Servo troubles.

skimask · - 21st September 2008, 03:44

Code:

@ device HS_OSC,MCLR_OFF,LVP_OFF,WDT_OFF,PROTECT_OFF
DEFINE OSC 4
'Use b1 to hold pulse width variable for servo 1
b1 var byte
'initialize variables
b1 = 150
low portb.0		' put the servoport low.
main:
        low portb.0
	pulsout portb.0, b1		'send current servo 1 position out
	if porta.0 = 0 then left1	'check for pressed switch 0
	if porta.1 = 0 then right1	'check for pressed switch 1
	if b1 > 150 then
               b1 = b1 - 1
        else
               b1 = b1 + 1
        endif
        pause 18 : goto main
left1:  b1 = b1 + 1 : if b1 >254 then max1
	goto main
right1:  b1 = b1 - 1 : if b1 <75 then min1
	goto main
max1:  b1 = 75 : goto main
min1:  b1 = 254 : goto main
END

This should go left with one button, go right with the other button, and if no buttons are pressed, should 'walk' back to center.
Note the BOLDED statements

**Glenn** · - 21st September 2008, 13:36

Originally Posted by skimask

This should go left with one button, go right with the other button, and if no buttons are pressed, should 'walk' back to center.
Note the BOLDED statements

Unfortunatly it gives exactly the same result, the servo goes to the endpoint and stay there..

..And just like in my program, if I uncomment the if-lines it "works" as in it stands in the middle position (more or less)

Strange.

**Acetronics2** · - 21st September 2008, 13:55

Hi,

Just place

PAUSE 18

just after PULSOUT command ...

instead of Before " GOTO Main" .

Alain

**Glenn** · - 21st September 2008, 18:18

Originally Posted by Acetronics

Hi,

Just place

PAUSE 18

just after PULSOUT command ...

No, exactly the same result

**Acetronics2** · - 21st September 2008, 18:49

That was to get a decent frame duration whatever you do with the buttons.

Seems the pot cursor is out of its lane ... or see PS !!!

Now, you should place the Max value for b1 to 200 and min value to 100 ... I know servos not responding for values out of this range.

something possible is the méchanical travel is over the pot travel ... not good at all.

and remember Futaba analogic servos MECHANICAL center is +/- 1300µs. you must take this into account if you try more than the +/- 500µS trip ...

Now ... an interesting question ...

Where do your servo take its power ???

Alain

PS1: you sure PORTA.0 AND PORTA.1 can't be 0 together ???
PS2: you sure your comparators are disabled ??? ... 16F628 !!!

... Lol ...

**Glenn** · - 21st September 2008, 21:30

Originally Posted by Acetronics

That was to get a decent frame duration whatever you do with the buttons.

Seems the pot cursor is out of its lane ... or see PS !!!

Now, you should place the Max value for b1 to 200 and min value to 100 ... I know servos not responding for values out of this range.

Well but it work with the lines uncommented, and stands fairly in the middle.

I also tried three different servos.

Now ... an interesting question ...
Where do your servo take its power ???

Well, my testsetup is built on an breadboard, and the servo is connected via a pinstrip and directly to the same power as the rest of the setup, which is powered from the +5V 2A output on my lab power supply.

Btw I'm using a pickit2 from microchip to program the pic via ICSP, and its permanently connected to the pic.

PS1: you sure PORTA.0 AND PORTA.1 can't be 0 together ???

Yes, I used a switch with three positions, (on)off(on) first, but now I just use a cable directly on the breadboard.

PS2: you sure your comparators are disabled ??? ... 16F628 !!!

No idea, how do I do that ?

skimask · - 21st September 2008, 19:32

Ok, try this...

Code:

@ device HS_OSC,MCLR_OFF,LVP_OFF,WDT_OFF,PROTECT_OFF
DEFINE OSC 4
temp var byte
main:
        for temp = 0 to 255
        pulsout portb.0, temp
	pause 18
        next temp
        for temp = 255 to 0 step -1
        pulsout portb.0, temp
        pause 18
        next temp
        goto main
END

This should do nothing more than swing the servo back and forth, from endpoint to endpoint. It'll probably hang up for a bit at the endpoints and might even move too fast or jerk around a bit trying to catch up to the program.
If it doesn't, you've got something else going on.
It all boils down to breaking it down to it's simplest form and building it back up again.
Try it and report back...

**Glenn** · - 21st September 2008, 21:32

Originally Posted by skimask

This should do nothing more than swing the servo back and forth, from endpoint to endpoint. It'll probably hang up for a bit at the endpoints and might even move too fast or jerk around a bit trying to catch up to the program.
If it doesn't, you've got something else going on.
It all boils down to breaking it down to it's simplest form and building it back up again.
Try it and report back...

Well, it swings the servoarm to one endpoint, stops for a while, then all the way to the other endpoint (or near it anyway) and directly start to go back again and repeats everything.

