Stepper Motor on BS2: Help!

putrification

I have just gotten a stepper motor, and am using a BS2 BASIC Stamp, and was wondering, is there a way for me to, instead of moving the motor forwards and backwards by individual steps, can I point to specific steps and move to those ones directly?

Here's the Sample Code that came with the motor, if it helps:

' {$STAMP BS2}
' {$PBASIC 2.5}

Phase VAR OUTB ' phase control outputs

StpsPerRev CON 48 ' whole steps per rev

idx VAR Byte ' loop counter
stpIdx VAR Nib ' step pointer
stpDelay VAR Byte ' delay for speed control

Steps DATA %0011, %0110, %1100, %1001


Setup:
DIRB = %1111 ' make P4..P7 outputs
stpDelay = 15 ' set step delay


Main:
FOR idx = 1 TO StpsPerRev ' one revolution
  GOSUB Step_Fwd ' rotate clockwise
NEXT
PAUSE 500 ' wait 1/2 second
FOR idx = 1 TO StpsPerRev ' one revolution
  GOSUB Step_Rev ' rotate counter-clockwise
NEXT
PAUSE 500 ' wait 1/2 second
GOTO Main
END


Step_Fwd:
stpIdx = stpIdx + 1 // 4 ' point to next step
GOTO Do_Step


Step_Rev:
stpIdx = stpIdx + 3 // 4 ' point to previous step
GOTO Do_Step


Do_Step:
READ (Steps + stpIdx), Phase ' output new phase data
PAUSE stpDelay ' pause between steps
RETURN

Edit:
I have this motor: 12-Volt Unipolar Stepper Motor (#27964)

erco

The short answer is no.

Long answer: steppers are useful because they rotate a fixed amount per pulse, so in order to go to position B, your software must know current position A and send the proper sequence and number of pulses to drive the motor to position B. You can rotate a stepper any number of times to any position, but your code always has to keep track of where the motor is.

An RC servo can be commanded to go to a certain position by sending a string of pulses to it. Servos generally rotate from 90-180 degrees. A servo requires just one IO pin, easier to use than a stepper motor. A Parallax ServoPal can be used to send a pulse train to the servo and free up your Stamp to other things.

putrification

So, there's no way I couldsay "Currently you're at position B, we want you at position A. Position A is (Position B - Position A) counter-clockwise steps away."? On a side note, I have already purchased the stepper mentioned above, and I have a deadline for my project coming up pretty soon, I'll keep that in mind for next time though, thanks.

Leon

You could do that if you have a limit switch that is read by the controller - rotate the stepper until the switch closes, and you then have a known starting point. Or, put an absolute encoder on the stepper. They are expensive, though.

putrification

Hmm, that limit switch idea sounds easy enough. Definitely something to look into. Thanks for the input!

Littlebuck

Hi,
It seems to me that if you use a few registers you can achieve what you want.
Keep the pulse count of where you are at in a register.
Put the pulse count for where you want to go in a register.
Perform a math operation and put the result in a register.
If the sum is negative, pulse the motor C.C.W. x sum in register
If the sum is positive, pulse the motor C.W. x sum in register.
Then, overwrite the new position (sum) in the original count register.
I don't know code for it, but that's the principle.
The only drawback is that you might accumulate error after extended use.
Maybe you could add a switch for home position / error check. Then reset the register of where you are at.
I have a project in mind for this as well.
Hope this helps.

Littlebuck

Sorry,
I didn't mean positive or negative,
Should be Less than or greater than original vakue in register.

Littlebuck

Hey, I ran across an old post which should be helpful as well. Go to Forum search, Advanced search, User name = Newzed, Topic = Stepper Control, Date is Mar 8 or 9 2005, hit search.

Stampmyster

Have you taken a look at the Little Step-U controller? You can find it in the Parallax Store.

They are easy to use and, I believe, will do all that you ask. No doubt.

However, if writing raw-code for stepping motors is an assigned school project requirement, it would certainly be considered cheating!