What is differential gear?
This video explains all.
On COGY or Profhand,
if the unit is WITHOUT differential gear,
right wheel is engaged to pedal, but not left wheel.
We tried both WITH and WITHOUT model with a post stroke person.
The difference was clear to me, though it does not appear all the time.
The difference is obvious when going up the curve.
WITHOUT model slips much more than WITH model, and has to be pushed from behind.
It is also said,
WITHOUT model can do pivot turn to right, but not to left (can turn with bigger diameter), where WITH model can do both R and L.
Do these matter?
It depends on how adventurous the user is.
If using only indoor, and using only with supervised, WITHOUT model can be good enough.
If using outdoor, with bump and curves, WITH model can do much better.
For me, the difference between using only public transportation and driving a car, seems similar to this.
Public transportation definitely do the job (it is supposed to do the job, at least). By driving a car, we can feel free to shop heavy stuff, go further mile without planning. We can go much more adventurous. Not just living according to the plan, but we can have fun being spontaneous.
What is the point of using COGY compared to using stationary bikes?
There are many points.
However, WITHOUT differential gear, many of these will be halved.