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Black Forest
08-22-2010, 11:45 AM
If I needed to bring 400 rpm's down to 5 rpm's. Would I be better off to do it mechanically or with a VFD? I couldn't tell you the torque reguirements but my gut feeling is there won't be a lot of torque required. This will be for my Sheep leg restraints to roll them side to side. Using air cylinders worked out to be not so practical. So I will use a gear motor and sprockets and chain. Would I be better to use a double reduction or one small sprocket and one large sprocket? The motor is three phase 360volts.

SGW
08-22-2010, 12:03 PM
You're talking about an 80:1 reduction. I doubt you'd get good results with a VFD, and if you tried to do it with a single-reduction chain drive you'd need a sprocket about 2 meters in diameter.

For that kind of reduction, you'd probably do better with a worm gear.

Paul Alciatore
08-22-2010, 02:21 PM
VFD means Variable Frequency Drive. At an 80:1 reduction you are going to be reducing the 50 or 60 Hertz line frequency down to 0.625 or 0.75 Hertz. That is asking a lot of a motor that is designed to run at line frequency. I doubt you will have much torque left even if it actually runs at that much of a frequency reduction.

Gear motors can be purchased in a wide variety of speeds. I would look for one that is closer to the speed you actually want. Or get a DC motor and use a chopper type speed control.

Black Forest
08-22-2010, 02:28 PM
I guess I will buy another motor.

oldtiffie
08-23-2010, 07:53 AM
If I needed to bring 400 rpm's down to 5 rpm's. Would I be better off to do it mechanically or with a VFD? I couldn't tell you the torque reguirements but my gut feeling is there won't be a lot of torque required. This will be for my Sheep leg restraints to roll them side to side. Using air cylinders worked out to be not so practical. So I will use a gear motor and sprockets and chain. Would I be better to use a double reduction or one small sprocket and one large sprocket? The motor is three phase 360volts.

Use two reduction drives in series as the reduction factors are multiplied.

A 1:2 belt or chain or gear reduction driving an old 1:40 rotary table will give a reduction of 1:2 X 1:40 = 1:80

The square root of 80 is 8.94 so two 1:8.94 reductions will give 1/8.94 x 1/8.94 = 0.112 X 0.112 = 0.1254 ~ 79.72, but using a pair of 1:9 reductions = 1/9 X 1/9 = 1/81 ~ 0.1235 ~ 81.0000

A 1/10 X 1/8 = 1/80 final drive.

etc. etc.