What is Torque Twist (TT) and how to fix it.

[Duuuuuuuude]

TT starts with the motor, and is made worse my resistance to movement.

No to the first part, 100% yes to the second part. The only reason that the motor is in the equation is because it is supplying the power, otherwise it has no relation to TT.

TT is all about resistance of movement. If there were no resistance, there would be no twist.

heres my test. if you have a rear drive car/truck, go start it up. now rev it a few times. what happens? front left lifts,rear right spuats= torque twist, no gears,tranny,or drive shafts involved

That is not quite the same. It kinda is, but it isn't.

 

[TSK]

The problem with your test is you are comparing a rwd car with unknown motor layout with a fwd car with a specified tea verse mounted motor. A typcal rwd buggy with a transverse mounted motor has no TT just like the fwd car with a transverse motor.

Hold either of those two setups from the front or rear end & you'll experience no TT. Grab the middle of the chassis on one side and nail the throttle & you experience TT, because the initially stationary drivetrain & wheels are resisting the powe the motor is producing.

Even if an AX axled rig had a transverse mounted motor, it would still experience TT because the power would be transferred& resisted longitudinally and not transversely.

 

[sloppy]

That is not quite the same. It kinda is, but it isn't.

sounds the same to me.. Torque.. gas motor spinning in place has torque, electric motor spinning has torque.. Both have torque and there is no way to get rid of it from either..

 

[opek]

Tests are good. Is the RF being pushed into the air by some torque reaction coming through the driveshaft, or being pulled into the air by a twisting chassis?

What if we do the angle board thing with the rf shock disconnected. If the drivetrain torque is twisting the axle up, it still will. But if the tire is being pulled up by the chassis, it will now stay on the board.

And that's why softer front springs reduce the appearance of TT. But in my experience - because of link geometry compared to the chassis is out of whack when one shock is bottomed out and the other is at full extension - the truck makes more traction when the front lifts a tire... all other things being equal.

 

[Duuuuuuuude]

sounds the same to me.. Torque.. gas motor spinning in place has torque, electric motor spinning has torque.. Both have torque and there is no way to get rid of it from either..

A spinning engine or motor can rock the chassis, but that is not the cause of our problem. Scorp nailed the reason why...

Even if an AX axled rig had a transverse mounted motor, it would still experience TT because the power would be transferred& resisted longitudinally and not transversely.

 

[mahgninnuc1]

Maybe a visual will help

 

[mahgninnuc1]

If you disconnected the axles, and pulled the trigger your crawler wouldnt lift the right front. it might rock side to side, but no twisting involved. You don't have twisting in drive train and chassis till you have torque applied to the wheels which are resistant to turning.

 

[Archangel]

Maybe a visual will help

Newton's third law of motion states that "to every action there is an equal and opposite reaction." The above picture shows the axle twisting or rotating clockwise (from our perspective) which means that the drive shaft is actually turning in the opposite direction. (counterclockwise) Everything in the vehicle that rotates/spins has rotational inertia. That means the motor armature, spur gear, tranny gears, driveshafts, ring and pinion gears, axles, wheels and anything else that spins doesn't want to when you hit the throttle. That causes anything they are connected to, to attempt to twist in the opposite direction. So TT is caused by the sum of all of the above items. Some just cancel each other out.

 

[Hardline]

Newton's third law of motion states that "to every action there is an equal and opposite reaction." The above picture shows the axle twisting or rotating clockwise (from our perspective) which means that the drive shaft is actually turning in the opposite direction. (counterclockwise) Everything in the vehicle that rotates/spins has rotational inertia. That means the motor armature, spur gear, tranny gears, driveshafts, ring and pinion gears, axles, wheels and anything else that spins doesn't want to when you hit the throttle. That causes anything they are connected to, to attempt to twist in the opposite direction. So TT is caused by the sum of all of the above items. Some just cancel each other out.

Okay, you made me look. The picture shows the front driveshaft rotating clockwise (looking from the front). My AX10 driveshaft actually rotates counter-clockwise (also LFTF). Does that "shaft" your argument? ;-) Or in your text are you arguing that the picture is wrong? I guess the red arrow could be referring to axle rotation even though it appears to be driveshaft rotation.

 

[EeePee]

TT is all about resistance of movement. If there were no resistance, there would be no twist.

