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Create servo motor out of an DC motor.

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71GA

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Hello i have a homework to create a servo motor out of a DC motor. I know i need to create some kind of a circuit, to be able to control angle of a servo with PWM.

Could anyone paste me a circuit scheme and explain a bit what a circuit does.


Thank you!
 
please specify what type of dc motor u have.
if it is a simple dc motor than it is not possible to use it as a servo motor(correct me if i am not wrong).
it is because in a servo motor a coded signal is send to the motor which decodes it and rotate the shaft to a specified position and stay there until next signal . it means that the motor is maintaining its position .in case of a simple dc motor when u power it up it will rotate and will not stop immediatly on the drop of power due to its inertia.
even if it is possible than it would be very costly or u have to deal with embedded controllers.
 
It is simple motor, but maybe it is possible to stop motor quick enough if i use a reductor?
 
If there isn't any limit on using a microcontroller, the answer becomes fairly simple. Assuming the assignment is to essentially create a servo that incorporates a simple DC motor, then you simply need to gear the motor down, and attach the final output to the shaft of a potentiometer in such a way that it doesn't slip. The output of the potentiometer is then fed into an analog input of a microcontroller, and the microcontroller is also connected to the DC motor via an h-bridge driver (sized for the motor). The microcontroller is then programmed to monitor the voltage level provided by the potentiometer (the potentiometer wired as a voltage divider, of course); when it changes, the software in the system needs to compare its value (position) to the requested position value (supplied via a serial link, or via reading another potentiometer's value), and then adjust the rotation of the motor such that it moves towards that new value. When the potentiometer is in position (you would need to set up a "deadband" - a window around the desired position that is a small percentage of values - this will help to prevent "seeking" oscillation), stop the motor. You can also do something similar with an op-amp or two controlling the h-bridge, but the microcontroller approach allows for other options (for instance, the ability to use a voltage, a pulse-width/PWM or serial command to control the servo - as well as the possibility of implementing a PID loop, ramp-up/ramp-down of speed; there's also the possibility of implementing optical feedback system in place of the potentiometer for higher positional accuracy, etc) - so if you can use it, go for it. Hope this helps... :)
 
Could this work as a simple (not PWM) servo motor?
**broken link removed**

Potentiometer is fixed on a shaft of a EM (DC motor).
 
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My knowledge of op-amp circuits isn't as broad as I would like it, but that circuit is something like I was thinking, so "possibly" it would work; you'd have to try it and see; I am not sure, though, where on the circuit you set the "deadband" (likely some combo of the h*R resistors?). The motor, though, would still likely need to geared down in order for such a circuit to react properly...
 
Yes simulation works in a Crocodile technology.... The only thing i still cant set is the "deadband". Maybee i could create deadband with a schmitt's trigger...

And a picture of a working simulation (no deadband).
**broken link removed**
 
hi,
Ref the 'deadband' that you are planning, if the servo mechanism is loaded, which it usually is in an actual system, you could still get hunting with a deadband.
The system should be critically damped, electronically for optimum performance.

https://www.cnccookbook.com/CCServoTuning.htm

**broken link removed**
 
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what if he fed in a frequency high enough so that the motor would act as a break, instead of rotating directions like at a low frequency,?
 
I am sorry my English is weak. What did you mean by "Ref"?
.

hi,
Its a lazy way of saying 'with reference too'
So in full I should have posted, 'with reference too ' the 'deadband' that you are planning, OK
 
hi,
Its a lazy way of saying 'with reference too'
So in full I should have posted, 'with reference too ' the 'deadband' that you are planning, OK

I haven't come up with any idea yet. I have been thinking alot about this lately but still... no idea. Iwill post it if i come up with one.
 
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