Chief Delphi - 4W Maximum Power Servos? Huh?

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- Motors (http://www.chiefdelphi.com/forums/forumdisplay.php?f=52)

- - 4W Maximum Power Servos? Huh? (http://www.chiefdelphi.com/forums/showthread.php?t=88913)

LinuxArchitect

23-11-2011 14:54

Re: 4W Maximum Power Servos? Huh?

Right, that's just what they chose to call it in their rules.

John	23-11-2011 15:00

Re: 4W Maximum Power Servos? Huh?

Quote:

Originally Posted by Ether (Post 1086396)

Just for the record:

The peak power is not equal to stall torque times no load speed.

Assuming the torque vs speed curve is linear, it is equal to 1/4 of that:

The peak power occurs at the middle of the torque vs speed curve, where torque is half the stall torque and speed is half the no load speed.

According to Update 3:

The servo industry rates servos using
power rating = stall torque X no load speed

Does anyone know if there is any reason for using a different formula than the one for DC motors?

Ether

23-11-2011 15:14

Re: 4W Maximum Power Servos? Huh?

Quote:

Originally Posted by John (Post 1086399)

Maybe it doesn't have a DC motor in it? Or it does but it's highly nonlinear?

EricVanWyk

23-11-2011 15:41

Re: 4W Maximum Power Servos? Huh?

Quote:

Originally Posted by John (Post 1086399)

Does anyone know if there is any reason for using a different formula than the one for DC motors?

I might be jaded, but I believe it is purely for marketing reasons. This formula gives a number 4x as large as reality.

Please take my grumblings with a grain of salt though - I'm still a bit peeved that that industry tries specifying torque in gram centimeters. Ounce inches is bad enough, but please don't inflict the travesty that is ounces* upon the metric system!

* To my count, there are 11 definitions for ounce: 6 for mass (28.3495231g, 31.1034768g, 28.0668g, 28.75g, 100g, 50g), 1 for force, 3 for volume (28.4130625mL, 29.5735295625mL, and 30 mL ), 1 for fabric (1/64th inch), and 1 for copper thickness (which is non-linear!)

Jared Russell

23-11-2011 17:52

Re: 4W Maximum Power Servos? Huh?

Quote:

Originally Posted by EricVanWyk (Post 1086406)

I might be jaded, but I believe it is purely for marketing reasons. This formula gives a number 4x as large as reality.

The servo industry also tends to specify speed in seconds (as in, seconds to travel 60 degrees) and torque in oz. (as in, force assuming a 1" moment arm). It's wacky.

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