Do Portal Axles Reduce Torque Twist? Part 1

[@RC-Homesteaders]

This channel is so scientific in detail to our Hobby 😊 thank you buddy for your love for this hobby and sport 👍 And most of all thank you for sharing your awesome knowledge to all 😊

[@BoomslangSuss]

So nice of you! I have more to come to stay tuned.

[@RC-Homesteaders]

@@BoomslangSuss can't wait my friend 👍

[@KlimovIlya]

So as far as i underdtood the 2 practical options to reduce the torque twist are 1. Increase the total reduction from motor to wheel, and 2. Reduce friction from motor to wheel as much as possible (for example replace bushings with bearings, make sure that the wheels are not binding, etc...). Another question is what about the worm gears? I think they produce less torque twist or is this also a misconception?

[@BoomslangSuss]

I don’t see how friction changes anything. More friction probably helps! Worm gears don’t change anything. They are just another gear reduction between your tire and motor and the only thing that matters is your total reduction between the tire and the motor.

[@Teasuti]

So if we redesign the motor placement to sideways, would the reactive forces act on the longitudinal axis instead, thus completely eliminating the wheel lifting and the leaning on one side? How about a vertical placement? It would hurt the CG, but it would be fairly easy design and it would fit probably every scale chassis and hard shell. It would be awesome for class 1 rigs to get rid of the torque twist.

[@BoomslangSuss]

You would have to eliminate the shaft drive and bevel gear as well. That means a parallel belt drive. Vertical placement is quite interesting. Haven’t thought about that. You might be on to something.

[@Teasuti]

@@BoomslangSuss so there's no cure after all? I didn't quite understand the video then, I suppose. I thought the only thing that mattered was the orientation of the two ends of the drivetrain. One of which is the motor housing itself. If the motor is placed on the pitch axis (or yaw axis), wouldn't the reactive force on the chassis be a pitch (or yaw) instead?

[@BoomslangSuss]

MOA is the only real solution.

[@Teasuti]

@@BoomslangSuss What's MOA?

[@BoomslangSuss]

“Motor On Axle” there are two motors, one on each axle that are parallel to the wheels. No driveshafts and no bevel gears anywhere.

[@garrett6217]

I am always interested to know why companies put the pumpkin of an axle in the center. Wouldn't an offset pumpkin on an axle help reduce torque twist?

[@BoomslangSuss]

That’s a good observation. The weight of the pumpkin would help AND the longer lever arm from the pumpkin to the far tire…BUT… this only works if the diff gear is on the correct side of the bevel to take advantage.

[@jamesstewart9970]

I hate to say it but you are wrong, simply changing a spur and pinion on the motor end won’t reduce torque twist in shaft driven rigs that have a transfer case because the amount of torque from the straight axle to transfer case for a particular obstacle through the driveshaft stays the same that way, however if you can increase the reduction in the axle housing it’s self it would require less drive shaft torque from the transfer case to overcome the same obstacle which will reduce torque twist, a greater reduction at the motor pinion will lower required amperage and reduce top speed and provide greater torque for the same amperage but doesn’t remove or reduce torque twist.

[@BoomslangSuss]

This is precisely why I produced this video because too many people believe as you do. Action and reaction. Action is at the content patch and reaction is at the skid. It doesn’t matter where the gear reduction occurs in between. There is no math that I know of that supports otherwise, but if you can show a correct force balance diagram that demonstrates your point…I’d love to see it.

[@jamesstewart9970]

It’s pretty simple, torque twist is a component of chassis the wanting to twist opposite of the drive shaft it’s self in relation to the axle housing, in order to reduce that force you have no other option than to increase reduction in the axle housing it’s self to reduce the amount of load on the driveshaft which reduces torque twist, it can never be eliminated entirely but it can be reduced but only through the axle housing it’s self unless you go to motor on axle. It wouldn’t matter if you had one million to one reduction between the motor and shaft because it would always require the same amount of shaft torque between the transfer case and axle housing to rotate the tires which is where the torque twist comes from. On non portal axles though it would require a lot bigger pumpkin with a massive ring gear and tiny pinion which means there would be even less ground clearance.

[@BoomslangSuss]

You are making the same mistake everyone makes. Your premise is based on the assumption that the shaft stops rotating at the axle pumpkin and the bevel gear. But the shaft doesn’t stop rotating at the bevel gear. It keeps on spinning until it meets resistance at the contact patch. Action and reaction. There is no reaction at the pumpkin. The axles keep on spinning in through the pinon and out the bevel gear. It’s not locked at the bevel and that’s what would be required for your calculation.

