Counter-rotating DSs =< twist?

[ekd]

Hi all, long time lurker here, ready to start my first crawler.

Within a 1/2 hour playing with a friends custom shafty, I'm hooked!

I need to know if setting the drive shafts up to counter-rotate will mitigate torque twist, and, if so, will it be enough to be worth building a TC from scratch?

I got plenty of info here, and some confidence as well... thanks to you guys. Time to commit!

[chops1sc]

I think a shafty will have torque twist no matter which way they rotate. All we do is try to minimize the effects of it.

How do you plan on making the shafts counter rotate?

[ekd]

I'm thinking of either a sandwich style case (spurs) with the pinion engaging 1 side (thru an idler), and the driven gears engaged... or something with 1 pinion and 2 ring gears.

I'm trying to envision how the torque would act on a typical 4 link setup.

Maybe squirming instead of rocking?

[chops1sc]

Another option would be worm gears. Virtually no twist. One of the items on my to-do list is to build a worm axle shafty one day.

[MadForce]

EGGRESSor tried a similar solution with a bolt on unit for an ax10 tranny as far as modern crawlers are concerned. He was naming it the "torquetwisteliminator".
I also tried, unsuccessfully I might add, in an older twin force project I had. That did not last too long but did reduce TT.
In any case physics are physics and as long as there is action, there will be reaction.

In the Twin Force TT was still there under hard acceleration but way less.

[oldhippie]

It will only make the twist backwards.

[2500hdon37s]

i think thatd just be too expensive i think and for less you could just tune it out

[ekd]

Thanks, guys.

I looked into precision worm setups, and found a really neat miniature box with a cool feature: the driven shaft was set in an eccentric mount that could be turned slightly (and locked) to take up all lash without shimming. They cost more than complete Worminators, even in large quantities, though.

A shafty worm setup sounds so clean and light, though, doesn't it?

Oldhippie, I'm only considering making 1 shaft rotate backwards, so it would only reverse the TT's direction at one end.

MadForce, I'm glad to know it's been done, and had an effect. I'll proceed with a more standard style, and keep it in mind for later when (if?) my upcoming rig has all the other parameters sorted out. Good job on the experiment... kind of you to share the results.

I'm playing "catch up", reading all I can find on crawlers, and I thought this might be the best place to ask...

I got that right.

Most appreciated, fellas.

[chops1sc]

Originally Posted by ekd

A shafty worm setup sounds so clean and light, though, doesn't it?

It does indeed! The only reason I have not tried it yet is the heat issues with higher wheel speed. Which I have not read anything lately to see if the problem has been fixed or if ppl are just dealing with it.

[ekd]

Let's see...

Seals, an oil bath box, oil pump, fan, and a remote cooler... x2.

There went clean, AND light! And, here come the threads on sealing leaks, belt driven vs. direct drive pumps, etc...



Yeah, worms never claimed to be efficient... but I had no idea there might be heat issues. It would be interesting to know what kind of temps are being reached during comps.

[goodoldlevi]

If you search the losi section there were some post of temp.'s guys were getting when the losi worms first came out.

[ekd]

People are burning their fingers on them?

Making an aluminum housing with heat sinking wouldn't help much... the only contact is through the bearings.

I wonder if there is a heat transfer grease that is also a decent lube?

[Terranaut]

In theory the counter-rotating front and rear driveshafts should balance the torque output from the tranny, so the chassis should not lean either way. But that's only theory. In practice, TT is at it's worst when climbing, weight transfers to the back axle and the front unloads. So most of the torque is between the back axle and the chassis, with very little torque to the front to balance it, so the chassis will lean over same as always.

If you are going to get creative, think about putting reduction gear units on the axles at the pinion input shafts, and run higher speed driveshafts (like Losi does). That will reduce torque twist, but is it worth the trouble?

Cheers.

[oldhippie]

All shafties have torque twist. Proper link placement will solve most torque twist issues.

[hitman46mod]

Transposed MOA. No torque twist.

[ekd]

Originally Posted by Terranaut

In practice, TT is at it's worst when climbing, weight transfers to the back axle and the front unloads. So most of the torque is between the back axle and the chassis, with very little torque to the front to balance it, so the chassis will lean over same as always.

This makes sense to me. And it explains why budget isn't the reason it isn't done more often.

The twist wasn't a problem on my friend's rig until it was almost vertical, so it looks like it might need slightly more tuning... and I need to find other ways to mitigate my rookie driving.

Thanks, guys. Appreciate the attitude towards rookies here.

[ekd]

Does an offset TC, with angled DSs (compound angles), tend to lift or lower rather than twist?

Is there any noticeable difference between them and a centered (1 angle) setup?