Calculating the driving force in a double-acting cylinder using air

carle

Hello!

I'm completely lost trying to derive an equation that'll give me the driving force in a DAC, and I really need some help from you guys.

The purpose of knowing this is to optimize the amount of air that is needed (24 litres are available, pressure up to 8 bar) to drive a radio-controlled car (60 kg), which needs 20 N to keep in linear motion.

The connecting rod from the cylinder goes to a scotch yoke, and I guess this is where I get a bit lost because of the force that varies through the angles from 0 to 2π. And I don't quite know when the ideal gas law comes in the picture (it should be used with 1 atm being the ideal pressure at the cylinder bottom, right?).

Data:

* Car wheel radius: 0,1 m
* Force needed to keep the car in motion: 20 N
* Gearing between wheel and engine: 1:6 (that is, one rev for the wheel is 6 for the engine)
* Efficiency is 10-20%
* 24 litres of air available and the pressure is to be choosen between 1-8 bar
* The volume of the cylinder is between 30-40 cm^3 (also to be decided)

My technical english isn't flawless so if something is unclear I'll try to do a better explanation.

Edit: Sorry, I should've placed this in the subforum.