[@jamesstewart9970]

And the housing and chassis are independent of each other with the exception of the suspension and drive shaft, and unless you reduce the load on the shaft you end up with the suspension bearing the brunt of of that load and causing torque twist, the only way to reduce torque twist is by reducing the required torque through the shaft and that can only be done on the housing end..

[@BoomslangSuss]

Build two rigs, one portal with 18t pinion and one straight axle with 9t. Identical in every other way, and see what happens.

[@yrusonoz5574]

Definitely interesting stuff Awesome video bro

[@BoomslangSuss]

Glad you think so!

[@nealesmith1873]

Very interesting! MOA may cause font to back tilting.

[@BoomslangSuss]

That is correct, you still have the wheelie effect from the back wheels wanting to flip the car over.

[@fazahirthaha7674]

How about counter rotating transfer case?

[@BoomslangSuss]

That’s not as simple as it seems. I’m working on a mathematical model for it. I don’t think it helps as much as we would hope, but I’ll break it down.

[@RiceCrisp320]

I think torque twist can be simplified. Assuming basic functions of gearing you are trading torque for speed and vise versa. If you look at the torque twist as coming from the driveshaft connection between the contained systems of the axle and transmission it becomes a simple argument of decrease the torque and increase the speed. Therefore an axle geared for more input speed from the driveshaft would impart less torque on the chassis i.e. the increased gearing of portal axles. If we pretend the transmissions and axles are perfectly ridged bodies in your example(wheels not allowed to turn) then the only places where torque can affect the system are at the connection points of the driveshafts. I think your test method is flawed since when the tires are in a bind the gearing the axles doesn't 'do' anything and the same forces from the transmission are able to lift the car just the same. If you allow the wheels to turn there will be much less chassis torque required to provide the same amount of torque to the axles. I think it would be interesting to attach a sled to rear axle and do a pulling test. At different weights on the sled how does a portal vs straight axle rig behave. I would hypothesize that the pulling force needs to come from the axis of the wheel for best results. A test done from the bumper of the truck or the diff of the axle would probably introduce too many variables.

[@BoomslangSuss]

I think what you are suggesting is inputting various levels of torque at the wheels with a sled. What I did was applied the maximum torque the vehicle could handle before flipping over. The magnitude of the force is not important - the reaction at the motor is the same and proportional. You will still get a proportional twist. I have a feeling I am going to need to demonstrate this to make it more clear. 100:1 reduction on both a portal and straight axles - it will produce the exact same twist.

[@WRIGHT-GARAGE]

@@BoomslangSuss in the rc world what you are implying is not relevant to us. what is relevant is resistance to lifting a tire under normal driving conditions.

[@BoomslangSuss]

Torque twist is the cause of the front tire lifting.

[@brianmassey7563]

what about counter rotating driveshafts? Does what you just showed mean that since the tires are rotating in the same direction, the the motor will want to rotate the same as if the driveshafts were spinning the same direction?

[@P0110X]

I've heard that one but how I deal with torque twist is by adding dual stage shocks and having a piston from one side with one additional hole than the other side. I get almost no visible torque twist on my axial bomber despite using 2800kv 3s

[@BoomslangSuss]

Are you essentially saying that you have slower damping on one side because of less holes on the piston? That is certainly one way to help.

[@BoomslangSuss]

Counter rotating shafts should work under ideal circumstances with equal traction front and rear. When torque twist become a problem is on a steep climb, at which point the front end is very light and the front traction is low, so the vast majority of twist is coming only from the rear axle and the front axle's contribution is diminished. This is certainly something I'd like to test.

[@AnanFakheraldin]

@@BoomslangSuss That would be a great topic for next video, one thing to add is that we are not always climbing , in comps there is a big part of the course that is side hilling.

[@themountain59]

Usually thre "torque twist" we encounter comes down to traction...so because the twist eliminates almost all traction on the front it doesent matter in which way the driveshaft rotates ...the twist will be the same .

[@taftdavis2282]

Who will engineer and build a trans with a sideways motor mount applying the torque twist to force the front end down?

