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.
Hi,
Yes, if the motor/gearbox requires 4096 steps to turn one revolution the first piece of code will move 360 degrees forward and then 360 degrees back. There are 4 "steps" each time thru the FOR-NEXT loop so 512*4=4096.
In the second piece of code it'll move 1440 degrees forward and then 1440 degrees back.
You can improve your motor performance in two ways:
1) Use half step sequence ( here a sample code)
Code:
HStep var byte [8] ' Half step sequence array
B0 var byte
C0 var byte
P0 var byte
W0 var word
TRISB = 0
P0 = 50 ' incrementing the delay will reduce the motor speed (max 255)
C0 = 0
B0 = 0
HalfMode:
If C0 = 0 then gosub CW
C0 = C0 + 1
if C0 = 2 then C0 = 0
If C0 = 0 then gosub CW
If C0 = 1 then gosub CCW
for W0 = 0 to 8192 ' one turn of the gear shaft ( 64 motor turns)
PortB = HStep[B0]
B0 = B0+1
if B0 = 8 then B0=0
pause P0
next W0
Goto HalfMode
CW: ' half step sequence (clockwise)
HStep[0] = 1
HStep[1] = 3
HStep[2] = 2
HStep[3] = 6
HStep[4] = 4
HStep[5] = 12
HStep[6] = 8
HStep[7] = 9
return
CCW: ' half step sequence (counter clockwise)
HStep[0] = 9
HStep[1] = 8
HStep[2] = 12
HStep[3] = 4
HStep[4] = 6
HStep[5] = 2
HStep[6] = 3
HStep[7] = 1
return
end
2) Use a constant current setup to your motor. The simple way is to use a LM317 configured as costant current supply. See the attached schematic (Resistor 33 Ohms 1 watt. Use 24 V dc as an input to the LM317)
cheers
Al.
Last edited by aratti; - 5th September 2011 at 22:31.
Re: Step motor control
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