Constant velocity when moving and after collision stopping immediately ... How to ?

Hi

I have a wheeled robot with colliders and I want to move it by pressing W,A,S,D (W,S - movement relative to the local axes; S,D - rotation relative to the local Y axis). But I want it to move constant velocity if I hold the key. So when I hold the key, it starts to move without acceleration, if I stop holding the key, it stops immediately. I also want to do that if the robot collides with other object, it just stops (same result as stopping holding the key, no physics)(it can happen during rotation, too). These things are the most important, but if it is possible, I want to have inclined surfaces in the terrain (so the robot is inclined when it is on any inclined surface, but still no another physics).

How to do it all ? Thanks

And sory for my English, I hope you understand everything ...