Hi, can anybody give me some ideas on a torsion system for a rollcage car I am making,

I am thinking about giving up as there is not much use in terms of bricks.

Incase you are wondering,, tortion is basically glass, carbon fible or spring steel which flexes then returns to its original position. F1 cards have it fitted.

I need the beams to be quite short but I will look at ideas because that would be easier as maybe they can be developed anyway.

It is also hard to say the exact size.

How about using rubber-rings? You could twist a few of them and mount them somehow (I know that "somehow" is the hard part...)

Or you could avoid the need of torsion rods and just use a simple axle as a fake and rubber-ring(s) placed somewhere it's not disturbing.

There's no need of much movement after all.

Edited November 3, 201113 yr by Lipko

If you go to this link, and look at the pictures, it appears that the tank uses a "torsion" bar suspension made from axles.

I've seen a few other people do it as well. One of the PF pneumatic valves I've seen uses axles as torsion bars to return the valve to center.

And just an interesting (to me) side note that has nothing to do with LEGO: My '90 Toyota 4Runner uses torsion bars on the front suspension. No coil or leaf springs. The cool thing about my torsion bars is that I can give them a few cranks with a wrench and gain an inch or so of lift. I still like the coil sprung front suspension on my '00 4Runner better though.

Edited November 3, 201113 yr by dhc6twinotter

If I'm not wrong this truck is suspended with torsion suspension:

P.s. Sariel's latest tanks are suspended with torsion (axles torsion).

Which truck is it again?

Note that the torsions must be able to work from side A and from side B

A and B are both close to the ground as the car can drive upside down

This means there has to be a limit in the stroke or flex somewhere in the middle not at top or bottom ends.

Edited November 4, 201113 yr by SNIPE

@ SNIPE: Yoraish was pointing out that Sariel's latest T-72 tank uses Torsion Bar suspension, which Sariel described this way:

"This was my second tank to use torsion bars suspension – the previous one [i.e., his Leopard 2A4 Tank] was almost 3.5 kg heavy, with nearly 0.25 kg load per road wheel, and its suspension worked perfectly. Here the suspension was very similar, except that the axles used as the torsion bars were kept at fixed angle by the toothed half-bushes and toothed connector joints."

Here is the detail from Sariel's Lego Technic Leopard 2A4 Tank webpage:

Edited November 4, 201113 yr by DLuders

Ok, are you sure these axles wont get deformed

A lot of my red 12L axles are twisted or bant from pull back motors, if you dont put it into the motor far enough there is not enough friction and it will probably slip / and get twisted.

Also if you put the axle through the motor enough and use a small brick to gain a mechanical advantage it will again twist the axle, using 4 pull back motors at the same time will also twist the axle.

I did see that the flex tubing is good as it returns to its original position however after a certain number of times it is bent it will stay that way, also it does not fully return to its original position and it is awkward to implicate into the idea.

I have not had time to test the rubber disks yet

My question is: if the body raised slightly when the suspention is compressed, is that just as equivelant as having a hardtail setup (no suspention)?

Edited November 4, 201113 yr by SNIPE

The axles would have to get deformed and twisted over time. A torsion bar isn't just a regular bar, it is more like a coil spring that has been twisted to be straightened out, that is why it can withstand the twisting motion without bending or breaking.

It will definitely damage the axles.

@ SNIPE: You could consider getting some of the x928cx1 "Technic, Axle Connector Rectangular Triple Spring-Loaded" parts. They are sometimes used for "Return-to-Center Steering" setups.

It will definitely damage the axles.

Nope, it doesn't damage the axles. This is based on a convenient bit of stress/strain relationships. While it is true that axles can be damaged by large torques placed on them by XL motors or cranking them with a high gear ratio, it takes a considerable amount of strain before this happens. Young's Modulus (the relationship between stress and strain) for ABS is quite low, and remains linear (elastic) for a very long time before permanent deformation (plasticity) occurs. The simple result of this is that you can twist an axle a lot as long as you keep it in the elastic range and it will always return to its previous shape. With a torsion bar suspension like Sariel uses on his tanks, the maximum rotation angle you could possibly put on the torsion axle is less than 45 degrees because the suspension will bottom out before it can twist any further. 45 degrees is not enough rotation to permanently damage an axle over 6L in length, so you are totally safe using this method. If, however, you had very large suspension travel or no stop, it would be possible to damage an axle.

@ SNIPE: You could consider getting some of the x928cx1 "Technic, Axle Connector Rectangular Triple Spring-Loaded" parts. They are sometimes used for "Return-to-Center Steering" setups.

DLuders,

:D this is perfect! in every way, I thank you!

This has a 0 degree stop meaning with one stroke it can only go one way (0 to +45 degrees), so if the car is upside down the stroke is opposite meaning the negative part is then used (0 to -45 degrees)

Nope, it doesn't damage the axles. This is based on a convenient bit of stress/strain relationships. While it is true that axles can be damaged by large torques placed on them by XL motors or cranking them with a high gear ratio, it takes a considerable amount of strain before this happens. Young's Modulus (the relationship between stress and strain) for ABS is quite low, and remains linear (elastic) for a very long time before permanent deformation (plasticity) occurs. The simple result of this is that you can twist an axle a lot as long as you keep it in the elastic range and it will always return to its previous shape. With a torsion bar suspension like Sariel uses on his tanks, the maximum rotation angle you could possibly put on the torsion axle is less than 45 degrees because the suspension will bottom out before it can twist any further. 45 degrees is not enough rotation to permanently damage an axle over 6L in length, so you are totally safe using this method. If, however, you had very large suspension travel or no stop, it would be possible to damage an axle.

