No-torque-twist solid axle

[fyrstormer]

So I've got this idea for a no-torque-twist solid axle: The diff is located in the main body of the chassis where the torque-twist can be canceled out by the rigidly-mounted diff case, as in an independent-suspension setup. Coming off the diff are two right-angle gears sets driving two counter-rotating driveshafts running back to the axle (one for the left wheel and the other for the right wheel), with two more counter-rotating right-angle gears to drive the wheels. This would allow a single-motor 4WD setup with solid axles with no torque twist, whereas a MoA design would require two motors to achieve 4WD. Sadly I lack the manufacturing capability to make it. :(

[Chumley54]

The losses in power due to all the gears,and rotating mass and weight may be a poor tradeoff to eliminate some of the torque twist.

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[fyrstormer]

It would eliminate *all* of the torque-twist, actually. On higher-powered vehicles like trophy trucks, the inefficiency can be easily overcome with a slightly more powerful motor, and for those vehicles eliminating torque-twist to improve handling is the more important factor. Plus, with each of the two driveshafts only handling half the torque going to the rear axle, they would only need half the strength as well; something like Axial's cheap plastic driveshafts might actually be workable, and two of those would still weigh less than a single MIP hardened-steel driveshaft.

[EeePee]

Trophy trucks? Try RCShortcourse or something.

Proper suspension set up outweighs any little bit of torque twist problems, really. On a crawler that is.

[makya]

Originally Posted by EeePee

Trophy trucks? Try RCShortcourse or something.

Proper suspension set up outweighs any little bit of torque twist problems, really. On a crawler that is.

on a short course as well.

on a TT as well.

I'll say the same thing I said on URC, your rotational forces are fighting traction with this design and inducing squat in the suspension by trying to "lift" the trailing arms. It's the same issues that sand rails have had when tying the same concept with individual chain drives running to each rear wheel.



You need the arms to push down into the ground without creating too much anti-squat.

I would recommend messing around with a 4-link calculator and getting familiar with suspension design characteristics (anti-squat, dive, roll center) and the different designs (watts link, triangulated 3 and 4 links, panhard). they all have their use, but are designed around how the rotational forces are applied.

again, the same thing I said on URC: if you want to eliminate Torque twist, use a chain or belt drive to the diff on a solid axle.

[msrace]

You would be far better off spending time with suspension design and weight placement than trying to package all that into something that won't get dragged over rocks. I don't see torque twist being that big of a deal.

[Chumley54]

Originally Posted by fyrstormer

It would eliminate *all* of the torque-twist, actually. On higher-powered vehicles like trophy trucks, the inefficiency can be easily overcome with a slightly more powerful motor, and for those vehicles eliminating torque-twist to improve handling is the more important factor. Plus, with each of the two driveshafts only handling half the torque going to the rear axle, they would only need half the strength as well; something like Axial's cheap plastic driveshafts might actually be workable, and two of those would still weigh less than a single MIP hardened-steel driveshaft.

Torque twist is always there, you are just making 90 degrees to the axial direction. The wheels try to pick up the frame in front of them. If one wheel has more traction, than the torque is uneven and will pick up one side more than the other. What you really want is to use the torque in way the helps the vehicle do want you want, but you can't eliminate it ever.

Complicated breaks more often.

A more powerful motor is a less efficient motor, as the power is being used to drive the drive train, means less to the wheels. So the more powerful motor ends up with the same wheel power.

Simpler: smaller motors right on the wheel. 4 smaller motors inside the wheel hub. Then the only torque direction is in the wheel direction.

Also simpler than all the shafts.

But ultimately, it is not about the greatest design, as there are rules about the class you play in. If you are not in competition, the torque issue can be avoided with less throttle.

The funny thing is, there are so many areas that torque happens. For instance, since the contact patch of the (rear) tire is below the rotational center of the axle, it creates torque, causing the front of the vehicle to be lifted, unloading the weight on the front tire. The correction for this is usually weights in the front to apply torque in the opposite direction.

Where there is power, there is torque.

A real torque avoided is counter rotating propellers on the centerline (and center of mass) of the vehicle. Torque is there, but the two props just provide equal force against each other, so the net torque is zero.

But with gears and tires and multiple centers of rotation, you can't eliminate it all or you won't move at all.

[Natedog]

Interesting discussion and lots of good advice. Suspension setup is key and is always a compromise.

[The Violator]

Originally Posted by fyrstormer

So I've got this idea for a no-torque-twist solid axle: The diff is located in the main body of the chassis where the torque-twist can be canceled out by the rigidly-mounted diff case, as in an independent-suspension setup. Coming off the diff are two right-angle gears sets driving two counter-rotating driveshafts running back to the axle (one for the left wheel and the other for the right wheel), with two more counter-rotating right-angle gears to drive the wheels. This would allow a single-motor 4WD setup with solid axles with no torque twist, whereas a MoA design would require two motors to achieve 4WD. Sadly I lack the manufacturing capability to make it. :(

On a shafty crawler if you reverse one of the drive lines rotation, most of the twist goes away. I had my wraith like that for a while. Handled well.

[Reflektr]

Originally Posted by Natedog

Interesting discussion and lots of good advice. Suspension setup is key and is always a compromise.

Word. Torque twist and bump steer is no fun. I've had both leaves and links that have performed better than the other in certain areas. What a guy's gotta remember is - We're just messing with tiny-trucks... Unless your rig is blatantly folding up on itself, or winding leaf springs tighter than an eight-day clock, I probably wouldn't lose sleep over it

[Natedog]

Originally Posted by The Violator

On a shafty crawler if you reverse one of the drive lines rotation, most of the twist goes away. I had my wraith like that for a while. Handled well.

Are the driveshafts both BOLTED to the tranny outputs? If yes, how did you do this?

[The Violator]

Originally Posted by Natedog

Are the driveshafts both BOLTED to the tranny outputs? If yes, how did you do this?

No. I used a diff on the rear output. So it went output - diff- driveline. The diff reversed the output direct. Slash 4x4 center diff.

It worked well, but got hotter than hell. I had a rear plate made to use pinion gears to not only reverse the direction but give you underdrive to the rear in one shot. But in the end ran it normally because I was worried about trash getting into the gears. I think the diff idea on a shafty comp crawler would be fine but it would get hot on long high speed runs.