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Playing around with a servo


#1

I’m playing around with a servo I bought on a whim (just to play around with…), and I don’t seem to see the full range of motion I’d expect. I understand that the servo can travel 180 degrees, and if I rotate the servo by hand (hey, it’s a cheap servo…) I can see that the range of motion is indeed a bit more than 180 degrees.

Driving the servo with GHI’s class from code.tinyclr.com, however, I see maybe 120 degrees of motion. If I drive the servo with the HobbyServo class also available on code.tinyclr, I see roughly 90 degrees of motion.

What gives?


#2

Thats ironic. I just finished writing up a project on “Rolling Your Own Servo Tester”. No need for $20-$40 tester. Already have a Fez, so save some money and have some fun. :slight_smile:

http://staceyw1.wordpress.com/2011/03/26/roll-your-own-servo-tester/

I had same kind of issue with a medium DGServo bought at SparkFun. I found the limits to be around 0.69 - 2.435ms. I guess the take away is do not assume a standard of 1-2ms range. Most docs and code I see seem to assume the std figures. So test drive it, to find the actual limits. Also hold your servo during testing. You can hear and *feel any buz at the range limits. Adjust your limits as needed. This is probably a good practice as you don’t want to drive past servo limits just to buz and draw more current neadlessly. HTH


#3

It certainly does. Oddly enough, it seems to get the full range of motion I must go fairly far beyond the mfr’s specifications: http://www.hitecrcd.com/support/product-support/faqs/servos/general-servos/index.html

Is that normal?


#4

Not sure. I suppose there is three reasons. Either the pwm output is not giving actual pwm values. Or, the servo mfg tolerance error. Or a combination of errors. Probably no matter. Once we find the limits in our actual world, the final numbers are relative. As long as servo gives you the range (~180) you need. IIRC the higher-end receivers/transmitters can account for this with their calibration and/or trim functions. HITEC is a high quality brand - right? Try some others out of interest. I will also.