Need some torque twist help with a customized FCX24 chassis

[ztrum]

Hi everyone, new-ish hobbyist and first time poster.

Built an FCX24 Power Wagon with some custom suspension links and a few chassis mods to lower the center of gravity. Really loved building this truck and love how it turned out. The flex is amazing!

Problem is, the thing torque twists itself in half, especially when going steep uphill. It will literally spin itself in half, the front right goes up and the front axel will go 90° to the rear and the whole thing does a corkscrew and rolls over horizontally!

I figure this has to do with the very mobile ball joints I put on the rear suspension links. I added some oil filled shocks and loaded up the pre-load on one side which helps a little bit but I still get one front wheel climbing up into the air pretty quickly on any serous uphills.

I read somewhere about flipping the differential gears and reversing the motor but I didn't quite understand and there was no video or pictures.

Anyone have any suggestions on how to tame the torque twist? I really like this truck but it's kinda not that fun to drive because it twists so bad!

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[diezel666]

I read somewhere about flipping the differential gears and reversing the motor but I didn't quite understand and there was no video or pictures.

I understand the methodology of why they recommend doing it, and I've tried it on 2 different vehicles. Mixed results.

Like you, I ended up increasing spring preload on the side it favored while twisting, and that actually helped more.

The secret sauce for my fix, was finding proper shock orientation and spring/oil/vehicle weight combo. Even then, there is going to be some twist.

When it comes to RC, what many of us aren't thinking about is the scale of the vehicle. Some of the drivetrain combinations we create, would be like stuffing a 1500hp engine into a Toyota Tacoma.

 

[ferp420]

flipping the ring gear doesn't help any just swaps what side lifts
sway bars are the easiest that is mostly for the rear of the rig
your other option is playing with the link geometry
if it's posable to run lower gears anywhere In the drivetrain that helps too

unfortunately there is no cure and big tires more power and more weight all increase the problem

 

[HumboldtEF]

With more flex comes more torque twist. More flex is not always better, eventually performance will suffer so there is a sweet spot. The shock angle in the rear provides lots of articulation but at the cost of adding more torque twist as its just too soft. Angleing over a shock will always lower the effective spring rate so you can try stiffer springs if available. As a quick test try standing the shocks up more vertical (also mount them at the axle not the link) and test the difference.

Another factor contributing to this is the way the shock mounts to your links, trailing arm style. This also has the effect of lowering the (effective) spring rate. Almost all 1:1 rigs with trailing arms are paired with sway bars to combat torque twist that come with the ultra soft suspension. Yes with crawlers you dont want sway bars... but we also dont want trailing arm suspension.

Anyway yes the common fix is to go with a stiffer spring or more preload on the opposite corner (typically passenger side rear). However your setup is likley so soft you may have to make bigger changes to stiffen things up.

 

[ztrum]

I moved the shocks to connect to the rear axel where the links connect. The twist is MUCH improved!

A lot less flex, but much better overall performance!

Thanks for ideas.

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