Further experimentation with servo PWM frequencies

Absolutely! I've only experimented a little for my own designs, but I've always thought there is a huge gap between the available serial servo controllers and what analog servos are capable of -- with a little creative effort.

Do experiment with slower frame rates if the motor doesn't need the holding torque. For a bipedal or walking robot it's a foregone conclusion you will need maximum torque pretty much at all times. But for rolling robots and basic push-pull applications, it's often possible to reduce or even completely remove the pulses from the servo. (This is what I always do with servos modified for continuous rotation...to make them stop I never try to hit that 1500 us middle-ground, which drifts anyway.)

A hobby servo has *maybe* 100 hours MTBF, and with increased current, I'm betting you'll get 50+ hours. If you add up the actual hours your robot is powered while you play with it, I think you'll find you'll still get lots of enjoyment out of your investment (knock on wood).

There's really no way to tell for sure how much shorter the motors will last, because there is so much variation in their design and quality. What will go first is the little wire brushes inside. If you're using coreless servos they ought to last a little while longer than regular PM motors. These have greater brush and commutator life, and are popular among the heli users. They are also more expensive.

-- Gordon

To update my post - I did some measurements today. Under a normal load at 50Hz the HS-81MG is drawing about 200ma. At 100Hz it is drawing about 280ma. At 125Hz it is drawing about 290ma.

I find it interesting that the current appears to be tapering off, though I suppose it makes sense since the motor spends less time unpowered so it has less time to move away from the correct position.

Performance seemed very similar between 100Hz and 125Hz, which again makes sense. There is a huge gain going from 50 to 75, smaller gain from 75 to 100, and hardly any gain in performance going from 100 to

I still think I'm going to move away from servos and design my own geared motor systems, but this absolutely massive performance boost that I'm getting from increasing the refresh rate makes that less of a priority. It seems that 100Hz is the sweet spot, as long as you don't change the PWM pulsewidth rapidly, so I'm going to make that my normal refresh rate.

-Mike