A number of solutions to create a compact, fluently working compressor. It’s pretty easy to create a motor-driven compressor. The challenge is to create one that works fluently while providing a satisfying air pressure. The easiest way to build a powerful compressor is to either use a large number of pumps or a fast motor. There are compressor designs built around e.g. RC motors, but I consider it too much for my needs. When an internal compressor powering some vehicle’s pneumatic systems is required, I find PF Medium or 71427 motors quite sufficient (both provide speeds below 300 RPM). There are basically two cases where a compressor of a particular power is needed. First case can be called direct powering, which means that the air is pumped directly to the pneumatic cylinders of the circuit we chose to use. In this case, the power of compressor determines how fast the pneumatics work, which means that it’s not always “the more the better”. Sometimes precision is preferred rather than speed, and here a low-power compressor comes handy.
Even a single-pump compressor operating at approximately 200 RPM (as I tend to use rechargeable batteries, which means that motors operate at 7.2V instead of 9V) can be used successfully. For medium-sized models of machines such as e.g. front loaders, where pneumatic circuits are usually composed of no more than two cylinders, a double-pump compressor is quite sufficient to operate pneumatics at realistic speed. The latter case can be called indirect powering, and it happens when there is an airtank between the compressor and the final circuits. This is a less popular solution, where the compressor is activated manually or automatically (by e.g. a pressure switch) to maintain the pressure inside the airtank. In this case the speed at which the pneumatics operate depends on how the valves are switched, and only partially on the provided air pressure. It means that a high-power compressor is often a good solution, because of the relatively large airtank’s capacity as well as of the low precision of pressure switches.
For instance in my Snowgroomer, where two pneumatic circuits could be operated at the same time, each consisting of at least four large cylinders, there were four pumps inside the compressor. As the number of pumps increase, so does the challenge of making the compressor work fluently. Setting all the pumps in the same position and the same working cycle is a bad solution for two reasons: firstly the air flow becomes irregular (which can be compensated by increasing the compressor’s working speed), and secondly there are vibrations transferred from the compressor to the rest of the construction. Both effects are highly undesired, and – just like with piston engines – can be reduced by splitting the working cycles of the pumps. The Snowgroomer’s compressor will be a good example here: There are four pumps here, clearly divided into two sets. When the first set is extended, the other set is retracted; when the first set draws air from outside, the other set pumps air into the pneumatic system.
It means the two sets work against each other, and the compressor’s working cycle is split in half. Thus, the air flow is twice as fluent as it would be without such a division, and the vibrations that occur in the compressor are only half as strong as they would be without such a division. Similarly, if we split the working cycle in three, the air flow becomes three times more fluent, and the vibrations three times smaller – and so on. Personally, I have never needed to split the working cycle more than in half – such a compressor performs dramatically better than a single-cycle one, while being only a bit more complex. I did, however, build a number of compressors with the working cycle divided up to four times, and these can be seen below. The key to make the compressor efficient and compact at the same time, is to use the full range of pumps’ movement (2 studs forwards, 2 studs backwards), and to drive the pumps by a common, simple driveshaft. I have tested several variants where pumps were located closer to each other at the cost of a more complex driveshaft, but they turned out to be much larger – which obviously doesn’t mean that it’s not a proper approach in some cases.
Similarly, it may be sometimes a better solution to use a simple compressor with a limited pumps’ movement and a single working cycle, to sacrifice its performance for the sake of size. It should be noted that the designs I have shown here have been created with focus on the performance, which is not always the key factor.With over 2,793 pieces of Lego in the box, the replica Mercedes-Benz AROCS 3245 (£169.99) made from Lego Technics isn't a build that you should approach lightly.Even blitzing your way through the 482 pages of the instruction manual is going to take you some time. It certainly did us, and supposedly the Mercedes-Benz team too who built there model in just under 9 hours.We weren't keeping track, we didn't want to show them up, but it did take an entire family a good chunk of holiday to get get it to a point where we only needed a couple of hours to finish it off when we got home.Not that you'll be keen to pack it in your suitcase either. When completed the Lego truck measures 31 cm in height, 14 cm in width and 54cm in length, and that's before you think about opting for the secondary build, a Mercedes-Benz articulated construction truck which is 77cm long.
So it's going to take you a while, but then as you can see as you work your way through the pages, there is plenty of detail to this grabber truck.There's good reason for all those pieces. It doesn't just look pretty, it does loads of stuff too.At the crux of the Lego AROCS 3245 is a pneumatic motor system that is powered by a new Lego Power Functions large motor and dozens and dozens of gears.The system, with the aid of six AA batteries, lets you operate the crane arm mechanism, open and close the grabber, extend the outriggers for stability or raise and lower the tipper body to dump your load.When you aren't doing that there is twin axle steering, a beautifully designed double differential drive and fully independent suspension for all of the 12 wheels.Once you've built the underbelly of the machine you get to approach the rather easier driver’s cab which tilts to reveal a detailed 6-cylinder engine with moving pistons. The engine is actually one of the first things you'll build.For the most part the building instructions are straight forward and it is nice the manual is broken down into a number of bags to make it easier in finding the right part (there are six sections in total).
We would also recommend going the extra step of separating the coloured pieces into separate trays to make finding the right piece easier. It really helps because there are just so many pieces.That the instruction manual isn't broken down into corresponding parts too so multiple members of the family could build together rather than it being a solo event. We would even go as far as suggesting a ring binder. That's not normally a huge problem with many smaller Lego sets, but the sheer size of this build, it is the largest LEGO Technic model ever produced, made this more of a necessity than normal in our opinion.As it is, you'll have to decide whether you want to rip apart the manual or not if there are more than one of you setting out on this building project.Still, there is no denying this is an epic build of epic proportions and one that if you're a fan of Lego will be gracing your shelf for years to come. parents can find all the advice they will need to keep their children safe online.