unusual motor controller

i would like to be able to control the speed and direction of a motor with a pot

the method would be to use the first half of pot rotation to run the motor in one direction and control its speed and in the in the second half of pot rotation run the motor in the other direction and control its speed

in the middle of the pots rotation the motor would be stopped and increase in speed in either direction of pot rotation

the mechanical analogue would be a disk driving a wheel that traveled from one side of the diameter to the other, increasing in speed as the wheel traveled from middle to edge and stopping as the wheel was in the middle of the disk

i would like to be able to set variables for min and max speed of the wheel and set the the zone on the pot of no speed

any ideas

i have a arduion uno r3 , i have a motor controller shield (Adafruit Motor/Stepper/Servo Shield for Arduino v2.3 Kit) and pots on order

in all my searching online i haven’t come across anything quite like this

from what i’ve read mapping will take care of half of what i want, not sure about the other half that would require decrementing

any help will be much appreciated

Doesn't sound hard. Read a pot, values from 0 to 506 control PWM to H-bridge one direction, values from 518 to 1023 control H-bridge the other direction. Change dead spot as needed.

would map be the right function?

and could i make the change in speed smooth and continuous, ie not stepped?

0 to 512 = 10 bits, you need 8 bits for PWM, so just take a reading and manipulate as needed:

speedBase = analogRead(A0);
if (speedBase<=511){
lowSpeed = speedBase >>1; // now it's 8-bits, 0 to 255
// however 0 is desired for high speed, so subtract it from 255
lowSpeed = 255 - lowSpeed;
analogWrite (highspeedEnablePin, 0); // turn off the other side
analogWrite (lowspeedEnablePin, lowSpeed); // turn motor the other direction.
}
if (speedBase>=512){ // other side 512 to 1023
offset set for 0 to 511
highSpeed = highSpeed - 512; // now 0 to 511
highSpeed = highSpeed >>1; // and 0 to 255
analogWrite (lowspeedEnablePin, 0); // turn off the other side
analogWrite (highspeedEnablePin, highSpeed); // turn motor the other direction
}

I don’t know if you need to give the motor a chance to slow down before changing direction, might see big current jump if not.
I wrote as two ifs so you can open the ranges a little for dead band.

i'd like the motor to respond as though it were the mechanical system i described

What about what I described doesn't do that?

i appriciate your time and effort and i'm not doubting you as i don't know much about the arduino only having just got one and waiting for the pots and motor controller

here is a link to what i'm trying to copy, it starts at 30:45 to 35:30

https://www.youtube.com/watch?v=bOwKh9XLO1c

i'd like the motor to respond as though it were the mechanical system i described

I suggest to wait until your parts arrive, put it all together and try out CrossRoad's suggested code. Then you can judge whether it does what you want, and if not, modify it to suit.

There is nothing unusual about your proposed controller.

I'm certainly not going to wade through half an hour of youtube....

You might do better just getting a reversible motor controller from ebay.

http://www.ebay.com/sch/Business-Industrial-/12576/i.html?_from=R40&_nkw=dc+motor+controller+reversible&_sop=15

Make the PWM proportional to the absolute value of the difference from the midpoint,
direction is a simple test:

  int reading = analogRead (potPin) ;
  int pwm_drive = map (abs (reading - 512), 0, 512, 0, 255) ;
  bool direction = reading < 512 ;

You might want to add a dead-band in practice:

  if (pwm_drive < 10)
  {
    direction = false ;
    pwm_drive = 0 ;
  }

zoomkat:
You might do better just getting a reversible motor controller from ebay.

http://www.ebay.com/sch/Business-Industrial-/12576/i.html?_from=R40&_nkw=dc+motor+controller+reversible&_sop=15

size, weight and it has to be remotely controlled and other functions make the arduino the best choice

this function will be the most elaborate and it will be a good learning exersize