Pulsing a standard servo

WILLQH

Hii,

· I am trying to use the parallax microprocessor to control a HITEC HS 55 servo. Based on experiment conducted on the servo, i found that at different angle of rotation, the measured potential difference across the servo is different, and it follows a linear relationship. (For eg, at·10 deg deflection, the output is 0.00451V). However, based on my understanding, the microprocessor sends pulses at constant voltage of 5V, with the only variable being the pulsewidth. So is there a way·to vary·the·voltage send·to the servo from the microprocessor .. or is there a relationship between the pulsewidth and the output volatge ? Anyone who has experience working·servos to control a RC airplane? ··Thanks for your help !!

Regards
·

Bruce Bates

WILLQH -

At what point, and during which time period, are you measuring this "potential difference across the servo"? Ostensibly, there is no external output produced by an ordinary analog R/C servo. Internally, the story is quite different however.

BTW, are you using PULSOUT to produce this output pulse, as you should be? If not, and you are using the PWM command, that's your entire problem. PWM WILL produce varying voltages based on the supplied parameters - duty and cycles. However, the R/C servo will not respond appropriately.

Regards,

Bruce Bates

Chris Savage

Will,

·· Even though the pulses are 5V, they are relatively short in duration, and therefore you're unlikely to get a measurement with a multimeter.· The pulse going to the servo should be between 1 mS and 2 mS every 20 mS.· These are 5V pulses, but your meter is probably averaging out the voltage.·· It's not going to be fast enough to measure the pulses actual voltage.· You would need a scope for that, such as our USB Scope.

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Chris Savage
Parallax Tech Support
csavage@parallax.com

WILLQH

Thanks guys. I will give it a try again.

Regards