servo problems

S

sub-bg

New Member
I hacked a standard servo to rotate above 360 .It was working fine the other day but now all the sudden the servos do not respond to the same programs I tried a few days earlier. They now rotate continually without responding to the actual program.

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init: servo 4,75 ‘ start servo on 4
main: servopos 4,75 ‘ move servo to one end
pause 2000 ‘ wait 2 seconds
servopos 4,150 ‘ move servo to centre
pause 2000 ‘ wait 2 seconds
servopos 4,225 ‘ move servo to other end
pause 2000 ‘ wait 2 seconds
goto main ‘ loop back to start
-------------------------------------------------------------


I'm sur there is nothing wrong with the program..but i don't know what could have caused this. I haven't changed anything at all , I have swapped servos around and everything.

Many thanks
 
S

sub-bg

New Member
we have done continuous rotation , the only thing we have changed today is the power supply. We usually use regulator power supply ,like those supplied in most university labs,but today we used a normal adaptor but for some reason it now rotating continually . where do u think we went wrong?
 
S

sub-bg

New Member
ya we tried that but still nothing different it is still rotating . Do u think its a problem with the actual servo???
 
B

BeanieBots

Moderator
When you say "normal adapter" could you explain in more detail.
Voltage?, Regulated?, Smoothed? Current rating?

A servo requires a good clean regulated power supply capable of at least 1A.

The neutral position of a cheap servo will certainly drift with supply voltage but the values you are using are more than extreme enough to drive either way from central with even the worst case.
Also, the low 4 suggested by Andrew should in most cases dissable it completely but no gaurantee. Does sound like a possible 'melted' output stage or very severe supply collapse.
 
J

jglenn

Senior Member
I would measure your dc supply, it should be 5V, go to ac mode and make sure there is no ripple. Try a normal servo and see if it responds, if it does, then your modified servos have failed. Maybe you put excessive voltage on them and the chip inside blew out, stuck in the full on mode.
 
A

Andrew Cowan

Senior Member
If low4 causes it to move, it sounds like it's the circuit in the servo has died. Have you got an rc system you can try them in?

A
 
A

alband

Senior Member
Perhaps the servo has gone round so many time (having been designed not to) that it is no longer pulling the POT round with it and thus, the servo doesn't think it can match the positions you gave it.:confused:
 
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Andrew Cowan

Senior Member
In the continous servo mod, you disconnect the pot. However, alband has a point - maybe the pot has been pulled from the centre position?

Actually, that wouldn't explain why it spins with no signal...

A
 
S

sub-bg

New Member
Today I tested the servo again with the following program:
----------------------------------------------------------
init: servo 0,150 ‘ initialise servo

main: servopos 0,150
pause 2000 ‘ wait 2 seconds
servopos 0,220
pause 2000 ‘ wait 2 seconds
low 0
pause 2000
goto main ' loop back to start
-------------------------------------------------------
The servo starts rotating at constant speed for 4 seconds and then it stops.
I have changed the potentiometer inside. Also I tried using two resistors 2.2k as potential divider. Both methods give the same result- it rotates at constant speed even if I turn the potentiometer.
 
A

Andrew Cowan

Senior Member
If you want cont rotation anyway, why not replace the circuit board with an L239D? It wouldn't be 1 wire any more, however, unless you stick an 08M in there too. Sounds like a good new project!

A
 
W

Wrenow

Senior Member
This is a case where an inexpensive servo tester like the http://www.hobby-wing.com/esky-ek2-0939-digital-servo-tester1.html can really be handy. But, if you are not getting it to stop on setting the signal low, methinks you have let the magic smoke out somewheres. If you are wanting a continouous rotation servo, hacking a standard servo is NOT your best choice. The controller (servo amplifier) is ill equipped, without further modification for fine adjustments in speed. You would be better off getting a "servo" designed for ccontinuopus rotation from the start like the http://servocity.com/html/hsr-1425cr__continuous_rotatio.html or the Vex Robotics motor. These have adjustable speed, based on the servo signal, for fine control. Fexlabs also sells the circuit board from their motors separately for USD$9.99 (look under Logic on the Vex Robotics site.

Good luck,

Wreno
 
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