Richards

01-14-2010, 05:54 PM

One of my customers asked me to choose a 34-size servo motor from Keling for his application. I visited the Keling web site and downloaded the three data sheets - and then the confusion started.

The KL34-180-90 motor lists the KE of the motor as 18.95 V / 100 rpm. In another place they list the max. speed at constant voltage as 3200 rpm and they list the terminal voltage as 90VDC. My calculator shows that 3200 / 90 = 35.555 rpm per volt. In other words, if I multiply 35.555 by 90, I get 3200. If I multiply 35.555 by 80 I get 2844 rpm. Since the maximum voltage of a Geckodrive G320x is 80V, I need to know how fast that motor will turn if I give it 80V.

The same problem exists with the KL34-170-90 motor and the KL34-150-90 motor. The 170 motor lists KE at 18.75V / 100 rpm but it also gives 4200 rpm @ 90V when 4200 / 90 = 46.666. The 150 motor lists KE at 13.36 V / 100 rpm but it also gives 6000 rpm and 90 V which would imply 66.666.

The KT ratings are just as confusing. The 180 motor lists a KT rating of 0.182 Nm/amp but lists constant torque as 1.6Nm and continuous current as 7.8A which computes to 1.41Nm.

What figures should I believe?

When I emailed Keling, they responded asking what my application was. I responded and have heard nothing more from them.

Are they just pulling numbers out of the air or have I made some fundamental computational errors in trying to make sense of their data?

The KL34-180-90 motor lists the KE of the motor as 18.95 V / 100 rpm. In another place they list the max. speed at constant voltage as 3200 rpm and they list the terminal voltage as 90VDC. My calculator shows that 3200 / 90 = 35.555 rpm per volt. In other words, if I multiply 35.555 by 90, I get 3200. If I multiply 35.555 by 80 I get 2844 rpm. Since the maximum voltage of a Geckodrive G320x is 80V, I need to know how fast that motor will turn if I give it 80V.

The same problem exists with the KL34-170-90 motor and the KL34-150-90 motor. The 170 motor lists KE at 18.75V / 100 rpm but it also gives 4200 rpm @ 90V when 4200 / 90 = 46.666. The 150 motor lists KE at 13.36 V / 100 rpm but it also gives 6000 rpm and 90 V which would imply 66.666.

The KT ratings are just as confusing. The 180 motor lists a KT rating of 0.182 Nm/amp but lists constant torque as 1.6Nm and continuous current as 7.8A which computes to 1.41Nm.

What figures should I believe?

When I emailed Keling, they responded asking what my application was. I responded and have heard nothing more from them.

Are they just pulling numbers out of the air or have I made some fundamental computational errors in trying to make sense of their data?