Servo not reaching full travel

[Jumper]

Let's just go over the basic idea:

Center position of futaba servo is 1.52ms puls length sent approx every 20 ms. To move it to min position 1 ms and to max position 2 ms.

But when I recently did a thingy for a RC receiver I found out that the pulses are acctually more in the 0.8 ms - 2.2 ms range to allow for trim settings.

If you plan to have more than one servo I would recommend you to have a look at DT software PWM.

If you want to have bigger movement try to change your limit values.

/me

[ruijc]

Hi Jumper,

when you say change the limit values you mean the :

If pos < 1800 Then

and

If pos > 25 Then

right ?

I added a lcd and did some studies. I did increased the upper value but the servo just stops when it reaches +- 1500.

The center is 700

I cant work with numbers bellow 0 i'm affraid.

The plan is to have only one servo, but i need to use it with more travel ( not continuous ) as 90º is too short

.

[Jumper]

Hi,

Hook up a 10k potentiometer (or whatever you have in your drawer) to i.e AN0. Vdd on one side of the pot. GND on the other and the wiper goes to AN0. Put a 0.1 uF cap between wiper and GND to reduce noice .Connect the servo on i.e PORTB.1 ... if you use a voltage meter on the wiper and adjust the voltage to ~3 V you should get a 1.5 ms pulse every 20ms. Now you can turn the pot and then you can try the end positions... your LCD will be great here.


DEFINE ADC_BITS 8

' DEFINE YOUR LCD SETTINGS HERE

SERVO1 Var PORTB.1
AD0 var word
SERVO1_Pulse var byte
Total_Delay var word
n var byte

TRISA 255 ' PORTA to input
?????????? 'set up as analog CHECK DATASHEET for you PIC
?????????? ' turn off comparators CHECK DATASHEET

n=0
Goto main


update_LCD:
n=0 'reset LCD loop counter
'Here you write your LCD code to send the Servo1_pulse value to your LCD
RETURN

main:

ADCIN 0, AD0 'READ POT
SERVO1_Pulse=AD0*10 'Scale value max = 2550 us
SERVO1=1 'Start the servo pulse
Pauseus(SERVO1_Pulse) 'wait a while
CH1=0 'Stop the pulse
Total_Delay=(20000-Servo1_Pulse) 'calculate loop delay so we
Pauseus(Total_Delay) 'get approx 20 ms loop time
N=n+1
if n>=50 then gosub update_LCD 'update LCD every 50 loops i.e once per second
goto main

end


try it and if it doesnt work let me know so I can help. This code is untested but should work if you set up the analog port correctly. After this you will atleast know how far your servo will travel.

/me

[ruijc]

Hi Jumper,

Fist of all thanks for your help

I had some issues with your code but i got the idea ( nice one by the way )

The problem is that even so the servo just moves a total of 90º

I've googled a bit and for futaba servos they state that you need :

center : 1,5ms
0º : 1ms
120º : 2ms
30º : 1.16ms

( stop time can vary from ~15ms to 30 ms - not critical )

I'm not being able to apply this to my servos

Even with a simple pauseus 1000 ( that should be 1ms and the servo should center ) this does not happen

.

[Jumper]

Do you have more servos? Try a different one since the one you are using might be bad.

If you connect the servo to a normal RC receiver what result do you get then?


/me

[skimask]

center : 1,5ms
0º : 1ms
120º : 2ms
30º : 1.16ms
Even with a simple pauseus 1000 ( that should be 1ms and the servo should center ) this does not happen
.

It looks to me like you might be confusing a couple of the values you stated above.
From what I'm seeing, you want 1000 to be center and work around that. That's all fine and dandy, but you want the rest of the program to work around it also, which it isn't doing.
Instead of thinking about it in terms of 0, 90, 120, whatever degrees, think of it in terms of -90 , 0 , +90, etc. degrees, where 0 is center.

Using your original code...with a few changes...

'.....set up your ports, adcon, cmcon, whatever else is required...

leftend = 1000
center = 1500
rightend = 2000
stepval = 50
pos = center

moveleft:
pause 19 'pause 19ms
if pos > leftend then
pos = pos - stepval
else
goto moveright
endif
servo = 1 : pauseus pos : servo = 0 : goto moveleft

Moveright:
pause 19 'pause 19ms
if pos < rightend then
pos = pos + stepval
else
goto moveleft
endif
servo = 1 : pauseus pos : servo = 0 : goto moveright

end

And with that code, when pos = 1500, the servo should be centered. pos decreases to leftend, servo moves left, pos gets to leftend, jumps to other loop, pos increases to rightend, servo moves right, pos gets to rightend, jumps to other loop, and over and over.
Change the value of stepval to change how fast the servo moves back and forth. Simple enough.
But if it really doesn't work, and your ports are set up correctly, you've got the right config fuses set, etc.etc., then, as Jumper said, it sounds to me like a goofy servo. What kind of Futaba servo are you using? A standard S148 or what?

[ruijc]

Jumper, skimask,

i did some more digging but all returning to the same thing...

I tryed skimask's code and the servo uses no more same travel than before.

I'm using a Futaba's S3152 which is a good servom ( IMO ) ...and so i left the "bad servo" mark to the end.

I tryed it with a receiver and same thing.

I'm guessing the servo is really goofy.

.

[skimask]

Jumper, skimask,
i did some more digging but all returning to the same thing...
I tryed skimask's code and the servo uses no more same travel than before.
I'm using a Futaba's S3152 which is a good servom ( IMO ) ...and so i left the "bad servo" mark to the end.
I tryed it with a receiver and same thing.
I'm guessing the servo is really goofy.
.

Does it move equal distances to the 'left' and 'right' as measured from 'center'? Or is one more than the other? What happens if you change 'leftend' to 500 and 'rightend' to 2500? Does it bind at one end or the other?
Are you sure you're PIC is running at the same oscillator speed as you have DEFINE'd?

I haven't done any checking lately, but, is a Futaba S3152 a 'standard' servo? Is it one of the new digital servo's? I don't have any of those, I haven't played with them, so I don't know about their operational characteristics. I'd ASSUME they would operate the same if they're backwards compatible, but I could be wrong...