Help to choose an ideal motor.

Other Hardware Motors, Mechanics, Power and CNC
1

Hi,

For a project I have to assign a position and speed to a motor .
Morever, I need to know in real time, the actual position and speed to this motor because sometimes I will break it and even reverse it way.
The must should be to have a captor of intensity quite precise inside this kit motor+encodeur+captor intensity.
When the motor turn in one or the other way, my captor of intensity will give positive or negative value so I will need a system which give me only positive value to send it to an input in Arduino.

I think I have to buy a motor with an absolute codeur as feedback and I will add an intensity captor (expect if a kit motor+encodeur+intensity captor exist) , but I don't know if it have to be a motor CC with an encodeur wheel or servomotor with a feedback position.

Thanks for your lights!

2

There is no such thing as "the ideal motor". You have to describe the application in which the motor will be used and the performance required in terms of speed and torque - and the amount of rotation (number of revolutions).

Superficially your description sounds like a stepper motor would be the simple solution. Controlling the position of a DC motor with an encoder is not a trivial exercise.

...R

3

Robin2:
Superficially your description sounds like a stepper motor would be the simple solution. Controlling the position of a DC motor with an encoder is not a trivial exercise.

Depends what you mean by trivial, I've implemented a proportional-only controller quite successfully before,
its not that far from trivial really. Something like this:

int P_term = constrain (abs (wanted_position - actual_position), 0, LIMIT) ;
digitalWrite (direction, wanted_position < actual_position) ;
analogWrite (enable, map (P_term, 0, LIMIT, 0, 255)) ;

plus the encoder code to maintain the value of "actual_position"

4

MarkT:
Depends what you mean by trivial, I've implemented a proportional-only controller quite successfully before,
its not that far from trivial really. Something like this:

Interesting.

I imagine that the motor must vary its position by +/- a few encoder steps compared to a stepper motor that will sit rigidly at a position even if the direction of the load changes (within the limits of the holding torque) ?

...R

PS. I'm assuming your encoder is on the motor shaft.

5

Yes, proportional only control is soft, but simpler and often will do. No need for accurate timing
information as no differential or integral terms are involved. Most hobby servos use it I suspect.

6

MarkT:
Most hobby servos use it I suspect.

But their position sensor is on the output shaft, not on the motor shaft.

I have made a crude servo with a DC motor with low gearing and a regular pot connected to the output shaft. It worked fine with simple PID control.

...R