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Would servos that are turned by hand need external flyback diodes?

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Rouverius
(@rouverius)
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I was watching "Analog Feedback Servo Motor - Improved Servo Performance."  Using the servo as an input device is really interesting idea. I do have a basic question since I'm not too familiar with servos.

I was told that it wasn't recommended to spin a device like this while it was connected to the control circuitry.  My understanding is that the motor in the servo converts the movement back into electricity and tries to feed it back to your drivers (i.e. blowback voltage).  One simple way to fix that I've seen is to add a reverse-biased fast diode across the motor (flyback diode).

So, is this something that is typically built into a servo or is it not really needed for some reason?
If a flyback diode needs to be added, how would it be added in this case?


   
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soumitra
(@soumitra)
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Hi

It is ok for servo. There is no problem,  you are giving feedback loop by potentiometer built in only as feedback signal.


   
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Rouverius
(@rouverius)
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@soumitra

Thanks. Actually, I understood that part. 

My question is that as the motor inside the servo is spun externally, it becomes a generator and would feed electricity back into its own control circuitry. My limited understanding it that if this is not addressed (like with an internal flyback diode) it will destroy the servo. In a catastrophic situation, that might even bleed back into the input of the servo and burn out a pin on the Arduino (or worse). 

Am I missing a basic point that would make this untrue?


   
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(@dronebot-workshop)
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Posted by: @rouverius

Am I missing a basic point that would make this untrue?

It actually is a good point, and I wouldn't categorize your understanding as being limited.

I would suspect that the internal servo motor would have a diode that prevents back-emf from harming the internal controller, as any servo motor could be subject to external forces and therefore act as a generator.

As for "bleeding back" to the Arduino I don't think this is a danger, the most catastrophic thing that could happen would be that the internal controller would be damaged. But, again, I suspect that the manufacturers have already considered that possibility.

This topic was also discussed on the Arduino Forum nine years ago, and they essentially came to the same conclusion that the manufacturers have already accounted for this.

?

Bill

"Never trust a computer you can’t throw out a window." — Steve Wozniak


   
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Rouverius
(@rouverius)
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Bill,

Good point.  Hey, thank you for your kind words and helpful explanation!  


   
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Bif99
(@bif99)
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@dronebot-workshop

There is a mechanical issue to consider.  Servos with plastic gearboxes like the S1213 used in your video are prone to gear damage if a high torque is applied to the control arm.  If high loads are expected, a metal gear servo can be used.  Adafruit has a B2122 Metal Gear Micro Analog Feedback Servo.  It has 25 oz.in. of torque @ 6V, much less than the S1213 Servo (90 oz.in.) but depending on the application could be a viable substitute.

Bif99


   
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