I tried two very different ways of building both models. The same problem exists in both. I would appreciate it if you could figure these out for me. Thanks.

This was my first attempt. The problem is less noticeable.

Hi, I am a new user with sketchyphysics. So far, I have able to figure things out for the most part, but I was recently trying to build a car with a steering mechanism, and something went awry. I built a gear with servo joint and two more things on either side of the gear with more notches. The gear was supposed to turn and send one of the notched sticks one way, and the other the other way. It worked alright, but both the gear and the notched sticks began sinking through the body of the car slightly. I tried to steady all the pieces by attaching another servo to the gear and a few slider joints to the notched sticks. They no longer went through the floor, but now the notches in the gear and the sticks will partially ghost through each other. Things still work fairly well, but I wanted to solve this problem for good. I couldn't figure out what was wrong so I started all over. I built the steering mechanism first this time, paying the utmost attention to details. This time I tried to build a little "box" (I wasn't a true box, just something to hold the mechanism together.) around the notched sticks. When I started the machine, it first wiggled and then ghosted part-way through the box I had made and then the gear failed to turn the notched sticks at all. I figured maybe the first part had something to do with the edges of the notched sticks being on top of the edges for the box. I gave the mechanism room all the way around, but I got the same result.
My question, then, is how I can get objects to become impassable to all other objects while still being able to move? I would love to know, any knowledgeable sketchup people out there. I appreciate your time.