SERVOS: Making myself a target for ridicule...
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Servos. I don't know how they work. I've looked through alot of pdf and such,
but I still can't figure out how to control them. I know that they are
positional mortors, I understand that much. Do you send a binary number to them
to move them? An analog signal? WHAT??? I can't seem to find a comprehensive
guide to servos. Any help is appreciated.
[noparse][[/noparse]Non-text portions of this message have been removed]
but I still can't figure out how to control them. I know that they are
positional mortors, I understand that much. Do you send a binary number to them
to move them? An analog signal? WHAT??? I can't seem to find a comprehensive
guide to servos. Any help is appreciated.
[noparse][[/noparse]Non-text portions of this message have been removed]
Comments
Basically, you have to send the servo a pulse of between 1ms and 2ms,
separated by 20ms. A 1ms pulse rotates the servo motor counter-clockwise and
2ms rotates it clockwise. 1.5ms moves it to its centre position.
There are two types of servo - modified and unmodified. Unmodified ones
operate as described above. Modified servos, however, will rotate
continuously in the direction specified by the pulse. The potentiometer
inside the servo must be disconnected from the output shaft and the stop lug
must be trimmed off in order to make them work in this way.
Have a look through the Parallax curriculum downloads - there is lots of
info within the rob_v1_2.pdf document (the "Robotics Student Guide for
Experiments #1 through #4").
HTH
Justin.
Original Message
From: Astro Fizzix [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=eoivWy7u1ff46juO0wp0EZo5rl4zOlpMf94iW40tSIfnDG_2QWS5xA2U_cF4If07P7Ty86mJ4g5QOi2CPksWCaw]astro_fizzix@y...[/url
Sent: 19 October 2001 17:40
To: Post BS Message
Subject: [noparse][[/noparse]basicstamps] SERVOS: Making myself a target for ridicule...
Servos. I don't know how they work. I've looked through alot of pdf and
such, but I still can't figure out how to control them. I know that they are
positional mortors, I understand that much. Do you send a binary number to
them to move them? An analog signal? WHAT??? I can't seem to find a
comprehensive guide to servos. Any help is appreciated.
[noparse][[/noparse]Non-text portions of this message have been removed]
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airplanes. They are, in fact, pulse width controlled. If you send a 1.5
millisecond pulse to the servo, every 20 ms or so, it will hold its center
position. If you change the pulse width to 1.0 ms, the servo will move to
the left. If you change the pulse width to 2.0 ms, the servo will swing to
the right.
The BASIC Stamp -- very conveniently -- has a command called PULSOUT which is
perfect for controlling hobby servos.
-- Jon Williams
-- Applications Engineer, Parallax
In a message dated 10/19/01 11:46:10 AM Central Daylight Time,
astro_fizzix@y... writes:
> Servos. I don't know how they work. I've looked through alot of pdf and
> such, but I still can't figure out how to control them. I know that they
> are positional mortors, I understand that much. Do you send a binary number
> to them to move them? An analog signal? WHAT??? I can't seem to find a
> comprehensive guide to servos. Any help is appreciated.
>
[noparse][[/noparse]Non-text portions of this message have been removed]
such, but I still can't figure out how to control them. I know that they
are positional mortors, I understand that much. Do you send a binary number
to them to move them? An analog signal? WHAT??? I can't seem to find a
comprehensive guide to servos. Any help is appreciated.
The position of a servo is controlled by the width a pulse on the signal
line. There's an app note on using a Stamp to do it but in general when a
servo is hooked up to an RC receiver it gets a pulse that starts every 20
milliseconds. I believe (from my fading memory) that full in one direction
is 1mS wide and full in the other direction is 3mS wide. Not certain on the
later numbers but you get the general idea.
Inside the servo there is a small motor a potentiometer and some circuitry.
The circuit uses the pot to create an internal signal based on the output
shaft position. It looks at the incoming pulse width and creates an error
signal that makes the motor drive the shaft one way or another until the
error goes away.
Tim
you specify. The servo always knows what position its in, and when you tell
it to move to another position it knows how fast to run and when to stop.
Servos are controlled by sending pulses to it over and over. On a typical
servo the data line from the Stamp, etc... to the servo is held at ground
potential (0 volts) and periodically goes to 5 volts for a known period of
time then back to ground.
The length of the pulse determines the position of the servo. A short pulse
tells the servo to move to one end of its travel, while a longer pulse tells
it to move to the end of its travel -- pulses of a length between the two
will move it to other positions.
You know how Tiger Woods bounces the golfball on his club? He has to hit the
ball with the club over and over to keep it in the air. He hits it soft and
it doesn't go too high, but if he hits it harder it goes higher? Same
concept.
Original Message
> Servos. I don't know how they work. I've looked through alot of pdf and
such, but I still can't figure out how to control them. I know that they are
positional mortors, I understand that much. Do you send a binary number to
them to move them? An analog signal? WHAT??? I can't seem to find a
comprehensive guide to servos. Any help is appreciated.