Wednesday, March 30, 2011

Shock absorber with adjustable damping

Though the full suspension could be considered standard on large Lego Technic cars, they rarely feature shock absorbers. Let's just remind those not familiar with car mechanics that the role of shock absorbers on real cars is to dampen the rapid movements of each wheel, caused by bumpy road surface. They also prevent the chassis from bouncing excessively after a bump, which reduces stability and handling.

Most Lego cars need no shock absorption, but they may actually prove useful in heavy vehicles on very difficult terrains, or could be added for realism. Here is one concept of a shock absorber mounted on springs, and based on a standard pneumatic piston.

Its principle is quite simple: when the springs move, they force the piston to move along. Since the air being compressed out or sucked in the cylinder offers some resistance and friction which is independent of the piston position, it serves nicely as a shock absorber.

Just attaching a disconnected pneumatic cylinder to the springs will absorb shocks, but the concept can actually be extended. By reducing the cross section of the passage air travels through, resistance the air offers changes as well, making the cylinder more difficult to move ― effectively stiffening the suspension. This is mechanically easily accomplished by attaching a hose to a cylinder (of course, not connected to anything else on the other side), and using some kind of a clutch to squeeze it. Here's an example utilising the linear actuator which requires very little input torque and allows very smooth adjustment, and there are tons of other options. This one can be easily expanded to compress four or more hoses at once, for all wheels at once.

This is more of a gimmick than a really useful option, as it is rarely seen even on real cars. However, some high-end cars actually do feature adjustable shock absorption, to balance between ride comfort and sport performance.

If the linear actuators or other continuous regulators are too much for your taste but you'd prefer to at least have a choice between hard and soft suspension, connect the other side of the hose to a valve switch, and choose simply between the air running freely through, or not at all. In the latter case, it will still offer a little bit of absorption due to flexibility of the hose and air compressibility.

Since the pneumatic cylinders have high structural strength, this system can be comfortably mounted into very demanding and heavy vehicles. Or in other words, it will be other bricks invoved in the wheel suspension that will break sooner than the cylinder!


  1. related question: can a cylinder with a fully blocked hose be used as a spring replacement entirely? i dont have any springs (i usually go with torsion bars) but now i have some cylinders to play with and im wondering if this works in a real application. it works in theory...

    1. Yes - but it offers much more resistance, i.e. acts like a very hard spring. Some levers could help increase the range while reducing the hardness.