Newby question re driving one side

[fieldknot]

Hi,
Unless I've misunderstood for the x an y the pinion is only driven one side.
Would it not be more robust/less strain on the motor to drive both sides?
Or does the added complication not result in any benefit?
Trying to understand the design.
Thank you - Kind Regards, John.

[Gerald D]

X is driven both sides - two X-motors running in sync.

Y is driven one side normally - a second y-motor would bolt straight on, but nobody has bothered with a second motor yet.

That would explain why everyone talks of 4 motors, no?