Picaxe and servo's

E

ElectricalStorm

New Member
Hi,
I have a strange experience with my picaxe (18X) and different servo’s.
I use this simple test program
main:
servo 1,75
pause 2000
servo 1,150
pause 2000
servo 1,225
pause 2000
servo 1,150
pause 2000
goto main
I have a very very very cheap micro servo and this one does the job he’s suppose to do: go left, go center, go right, go center, …
Another cheap servo starts humming on the right, doesn’t go to the center and certainly not totally to the left. To force the servo to make the movements he should do the program must be modified like this:
servo 1,55
servo 1,180
servo 1,115

A third and digital servo only takes two positions with the original program.
The digital servo (Futaba S3152) only accepts numbers between 67 and 194. Any number above or below this range blocks the servo completely. I lose a ¼ of my servo range with these numbers.

Is there someone who has the same experience? And if so how can I solve this? Or should I keep programming the picaxe out of the pre-determined ranges?

Chris
 
B

BeanieBots

Moderator
The Futaba S3152 is a digital servo.
I don't know that particular one but digital servos usually require a much higher update rate than the 'normal' 20mS frame rate.

Do you have an RC receiver (or servo tester) that you can use to check that particular servo with?
 
B

BeanieBots

Moderator
You only need the servopos command when updating the servo rapidly.
If there is a pause of several seconds between updates, (like you have in your code above) then there will be no noticeable difference. Try it.
 
W

Wrenow

Senior Member
My understanding is that most of the digital servos are programmablle with a servo programmer as to endpoints, deadspace, etc. with a servo programmer like this one:http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXWCE8&P=7 or this one http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXSYU0&P=7 (the least and most fancy of the Hitec type programmer range) - not sure how Futaba are programmed.

As for the second cheap servo being off - could be a bad pot in the servo - sounds like the pot band is off (coming to a stop at one end, not reaching the stop on the other).

Remember, if you are hittting a stop, you are trying to turn the servo way to far in that direction. Most are only designed for 45-60 degrees of motion - few are really designed for 180 degreees (though sail winch servos are up to 720 degrees or more - the Hitec is 1260 degrees (3.5 rotations) http://www.servocity.com/html/hs-785hb_3_5_rotations.html).

Cheers,

Werno
 
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