Jerry Brown, a long-time contributor to web handling, recently inquired about the use of pancake motors in web handling. I have not run into them in my experience.
Pancake motors are thin as a pancake (slight exaggeration) and have a large diameter. You may have seen them in some electric lawn mowers or automatic vacuum machines. The pancake shape by itself has no advantage for mounting the motor in web handling equipment. The shape, however, allows more poles to be put into the motor. More poles result in a slower base RPM for the motor.
In many web handling lines, the motor RPM is not well matched to the roller RPM. The speed reducing gears are required with ratios from 2 to 20 to 200. A slower motor would eliminate the gear and problems associated gears including lubrication, cooling, backlash and mechanical resonances.
I expect that pancake motors will be more expensive than equivalent four pole motors and harder to source. This is because there is a cost for each pole. Also, for equal power, a slow motor provides more torque – requiring a larger shaft. Pancake motors have low-production rates.
We should keep out eye on the electric car industry. Slow motors shaped like a pancake would have enormous advantages here. Nothing drives down costs like the economies of scale in producing autos.