Barn Door without the Door?

Looking online at these types of mount for widefield. I have read plenty
about the fact that a simple drive will lead to errors as the angular rate
changes over time, and that a "double hinge" method is better.
What I was wondering is if anyone has ever tried driving the hinge mechanism
directly? Instead of the threaded rod, simply gear down the motor enough
(which would increase the torque) and drive the hinge directly at the right
speed?
I'm guessing I am missing something obvious here else I'd have found people
who have done it... is it too hard to get the right speed through gearing?
Or is there some other reason? If it could be made to work it would surely
produce a lighter and more compact mount.
James.