Its not a very smooth movement but it looks ok.

skimask · - 22nd September 2008, 02:57

Originally Posted by Glenn

Well, it swings the servoarm to one endpoint, stops for a while, then all the way to the other endpoint (or near it anyway) and directly start to go back again and repeats everything.

Its not a very smooth movement but it looks ok.

Ok, that's good...at least you know stuff is working.

Now take the program and modify it to 'pull the endpoints' in a bit until you get to the actual endpoints.
When it 'stops for awhile', the program is probably trying to drive the servo past it's endpoints. The program goes to 0ms pulse width, but the servo can only actually drive to a 1ms pulse width, actually it'll probably drive farther than that, a lot farther, just not all the way to zero, or by the same token, won't drive all the way to 2.55 ms pulse width.

Code:

@ device HS_OSC,MCLR_OFF,LVP_OFF,WDT_OFF,PROTECT_OFF
DEFINE OSC 4
temp var byte
main:
        for temp = 100 to 200
        pulsout portb.0, temp
	pause 17 'try lower numbers until it starts acting even stupider than it's acting now
        next temp
        for temp = 200 to 100 step -1
        pulsout portb.0, temp
        pause 18 'try lower numbers until it starts acting even stupider than it's acting now
        next temp
        goto main
END

Decrease the 100 until it starts pausing at one end (meaning the PIC is trying to over-drive the servo) and increase the 200 until it starts pausing at the other end (again, meaning the PIC is trying to over-drive the servo in the other direction).

**Acetronics2** · - 22nd September 2008, 10:15

Hi, Glenn

This one Should run

Code:

@ device HS_OSC,MCLR_OFF,LVP_OFF,WDT_ON,PROTECT_OFF
DEFINE OSC 4

CMCON = 7 ' Disable comparators

PORTA = %00000011
PORTB = 0

TRISA = %00000011
TRISB = 0

'Use b1 to hold pulse width variable for servo 1

b1 var byte

'initialize variables
b1 = 150

low portb.0		' put the servoport low.
main:

        low portb.0
	pulsout portb.0, b1		'send current servo 1 position out
	if porta.0 = 0 then left1	'check for pressed switch 0
	if porta.1 = 0 then right1	'check for pressed switch 1

bugtrap:

        if b1 > 150 then
               b1 = b1 - 1

        else
               if b1 < 150 then b1 = b1 + 1
              
        endif
        pause 18 : goto main

left1: 
         IF porta.1 = 0 Then bugtrap
         b1 = b1 + 1 
         if b1 > 199 then max1
         Pause 8 : goto main

right1:  
           IF Porta.0 = 0 Then bugtrap
           b1 = b1 - 1 
           if b1 < 100 then min1
           Pause 8 : goto main

max1:  b1 = 100 : goto main ; jump to other side

min1:  b1 = 200 : goto main ; jump to other side

END

and do not forget : courtesy SKI !!!

Alain

**Glenn** · - 22nd September 2008, 14:42

Originally Posted by Acetronics

Hi, Glenn

This one Should run

Well, it kind of works, the servo stands still until I touch the switch, but it moves in very strange ways, I'll try to adjust the values a bit and see if it changes anything.

But it sure looks like the comparators was the problem, great!

**Acetronics2** · - 22nd September 2008, 15:02

Originally Posted by Glenn

Well, it kind of works, the servo stands still until I touch the switch,

Looks it should be in the 1500µs position ...

but it moves in very strange ways, I'll try to adjust the values a bit and see if it changes anything.

should reach slowly one end, then RUN to the other end, then slowly to the other end , Then RUN ...

WHILE pushing a button

and going back to center if buttonS realeased ... or both buttons pushed.

But it sure looks like the comparators was the problem, great!

Alain

**Glenn** · - 22nd September 2008, 13:50

Originally Posted by skimask

Decrease the 100 until it starts pausing at one end (meaning the PIC is trying to over-drive the servo) and increase the 200 until it starts pausing at the other end (again, meaning the PIC is trying to over-drive the servo in the other direction).

Well, as you said before the values depends on which servo I use, I settled for the servo that I'm going to use (the brand new china-made) and with that 75 and 255 seem to be the correct values, however, when its 255, its still not at the endpioint, its a few mm more left. ..However this doesnt matter.

skimask · - 22nd September 2008, 15:26

Originally Posted by Glenn

however, when its 255, its still not at the endpioint, its a few mm more left. ..However this doesnt matter.

Change your BYTE variable to a WORD variable and you'll be able to go beyond 2.55 ms. But that sounds a bit goofy since a 2.55ms pulse width is out of spec for most servo's. But hey, if it works for you, go with it...

**Acetronics2** · - 22nd September 2008, 16:04

Hi, SKI

The maximum I ever reached is 250 µs to 2600 µs ... with a Futaba S3001 or a Robbe RS100 ...

not linear at all between 250 and 600µs !!!

regards
Alain

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