[Al Skierkiewicz]

D.
I have seen some two motor designs. It is pretty simple to have both motors gear-coupled to a common driven gear. (i.e. when viewed from the shaft end you would see three gears, two small and one large)If you are attempting to have the motors turn on in a single and/or dual drive then it is recommended that you make provisions to take one motor mechanically offline when not used. I would not recommend that you feed two motors from one speed controller either as this produces some unusual loads for the controller. One controller feeding each motor should work OK. (BTW if you are going to use this approach be mindful that the braking function of the speed controllers need to be set the same and you may find that using braking at all is a problem when hard coupled) Keep in mind that if the motors are not closely matched or compensated for in software, the slower motor will provide some loading on the faster motor. In general this will not be a problem but off the top of my head the current in such a case would seem to be a little higher than the sum of the two motor currents when operated as single units.
Happy New Year