Well I am going to create a hover car type thing, with four thrusters. WASD will make the thrust go from one of them and I will use the addforce to make it move in that direction, but if the player keeps holding the button down it will continue adding a force to it so it constantly accelerates. How can I make it add the force, and then define a limit so it doesn't get past a certain speed?
Generally you'd set a drag value which is high enough to force a specific terminal velocity
A lot simpler than trying to code it in yourself