Hobby Servo Overdrive?

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BRW's Avatar (by Gravatar)BRW posted on
February 20, 2007, 9:18 am
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Our team is building a robot for a competition this week.  We are
using HiTec HS-475B hobby servos for some motion. The system is driven
with a 7.2 VDC battery. The servos are really straining on a couple of
tasks. They don't have quite enough torque to make me comfortable. We
are supplying the servos with power via two ~0.7V drop diodes in
series from the 7.2 VDC battery. I measured about 5.8 VDC at the servo
under heavy load.
My question is this - does anyone have experience or knowledge about
driving these servos (or any hobby servo) with 6.5 VDC (one drop
diode) or 7.2 VDC (no drop diodes)?
The duty cycle for this application is pretty low. The servos will run
under load for only about 10 seconds for the entire competition.


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Joe Strout's Avatar (by Gravatar)Joe Strout posted on
February 20, 2007, 10:10 am
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Re: Hobby Servo Overdrive?



Yes, lots of people do this and it generally works fine.

Best,
- Joe

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dan michaels's Avatar (by Gravatar)dan michaels posted on
February 20, 2007, 12:10 pm
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Re: Hobby Servo Overdrive?


7.2v is outside the general spec limit of 6v for servos, but I've been
powering the Hitecs on my walkers for several years from 6 NiMH AA-
cells in series with no problems.

http://www.oricomtech.com/projects/nico6prj.htm

If you don't have enough torque, usually you go to a larger servo.
However, torque is also dependent upon update rate, and if your servo
controller can drop it to 15-msec or 10-msec, that might help. I don't
think many analog servos will operate properly below 10-msec updates,
however. They do get extremely wimpish for slow updates, 30-msec and
longer.

- dan michaels
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