Society of Robots - Robot Forum
Electronics => Electronics => Topic started by: gdp50 on November 17, 2008, 05:34:18 PM
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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
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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 (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
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A servo has at least 4 gears, and gears are known to have low efficiency.
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thanks miha! all makes sense now I was being a bit dumb hah
al
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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.