Hint M11 - K'NEX Battery Motors plus Controller Pack
This interesting pack includes 2 x 92875 battery motor (see Hint M2), both connected by a long flex to a single hand-held controller. The two rocker switches on the controller provides forward and backward movement independently for each motor.
This approach is ideal for K'NEX robots and other steerable vehicles, but sadly this type of motor can no longer be purchased.
The two motors may be attached to K'NEX models in an identical way to the tethered battery motor.
The photo shows an example of attachment. Note that vehicles using two driving motors in this way steer much better with 2 wheels plus a "skid", rather than having two front wheels and two back wheels.