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Torsion on Axle

Reduce and prevent torsion on axle

Thursday 11 March 2010, by Nico71

Torsion torque can break axles, especially if it’s high. In Truck Trial, torque on axles are very high, that is why it’s important to reduce and prevent the torsion on axle.

To know what is the torsion, please read this on Wikipedia

The important fact to know is that torsion angle is all the higher as the axle is long. Therefore, first rule is to have small axles as possible.

But if we don’t have the choice to put small axles ? You can build a special construction with axle joiners to reduce the length of axles.

With 2 studs length axles, the torsion angle is small. As the axle joiners are quite strong, they absorb a part of torsion angle. It seems that new axle joiners will be stronger than the older. So you should use them.

Also, you can reduce the torque on the axle to reduce the torsion angle. Per example, put a reduction reduce the torque on input and increase the torque output. That is why the portal axle is placed near the wheels.

Forum posts

  • And remember to keep the high torque carrying axle at the minimal length as possible! Good job with the article, Nico!

  • Ok, high torques are not good for axle, but do we really need to strengthen the axle? I think the drivetrain weakpoints are at the gearing; axle torsion doesn’t really influence the reliability. I haven’t seen any broken axle - during normal use. Torsion rather just increase the flexibility of the drivetrain.
    So I don’t think you need to increase the weight of the moving parts...

    But it’s just my opinion:)

    • Long axles arent good, because they create windup. This make the truck wobble when going through obstacles.

    • Ok, I get it. Wobbling isn’t good, so it might have sense.
      In spite of this fact, I keep my opinion, that it’s not so important during designing. I will try to avoid long axle, but in most cases the other factors already determined the length of the drivetrain.

    • I have broken 2 axles already because of torsion... 1 13L axle and one smaller than the 13 I can’t really remember what size was it... Anyway, the vehicle (Looked like a SUV :D) was going over a fairly big obstacle and suddenly I heard a SNAP! =@ And then the suv started rolling backwards =@ I was yelling: "Catch it! Catch it!" And ahhm we did =D Anyway, what I’m trying to say is that strengthening the axle is really important, you don’t have to use a dozen of 2L axle with another dozen axle joiners, you can use 3L axles and axle joiners or 4L or even 5L, doesn’t matter, just It’s better to be safe than sorry xD

    • Probably I’m not too up-to-date with the newest lego parts, but as far as i know, 12l and 32l are the longest.

      On Brickshelf, I’ve already seen axles that looked like a screw, but I never knew how they did it in a normal vehicle. The only way I can imagine it’s possible, is that they built a heavy hauler, throwing 20kg on the hauler to get enough grip, and then towed sg very-very big...

      Could you post (link) some pictures, about that SUV, and it’s broken axles? What motor(s) and gear ratio did you use?

      2l axles - with joiners are the best solution, cause the torque is the same whether it’s a 12l axle or 6*2l axles. If the torque is constant, than the torsion angle depends on the "strength" of the axle. The bigger the axle’s diameter the lower the torsion angle. Axle joiner is sg like a diameter increaser:).

    • Yeah my bad it’s 12L. Well, the thing is that that happened a while ago, and I don’t have any pictures of the SUV, but I think a have some pics of the broken axle...somewhere... =?
      If I find the pics I’ll post them on BS, and then post the link here =D

    • it also creates lag between the front axles and the rear axles because it twists!