As a kid I had a an air powered toy car. Yesterday I got the idea to try and design an air powered motor which can later be incorporated in all kinds of applications.I'm not going to explain the principle as the animated GIF in this link explains it perfectly:http://www.animatedengines.com/co2.shtmlAs I have only completed my design work today I haven't yet had a chance to print it and look for any flaws. Also for the sake of easily printing all the parts the design might be slightly over complicated. It is however fairly small (6.28cc capacity) and therefore all parts "should" print straight and square.One major feature of my design is that multiple motors can be daisy-chained to form a larger multi-cylinder motor.So far the only thing missing is a 3mm wrist-pin connecting the piston to the con-rod.As this is a work in progress I do not know what the clearances are and therefore how freely this will turn once assembledPrint the following to build one single-cylinder motor: 1 x valve cover.STL 1 x cylinder head.STL 1 x cylinder block.STL 1 x piston.STL 1 x piston valve pin.STL 1 x conrod.STL 2 x conrod - piston spacers.STL 2 x conrod - crank spacers.STL 2 x crank arms.STL 1 x crank big end journal.STL 2 x crank main journal.STL 1 x crank case.STLExtra parts required: 1 x soft compression spring (6mm o.d. x 12mm long) (I'm using one from an AA battery holder so it's 6mm dia on one end and 11mm dia on other end) 1 x 6mm plastic BB pellet 8 x M3 x 10mm screws 4 x M3 x 25mm screws 18-19mm x 3mm pin or filament Some sort of bottle into which you can compress some air Tubing connecting the air-bottle to the valve cover inlet.Assembly: Clean up all holes. Top and bottom corner holes of cylinder block and 4 holes on top of cylinder head can be tapped to M3.Drop the BB pellet into the cylinder head and let it rest in the bottom hole. Insert the spring on top of it. Screw down the the valve cover on top of this assembly with 4 10mm screws.Screw the cylinder head assembly down onto the cylinder block with 4 10mm screws.Take one crank arm and install the big-end journal into the hole oppsite the hole with the raised edge and also on the opposite face ofthe crank arm (the journal must point away from raised edge). Slide a conrod crank spacer of the journal, then the conrod and then the other crank spacer. Install the other crank arm so that both arms are parallel and in the same direction and both raised edges on the outside of the assembly. Now install the 2 crank main journals into the holes with the raised edge.Install the piston onto the conrod might be a little trickier. Basically the two conrod piston spacers must be on either side of the conrod, the piston over them with the 3mm pin/filament through them to hold them together.This whole piston and crank assembly can be dropped into the cylinder blockfrom the bottom (piston first obviously) so that the two crank main journals rest in the notches in the bottom of the block.Now install the crank case of this and screw in place with the 25mm screws.Fill your air "reservoir" connect the tubing from it to the intake valve on top and give the motor a spin. If everything is just loose enough it will run on it own until the air supply is finished