Portals & Twist - Part 2
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- Опубликовано: 18 июн 2024
- Here I revisit the topic of Torque Twist and Portal Axles on RC Crawlers.
00:00
00:39 Review
02:22 Axle
03:28 Myth One
05:04 Myth Two
05:21 Demo
06:52 Demo with Brakes
08:12 Slo Mo
09:22 Other Resources
Werewolf
werewolftech.com/en
74 Weld
motorsports.74weld.com/
#rccrawling #rccrawl #rc #rccar #rc4wd #torquetwist #rccrawler #rccrawlers #rcextreme4x4offroad 
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Its great seeing these videos pop up in my feed. I enjoy the clarity and demos on these topics. Reminds me just how long its been since a took physics classes.
Great to hear!
Thank you for this explanation!
You're very welcome!
A number of things caught my attention while watching this. I should state that all of my experience comes from the full size world. However, vehicle dynamics are vehicle dynamics.
1. The geartrain at 1:50 - There is a force trying to rotate the box. It is the nature of gear housing. For an even number gear box, 2:20, the reaction is torque out + torque in. Odd number gears, like the 1:50 example, the reaction torque is torque out - torque in. This is a pretty fun example to do with a free body diagram.
2. The example at 3:00. The light gray box will try to rotate about the shaft from the dark gray box. The dark gray box will try to rotate about the shaft from the light gray box. The light gray box will also try to rotate about the axle to the wheel, this is why solid axles without portals draw the antisquat line to the contact patch.
3. Starting at 3:54 through 5:00. Incorrect. The amount of torque that causes the axle and chassis to rotate in opposite directions is reduced.
4. The first example without the wheel. The torque that the axle ands chassis react to is purely based on the torque needed to spin the hubs. In this example the little gear and bearing friction are not putting enough drag to generate a noticeable amount of torque. If you need proof, watch the movement of the chassis rails. They move from the torque spikes of you hitting the throttle.
5. The second example with the wheel. I am not convinced that you are not feeling the torque at the axle. What is likely happening is that the order of magnitude or two larger lever arm to the hand grabbing the tire is causing a reaction force that is to small to notice. Add in that the force may not be noticeable while grabbing the tire.
The last few things are more notes and semantics that anything else.
6. 9:50. Any shaft driven live axle, counter rotating driveshafts to the same axle excluded, will have torque twist. Chassis mounted diffs, like in independent suspension do not have torque twist. Setups with counter rotating driveshafts from and rear will only exhibit no twist if equal torque is going to both ends.
7. 9:55. It can be tuned out with linkage geometry. The full size crowd has been doing it since at least the mid 2000s on 3 link with panhard setups. They recommend against trying to do it if you are uncertain about what you are doing since it is easy is easy to mess up and even magnify the effects. Early moon buggies liked that setup because it kept even force to both tires.
There may be some miscommunication going on. You are the first person who I have seen call the axle assembly rotating torque twist. I have only seen it used to refer to the movement of the chassis under drivetrain load.
An experiment that should show the gear reduction effect is to pull a load at constant speed with a crawler. Change the total axle ratio, portal and ring/pinion, and tow the same load. The bigger the ratio change the more obvious the difference in chassis twist. Next, put the transmission in a lower gear and pull the load. The chassis twist will match the twist of the same total axle gearing.
An experiment to show the axle wanting to rotate about the driveshaft is to hang the axle by the driveshaft. Put a resistance between the tire an axles housing. Rubber bands holding a pencil against the tire might work. The axle should rotate about the driveshaft.
That's a lot of typing for someone who goes by toolazy :)
@@BoomslangSussI was putting off doing something else.
@toolazy4340 ive had this same conversation explaining this exact thing to great extent with him already a few months ago, pretty sure im part of the reason this video exists. im convinced theres a misunderstanding on what the torque twist we experience actually is. hes calculating reaction force from the motor, which is a factor, but completely ignoring the relationship between the gearbox and the axle assemblies, which is the exact thing almost single person ive seen relate to the term torque twist experiences. example: i have 2 rigs with near exact builds besides straights vs portals, and despite all the math done in these videos saying the straight axle rig should have less twist (has greater overall reduction), the twist is blatantly more obvious on the straights vs portals. portals will still have torque twist, but on the straight axles its something ive had to actively chase and tune out in the setup, despite "the math" saying it should be better for said torque twist... dropping down in pinion has never helped the situation either, not one bit...the only things that made any tangible difference was underdrive gears at the axle, and suspension/link tuning. and yet, here we are...
Great explanation, thanks 👍🏻
No problem 👍
Very well explained and for me quiet logical. My portalaxle rig has nearly no torque twist in the open field. The straight axle one instead always fight with the font axle twist. Only a swaybar, thicker oil in the rear shocks and the smallest pinion helped a bit.
BTW, nice tshirt , that someone knows these days Einstürzende Neubauten is a miracle. Loved Blixa.
I grew up near Wax Trax in Denver, lol.
