Can an IC 741 with a negative feedback be used to control the rotation of a DC motor?

[inc0gnit00]

This is a flow chart that someone sketched for me, but is this feasible?
Also, can someone explain to me the working of the circuit in a simple manner.
I'm from a mechanical background, so my knowledge of circuits is limited.

P.S: I'm not looking for alternatives, my query is with reference to this specific question

 

[Nigel Goodwin]

It's called a servo - they are commonly used in radio control models, where the link between the pot and the servo is via the radio link, as a variable width pulse.

For local operation, you just need an opamp as a comparator, along with suitable bi-directional drivers for the motor - the monitoring potentiometer needs to be fed from a substantial reduction gearbox.

 

[inc0gnit00]

"For local operation, you just need an opamp as a comparator, along with suitable bi-directional drivers for the motor"
Could you explain it to me in a bit more simple manner?
Also, a servo has a 180 degree limitation right w.r.t the rotation of the motor?
My requirement states that the motor should rotate more than this

 

[Nigel Goodwin]

Have a look here, for an RC example:



If you want more rotation than the pot will allow, you need to take the drive from earlier in the gearbox.

 

[inc0gnit00]

Ok, but that would require a servo-controller right. I'd like to use ONLY an OP-AMP.
Is that possible?

 

[Nigel Goodwin]

Ok, but that would require a servo-controller right. I'd like to use ONLY an OP-AMP.
Is that possible?

As I said, just an opamp wired as a comparator, and a driver for the motor (essentially a crude power amplifier).

 

[MikeMl]

You can use a "POWER OpAMP", like a **broken link removed**. You will need split supplies. It will drive a DC motor directly. Position feedback could come from a potentiometer coupled to the motor shaft.

 

[inc0gnit00]

As I said, just an opamp wired as a comparator, and a driver for the motor (essentially a crude power amplifier).

At the risk of annoying you further, could you sketch out the circuit to make it easier for me to understand?
Trust me, I really appreciate the effort taken by you.

 

[inc0gnit00]

You can use a "POWER OpAMP", like a **broken link removed**. You will need split supplies. It will drive a DC motor directly. Position feedback could come from a potentiometer coupled to the motor shaft.

Hi Mike, thanks for the reply. Are you suggesting the same comparator circuit proposed by Nigel?

 

[inc0gnit00]

This thread seems to answer a question very similiar to mine. (Except that I'm using a 12 V DC motor)
https://www.electro-tech-online.com/threads/driving-a-dc-motor-from-the-output-of-an-op-amp.99981/
In case this helps you understand my requirement.

 

[MikeMl]

Hi Mike, thanks for the reply. Are you suggesting the same comparator circuit proposed by Nigel?

No, I am assuming you want a create a motor drive voltage/current which is proportional to an amplified error term = (actual position - commanded position), so as to drive the motor to null the error term. That is, by definition, a Proportional POSITION SERVO. The OpAmp is set up to subtract the (Actual Position) from the (Commanded Position), amplify the difference, and supply the operating voltage/current to the motor.

Be advised that a simple proportional servo controller is usually not considered optimal for position control because it is marginally stable, and always leaves some residual error. The better way is to use a PID (Proportional Integral Differential) Controller, where the OpAmp I referenced above can be used as the motor driver, but requires a lot more stuff upstream. Google "PID control"

 

[inc0gnit00]

Thanks a ton Mike!
I looked it up just now, why does the configuration look similiar to that of your normal OP-AMP with a negative fedback?
Lol..Or is it because I'm a mechanical engineer?
mackys: Making a PID controller out of an op-amp.

 

[MikeMl]

The reference you linked to is not quite a PID. It has a Differential term (C1), it has an Integral term (C2), but is lacking a Proportional term (no DC feedback). Most position servos require P and I, D is optional.