Wednesday, September 30, 2009

TBs TechTips 27 - Torsion bar suspension

The torsion bar suspension, is something being used in the automobile industry for long time. However it is a technique you may have not seen reproduced in a LEGO model before.

"A torsion bar suspension... is a general term for any vehicle suspension that uses a torsion bar as its main weight bearing spring. One end of a long metal bar is attached firmly to the vehicle chassis; the opposite end terminates in a lever, mounted perpendicular to the bar, that is attached to a suspension arm, spindle or the axle. Vertical motion of the wheel causes the bar to twist around its axis and is resisted by the bar's torsion resistance. The effective spring rate of the bar is determined by its length, diameter and material."

Julien Florent (Yurikostar) presented his solution, during the latest FreeLUG meeting, applied into one automobile chassis.

Simultaneously reliable and simple.

Thanks for the tip, Didier.


RicardoJCMarques said...

Its cute =P

Anonymous said...

won't it ruin your bars?

TechnicBRICKs said...

Don't think so.
The flexibility of these parts, specially longer ones, should be good enough.

Ricardo Oliveira said...

Congratulations, that's pretty cool!

Yes, it seems not to break, but won't it get twisted permanently? That's very simple and successfully done, but just for small buildings.

For bigger vehicles, maybe we could use a bar built with more pieces, like two long axles mounted in parallel with thin liftarms 1 x 3 like this:

o o

...or more liftarms than in the ends.

Anonymous said...

For a torsion SPRING (not bar), one could use Lego Part #x928cx1 (Technic Axle Connector Rectangular Triple Spring Loaded), used in the Lego Hockey sets to return the hockey stick back into position. The spring could be used for a Lego tank with a suspension that rolls over obstacles.

Anonymous said...

I hate that kind of system that force the parts. :o


Unknown said... used torsion bars on one of his half track vehicles.

in fact that MOC had like 3 different kinds of system in one vehicle. check it out!

Alex Campos said...

Indeed, a torsion bar is much easier to fine-tune in LEGO when compared to a coil spring, but I'm with Anio: the thought of forcing parts gives me shudders! :|

Jetro said...

As long as you stay well within the elastic limit of the part there's no harm. Trouble is, how do you know you're not going beyond the limit. Trial and error?

Juan said...

That Completely goes against the purity of building. Parts are not meant to be used that way. There is nothing impressive about that at all.

Didier "6StudS" said...

About harming the axle, you should think in term of torque. Don't you think you apply far higher torques to axles and gears in some LEGO gearboxes?

Anyway, a 12L axle on BL is less than 5 cents...You really should not care about axles, pins or bushes.

Parts are not meant to be used that way? Where's this written? And eventhough they are not meant to be used that way, you should open your mind. Do you know you are allowed to build a different way you are taught by the official building instructions ? And as said in the post, that's the way real torsion bar works : by stressing the element.

In applied mechanics, torsion bar are not the only case where elements are stressed. For instance, we tend to delete frictions in mechanics, but the brakes are based only on the use of frictional phenomenon.

Anonymous said...

Didier, while this specific example is not explicitly mentoned, I think it fits into the general concept written here in official Lego guidelines: (.pdf doc)

Clearly an "illegal" build method.


Juan said...

First off, A torsion bar is actually a Spring that has been straightend out, not a regular solid bar.

It doesn't matter if an axle costs 5 cents or 5 Dollars, this is going against proper building, so there for, it is unimpressive.

So Didier what you are saying that We should all keep an open mind to destroying parts because Pins, axles, and bushings are irrelevent and cheap? Yeah, I want to have to tear apart my model every other day because I built it to consistantly break. That makes alot of sense.

Are you also a fan of butchering and gluing parts and creating new ones that don't exist?

Didier "6StudS" said...

Am I also a fan of butchering and gluing parts and creating new ones that don't exist?

No, I'm not.

But why shouldn't we?

There are a lot of guys out there who do so.

