3D printer fun with powder

I've got a little further, I have two powder bins with stepper motors
to adjust the height working fine. I also have a counter roller for
powder spreading. However I've met a small hick up when the little
motor I selected to spin the counter roller spun it at such a speed
that the aire picked up on its surface was enough to throw the powder
backwards. I've confirmed with my electric screwdriver that lower
speeds work fine so just need to get a suitable motor with gearbox.
FWIW the electric screwdriver was spinning at about 120-150rpm.

Graham