Isn't ABS subject to creep or relaxation? (sorry, English is not my first language. I'm talking about the phenomena when for example a piece of wood deforms over time under load that's way smaller than the elastic limit) Most plastics are subjects to it, even with low loads. So even if it seems that the axle returns to its original shape, a few months later it will be deformed permanently.

Metals are different, they don't (at least steel) suffer from this kind of deformation. Is ABS similar? (well, I have seen deformed axles and they were just sitting inside a bag of Legos for a few years.)

Edited November 4, 201113 yr by Lipko

Just as a test I mounted one end of a 8 length axle to a 2x4 L shaped liftarm and the other end to another 2x4 L shaped liftarm and placed a minimal amount of torque on the axle stressing it maybe to the 25 degree mark and set it down on a flat table to check and it most certainly twisted the axle a bit from it's original form.

Edited November 4, 201113 yr by Meatman

Isn't ABS subject to creep or relaxation?

To some extent, yes. If the load is large enough and is left applied for a long enough period of time, especially in the presence of heat, then the material could creep. However, when the vehicle is parked the deformation should be small. Most deformation occurs dynamically when driving over an object.

Just as a test I mounted one end of a 8 length axle to a 2x4 L shaped liftarm and the other end to another 2x4 L shaped liftarm and placed a minimal amount of torque on the axle stressing it maybe to the 25 degree mark and set it down on a flat table to check and it most certainly twisted the axle a bit from it's original form.

Hmm, this is completely inconsistent with everything Sariel and I have found. I can twist an axle 25 degrees with my fingers and I can't detect any permanent deformation. There are plenty of axles inside real Technic sets that twist a lot more than that.

In any case, anyone who is critically concerned about maintaining the perfection of their LEGO axles should probably not use them for torsion bars, or for any motorized application either.

Perhaps it's not worth worrying about damaging CHEAP Lego Technic Axles. If they are permanently deformed, replace them for a few coins!

Heres some advice, NEVER take apart a x928cx1.

But yeah i have the first model of the suspention system done but I am trying to make it simpler by using different bricks.

Basically this 90 degree angle box will move the short wishbones but it wont do it the wrong way because it is impossible , IE you cant have it go to -45 degrees out of thin air because the spring keeps it at 0 degrees,

If you move the car upside down then it will work at -45 degrees

The wheels are taller than the body so it can drive upside down, the mid rear and front diffs are electric (not electronic) , there is no gearbox and the engine/motor is denerally speaking, 'electric' too. this means the car is very light and can do by itself.

The hardest part would be the self leveling cockpit so when the car turns upside down it will not go upside down with the car.

I was thinking about using magnets but they would have o be strong enough to not disengage with jolts but disengage when the car is literally on its side about to turn over. Maybe weights using some sort of metal part or maybe lifquid may work too.

Again, that idea I got to use return to centre boxed was most clever!

Edited November 4, 201113 yr by SNIPE

Of course the axles are cheap, I was talking more about the correctness of the statements made in the thread. I wouldn't worry about it myself, if the vehicle is not too heavy.

But it's a bit strange that some are worried about "illegal methods" such as a 3L friction pin plugged through 1/2 - 1 - 1/2 width beams. What's the difference then? Why is it more legal to use a part for something it's not intended for?

I'm still new to this stuff, I may be too pedant, but I'm learning.

Ok, after building then making simpler with fewer parts i desighned the rear part of my project , where the three pins are (on the right hand side of the image) is where the reurn to centre spring,

It has a total of 16 bricks and should be quite strong, maybe if I look on bricklink there may be some more bricks that are not in LDD that can replace a few parts too.

As I said prior, the car Im building can drive upside down because the wheels are taller than the body so the suspention needs to have a downwards stroke (in other words the suspention would pull down towards the ground) when the car is one say round but not when it is on the ground (in other words it pulls down but if it is upside down it works just as normal, the car does not pull the springs down because the road is there to stop it and because it is not heavy enough.)

Note that the suspention is only single point, this is because if the wheel was flat all of the time the body would hit the ground due to super low ride height for low downforce.

The triangular parts are just wishbones and the main brick is part of the chassis.

Here is the return to centre spring box:

Edited November 10, 201113 yr by SNIPE

Interesting idea. So, you are going to use 4 or those hockey puck springs? They aren't cheap, unless you have a secret stash somewhere. If you have a secret stash, I'd be interesting in some.

Why can't you use rubber rings?

Something like this:

I like the idea as ir is but for this model it would not be as good as using the spring boxes, this is because there is more parts and more weight and more movement, and it is not as atached to the chassis as well, note that the chassis is holding the things in place by each side, so you have to assemble it by putting the wheel axle spindol and 3l axles wth stud through the wishbones LAST otherwise it wont attach line up to attach.

I did think about additionaly using the 2x2 cross hole rubber liftarm from the hockey set but i cant see anywhere to mount it where it would still function.

Yes i would be using 4 spring boxes , but i may use another 4 with the springs taken out , this is because it is less bulky and possibly ighter than using the 'T' linkarm (3x3 holes).

I have one spring box at the minute but it is a little clicky and I dont like its colour compared to the other availabile colors, the hockey sets are good but there is some bricks in there i find hard to build around so id probably buy them as parts.

Edited November 6, 201113 yr by SNIPE

Here is the return to centre spring box:

i broke my black one today , the inner plastic clip is broken.. luckely i have 2 others as a reserve :(

I might be intrested in some of those bricks that are broken if they are indeed lighter than the T beam liftarm because they are 2x 3 studs which is what I need.

Of course I would take the spring out of the box because it will only jam and use the rest of the components, this would mean that it would turn just fine but without any resitance from the box.

note, it is early yet days at the minute

Edited November 6, 201113 yr by SNIPE