Actually, LEGO designers cut, glue, and paint LEGO parts.

They're evil ^^

Anonymous said...

who cares about "proper building"? its your creation; if The builder thinks it impressive,let him think it. it looks fine to me. THERE IS NO PROPER BUILDING, IF THERE WAS WE WOULD NOT HAVE THE THINGS WE SEE AROUND US. the guy you made the first wheel did not have rules....

Ricardo Oliveira said...

And what about those that broke down XL motors on water to have a remote controlled aquatic robot (sorry, I don't know the names)? lol

Forget it, LEGO fans and children are not massively going to destroy pieces... I hope to see more strange things here! ;-)

TechnicBRICKs said...

Don't tell me about those underwater broken XL motors...
They have been extremely helpful and that's all that I want to say for now. ;)

Juan said...

Who cares about Proper building? Uh, probably 95% of the Lego community.

The rest are Mad Scientists who like to create their own parts and use them in ways that they were not meant to be used.

If the Person who made that video was impressed enough with himself to post that video on youtube, then he should expect positive and negetive comments about it.

Everytime that axle gets twisted, it gets weaker and weaker. A torsion bar is a spring, an axle is NOT a spring.

Anonymous said...

no one cares about your stupid comment juan. 95% of don't care.

nxtinventor said...

anyway, some torsion bars are supposed to bend. take alook at this:

nxtinventor said...

torsion bar is also not a spring. it is a piece of metal that bend, causing resistance.

TechnicBRICKs said...

Take it easy guys!

While everybody is free to express their own opinions, this kind of dialog never happened here before.
And it doesn't need to start now!

nxtinventor said...

ya i agree with conchas. whoever anonymous was, they need to tone it down.

Didier "6StudS" said...


You seem to be upset by the fact the ones who share this video are "impressed" by themself.

They are not.

They are adults who enjoy to play with LEGO and who enjoy to SHARE with other TFOLs and AFOLs.

Yes, we expect comments - we call them feedbacks. We try to answer constructive feedbacks (to be polite, no to get the last word). If I replied to yours is that i feel it was constructive and argumented.

And, 95% of people agreeing about one topic do not make them right on this topic - whatever they agree on. (not that the remaining 5% right either :-) )

Juan said...

Well then, someone answer me this:

Is it Ok to flex and bend an axle to make a curve for a body panel? Or to connect 2 points that are otherwise impossible to connect together with the proper liftarm?

I mean seriously, where is the line drawn here when it comes to flexing and over-stressing parts?

Didier "6StudS" said...

It's up to you.
It's up to everybuilder.

We don't have the same borderlines when it comes to parts use.

Some cut and glue train tracks, others drill parts to put some LEDs in, some cut flex tube.

In the case of axles, no need to bend them to make them fit a panel curve, flex axles do exist and that's a nice idea :-) And, maybe, these flex parts do exist because one day, a guy at TLC bent an axle to fit a curve.

Meshing points that are not properly distant? Yes. Check this :

(loose and tight gear meshing with value errors)

See, you are opening your world to new opportunities :-)

TechnicBRICKs said...

Well... tried to put a new post in front yesterday night, to relief some tension here, but got asleep before... :(

Myself tend to be impressed yes, by the enthusiasm to share new things (in inf act as we haven seen, it was not so new anyway).
I agree this is not a valid technique officially supported by LEGO, but for me it is still interesting to realize on the advantage we may take on some properties from the material, whether I will over use or not and most probably not.

It is up to each of us to decide when it is still making use of some flexibility, or over-stressing parts.

While I tend to be purist and not liking to mod parts, it doesn't mean I am fundamentalist and can't appreciate some developments with modded parts.
I've done in the past and will certainly do it in the future as well. It is mainly one way to explore and test new possibilities/ideas or getting something useful that's not available on the shelf, but one day may become. And sometimes one small attempt, valid or not, to make TLG realizing on a gap.
What do you think of those who tried to make longer pneumatic cylinders by modding existing ones?

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