[HELP] Pneumatic Engines

[LiamM32]

I was reading about compressed-air engines on Wikipedia; http://en.wikipedia....Pneumatic_motor

Compressed-air engines have been widely used with success in hand tools. They were used in torpedos, which demonstrates the short-distance, fast use that someone may want for some Technic cars. They have also been used for rail locomotives in mines for short distances, where any fire would be hazardous. This also may be similar to the potential uses in Lego Technic.

So Pneumatic engines haven't reached the high energy efficiency and capacity of electricity, internal combustion, or even steam; but they have certainly been used with more success than the Lego Technic Pneumatic engines. I have an interest in Lego pneumatic engines. But the models I have seen are generally not even enough to propel a Technic car of it's size a few meters.

I want to ask; What the barriers are that make Lego Technic pneumatic engines so much less powerful, less energy-efficient, and lower energy-capacity than the engines on working machines such as those mentioned above? What would need to be changed or added to the Lego Pneumatic system to bring it closer to the performance of these machines? I hope that there are people here on this forum that understand compressed air power well (which there probably are).

I don't imagine Pneumatics ever replacing or competing with electric motors, such as Power Functions. I just imagine it being a step up from pull-back motors, as a relatively space-efficient way to test vehicles, while adding to the technology of Technic models.

[piterx]

i was "studying" how to make a pneumatic engine out of the small cylinders we got...let me check if i can find that topic :)

[hrontos]

LPE Power or nicjasno or Nico71 have a lot of informations about pneumatic engines. There are also videos of RC cars powered by these engines. V8 from nicjasno has power around 100W which is far beyond power of electric LEGO motors. May be a model with pneumatic engine could even fly.

[jantjeuh]

Yeah, but the LPEPower guys modify their cylinders and use external compressors.. so they cheat ;-)

[hrontos]

Yeah, but the LPEPower guys modify their cylinders and use external compressors.. so they cheat ;-)

Yes, they use external compressors and you would like to stick to compressor built from LEGO parts? In that case a big air tank is necessary, since air consumption is huge and brick built compressors do not produce enough air flow to continously supply engine (or a big compressor is needed).

[jantjeuh]

All I'm saying is that it's not 'pure' Lego :) To each their own.

[Saberwing40k]

There are two primary reasons that Lego air motors are not all that efficient: the fact that the Lego pneumatic cylinders are not designed to move fast, and have high internal friction, and then there is the fact that real world air motors do not use pistons at all, aside from a very small few in model airplanes. Most air motors are actually more like turbine engines.

But, your idea of an air motor being somewhere between Power Functions and pull back motors could work. However, I think it would need new parts, such as linear valves, or even a dedicated air motor piece. But yes, it would be pretty cool to have a small vehicle, like 42002, with a buildable engine that was connected to an air tank. All you would do with a model like that is pump it up, and flip a switch. It would probably move a bit slower than a pull back vehicle, but it would be cooler.

[Boxerlego]

Hi LiamM32,There are many barriers to get past. I like the fact that the LP engine uses air as a source of energy. However, almost every air tool is a air turbine. Lego would haft to make a Air turbine to get the same results.

Edited January 6, 2013 by Boxerlego

[Saberwing40k]

Holy crap! how did this dude make 100% Lego air turbines? I think we may have an interesting new form of Lego competition.

[Hopey]

Holy crap! how did this dude make 100% Lego air turbines? I think we may have an interesting new form of Lego competition.

Explanation video:

Basically they blow air onto the teeth of one of those great big ye-olde gears such as these:

and it works kind of like a paddle wheel.

This produces very little torque but at very high rpm (100,000rpm, apparently!), which is then geared down to high torque at useful speed.

Edited January 7, 2013 by Hopey

[LiamM32]

Thanks for the information. You said that real air motors generally don't use pistons, but I have seen compressed-air reciprocating engines on the internet before. Here's a locomotive with a piston engine;

These locomotives probably work pretty slow though. But that will work for some Lego applications.

I imagined future Lego models using Pneumatic reciprocating engines that are made to look like internal-combustion and steam engines. I had the idea of pneumatic versions of part 2850b, so that you wouldn't have a dummy engine for looks and a real engine hidden to power it; just one engine to save space. But some of you said that Pneumatic engines are generally rotary. Would this idea work if a turbocharger was added (as a new piece)?

The rotary engine from a Lego gear is impressive. Is this more or less efficient than the propeller-like turbines, with the angled blades? I also noticed that you used wider tubing than the official Lego tubing. Maybe new wider tubes would help, or wider connectors.

[gtoby001]

I made a twin red gear setup and the air is blown in between them then slowed down with a ratio of 560:1! Works like a charm (needs a wider tube though)

[nerdsforprez]

Yeah, but the LPEPower guys modify their cylinders and use external compressors.. so they cheat ;-)

I don't consider it cheating. The OP asks what can be done to make Lego pneumatic engines more powerful, efficient, etc. and the answer lies in exactly what Alex at LPE is doing. You have to modify things. SOme may call it cheating..... I can it an answer.

