Ds620

[pgkevet]

I've been messing about with one that failed on me about a year ago.. I was using it on throtle and it made a nice auto..

As best I can understand my results.. the motor runs fine but there has to be a positional sensor underneath the output shaft that feeds back to control the motor. If I turn the output shaft by hand I can find the dead spot that co-incides with the position and motor slows right down but doesn't quite stop. If I re-assemble (with new gears) and with the output gear offered up both ways around the servo promptly jams.

I'm guessing that the sensor isn't quite working right and after playing for an hour it's back in the spares box.

..just wondering now whether I should have sprayed it out on underneath the output shaft in the 'electronics bay' with somethign to try and clean that sesnor..if that's possible...

..anyone fixed one of these?

[electricsceadu]

it will be cheaper in the long run to fix it with this
(just think of a cost of a servo related crash)

[coolice]

Hey.

Basically all servos use a potentiometer (simply refered to as a pot) connected to the output splines to know it's actual position and loosely all this is is a variable resister which combined with some electronics provides the positional feedback.
The majority of servo failures are normally pot related as they use wiper contact points running over carbon tracks to allow rotation and eventually they just wear out. Vibration also kills pots quickly which is why helicopters are harsher on servos than most other models.

It is possible to replace the pots, the difficult part is finding one loose that is the racy same spec such as size and ohms value.
Of course even if you fix it will you feel confident fittting it into a model again? If it's on the throttle and it fails you just hover out the tank of fuel, but if it fails and shorts out you could have major problems.
.

[electricsceadu]

having had a servo short out when the brush broke i'd still use my special tool on the servo

[pgkevet]

..that's roughly what i figured..just wondered if accessing the track and cleaning it might be enough.. if it is a track. I assumed in my ignorance that there might be something cleverer than a resistor/contact being used in modern servos for the position.. such as a preset null point and calculated steps..

You're right that I wouldn't use an untrustworthy servo in a costly ship..it'd have to be a reliable fix. It was almost new when it died on me.. fortunately died and closed throttle before jamming that time.

[electricsceadu]

if the pots anything like the flyby wire throttle pedals on a car it will wreck it trying to clean the surface up