I have a cylinder with a shaft in its center that I need to rotate at 120 RPM on 180°, for costing reasons, I would like, if possible, to reuse the same DC motor that I already use for another system. That motor has a speed of 6000 RPM so I need a reduction ratio of 1:50.
I don't have a lot of space under the cylinder, so I decided to move that motor to make it parallel to the cylinder (and then to the cylinder shaft), this also means that I won't be able to direct drive the cylinder shaft and I will need to use at least a pair of pulleys (with belt :)) or gears.
So what would be the best way to reduce the speed of the motor adding the least backlash ?
Currently I see these 5 solutions on which I would like to get external reviews on them :
Only pulleys: since I'm using GT pulleys and the maximum reduction ratio with 2 pulley is 1:4, I need at least 3 pairs of pulleys to get 1:50.
Planetary gearbox with 1:50 ratio + a pair of pulleys or gears having the same teeth count (just because the shaft are parallels)
Planetary gearbox with a ratio smaller than needed + a pair of pulley or gears that reduce again the speed appropriatelly to get the 1:50 at the end.
A pair of gears giving me the 1:50 ratio directly (if I find a gear with enough teeth..)
Replacing the motor by a servo which I do not know why are larger but shorter than the motors I found, and so it could fit under the cylinder.