We focus so much on the limitations of actual LEGO elements, whether they be PF, pneumatics, bricks vs. liftarms, etc. But we have to remember that LEGO did not design their elements to be used in the way that they are being used by adult technic builders that are trying to make them as functional as possible. I see modifying the parts as an answer or extension of LEGO limitations, not an undesirable practice.

With modified parts and external ways of providing pressure, pneumatic engines can produce far more power than PF motors.

[bonox]

damn - just lost a large typed reply because I wasn't logged in.

SUmmary:

energy storage requires pressure and volume. Lego uses plastic at, what, 40psi guage, before the hoses pop off nozzles and the little plastic tanks start trying to become spheres.

The examples given use pressure at least an order of magnitude higher than that. A baldwin low pressure steam locomotive works at about 350psi and LMS made a prototype with a high pressure boiler running at 1800psi.

Consider how much air you get out of a scuba tank - 11 litre stores about 2300L of atmospheric air at 3000psi, giving you about an hour of use. (I picked that example because you can get an hour of use from lego batteries). Now the regulator pressure of a scuba tank is approximately 0 psiguage at the surface, not a high working pressure, so your usable working time at 40psi would be much much less. A scuba tank is also very heavy and in scale terms, and this will not improve. pressure doesn't drop just because you store it in a smaller tank. Let's continue this idea with an example:

In scale terms, a lego cylinder might use, say, 4mL of swept volume. To get 100 strokes out of it would require 400mL at 40psi. This is already much much bigger than the largest TLG set of two storage tanks (the blue tow truck). Consider also that to keep 40psi at the end of the run, you'd need a much larger storage volume, and/or higher storage pressures, meaning you'd now need a regulator.

Carrying milk bottle sized air vessels doesn't really fit in with most models. You could improve this slightly with air re-use (ie multiple expansion engines) however this gets complicated fast.

Finally I have some other points - air receivers of all types are:

1. expensive

2. require identification - eg serial numbers that the manufacturer needs to keep track of

3. require periodic testing in accordance with local legislation and work health and safety requirements.

4. turbines are loud and high pressure air release at the end of a cycle is also loud - you'd have to consider supressors and what it would mean to the company image if kids didn't use them. The brake air release on heavy trucks is loud, and they're often throttled!

5. Support equipment - high pressure tanks need high pressure valves, fittings and pipe and/or regulators and with high cylinder seal pressures comes a need for lubrication as well. If you want long term use, you'll probably also have to consider water drains as well.

Edited January 7, 2015 by bonox

[bonox]

an example from nerdzforprez

I believe you can put something like 150-200psi in those smaller plastic bottles before the bottle fails, however there won't be anything like that in these ones given the tube attachments.

His is throttled through the valve and essentially unloaded, so the run time is probably a fair bit longer than if you wanted to actually drive it around. At any rate, how keen are you on dragging a few 2 litre bottles around with your MOC?

Edited January 10, 2015 by bonox

[nicjasno]

The biggest limitation of the cylinders isn't friction. Once they are properly lubricated and cleaned, they slide easily, but the biggest problem are the tiny air inlet holes, that force the piston to move slowly (left drilled inlet, right stock lego inlet).

The second limitation is in the switches. They are designed to be stopped at each position, that's why one needs to remove the stoppers, that cause a great deal of effort to move the switch handle. And of course the inlets need to be drilled to match the ones in the cylinders for greater airflow.

From the outside, the parts look the same.

I don't consider this to be cheating.

The parts were designed for model cranes, excavators and such machinery. So they need to mimic the slow movement of hydraulics. If the cylinders had big holes from the start, the movements in those models would be too quick and jerky. Likewise if the switches would have no stoppers, you couldn't easily switch between positions.

An engine using unmodified parts will work, but expecting any performance from it is really naive. The cylinders act like shock absorbers and severely limit the speed just with the small inlets alone.

Edited January 10, 2015 by nicjasno

[nerdsforprez]

an example from nerdzforprez

I believe you can put something like 150-200psi in those smaller plastic bottles before the bottle fails, however there won't be anything like that in these ones given the tube attachments.

His is throttled through the valve and essentially unloaded, so the run time is probably a fair bit longer than if you wanted to actually drive it around. At any rate, how keen are you on dragging a few 2 litre bottles around with your MOC?

Admittedly, hauling the bottles around is not all that fun However, I think that most people that are into these type of builds are more in it for the creation and testing the limits of stuff then pure drivability. It is the creation of things that gives me the kicks. If I simply want fun out of driving, grab an RC car or truck, not your LEGO stuff. But can't beat LEGO when it comes to creativity, functionality AND fun.