[@BoomslangSuss]

You’d need a belt drive from the motor to the axles. At which point MOA probably is simpler. I’d like to see 1 motor on the front axle and a belt traveling to the rear. 😅

[@yungliquid7053]

Have u talked about the shock angle ? More so like diagonal from the rear instead of a caster angle forward? Hard to explain. Like triangle rear shock / - \

[@BoomslangSuss]

/ - \ this orientation is looking from the rear?

[@yungliquid7053]

@@BoomslangSuss yup! I was actually just finishing reading on triangulation? Its kinda rough in my head but it seems like something not covered as much unless i never seen. Its my first year crawling RCs so im learning everything brandnew

[@yungliquid7053]

@@BoomslangSuss i had installed my shocks in that way as an experiment just on how i can mount shocks “creatively” but didnt drive it yet. I had put it back to normal because i wasnt too sure

[@BoomslangSuss]

@@yungliquid7053 I am presently working on a video specifically for shock mounting angle, so stay tuned. Typically, in the mounting direction you are referring too, you don't have a lot of options on how to mount them, so mount where you can and then tune accordingly.

[@yungliquid7053]

@@BoomslangSuss hell yeah awesome! Thank you, sounds funny but i was asking the “AI” on snapchat questions about it LOL! Honestly got alot of information from that too. Not many spots to mount unfortunately, but we can get creative like ive seen all the cool builds. Imma put that set up on today and drive it this weekend and see how it is and at lwast worth it. I think it can help with side hilling

[@yonicozac]

Mmm, I must say that your video is extremely well detailed and explain, very nice!, but I think that the part on axle vs. trans reduction (which is the crucial part) is wrong. Bearings doesnt magically transfer the forces away, Newtons third law works between every force and load, so when a gear pushes the teeth of the other gear down, it itself pushed up. the fact that the gears rides on bearings doesnt eliminate that, and in the case of bevel gears it manifests as a twist forces.. The issue with torque twist is that one segment of the gear train is riding on soft springs instead of rigid gear case. so having this part face the least toque possible (and instead speed) is beneficial. That's why UDR is using extra planetary gear in the axle, and indeed having very little torque twist for a big 6s car..

[@BoomslangSuss]

If you are talking about the Traxxas UDR it uses sway bars to control twist.

[@yonicozac]

@@BoomslangSuss then why adding the complexity of a planetary gear on the axle, where they could more easily add this reduction on the gearbox before the driveshaft

[@BoomslangSuss]

Maybe I’m not looking at the same thing as you. Can you point me to this planetary gear on the axle that you are referring to?

[@robaki-dev]

@@yonicozac did you mean "portal axle" instead of "planetary gear on axle"? Portal axles mainly increase ground clearance. They can provide additional gear reduction, as shown in the video, but they can also have a 1:1 gear ratio. Edit: I just noticed you mentioned the Traxxas UDR; it does indeed have planetary gear reduction on the rear end. However, I don't think it’s a design choice to reduce torque twist. Having a gear reduction as a unsprung mass on an axle seems like a less ideal solution for the suspension... Why not use a regular gearbox on the chassis? idk but I'd love to learn :)

[@mikekoblas9064]

The UDR has planetary gearing in the nose of the differential. It does in fact do a huge part to reduce torque twist. This was an excellent video, and I have spent many hours researching this, but in my opinion, I still believe the more the gear reduction is done in the axle the less torque twist. I am actually experimenting with this in a build and it will be interesting to test the theories! This video does have me questioning my thoughts!

[@jerryvolpini7987]

You mean there's science in RC?! I'm out, lol! Well done video, thanks!

[@BoomslangSuss]

Pretty much!

[@themountain59]

Very good clip ! 👌

[@BoomslangSuss]

Thank you! Cheers!

[@CAPRAQUEENRC]

These are great videos that explain everything I try to teach people but they always ignore me because women apparently can’t know anything about RC or Engineering so now when people say I’m Full Of S. I follow up with posting these videos and suddenly they have an epiphany and say yes the information is correct but only because it’s because a guy posted a KZbin video reaffirming everything I try to teach in the first place.

[@BoomslangSuss]

Well, I am happy that the videos help, but sad that it takes a man to convince people. Hang in there - you'll eventually get the respect you deserve. We need more women engineers.

[@freshboy3968]

That's a lot of bikes.

[@BoomslangSuss]

My other car is a bike.

[@OGRadGrow]

Awesome torque twist explanation 👍🏾

[@BoomslangSuss]

Thanks 👍