Confused on Crab Drives

I understand the basic concept of a crab drive, but I do not understand how the power is distributed between the wheels, motors, and getting the wheel units to rotate. If someone could better explain how all of it work I might be able to better grasp the concept.

I am basing my beginners knowlege on this picture-( Any help would be much apriceated.

if you look at the set of belts and pulleys, you can see the method of power transmission to the wheels. As you can see, a gearbox provides power to each side of the robot. the output shaft of the gearbox is turning a set of pulleys and belts which then connect to shafts on each set of wheels. The shaft is turned by these belts and pulleys, and uses a series of bevel gears to rotate the “power” 90* from turning in the x-axis to turning in the y-axis, if that makes any sense to you. these gears are then connected to the wheel its self and the wheels are turned.

The actual modules, inculding the wheels, are turned by the set of sprockets and chains. If you look in the very back, right of the picture, you can see a globe motor that is turning the chain. This allows the front 2 wheels to turn as one unit, and the rear 2 to turn as a separate unit. You can then rotate all 4 together and get what is called “swerve” in which you can be traveling in a different direction than the front of the robot is pointing. You could turn just the front 2 wheels and have steering like a car. You could turn the front 2 wheels one direction, and the back 2 the opposite direction, and you would have steering similar to monster trucks, and the new (Dodge?) truck, that allows for tighter turns. Lastly, you could not rotate the modules at all and simply drive it “tank style”

Hope this helps.


Yes that helped a lot, I failed to see the Globe motor in the back, and that was the main extent of my problem. My only remaining question is how to mount this to a frame to allow it to spin freely.

the dark grey is the chasis
the magenta is the 4" lasy susan bearing witch will hild up to 300 pounds and cost $1.79 each