servo command

[scottie2]

Hi
I have problem driving me nuts, I have modified a futaba 3003 servo for continuous driving, I have removed the pot, the stop and fitted 2 10k resistors across the pot position,
using the code below i though it would drive one way pause then drive the other, it changes direction okay but does not pause, I assumed that servo 1, 150 would stop the servo spinning, what am I doing wrong?,

main:
servo 1,150
pause 5000
servo 1, 75
pause 5000
servo 1,150
pause 5000
servo 1, 225
pause 5000
goto main:

Cheers scottie

 

[Rick100]

You can try adjusting the 150 number up and down until you find the center value needed . The 150 is an approximate value for the center . I'm not sure about the 10K values for the resistors, or if the value matters . I have seen 2.2k used like in this example .

http://www.ranchbots.com/club/papers/Modifying Hobby Servo Motors for Continuous Rotation.pdf

 

[scottie2]

I did try that, moving a couple of points either side, it still failed to stop, did wonder if the reqd value as a point value ie 150.7, but you can only use round values,
I also did it with 2.2k resistors, as you say in theory makes no difference as they are only acting as dividers, i think
I did modify the servo in the same manner as per your pdf link

 

[premelec]

Just to see if it's working the way you think - put in a pot instead of the 2 resistors in and then adjust the pot while feeding the pulses to it and see if you can get it to stay in one position... I'm an empiricist

 

[Rick100]

You can try this piece of code to cycle through the positions to see if it stops .

servo 1,130
for b2 = 130 to 170
pause 5000
servopos 1,b2
next

It uses servopos instead of servo to reposition the servo .

Good Luck

 

[scottie2]

Gotta say that is a awesome idea, i shall try it tomorrow as you say i can balance the resistance until it stops
thanks
scottie

 

[westaust55]

Not all Servos use the pulse duration range from 75 to 226 with 150 as
Mid point.
Past posts on this forum have indicated some need 130 as a mid or off point.
I have some that work over the range 60 to 199/200

 

[scottie2]

Quick update, i put a 10k trim pot instead of the usual 2 resistors, trimmed out with 150 duration, it now works a treat, stops every time when reqd,
Thanks everyone

 

[erco]

Glad you got it sorted out. From my experience, most servos' center point is far from the 50% voltage divider achieved with 2 identical resistors, and a small multiturn trimpot is necessary if you want the servo to be stopped/centered at a value of 150. And quite frustratingly, it will drift over the course of an hour and require readjustment, so make sure you have access to the trimpot once you reassemble the servo.

Also, not all servos respond equally well to the CR modification. I modded some Futaba 3004s that did not work well, they were overly sensitive to the servo pulse width input. Very twitchy to adjust over a narrow PW range; no fine low speed control. Then I modded some cheap 3003 clones from Ebay China that worked much better, they were nicely adjustable over a wide PW range. In this case, the cheap servos' wide deadband was a plus. They also stayed 'centered' longer.