Servo not reaching full travel

[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...

[Jumper]

http://www.futaba-rc.com/servos/digitalservos.pdf

the s3152 is a digital servo but as the link sais... it is more or less the same thing. No special codeing and other stuff. Have you torn it apart and had a look at the feedback potentiometer. That pot is the one that feedbacks the position of the servo-horn to the MCU inside the servo (since it is a digital servo).

Did you try with some other servo yet?

/me

[BrianT]

1. Centre adjustment.
In most better class servos there is a centre adjustment. To access this, take the servo horn off and use a very small flat blade screwdriver to tweak the potentiometer at the bottom of the servo horn screw mount. This allows you to make an electrical zero adjustment instead of the normal linkage length adjustment.

2. Digital servos will self destruct if driven against their internal stops.
Analog servos are fairly benign when driven past their normal stops. They will stall and draw a few hundred milliamps which is tolerable for a few tens of seconds. A digital servo however draws several amps when moving to the command position and if up against the stops the servo motor will get so hot it melts the plastic coil former used in the coreless motor in seconds. Been there, done that - costs hundreds of dollars when the code in a UAV gets it wrong at power up and burns out aileron and flap servos.

3. Left Right rotation limits.
1.5 mSecs seems to be the universal centre position. 1 mSec is guaranteed to work for one direction and 2 mSec for the other direction with all brands and types of servos. Outside the 1 and 2 mSec limits you are on your own - it might work with brand/type A but not necessarily with brand/type B. There is NO agreement on normal rotation angles - even within one manufacturer. Servos can have +/- 45, +/- 60 and +/- 90 degrees as their internal design limits. Attempting to push a servo past that will shag the servo quick smart.

4. PulsOut is a toggle.
If your code uses the pulsout command to drive the servo make certain you preset the state of the servo drive pin before calling the pulsout command. This command is a toggle and merely sets the pin to the opposite state for the command period. You might be expecting the pin to be low and go high for the pulsout period but real world interference can trip you up and give you the opposite effect. Been there - done that.

Use
Low ServoPin
Pulsout ServoPin, 150 'etc

HTH
Brian

[ruijc]

Hi all,

skimask,

i'm not really sure if the servo moves equally to both sides because it will depend on where the center is.
In my program the center is at pos = 700

The servo never came to the point of hitting it's internal stops and "keeping the motor running" ( if you know what i mean )

I can increase the pos value but the servo stops when reaching pos +- 1300.

I think that the minimum value could be the key here...i mean...the min value is 25...can i go lower than this ( minus ) ???

Jumper,

I did not opened the servo yet.

BrianT,

My servos do not have the center adjustment screw. Were did you see this ? I have never seen this in any of my servos ( hitec, futaba, digital/analog ).

About the pulsout method...i tryed once that but for some reason it didnt worked as well as my code above...will try it again though

.

[BrianT]

Not all servos have a centre adjustment. To check, remove the philips head screw that holds the servo arm on. Look down the hole in the splined shaft that holds the servo arm. If your servo has a centre adjustment, you will see a very small flat blade screwdriver slot. That is the centre adjustment.

HTH
Brian

[skimask]

Hi all,
i'm not really sure if the servo moves equally to both sides because it will depend on where the center is.
In my program the center is at pos = 700

Put a mark on the servo horn and eyeball it.

The servo never came to the point of hitting it's internal stops and "keeping the motor running" ( if you know what i mean )

Stalling perhaps?

I can increase the pos value but the servo stops when reaching pos +- 1300.
I think that the minimum value could be the key here...i mean...the min value is 25...can i go lower than this ( minus ) ???

Somehow, I think you're Oscillator and you're DEFINE's don't match up. Grab an LED, and try a simple one second per flash LED flasher type thing and see what happens.
I still get the feeling that you're a magnitude or two off the mark here.
The servo stopping at 1300, tells me that if your oscillator was off by a factor of 2, that the 1300 might actually be 2600. A pulse width of 2.6ms on a servo is 'off the scale' at one end by quite a bit, I don't think it's completely unreasonable that you'd be hitting a stop there rather than around 2-2.1 ms like it should be.

And another thing...You also said that your center is 700.
Well, 700 (.7ms) x 2 = 1400 (1.4ms) ....pretty close to 1500 (1.5ms) dontcha think!

Double check your oscillator settings, frequency, code, etc.etc.etc. I'm sticking with that theory for now....in the absense of better information of course...

[ruijc]

skimask ,


just a note:
When i say the center is pos = 700 means that it's 1700 (pauseus 1000+pos ) which is equal to say 1.7ms, right ? ( pretty close to those 1.5ms ).

About the osc you are right because i already did some work there. I started with a define for a 4mhz speed and ended at a 3 mhz define ( with a define osc 3 i got closer to the real thing )

this is because i noticed that using define osc 3 i could get more travel with the lower limit ( pos = 25 ) rather than with define osc 4

.

[Jumper]

Hi

DEFINE OSC 4

you must use capital letters in the define line.

/me

[skimask]

When i say the center is pos = 700 means that it's 1700 (pauseus 1000+pos ) which is equal to say 1.7ms, right ? ( pretty close to those 1.5ms ).

Ok, that makes a bit more sense now...

About the osc you are right because i already did some work there. I started with a define for a 4mhz speed and ended at a 3 mhz define ( with a define osc 3 i got closer to the real thing )

You do realize that DEFINE OSC 3 doesn't really define 3Mhz, it's actually 3.58Mhz, (14.31818 / 4, for use with colorburst crystals, which used to be dirt cheap and easy to find and accurate).