Hello,

I'm in the middle of making a futuristic racer, and in essence I'm using a sort of spring to keep the ships hovering above the track.

Very simple process. I cast a ray out of the bottom of the ship, along it's Y axis, and if the ray hits the road I calculate the magnitude of the penetration distance into the road.

Then simply do

velocity += roadNormal * (penetrationMag * k)

where k is 0.01

Obviously this does keep the ship hovering, but with constant bobbing up and down. I've tried a few (probably hacky) things, but just can't stop it at all.

Any good ideas of how to implement damping on a simple spring system like this?

Cheers.

Thanks for the replies.

Alvaro, so just project the velocity onto the roadNormal? How small a number would you imagine to work best?

If I can't get the correct behaviour by tweaking my existing function with this, I'll rewrite it with brucedjones' equations.

As it happens subtracting a % of the velocity was one of the first things I tried (as per damped spring equations), but it made the ship go haywire and bounce miles into the air.

I thought my overall implementation must be too different for it to work, but actually I just had to invert the projected velocity onto the y axis.

That works very well and does indeed stop the infinite oscillations.

With a spring stiffness coefficient of 0.01, and a physics rate of 120hz, I found I needed a damping coefficient of around 0.04 to stop bounciness. 0.01 results in a very bouncy ship, that takes a while to settle at the target spring length. 0.06 settles quick with no bouncing but has a weaker spring, sometimes resulting in the ship hitting the ground.

What do you think is the best way of keeping the ship stuck to the track like glue (or like a rollercoaster), as if there is an infinite amount of gravity, so it never leaves the track? Having a huge amount of gravity is no good as the spring then becomes too weak. What I want is to have a method of keeping it exactly to the track as descrived, then switching to a normal gravity behaviour when going over a designated jump pad.

Actually I was considering something like the thruster particles, as although my engine is a slow, web based software engine, particles are one thing I can do fast.

One thing though, how is the thruster implementation significantly different to a spring? They both apply a force proportional to current length Vs target length. Is the main difference in your suggestion the lack of gravity?

I read up on PID too, thanks for the tip, seems like the tricky part is just tweaking the 3 numbers to get the desired behaviour.

I don't see why you would allow bobbing. If the current velocity would cause penetration (downwards into the road), you can project the computed velocity along the tangent plane of the road (i.e. a bit of slow down due to friction) and use that, possibly triggering an extra slowdown or an accident if the interpenetrating velocity or displacement component exceeds some threshold. If velocity points away from the road, or into the road but with no immediate collision, you can apply a vertical thrust to maintain the desired height as CombatWombat suggests.

Purely because a spring was the first thing I tried, and before I successfully implemented damping to the spring, the bobbing is a byproduct of basic undamped spring+gravity.

The bobbing is eliminated entirely now, I'm just playing with gravity being switched on an off, and about to try Combat's PID implementation and no gravity, rather than a spring.