Controlling a Servo Motor

[shaneshane1]

I have a Mini Servo 4.8V-6V, and i have modified it so it will rotate continuasly,is there a way i can pulse the motor without programing it,is there some way i could use a 555 timer,it doesnt have to be perfect,im just trying to get it to turn around,my aim is to use some sort of turn switch (like one you would find on an old tv or radio) so when i turn it one way the servo will move as i turn the switch and the same for when i turn it the other way,

could someone please explain how i could do this the basic way,assuming i know nothing about this topic.

thank you very much to anyone that can help.

 

[blueroomelectronics]

Google is your friend
**broken link removed**
**broken link removed**

 

[Wingmax]

Most standard servo motor works between pulse width of about 1ms to 2 ms with period about 20ms. they are not that critical.
You can also try this site:

http://www.kpsec.freeuk.com/555timer.htm#astable

You'll learn all the formulas to work out how to produce the frequency, duty cycle of the waveform you need.

 

[shaneshane1]

thanks for all the help guys,ill get straight into looking at it.

 

[shaneshane1]

i followed the instructions for the servo pulser, and it works great, this may sound like a real noob question, but how do i get the servo to change direction?, it currently is only going clockwise

 

[Nigel Goodwin]

i followed the instructions for the servo pulser, and it works great, this may sound like a real noob question, but how do i get the servo to change direction?, it currently is only going clockwise

Alter the width of the pulse, the servo compares the pulse width to the internal potentiometer setting - if the pulse is smaller than the pot is set it rotates one way, if it's larger it rotates the other way - if it's exactly the same it stops.

 

[shaneshane1]

ok,well i think my servo might be stuffed then, about six months ago i done something wrong with it and it got really hot and started to smoke a little,lol and i havent used it until now.

so do i alter the pulse with the 2k7 potentiometer that is in the shamatic to change the sevo's direction?

 

[mynameisdan]

What you need is a 555 timer astable running at 100Hz (i think). Then that should trigger a monostable 555 timer. You can then change the delay on the second timer to determine the direction.

 

[shaneshane1]

so wont the servo pulser that blueroomelectronics gave me do that???

 

[mynameisdan]

The the pulse width on the circuit diagram above can't be changed.

 

[Omar.M]

A servo motor relies on the width of a pulse (while it is constantly being pulsed to) to determine the angle of the rotation.

The width of the pulse is between 1-2 ms as others have pointed out.

So for example. If the width is 1 ms, the servo will be at extreme left position. If the pulse width is 1.5 ms, it will be in center position, if it is 2 ms, then the servo will be in extreme right position.

Anything in-between-- you can figure that out.
The link that Bill provided should be able to do that-- the output is 1-2 ms (or at least the diagram says)...

 

[shaneshane1]

ok well i think i will wait until i get a servo that works properly,because what iv been doing should work

 

[mneary]

The the pulse width on the circuit diagram above can't be changed.

Looks OK to me. Pulse width is controlled by P1 and R1, repetition rate is controlled by R2.

 

[blueroomelectronics]

The the pulse width on the circuit diagram above can't be changed.

There's a variable resistor in the diagram. Can't see why that wouldn't adjust it.
The link below the diagram says it will adjust from 1ms to 2ms...

 

[shaneshane1]

thats the conclusion i came to and it didnt seem to work properly, changing the pot didnt seem to change the servo direction, just slowed it down,it just goes clockwise, so i assumed that my servo is stuffed.

 

[Omar.M]

Well, I think it has to do with how you "modified it to allow continuous rotation". If you wanted continuous rotation and just wanted to change direction, any old motor with an H-bridge would do. For more control, you could even use a stepper motor.

So can you explain exactly what you want it to do?

 

[mneary]

I missed the part that said you modified it. My bad.

When you modified the servo for continuous rotation, you probably left the feedback potentiometer at a random location. For the control that you appear to desire, make sure that it is at the midpoint of its rotation.

 

[shaneshane1]

ok well at first i wanted the servo to act as a wheel but now i just want the servo to do what it is intended to do, and i am using it to steer wheels left and right and mabye a robotic arm of some sort, i think this servo is completley stuffed anyway, so if i get a new servo do you think the diagram on the first page by blueroomelectronics will do the job?

 

[mneary]

1) If the speed varies by the pulse width, then your motor is still being controlled. It is not stuffed, and you simply need to set the feedback pot of the servo.

2) The diagram on the first page will work for any (unmodified) (properly functioning) servo.

 

[shaneshane1]

I bought a new servo, and it works how it is suppose to, so my other servo was stuffed, i have followed the servo pulser diagram on page 1 by blueroomelectronics and it works, but its jerky and twitches a lot, and it only goes full 90 degrees one way and the other way only goes about 70 degrees, i am using a 5k pot instead of the 2k7, because i cant get one anywhere, does anyone know how i might be able to fix all these problems, i am running the 555 and the servo of 5V (im not going to modify this servo if anyone was wondering) THANKS for any help!!!