Quick Servo Efficiency Question

[gdp50]

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

[mihies]

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

[izua]

A servo has at least 4 gears, and gears are known to have low efficiency.

[gdp50]

thanks miha! all makes sense now I was being a bit dumb hah

al

[Admin]

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.