linear constraint question

[dwells254lb43]

I have a question. I looked at the constraint demos and on the linear constraints they seam to be able to be knocked around at will. Is there a linear constraint that can only move when told to? (and not by anything that hits it)

What I am attempting to do is attach a slider box to the front of a btraycastingvehicle that could slide forward to hit things in front of it, then return to its original position. The fixed body would be the vehicle's chassis.

Any help would be great, Thanks.

[Erwin Coumans]

You can use motors.

Check out the Bullet/Demos/ForkLiftDemo.
Cheers,
Erwin