I've heard this from several people and I am still working on an explanation. The short answer is that usually there are more differences than you think between someone's portal v. straight rigs. Most importantly, total gearing. But also, track width (portals are usually wider) motor kV, weight balance, tires and testing method.
@@BoomslangSuss Thanks for your answer. I'm from Germany, saw Neubauten live a few times in the 80's.
For the rigs i still use voltage up and gear down. You are absolutly right, there are so many factors involved and not explained in one hour. Usually i'm a straight axle guy and try a lot. The transfercase is also important and made a good experiences with driveshafts running in oposite directions. With Axial and Traxxas they are running in the same direction. But this example is only for straight axles and only a few axles allows this set up.
@@1500chessie Lucky!
@@BoomslangSuss Same here ....I have one of those chinese 3 gear transmissions which have the drive shafts rotate in different direction for a mullet setup and it works well.
Good. Thank you!!
Thank you too!
🤘Love your T-shirt 🖤
I love that you recognize it. I guess I'll have to get even more obscure. lol
@@BoomslangSuss I am German ...so ...😁
Welp, should have waited ten more seconds before posting my question lol. Thanks!
haha
Does adjusting the pinion angle (upper links) coming off the rear housing, affect the amount of torque twist? I can see yes and no, but I'm not educated as well as you 😊.
This isn’t directly related, but it might be helpful to note that torque twist is opposite in a portal vs straight axle truck. Because of this there are left leaning climbs my VRD Carbon can’t get and right leaning climbs my SCX PRO can’t get.
Did you actually see the clip ??🙄
This is true
That is a great point. The direction of twist actually depends on a few things - motor facing fore or aft, total number of gears in the drivetrain, motor rotation direction and bevel gear orientation. Vehicles could twist left or right and neither is better or worse..
@@themountain59 I don’t know what you mean? My point was that even though portals don’t change the amount of twist, they can change the direction. Which in a side by side comparison video on a side leaning obstacle can make it look like one has more twist than the other, when it’s really just the direction change causing the difference.
I think I see your meaning. In other words, twist may be more obvious when sidehilling in one direction than the other. That would totally be true. Use twist to your advantage if you have the option.
Thanks for another video! One small correction if I can, not all shaft driven cars have torque twist, the Losi LMT is an example, as it uses bevel gears both on the axle and on the skid
You mean it has a center diff? The same rotational force goes out from the skid. The lmt still has TT.
@@The_RC_Guru It has TT, but the TT tilts the skid forwards (which is contradicted by the squat from acceleration), and the tilt is not sideways like in crawlers
@@yonicozac yes it is exactly the same effect. You’re talking about weight transfer to the rear on acceleration. The tt is reduced in the lmt from being able to unload some torque to the front from having open diffs and the sway bars. It has torque twist just like every shaft drive. Even all full size vehicles with center shafts still do. I see why you were confused here but they all experience it. Some are better at managing it or reducing the noticeable effects. Just Google even losi lmt torque twist. The guys running more power amplify TT and have made posts on how to fix it.
@@The_RC_Guru No no i disagree. On the LMT the motor is mounted at 90 degrees compared to regular crawlers, which means that the motor is twisting the skid to the front, and not sideways. My friend has an LMT roller and he put alot of power on it, it has zero torque twist. zero. even without sway bars
@@yonicozac the motor is also rotational mass. Ever run a single motor brushless rc boat? When you mash it, it’ll tilt. The motor being that direction in the lmt helps with that. This isn’t an opinion topic. It’s testable and a verifiable fact. If it’s shaft drive with links and the rear differential isn’t directly connected to the same solid chassis as the transmission like an emaxx is, there is torque twist. Put your phone camera directly behind the truck on slow mo record and a hard accel. You’ll see it torquing over. The guy in the video here literally gave you a real time demonstration. The lmt is not immune because it has open diffs and a sideways mounted motor. I’m done explaining maybe the channel guy will convince you if you won’t try to verify it yourself through googling or testing. Maybe your buddy has rock hard shocks or something else going on. But if it’s shaft drive with a 3 or 4 link, it’s experiencing tt. It’s not a philosophical subject where two people can be right with differing opinions. It’s subjective and easily verifiable.
Does reversing the direction of one of the transmission outputs reduce the effect of torque twist? The Dlux Cheezburgr has this feature and I believe the concept is applied to some full scale crawlers as well.
It helps yes.
No, not really on an RC crawler. In order for twist to occur, you have to have traction. Traction comes from weight and downforce. Twist becomes a problem on steep, high traction climbs. Under these circumstances, the front wheels are very light, front traction is low and may even be non-existent. So in this situation, >90% of your twist is coming from the rear axle. It doesn't really matter what the front axle is contributing. I'd like to do a video on this because it's a great question.
@@BoomslangSuss I was wondering this as well for a mullet build. Does a portal rear and straight axle front cancel each other out? But I agree that if all your traction is on the back tires, the front probably isn’t in play.
@@ShoddyRC Nope, that does not change anything.