Servo protection

[Phill Tadman]

Hi all

Has anyone any experience with Florian Schambeck servo protection units or the Hitec HS-7954SH overload protection feature?

http://www.klapptriebwerk.de/produkte/z ... ul-07a12a/

I'm plannng my next 13kg scale glider gear and tow release but want to move away from the Emcotec protection units I've used before as they can only handle 6V.

The Schambeck ones are HV capable but have a Ncm rating. I've tried asking what this means but my question gets lost in translation.

The Hitec manual states that overload protection will reduce the output signal if the servo is fully stalled. Perhaps this negates the need for a separate protection unit.

Best regards,

Phill

[Simon WS]

That's the torque rating Phill
The servo you mentioned has a torque of 285 Ncm so it looks like they don't have a unit for that much torque

That's a pretty meaty servo - with a 10mm servo arm it will lift a bag of cement! I would have thought using Hitec's overload protection feature would be fine


Simon

[spike spencer]

If those figures are correct, I am intrigued as to how you envisage forces of that magnitude being encountered in a 13kg glider.
To protect a servo of that power from overload, might a mechanical shear pin or 'spring-detent' saver be more appropriate ? Nevertheless, if that event occurs, something more serious is probably in progress and it is not only the servo that needs protecting.

[Ken Kaye]

I'm not sure if it was that particular servo, but I recently saw one of the high power Hitec's on a large Duo Discus retract cycle on and off several times due to overload. It would go limp for awhile and then power up again. Someone finally realized what was going on. It was nice that the servo did not fry, and once the retract geometry got fixed it worked fine. It would seem safe to me to skip the overload protector if a servo with the built in feature is used.

Edit: I believe that with a servo programmer that the level of current draw which triggers the shutdown can be set, so it doesn't necessarily have to be at stall current.

[Phill Tadman]

Thanks for your comments gents!

I was originally going to regulate the gear and tow servos down to 6V and use Emcotec DSPIs. At this voltage the servo torque was reasonable for the glider AUW.

I have now set the overload protection feature on the servos that will reduce the servo power output by 50% if the servo stalls. I can't find any documentation regarding the setting of the maximum current before the overload trips.

I think I'll still use the Schambeck units as they should trip around 10 - 15 Kg and not the 28Kg torque stall of the servo.

Best regards,

Phill