Re: [Algorithms] Car engine behaviour

 Re: [Algorithms] Car engine behaviour From: Graeme Harkness - 2006-04-27 10:48:45 ```Madoc, > The unfortunate result of it however is > that high gears are not really much worse at accellerating from a stand- > still than low gears, and in fact the feed-back from the wheels acts > more as break limiting top-speed rather than accelleration. I can see > that this might be a result of drag at higher velocities resulting in a > greater shift in velocity at each integration step. You might be missing one important point. It's not the torque that accelerates the car, its the LINEAR force that is applied at the contact between the tyre and the road. These are related through the *effective* radius of the wheel (which is affected by the current gear ratio). Therefore, if you are in a high gear that has twice the gear ratio of first gear, then at 2000rpm (for example) you will be applying half the force at the wheel. This is why it is much easier to accelerate in low gears. Of course, as the speed of the car increases, aerodynamic drag *will* become important, but you probably don't need that in your code immediately. > Out of my > ignorance, I'm thinking that this could be the lack of consideration of > the vehicle's mass and momentum. Something along the lines of: > accellerating a mass from 4 to 5 kph takes far more torque than > accellerating it from 40 to 41 (bare with me for the simplication). I don't think this is true :-| In terms of pure dynamics, not considering aerodynamic drag, it is just as easy to accelerate a car from 40 to 41 kph as it is from 4 to 5 kph!! The laws of physics are the same in any inertial frame after all !! :-) The difference you want is related to the gears I think. Another thing you might need is that forces applied to the car wheels also cause a feedback to the engine (again through the gearbox). You might need that, but I've done plenty of simulations that just fudge that. > So, to narrow my > most immediate problem down: How should I describe the fact that higher > gears will have a harder time at accellerating at lower velocities > while they fair pretty well at higher velocities? I get the idea that > this is simple dynamics and I'm just being dumb by not just working it > out but I don't feel confident with basing it on my own assumptions. HTH, G ```