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Author Topic: Quick Servo Efficiency Question  (Read 2004 times)

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Offline gdp50Topic starter

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Quick Servo Efficiency Question
« on: November 17, 2008, 05:34:18 PM »
Guys I've got a quick question about the efficiency of DC servos, for example I am thinking of using a Tonegawa-Seiko SSPS105 (I need high torque!) in a project I'm doing. But I'm trying to select a battery for it and stuggling to work out the efficiency.

Using the specs off http://www.tonegawaseiko.co.jp/pro/e_pro02.html

Max torque = 380 kg/cm = 0.3874 Nm
Top speed = 0.95 sec/90 degs = 1.65 radians/second

Therefore the Mechanical power is Torque x Angular Velocity..  = 0.64 Watts

But the Input voltage is 12 V with 9 Amp Current which = 108 Watts

So the efficiency should be 0.64/108 = 0.00593

Or 0.59%

Hmmm

Surely the servo is more efficiant than that!! Probably I am missing something... I thought that DC motors were about 50% efficient.

Hope someone can explain

thanks

Al

Offline mihies

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Re: Quick Servo Efficiency Question
« Reply #1 on: November 19, 2008, 01:32:20 AM »
Max torque = 380 kg/cm = 0.3874 Nm


Hi Al,

Your conversion is probably wrong, it should be
37.26527 Nm http://online.unitconverterpro.com/unit-conversion/convert-alpha/torque.html

That would yield the power of 61.49W and efficiency of more or less 57%.

HTH,
Miha

Offline izua

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Re: Quick Servo Efficiency Question
« Reply #2 on: November 20, 2008, 03:47:41 AM »
A servo has at least 4 gears, and gears are known to have low efficiency.
Check out my homepage for in depth tutorials on microcontrollers and electronics.

Offline gdp50Topic starter

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Re: Quick Servo Efficiency Question
« Reply #3 on: November 21, 2008, 10:58:30 AM »
thanks miha! all makes sense now I was being a bit dumb hah

al

Offline Admin

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Re: Quick Servo Efficiency Question
« Reply #4 on: November 25, 2008, 03:20:38 AM »
You really can't calculate efficiency of a motor, too many factors to incorporate. You will only know by experimenting, or a datasheet that has efficiency curves (which come from experiments).

I often see 30%-40% efficiency with hobby servos.

 


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