Arduino as a digital motor controller (DIY servo)

Projects General Guidance
1

I'm learning control theory. I'm trying to find limits on how good a servo I can make just with a pot, a geared dc motor and an arduino. Well, some other hardware too, and a processing sketch for graphs and tuning. It works, but I believe it could be better. I can make it quite accurate for step changes, but I can't make it move slowly.

I have velocity control as inner and position control as outer loop. The potentiometer is read at 100Hz (10 ms per loop). I don't see noticeable differences if I increase the update frequency to 200Hz.

The pot measures angular position. Velocity is calculated from position change.

Here is some relevant code:

   starttime = micros ();
   ref = analogRead (1);
   pos = analogRead (0);

    err = ref - pos;
    vel = pos-lastpos;

    lastpos = pos;  

    Qo = Kp*err - Kv*vel;
    
    Qo = constrain (Qo, -255, 255);
    Output (Qo);
    DebugOutput();

   if (starttime-micros() < period)   // period is 10 000 microseconds
         {  };

So, I would like to make it possible for the servo to move accurately and slowly if needed.
Would I benefit from a 16 bit adc? Do I need a faster velocity loop?

edit:
I'm using Arduino Mega. For the motor driver I use SN754410.
Motors are similar to these: Micro Metal Gearmotor 100:1 (Sale) - ROB-08910 - SparkFun Electronics
The pot that measures angular position is mounted on the motor output shaft. I've drilled it and added just a bit of super glue.
I tried voltages from 3 to 12V. Currently testing 9V.

2

I get the impression you know how to write code but you are looking for advice about possible improvements to the concept of the program.

Rather than post a piece of code I think it would be more useful if you described in english how your control system works and where you would like to make improvements.

The usual way to make hobby servos move slowly is to instruct them to move an extra degree or so every few millisecs, seconds, minutes as appropriate.

...R

3

you might consider using a PID algorithm to set the position