Robo-Rats Locomotion: Synchro Drive


The synchro drive system is a two motor, three/four wheeled drive configuration where one motor rotates all wheels to produce motion and the other motor turns all wheels to change direction:

               

The left figure shows the wheels in the 0 degree position--in this position the robot will move up.  The right figure shows the wheels turned -45 degrees.  Note that all wheels have turned an equal amount.  Using separate motors for translation and wheel rotation guarantees straight-line translation when the rotation motor is not actuated.  This mechanical guarantee of straight-line motion is a big advantage over the differential drive method where two motors must be dynamically controlled to produce straight-line motion.  Arbitrary motion paths can of course be done by actuating both motors simultaneously.  Wheel alignment is critical in this drive system--if all wheels are not parallel, the robot will not translate in a straight line.

The B14 series from RWI is a commercial example of a synchro drive system:

Motors:

Two: One to rotate all the wheels, and one to turn all the wheels.

Pros:

Control - Separate motors for translation and rotation make control much easier.  Straight-line motion is guaranteed mechanically--there is no need for interrupt-based control as in the case of the differential drive method.

Cons:

Complexity - The mechanism which permits all wheels to be driven by one motor and turned by another motor is fairly complex.  It is an open problem whether it can be implemented using Lego components (it probably can, but it might not be easy or practical).  Also, wheel alignment is critical--it is unclear whether a Lego implementation could achieve proper wheel alignment.


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Last modified: 04/04/01 22:30