A Simple Air Suspension Demo With Lego Technic

The most common suspension systems on automobiles rely on simple metal springs. Leaf spring and coil spring designs both have their pros and cons, but fundamentally it’s all about flexing metal doing the work. Air suspension works altogether differently, employing gas as a spring, as demonstrated by this simple Lego build from [JBRIX]. 

The suspension system is employed on a Lego Technic car, with a relatively unsophisticated design. The car has no real form of propusion, and serves solely to demonstrate the air suspension design. They may look like dampers, but the system is actually using Lego pneumatic pistons as springs for each wheel. The pistons are connected to the upper control arm of a double wishbone suspension setup. Each piston is pneumatically connected to a main reservoir. With the reservoir, and thus the pistons, pressurized, the suspension system can support the weight of the car. If a bump perturbs a wheel, the piston compresses the air in the system, which then returns the piston to its original position, thus serving as a spring. If the reservoir is vented, the suspension collapses. Air springs on real, full-sized automobiles work in basically the same way. However, they usually have a separate reservoir per corner, keeping each wheel’s suspension independent.

Overall, if you’re working on some kind of Lego rambler, you might find this suspension concept useful. Alternatively, you might simply find it good as a learning aid. If you want to learn more about oddball suspension systems, we can help there too. Video after the break.

15 thoughts on “A Simple Air Suspension Demo With Lego Technic

        1. I was lucky enough to have 8860, 8855, and 8848 when I was a kid. With the parts from those I was able to explore all kinds of automotive tech, and even managed to build a rather fragile 4wd car with steering and independent suspension (which would be fairly easy with today’s specialized Lego parts, but back in the 1980s was quite difficult).

          1. You kids were spoiled. We had Tinker Toys and an extra helping of imagination. Unless you were rich, and you had an Erector set( Meccano).
            Although, I do remember my dad once came home with some obscure, Japanese construction set, once. I remember it had grey, plastic beams with channels down the sides and a black peg on the ends which fit the channels, and some wheels and axles. It was a small set with only enough to build a car, and I always wished to get some additional sets, but I never new what it was called because the package and instructions were all in Japanese. Never saw them anywhere else.

  1. That is pretty cool. I’ve been working on a pneumatic GBC MOC for a while. I wish LEGO had made more pneumatic elements, for instance a miniature turbine, a rotary valve and an oscillating mechanism (like an air engraver) would be great to have.

    1. As always Lego is an engineering model, and this model is showing that it is difficult to strike a balance. In one or two strokes of his pump he goes from one extreme of his suspension to the other.

      Suspension is designed to be at a midpoint, because you will encounter a high spot or a depression in the ground and you need powitive or negative travel.

      The fact that he pumps it straight to the max shows he does not understand this, or is not attempting to demonstrate a working suspension, merely one that ‘may’ be capable (with tuning) of working.

      He has a lot of, surmountable (pardon the pun), issues. Low sprung mass/high unsprung mass is one. No damping aside from restrictions in the air system is another he will run into if he addresses the lack of space for the air. A reservoir, ideally at or in the piston, is needed to provide a usable spring rate or action.

      Many luxury cars and most Semi trucks use air suspension in the form of an air bag, now that he has a chassis he can experiment with making an airbag. The beauty of Lego is you can get a quick grasp of what works and how (physics) quickly.
      Without getting greasy or spending 100s of thousands of dollars.

  2. Ok now add hydraulic automatic leveling and you end up with a system Citroën has been using from 1954 onwards. I drive a 1994 Citroen BX just for it’s suspension. Road bumps? What road bumps?
    Of course I had troubles with the system: the cheap rubber low pressure hoses returning the hydraulic fluid back to the reservoir would break all the time after 20 years of use, so I’ve replaced them all during a motor overhaul (cheap oil scrapers and axle sealers anyone?)

    1. It’d be cool to add a bellcrank and inboard suspension/damping like the fancy race cars. It’d be pretty visually appealing in a LEGO model and would provide a good place to talk about unsprung weight and the joys of inboard brake rotors.
      I wonder if it’s possible within the LEGO ecosystem to make a hydropneumatic suspension like Citroens had. That would be fun!

  3. A pneumatic suspension such as this that shares a common resevoir will, except for the flow damping between units, have zero resistance to pitch or roll. Individual resevoirs for each wheel are necessary. However interconnection can be used, as in the BMC Maxi vehicles of the 60’s and 70’s, to provide damping in pitch.

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