Yes, like the pinion gear trying to climb the ring gear.

 

[Duuuuuuuude]

Yes, like the pinion gear trying to climb the ring gear.

Only because the ring gear is transmitting resistance. It makes no difference what is trying to climb what. You've got one thing trying to spin and another thing trying to keep it from spinning.

 

[C*H*U*D]

I still think the best way to experience this first hand, is with the electric hand drill and the drill bit stuck in the wood. The drill bit is the driveshaft and your hand is the chassis. Pull the trigger and what happens?

 

[Duuuuuuuude]

I still think the best way to experience this first hand, is with the electric hand drill and the drill bit stuck in the wood. The drill bit is the driveshaft and your hand is the chassis. Pull the trigger and what happens?

You are 90% there with your analogy. The bit is the driveshaft, the drill case is the chassis, you are the flexible suspension connecting it to the ground. "thumbsup"

 

[Hardline]

Yes, like the pinion gear trying to climb the ring gear.

^^^ is the closest to my version. Resistance at the tires applies forces the same as if you tried to push a car backward. The motor and drivetrain won't let the pinion spin backward, and the result is the ring gear attempts to climb the resisting pinion. The ring gear climbs and twists the axle with it.

Anyway...it works for me. ( I hope it's not wrong -- I'd hate to have to try to figure this out again. It's taken me months )

 

[Duuuuuuuude]

^^^ is the closest to my version. Resistance at the tires applies forces the same as if you tried to push a car backward. The motor and drivetrain won't let the pinion spin backward, and the result is the ring gear attempts to climb the resisting pinion. The ring gear climbs and twists the axle with it.

Anyway...it works for me. ( I hope it's not wrong -- I'd hate to have to try to figure this out again. It's taken me months )

I find that a bit misleading. The ring gear has nothing to do with it other than it is just another link in the chain.

 

[Hardline]

I find that a bit misleading. The ring gear has nothing to do with it other than it is just another link in the chain.

I don't think so. The ring gear is the only chain link that is actually coupled to the axle housing (via the two differential bearings). That IS the force path responsible for pulling the tire off the ground. The pinion can't do it -- it pivots with the housing. The LF tire isn't pulling the RF tire off the ground. It's truly the ring gear/carrier & inner bearings that transmit the lifting torque to the axle assembly. Its where the resistance of the front tires meets the counterforce of the motor/driveshaft/pinion. The ring gear climbs and pivots due to that confrontation and twists the axle housing with it.

But it's too complex a concept for all of us to see it the same exact way. This way works for me. But I think that any solution that acknowledges the role of drivetrain twisting plus resistance to forward motion is on the right track. For a long time I thought the motor torque and motor case reaction to the chassis was the culprit. I've totally given that up.

 

[Erock]

Indeed. The ring and pinion relationships only effect on the suspension is for antisquat. If you could have a transverse (sideways) mounted motor, and use a chain like drive system you would eliminate the actual torque "twist" effect, you would however have other effects. Like said before the actual twisting effect on the chassis/drivetrain is caused by the motor and drive shafts spinning the way that they do. So at the end of the day there is no actual cure for torque twist that does not eliminate the benefits gained from this system - antisquat.

Look at IRS vehicles, they have far less torque twist but also cannot get the power to the ground.
Look at chain drive ATVs they have no torque twist, but they can get extremely rigid suspension in a bind, and have no articulating suspension.

Ok, yea there is a "real" cure - A transverse mounted motor on the axle (MOA), you still get antisquat but have no torque twist.
If you mounted a motor right on the pinion of normal axle (like AX10) you would still have TT, such as a LCC with the MOA mod, though I think worm gears do eliminate TT.

 

[ManxCrawler]

AX10 with front mounted MOA and flexy drive from front axle to rear would eliminate it as the chassis wouldn't experience any forces as such and is a project I've been thinking about for a few months now

 

[Duuuuuuuude]

If you mounted a motor right on the pinion of normal axle (like AX10) you would still have TT

No you wouldn't.

 

[C*H*U*D]

You are 90% there with your analogy. The bit is the driveshaft, the drill case is the chassis, you are the flexible suspension connecting it to the ground. "thumbsup"

Now you're just getting "fancy".



but I concur.