Step motor control

[dragan77]

Can someone write me code in picbasic for stepper motor control!

I would like to control a stepper motor, for example:
to turn through 360 degrees, and to stop, go back 180 degrees, and to stop, and so on,
I would need a program that works fine, I have tried with some, but always the first mistake and the engine moves a step forward for some step,is not precision.
I use pic 16f628,I forgot say that!

I use this code,but make some mistake after few circle work,not back in same point:

i var byte
k var byte
symbol brz=900 'speed



'360 circle-----------------------------------------
allcircle:
pause 500
For k = 1 to 4
For i = 1 to 128

PULSOUT PORTB.0,brz
PULSOUT PORTB.1,brz
PULSOUT PORTB.2,brz
PULSOUT PORTB.3,brz
next i
next k

pause 2500
goto halfcircle
'-----------------------------------------

'180circle-----------------------------------------
halfcircle:
For k = 1 to 2
For i = 1 to 128

PULSOUT PORTB.3,brz
PULSOUT PORTB.2,brz
PULSOUT PORTB.1,brz
PULSOUT PORTB.0,brz

NEXT I
next k

pause 2500
goto minushalfcircle
'-----------------------------------------

'minus180circle-----------------------------------------
minushalfcircle:
For k = 1 to 2
For i = 1 to 128

PULSOUT PORTB.3,brz
PULSOUT PORTB.2,brz
PULSOUT PORTB.1,brz
PULSOUT PORTB.0,brz

NEXT I
next k

pause 2500
'-----------------------------------------
GOTO allcircle

[Ioannis]

Is your motor loaded?

Have you tried to test it with no load at all?

Ioannis

[dragan77]

How do you think you loaded?
I tried to test it and no-load, but it is the same.
problem is that when running the operation is complete, not return to the same starting point, but perhaps the real fault of a few steps, and I really should be the precise.

[HenrikOlsson]

Going by your code it seems that you have a unipolar motor (6 wires) and 4 switches (transistors or whatever). If so, using pulsout is not the best way since there will be a short delay between each pulsout statement where no current is flowing in any of the coils. When no current is flowing the torque drops and the rotor can "jump" to the closest natural step (magnetic pole).

Delay VAR BYTE
i VAR WORD

TRISB = 0  ' All outputs.

Delay = 10   ' ~100steps / second

For i = 1 to 1000    '1000 steps forward.
  PORTB = %00000001
  Pause Delay
  PORTB = %00000010
  Pause Delay
  PORTB = %00000100
  Pause Delay
  PORTB = %00001000
  Pause Delay
NEXT

Pause 2500

For i = 1 to 1000    '1000 steps reverse.
  PORTB = %00001000
  Pause Delay
  PORTB = %00000100
  Pause Delay
  PORTB = %00000010
  Pause Delay
  PORTB = %00000001
  Pause Delay
NEXT

Now, there are other ways to "produce" the step sequence than this rather crude one but try this and see if it helps.

[dragan77]

Thks for help HenrikOlsson,
is work but is not precision,make mistake every 5-6 circle working.
I use this step motor,ST-28 have 5 wire uni polar step motor,
this is specification:

Rated voltage: 12VDC
Current: 32mA
Resistance/phase: 280
Fases: 4
Angle/step: 5.625 deg
Gear ratio: 1:64
detent torque: 350gfcm (0.034Nm)
pull-in torque: 6360g (0.059Nm)
max. starting pulse rate:700pps
max. slewing pulse rate:1400pps
max. speed: 20.5 rpm
steps/rev: 2048 (tested!!)
connector order:

B2: Blue
B1: Pink
A2: Yellow
A1: Orange
GND: Red

And one more question in your code I will see you dont use this like in my code:

Delay VAR BYTE
i VAR WORD

TRISB = 0 ' All outputs.

Delay = 10 ' ~100steps / second

For i = 1 to 1000 '1000 steps forward.
PORTB = %00000001
Pause Delay
PORTB = %00000010
Pause Delay
PORTB = %00000100
Pause Delay
PORTB = %00001000
Pause Delay
NEXT here dont have i whay

Pause 2500

For i = 1 to 1000 '1000 steps reverse.
PORTB = %00001000
Pause Delay
PORTB = %00000100
Pause Delay
PORTB = %00000010
Pause Delay
PORTB = %00000001
Pause Delay
NEXT

and tell is when I change speed of motor maybe I must change some number of steps,of some else... I dont now!!!

[aratti]

Can you post the wiring diagram?

Al.

[HenrikOlsson]

Hi,
It's not easy to say what the problem is. It might be that you need to start even slower than ~100Hz and then ramp up the step frequency, in order to see if that is the case increase the pause time between each step to something like 25ms.

The above is also the answer to how you change the speed. There's the DELAY variable which, in my example gets assigned the value of 10. Between each step there's a delay of 10ms, change that and the motor speed changes.

A schematic of how you have it wired would help too. Usually you run step motors at much higher voltage than what they are rated for and then limit the current. For unipolar drive this was usually done by big series resistors. In todays bipolar drives it's done thru chopping/PWM.

With PBP you don't need to specify anything with the NEXT statement. It automatically belongs to the FOR that is "closest to it". You CAN definitely add a variable to the NEXT for added clarity but it's not needed.

Finally, you say the motor has a step angle of 5.625 degrees, that's 360/5.625=64 steps/rev. Then you have a gearbox with a ratio of 1:64, so 64*64 is 4096 and not 2048 as you've stated....something isn't correct there but it's not related to your problem so it doesn't really matter right now.

/Henrik.