[glassdoctor]

Your dad can probably explain what a diff does... it's exactly like a real car diff... the "rear end" of a solid axles car/truck.

The center diff in r/c does the same thing except that it's sharing the load betweeen the front and rear tires instead of the left/right.

The diff distributes the power to where it has the least resistance... it you hold the front tires, it will only spin the rears... if the resistance is equal on both, then both will get full power.

To see how it works, think about what happens if the truck tries to do a wheelie... when the front tires would begin to lift off the ground, much of the power will be transfered from the rear tires to the front. For racing, this is a good thing.... it tends to keep all four tires on the dirt. If it does this too much it's a bad thing because there will always be some tires just spinning wihtout traxction. So, we use heavy fluids inside the diffs so it's not so easy for the diff to transfer power... it makes it a limited slip diff. For example, in a full wheelie, the rear will still have some power driving it because the thick fluid in the diff is trying to stop the diff from "working".