with my wraith. I tried all different electronics (motor, esc, reciever) didn't change, also pulled apart and checked my tranny axles couldn't find anything wrong. I changed remotes and it got a lot better, really not that noticeable anymore. So I don't really have a good explanation for it other then I also had the problem.

[RiceBurner]

Only chugging I've had, had to do with drive shaft angle...?

[Shadow Fox]

Originally Posted by Trubble

What radio are you using?
ABS turned off?

Fly Sky GT3B 2.4Ghz

and I'm not sure...I think it's on. But wouldn't it chug in forward too?


and I use the same remote with ABS on for my Mini Revo,and I haven't had any problems...

[Duuuuuuuude]

Running od/ud gears? That'll do it.

[Shadow Fox]

Originally Posted by Duuuuuuuude

Running od/ud gears? That'll do it.

not that I know of. It might or might not.....as I pulled the axles off another rig I had and never looked inside them....what would be the defining factor in identifying the gears as Ud//od gears?

[cragv]

If it's only in reverse then you can rule out most mechanical factors. If you drive in or near water, my first guess would be water damage to probably the ESC (different MOSFETs for fwd and reverse in some models, for example) or else possibly the Rx. If you can swap these one at a time to rule them out, your Tx then might be the next culprit to swap/test. It may not be water damaged, but the throttle trigger is a moving part, so maybe it's connection or pot is dirty, damaged or failing.

Of course, this is assuming you've thoroughly ruled out batteries, possible mechanical issues if applicable, etc.

From my own experience, I had an earlier version of my MRC that was 'fully' waterproofed, but after turning upside down whilst 8 inches completely below the surface, a small amount of water worked its way into my ESC. Reverse was perfect but forward was choppy and random. I cut my waterproofing surface open, dried it and then reapplied the same treatment, twice this time. Lakes and streams were never a problem again

Good luck. I hate electronic gremlins!

[turbomini]

when you notice this chugging are you turning? it might be something as simple as drive train bind from the tires wanting to spin at different speeds,

[cragv]

Originally Posted by turbomini

when you notice this chugging are you turning? it might be something as simple as drive train bind from the tires wanting to spin at different speeds,

One would think that might also happen when going forward as well as backwards, though... My money's on electronics.

Duuuuuude, presumably od/ud gearing refers to 'over-driven' and 'under-driven'. Is that to say that the trannie would be happy forwards, but in reverse the ratios would be somehow different, causing this 'chugging'? I don't quite understand - would have thought the ratios would remain the same. Would love some further explanation to help get my head around it! Thanks

[Trubble]

With od/ud gearing, the front axle would turn faster than the rear axle. When going forward, this would cause (with any traction at all) the wheelbase to be stretched, and the suspension would be 'sucked down', for lack of a better term. At some point one of the axles is going to lose traction and either spin (f) or be dragged (r). This will likely happen before all suspension travel has been used, and at the point of slip, the suspension can actually absorb some of the shock of the axle whose traction is failing. The weight of the vehicle prevents the springs from 'springing' back to full length, so it usually ends up looking like just a nice, smooth drag.
When going in reverse with the od/ud setup, the front axle will go in reverse faster than the rear axle. This will cause the wheelbase to shrink and when you push the axles together, the links act to 'lift' the vehicle. As soon as one axle loses traction, the weight of the vehicle 'pushes' the suspension back down. Then the axles regain traction and the process starts over again. Winds up looking a lot like a bind in the drivetrain.

Originally Posted by Shadow Fox

Fly Sky GT3B 2.4Ghz

and I'm not sure...I think it's on. But wouldn't it chug in forward too?

No experience with that radio, don't know if it has ABS or not.
But I wouldn't think it would chug going forward, since ABS (Anti-lock Braking System) would typically be on the 'braking' side of the trigger (ie, trigger forward, or in reverse).
No idea why it wouldn't affect your other vehicle. Just figured it'd be quick and easy to turn that off to rule it out.

[cragv]

Thanks Trubble, that's a really thorough explanation! So you're saying that over time this condition may worsen, resulting in the OP's "weird chugging issue", yeah? Makes sense I spose. Same reason I don't leave my 1:1 truck's front hubs locked on the blacktop - avoiding diff wind-up. Cheers

[Shadow Fox]

I'll check the ABS, as everything is pretty much brand new...the ESC Only has 2-3 runs on it..and it's a new receiver.

[turbomini]

Originally Posted by cragv

One would think that might also happen when going forward as well as backwards, though... My money's on electronics.

trubble said it best, and i also thought about this, when the tires get finned one way they will grab harder and bind more.

[Tonysmini]

My truck with the UD/OD gears does this too, try driving it in some really slippery mud or a really dusty garage floor and you should see where the tyres are gripping and slipping. If I run mine suspended off of the floor it vanished, that's how I figured it out.

Having really grippy tyres made it worse, as did having alot of weight in the truck.

[spoo76]

I had the same problem twice. The ABS feature on the GT3B somehow got turned on.

[Shadow Fox]

yea, it's fixed, ABS was to blame.

[Trubble]

Thanks for coming back with your findings.
Glad you got it figured out.

[Postclanker]

Thank you for this thread.....
I had this issue with a brand new GT3C.....my ABS was on...

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