Most servo motors out there are driven within 180° (at least hobby ones). There are more bulky and expensive servos out there as well. Since, I have tight space constraints, I am looking for a solution to have full positional awareness (0-360°), an can even cross 360° boundary for shortest path rotation.

e.g. from 350° to 10° in 20° step and not with a 340° backwards rotation.

The servo modifications, which I have found remove positional awareness for continuous drive. I have been wondering, what solutions are common out there? I remember taking apart an inkjet printer to find a transparent disk attached to the motor with black stripes for opto-interrupt encoding. I guess, this would be solution. I might as well use a geared DC motor or a stepper motor for this purpose. I was wondering, what solutions are commonly used for this purpose. I will have an IC to do the controlling but more plug and play solutions are welcome.


2 Answers 2


The "servo" you are describing is a hobby "servo-actuator" with its origins in the RC model aircraft, etc., hobbies.

servo /ˈsəːvəʊ/

  • short for servomechanism or servomotor.
    "the servos should faithfully follow the input commands"
  • relating to or involving a servomechanism.
    modifier noun: servo
    "hydraulic and electrical servo systems"

Source: https://languages.oup.com/google-dictionary-en.

Most industrial servo motors and actuators will use a rotary encoder to track position. These are available in two types:

  • Incremental: These just need two sensors looking at an encoder disk with radial stripes as you described in your question. The servo controller keeps track of the position and adjusts the drive to the motor to move the actuator to the target position (or velocity). If necessary, a homing sequence is run on power up or reset to give a zero reference to the position counter after which the controller can keep track until the next power cycle.
  • Absolute: These have a more complex coding pattern and allow the controller to read the current position on power-up without a homing sequence. There are also multi-turn versions which use a variety of techniques to keep track of how many turns have been used.

Stepper motors may be an option for you. They generally run without encoders and this is fine for many applications where stalling is unlikely. The motor is referenced on power-up and then its position is determined by the number of pulses sent to the driver. Resolution is typically 200 steps per revolution.

It sounds as though you're looking for a BLDC (brushless DC servomotor) of suitable power and matching controller.

  • \$\begingroup\$ Is there a term for for such industrial motors/actuators to do some research? or even find readily available solutions? \$\endgroup\$
    – VPNer
    Jan 11 at 23:40
  • \$\begingroup\$ Try youtube.com/… and this one in particular: youtube.com/…. (I didn't watch it.) \$\endgroup\$
    – Transistor
    Jan 12 at 4:00

Most available stepper motors rotate 360deg. If you need position then you'll need one with an encoder or other rotary position system (resistive). You can however drive steppers open loop so you can 'home' them with a switch and then step them X steps away from that position and they'll go there if within their torque range (ie nothing blocking it)

You can also take many hobby servo motors that are 90deg or 180deg and make it into a 360deg, but I don't know if that will give you 'position-ally' aware.

Instructions here: https://www.circuitbread.com/tutorials/how-to-make-a-360-degree-continuous-rotation-servo-motor


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