VEX pneumatic engine

Hi there,

Here is a video of a pneumatic engine I made.

It worked pretty well.

Can post the RobotC code for timing the pistons if anyone is interested.

Pikey ~ Team aMEss, Massey University, New Zealand

yes please :slight_smile:

Looks very cool. hat is the black material that you used in between where the pistons mount?

It is similar to this project from a while back.


Cool, here is the code. You will just need to tune the offset depending on where the limit switch is relative to the pistons:

#pragma config(Sensor, in2, reset, sensorTouch) // Limit switch
#pragma config(Sensor, in3, rsol, sensorDigitalOut) // Right solenoid
#pragma config(Sensor, in4, lsol, sensorDigitalOut) // Left solenoid
#pragma config(Sensor, in14, encoder, sensorQuadEncoder, int6) // Encoder

task main(){

int offset, rpm, maxrpm;

offset = 23;      //Change this to fine tune 


	if (SensorValue[encoder] > 120 && SensorValue[reset] == 1){ 
		SensorValue[encoder] = 0; 
	        rpm = 6000/time10[T1]; 
                    if (rpm > maxrpm){ 
			maxrpm = rpm; 
		time1[T1] = 0; 

            if (SensorValue[encoder] > offset && SensorValue[encoder] < offset + 180){ 
		SensorValue[lsol] = 1; 
		SensorValue[lsol] = 0; 

	} if (SensorValue[encoder] > offset + 90 && SensorValue[encoder] < offset + 270){ 
		SensorValue[rsol] = 1; 
		SensorValue[rsol] = 0; 


It is very similar to that other project. I modeled mine after a Lego one I saw on Youtube.

The black material is just a piece of plastic that we made some holes in so we could get the spacing of the pistons just right to produce the maximum torque (it was a competition between my engineering class).

My original crank shaft used 3 bigs gears and a few standoffs and worked just fine. The only reason we used the the plastic was for the extra bit of torque in the competition (which we won).

Just out of curiosity roughly how much torque are you seeing. I guess if you have two pistons mounted on 1 inch radius arms you could see about 24 inch pounds (12 pounds at one inch out for each piston) at a certain point in the cycle it they are mounted 180* out of phase, I can’t tell how yours are mounted. But you are not pulling or pushing at the optimal angle very often so there is bound to be some losses there plus again assuming you are using a 180* out of phase setup you are relying on momentum at certain points to keep you going.

If you are using a 90* out of phase setup you would have one piston at full power while the other is at it’s weakest point and the sum of the forces of each piston would never be equal to more than the force of 1 piston at it’s max force so i wouldn’t expect to see any more than 12in pounds of torque without any losses.

If you don’t feel like measuring the torque don’t worry about it I was just curious.