Which is better...a direct drive polar bear or a pulley driven KMG with the same HP ?

LARRYZ10

LARRYZ10

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Feb 6, 2010
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Is there a distinct advantage in running a 1800 rpm 220 motor with jackshaft and pulleys in comparison to using a 3400 rpm motor with direct drive if both setups are driven through a VFD? Logic would dictate that the direct drive has a mechanical advantage and should produce more power at the drive wheel but I have heard that motor experts suggest an advantage with the 1800 rpm motor versus the 3400 rpm motor. Is this all just opinion because the motors usually cost the same amount or there really a good reason to run a slower motor? Reliability, better variable speed control, lower power consumption, or more torque...do any of these things come into play in designing a grinder? I use a 2 hp KMG with Kbac drive and it works fine. Is the polar bear grinder with the faster direct drive a better grinder in any quantifiable way? Does anyone have both types that has a preference?
 
I recently finished a GIB build and I am very happy with it. I built mine with its own dedicated stand that allows me to flip it to horizontal. Making the pulley driven grinder do that would certainly be more involved. That said, my biggest complaint about the GIB design is the drive wheel engagement. The shaft of a standard 56C motor is too short to reach all the way through the wheel. Having a jackshaft allows you to fit things correctly. As for the motor, I am running a Weg 2hp 3400rpm motor and have had no issues running full speed or at low RPMs.

Bob
 
I have a couple direct drives & one belt drive. There is no difference I can tell in power or smoothness or anything.
 
There's a torque advantage to using the 1800 RPM motor and doubling speed throught the VFD rather than using the 3200 RPM motor. The output speed is the same, but the torque changes. Direct vs. belt should make very little difference.
 
a motor driven at 2x the nameplate speed will produce 1/2 torque compare to running at 100%. this is per the kbac drive manual. if you have a big enough motor it shouldn't make a diff. but with a smaller motor it would be noticeable.
 
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