Motor Selection Help

[schmt1i]

Hi all,

I'm a mechanical engineer and my knowledge on electrical motors is limited so I'm asking for some help here. I need a motor to spin a shaft which will be geared to another shaft. I have the power needed, but I'm wondering if there is a difference in a 1750RPM motor or a 3500RPM motor for example.

a) Will there be any more/less power drawn to either motor?
b) Is there a noticeable lag from electrical input to mechanical output for either motor?

Any help on this matter would be greatly appreciated.

Thanks!

 

[Sparweb]

Funny, many of the issues that arise from your choice are entirely mechanical...

Higher speed means:
Higher gear ratio to drive the load
More noise
Shorter bearing life
Magnified vibrations
-which require better shaft balancing

As to whether you will have less starting torque or less efficiency with the higher speed motor, only the manufacturer's data plate will tell you for sure, but on the whole, that's what I'd expect.

If you want a good introduction to selecting motor types, try looking for the "Cowern papers" on the Baldor website. The PDF is a compilation of application notes and data that any engineer should understand.


Steven Fahey, CET

 

[electricpete]

a) Will there be any more/less power drawn to either motor?

If you achieve the same target speed through gearing, there should be no significant differences. Yes, there may be differences in motor and gearing efficiency which cause change in power drawn. Also differences in power factor. Slip is a small factor in determining load speed.

b) Is there a noticeable lag from electrical input to mechanical output for either motor?

For fixed speed application, we would consider that the motor reacts to the load rather than load reacting to the motor. Unless you have some unusual controls in mind?

Higher speed means:Higher gear ratio

It’s not clear which motor gives higher gear ratio since we don’t know the target speed of the load.

I agree it wouldn’t hurt to peruse the Cowern papers for an overview of motor selection.



=====================================
(2B)+(2B)' ?

 

[rhatcher]

SparWeb and Pete have provided some good answers. My preference would be for an 1800 rpm motor for reasons similar to those Sparweb listed. However, it is just a preference.

 

[DickDV]

In many cases but not all, a four pole 1800rpm motor will be in a larger frame than a two pole 3600rpm motor.

 

[schmt1i]

Thanks guys! I think that due to our need to spin faster, we will be using a higher-RPM motor because we need the motor, though the pros of lower-rpm seem to outweigh the cons.

I appreciate all the help -- i plan on reading up on the Cowern Papers to hopefully make my motor knowledge more robust

 

[waross]

It is unusual to see a 3600 RPM motor applied to a reduction gear box. 3600 RPM motors are generally used for loads such as pumps which need the greater speed. General practice seems to be to try to keep the reduction ratio as low as possible.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[tygerdawg]

If you want to educate yourself, you can hit the websites of gearmotor manufacturers like SEW-Eurodrive, Nord, Dodge, many others. My experience is that they usually have useful engineering application guides for free download explaining this stuff.

TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering

http://www.bluetechnik.com