Pneumatic piston engine

[Tamas Juhasz]

Piterx showed in this topic( http://www.eurobricks.com/forum/index.php?showtopic=73542 ) a piston engine concept. I think that's a very good idea, and I wanted to make it working only with Lego parts. That's the hardest part, because there isn't a good Lego piece to prevent air loss. So this engine has a lot of air loss, but works:

A compressor is required, the rpm can be regulated by the 8879 speed remote controller. It's very weak, the next step would be a good sealing, similar like Piterx's.

[piterx]

yeah it seems to work :P

ok now, we need to improve sealing of the cylinders heads, i've posted a pic picture in the other topic... you need to seal well the pistons too...mine requires really a weak blow to make the piston work

anyway the idea of the M motor seem to work good :) but i had another idea :) let me build it and ill post it in half an hour

[AndyCW]

I'm impressed.

[allanp]

Like a real life small engine, if you want to get any usuable power out of it you will need it to go several thousand rpm and add a flywheel. Then you can gear it down many times. For this you will need valves that switch equally as fast very near to the pistons they are switching, like within an inch.

Edited August 27, 2012 by allanp

[hrontos]

Very nice experiment.

"Real" compressed air or carbon dioxide engines used by plane models do not use any valves.

They have a small ball on the top of the cylinder. This ball covers the hole which is used to get the air into the cylinder. Piston has a small pin on the top. When piston reaches the top position within the cylinder, pin hits the ball, the ball at that moment will let the air get into the cylinder and the air moves the piston down. In the lower most position there is another hole in the wall of the cylinder which lets the compressed air get out so that piston can return back to top most position, hit the ball again, let the air in again, go down... like illustrated here.

In this case two 2x2 plates would be needed for each cylinder. One base plate containing tiny hole with some cone for the ball and the other plate as they are - for the pipes. Pin has to be added to the piston.

Real carbon dioxide piston contains a small hood on the top - it looks like you would wrap whole piston into selfadhesive plastic tape and let it be 1 mm over the top of the cylinder. Ballpoint pen tip can be used to "bend" that 1mm a bit outwards so that it is bit wider than the cylinder. Actually also the air presure will push it in that direction. Just take a look at your bicycle pump. Such small hood is also there. Benefit of this construction is, that it is air tight and still does not generated any unwanted friction. Friction is there only when air presure is there, which is ok.

This construction would also need some kick to start. And of course a flywheel (spinner from Ninjago?).

Edited August 27, 2012 by hrontos

[locoworks]

Like a real life small engine, if you want to get any usuable power out of it you will need it to go several thousand rpm and add a flywheel. Then you can gear it down many times. For this you will need valves that switch equally as fast very near to the pistons they are switching, like within an inch.

i would expect the plastic to melt once proper load is put on the conrads at high revs, lubricating will then be a consideration for long runs.

[Tamas Juhasz]

Yes, at so high rpm lubricating is necessary. I have some experience with several thousand rpm: long ago I used a non Lego motor with about 9-10000 rpm to try out something. An axle in the driven shaft melted, so Lego isn't for this. Sometimes I really need a ball bearing even to RC buggy motors, the most of the power loss is generated by the friction in the liftarm holes(and in the teeth of gears).

I could seal this engine like Piterx did, but I like more to use only Lego parts, except strings and rubber bands. Maybe a small string could help in sealing around the piston.

[piterx]

yeah dude! oakum is just like a string :) it's only thinner so you can apply it better...try with that, im curious to see how it goes with a better sealing :)