I know there are limitation with rack and pinion mates, and am looking for alternative methods of mating for a machine I am working on. Specifically, I use a rack and pinion mate twice on a single pinion. The purpose is to get the two racks to move in opposite directions. Attached is a simplified picture of what I am doing.

I suppose one solution is to create a sketch that drives the assembly, and use an equation to drive the dimensions. However, for this machine, it is really useful to see the motion as you drag the parts, and the sketch equation idea would not allow that.

Any other ideas?