Hi there. I have got very good help from this forum in the past and I have yet another question. Take a square platform with a thruster at each corner. Put a weight in the centre of it. Now, with the weight in the centre the platform is stable but as you move the weight to one side the platform tilts as the centre of gravity changes. I am trying to create an intelligent system that will increase power to the appropriate thruster to keep the platform stable. I started with a basic spring/damper formula something like this: SpringForce = SpringConstant * CompressedSpringLength DamperForce = DamperConstant * RelativeVelocityOfConnectedBodies OverallThrustForce = SpringForce - DamperForce This works when the centre of gravity is also the centre of the platform but if I move the centre of gravity back the platform will tilt back. I had thought that the compressed length of the springs at the back would provide the necessary input to produce the correct thrust amount to keep the platform stable but I was wrong. My current theory is that I need to take the mass over each thruster into consideration when calculating the spring constant for each one but I am not really sure. I can make it work by incrementing the spring constant for each of the back thrusters and running the program and eventually getting a stable hover through trial and error but this is no good as the positions of various masses on the platform need to be variable (Like as the fuel is used the mass of the tank will decrease). I am a little bit stumped now so any input on this would be much appreciated chaps.