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Is there a type of servo that can be de-energized and moved manually while giving input back on its position?

So say it's at 0 degrees, I turn it to 5 degrees and I get input back from it indicating it is at 5 degrees. Obviously it would have to be de energized or else you would not be able to move it manually

Thanks

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    \$\begingroup\$ It's called "encoder" (absolute). Or you can get away with a potentiometer. \$\endgroup\$
    – Eugene Sh.
    Commented Jul 4, 2018 at 14:19
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    \$\begingroup\$ They do exist in systems, not typically as a component, but this sounds like a custom requirement. It could be a stepper motor driver , back EMF detector or a linear motor with a sensor or anything custom. \$\endgroup\$ Commented Jul 4, 2018 at 14:30
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    \$\begingroup\$ This sounds like a purchasing question and if it isn't then the answer is clearly and unambiguously yes. Voting to close. \$\endgroup\$
    – Andy aka
    Commented Jul 4, 2018 at 15:23
  • \$\begingroup\$ What kind of servo are you talking about? It largely dependant. \$\endgroup\$
    – ahm_zahran
    Commented Jul 5, 2018 at 9:38
  • \$\begingroup\$ @Andyaka I'm on the fence with this question. Asking "Is there a device that does X?" isn't quite the same as asking "Which device(s) do X?" While an OP could search products and datasheets to answer that question, it may have value to ask the community with more experience. Sometimes it is just helpful to have a more experienced engineer point you in the right direction. "Ah, you're looking for self-sealing stem bolts." \$\endgroup\$
    – JYelton
    Commented Jul 19, 2018 at 21:19

3 Answers 3

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What you are wanting to do is to break the feedback-loop in a servo system by removing power from the actuator. You can do this in any servo by cutting a wire but as the feedback sensor is INSIDE the servo unit you need to add probe wires to read the position back.

Unless you are implementing the servo function in your own controller, in which case you have the ability to power the actuator off and read the feedback as before.

The case where this is not possible is if the actuator cannot be mechanically driven in reverse. This situation is possible if there are typical worm reduction stages in the gearing or other techniques used to hold the position in the event of a power failure. A work around here is to manipulate the feedback signal to the control system and have the actuator power to your chosen position and then check or know what the error was that you added to the feedback loop.

In a typical hobby/RC servo the feedback is from a potentiometer and you could read the wiper voltage and compare it to the potentiometer end. If you have a more elaborate servo system you may have to read out more elaborate absolute or indexed incremental encoders (or other stuff).

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    \$\begingroup\$ I "hack" hobby servo feedback like this all the time. Here is an easy guide: instructables.com/id/Servo-Feedback-Hack-free \$\endgroup\$
    – techSultan
    Commented Jul 4, 2018 at 22:34
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    \$\begingroup\$ There are MCU-based boards available for retrofitting hobby servos; this would be a merely software modification to those. \$\endgroup\$ Commented Jul 4, 2018 at 22:52
  • \$\begingroup\$ I'm having trouble fulling understanding. are you saying that i can open up the servo and power the encoder separately from the main power wire? that way I can read the encoder feedback (servo position) while the servo is off. I will be using an arduino or raspberry pi to control the servo. \$\endgroup\$
    – birddseedd
    Commented Jan 11, 2019 at 15:29
  • \$\begingroup\$ @birddseedd Yes, if you disconnect one of the motor wires with a relay (or perhaps find a motor enable feature on the servo control IC if data is available) The servo will loose power and you can then measure the top and wiper of the feedback pot to determine the current position. \$\endgroup\$
    – KalleMP
    Commented Jan 13, 2019 at 0:14
  • \$\begingroup\$ from what i gather, i need a servo that has 2 power wires. one for the motor and another for the potentiometer. The pot will run even if energy is cut to the motor \$\endgroup\$
    – birddseedd
    Commented Jan 13, 2019 at 5:06
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Sure, one example would be a dual shaft stepper or servo motor with a hollow shaft rotary encoder (incremental or absolute depending on the requirements) mounted on one end, and a crank on one end.

Some machine tools have this kind of thing to allow it to be used manually as well as with the CNC controller.

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  • \$\begingroup\$ so a shaft on one end for output and another shaft to attach a potentiometer? \$\endgroup\$
    – birddseedd
    Commented Jan 11, 2019 at 16:02
  • \$\begingroup\$ from what i gather, i need a servo that has 2 power wires. one for the motor and another for the potentiometer. The pot will run even if energy is cut to the motor \$\endgroup\$
    – birddseedd
    Commented Jan 13, 2019 at 5:06
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Are you free to use external component to determine the position? Else with the use of photo sensors or anything, you can use a rotary encoder to always be able to determine the rotation of the motor. By counting the amount of unique (black,white) dots you see measure at that time. You just need to determine a starting position.

enter image description here

edit: fixed labels binary,gray as suggested by ratchet freak

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    \$\begingroup\$ the left and middle labels are swapped. The middle encoder is binary while the left one is gray. \$\endgroup\$ Commented Jul 4, 2018 at 15:47

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