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!

Saturday, March 19, 2011

Pratical power transfer: Linear actuator-driven pneumatics

Here is one solution I came up with while looking for a practical way to transfer significant forces over large distances or into moving components, without the headaches related to gearing mechanisms, axle extenders, etc. It is a linear actuator that drives the piston of a standard pneumatic cylinder directly, and the piston is cross-connected to another one, which reflects its motion and does the required job. (It can also inverse the motion by connecting them directly, rather than "crosswise".)

Of course, this is just a concept and design could be vastly improved on, especially regarding reinforcements that may be needed when the forces become really large. Theoretically, it could work with only one of these two hoses as well if the power is needed only in one direction, but is much more reliable and easier to control when their both ports are in use.

Unfortunately, due to the friction within the cylinders, the target piston is not nearly as precise as the input set by the linear actuator. However, its primary task is to transfer serious force, rather than do it extremely precisely. Due to an enormous gearing ratio of the linear actuator, its input torque is easily handled by almost any Lego motor. Just keep in mind that the total stroke length of the linear actuator exceeds that of a pneumatic cylinder, therefore (at least in this configuration) it can't be retracted completely.

Of course, the concept of cross-connected pneumatic cylinders that follow each other's motion can be practically applied in various other ways, however they must be driven "externally" ― that is, introducing a pump with a T-connector would not work as there is no output for the compressed air to escape from the system!

Monday, March 7, 2011

Lego Technic 8049 Log Loader Review: Pneumatics live on!

Compared to the massive mobile cranes or shiny Ferrari supercars we've seen among the Technic models in the last years, a classic tractor with a log loader perhaps can't achieve as much stage light. But even if it isn't something Sonny Crockett would gladly be photographed in, it's a set that should not be overlooked, and here is the main reason why.

Pneumatics, of course! This is one of the rare currently available pneumatic sets, especially as the trend seems to be moving in the favour of the recently introduced mechanical linear actuators. Let's be honest: mechanical actuators unquestionably offer some advantages in comparison to pneumatics (among which the accurate actuator control is the most important), but pneumatics don't need complicated gearing and axle mechanisms behind them, while they provide some serious power nonetheless. I think pneumatics should, therefore, not get ignored (or even worse, discontinued by TLG), and this is one of the sets that keeps them a part of the Big Picture.

So what does the set consist of? A nicely shaped tractor of an unsung green colour, with the "Hand of God" roof steering control, and a detachable trailer with a biaxial pneumatically operated crane, that can "grab" the provided log and rotate 360° as well. Though, these two latter functions do not rely on the pneumatics, but on the good old gears instead. You might argue that only the steering might be a bit shallow functionality for a Technic tractor of this size, but there is in fact very little available space for anything else, at least if one intends to keep it looking like a tractor. The crane is controlled by two valve switches on the trailer side, a pneumatic pump and a turntable rotation knob at the back, and a gear on the claw mechanism.


Its mechanical solutions parhaps aren't breathtakingly revolutionising the Technic as we know it, but it is still a nice example of a tidy, sturdy and efficient Technic design with a grain of decoration.

However, "efficient" and "sturdy" doesn't necessarily mean "simple". In fact, this set isn't the easiest to build (most of the time it's actually not difficult either, but a few steps regarding the weaving of pneumatic hoses could be very tricky for beginners), and it takes about an hour and a half to build the first time. But it's  even harder to disassemble as it has lots of tightly neighbouring half-stud beams connected by the axles, a 'feature' I'd cheerfully live without.


This set relies on a few non-typical parts, but a vast majority are good standard Technic building material. 525 parts altogether, which will suffice for some cute small-to-medium scale models (as is the 'B' model log loader), but for some more serious building, it will not suffice alone.

It will provide you with six medium-sized and two large offroad wheels, an always welcome turntable and, of course, pneumatics ― consisting of one large (spring-loaded) pump, two cylinders, two T-distributors, two switchvalves and a (drum roll!) rare small pump.


Officially, the 8049 set can be expanded with Power Functions to build its onboard compressor (that's what the small pump is for, which is otherwise unused in the primary model!).

Besides, the log-loading trailer is sturdy enough to be used as a base for some larger, custom contraptions. I guess it could support the crane at least twice the size and capacity, if one had the inclination and the hardware to modify it.


+ Pneumatics! Two pumps, two cylinders!
+ Fine supply of other parts (wheels, turntable...)
+ Easily customisable
+ Nice to play, well-placed controls

- Not the easiest to build
- Even less easy to disassemble
- The crane theoretically turns 360°, but the hosing gets twisted soon


Perhaps not the Technic flagship, but nevertheless a cute little playable set that keeps the pneumatic systems in the game, and as such, a great start for people interested in them. Not breaking new grounds in terms of mechanical solutions or functionality, but a good role model of simple and clean design, for a very reasonable price.