servo position feedback
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Posts: 46,084
I just read that the PSC (parallax servo controller) has position
reporting which enables you to get feedback on servo positions at any
time. Very useful.
Is there any way to get the same feedback from a servo using only a
basic stamp and the BOE (board of education)?
reporting which enables you to get feedback on servo positions at any
time. Very useful.
Is there any way to get the same feedback from a servo using only a
basic stamp and the BOE (board of education)?
Comments
hejpatrik@h... writes:
> Is there any way to get the same feedback from a servo using only a
> basic stamp and the BOE (board of education)?
>
Don't really understand what you are looking for. The position of the servo
is the last pulse command sent to it. If you wanted to debug that you could
write:
pulsout servo, 800
pos = 800
debug dec ? pos
Sid Weaver
256K of plugin EEPROM................
http://www.visualmuses.com/chipcircuit/index.html
[noparse][[/noparse]Non-text portions of this message have been removed]
PULSOUT 15, 750
... store your position in a variable.
PULSOUT 15, leftPos
The variable will tell you where the servo is (supposed to be).
-- Jon Williams
-- Applications Engineer, Parallax
-- Dallas Office
Original Message
From: pasotomaso [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=dKrybNz4qDKnFq4_5d1Th6B1lSJ2coNTH3wBoA4mNqvf1_M0DmoYH1V3GSQkTOKSR5Bo0kNpV5cFASB8UQ]hejpatrik@h...[/url
Sent: Tuesday, May 04, 2004 4:19 AM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] servo position feedback
I just read that the PSC (parallax servo controller) has position
reporting which enables you to get feedback on servo positions at any
time. Very useful.
Is there any way to get the same feedback from a servo using only a
basic stamp and the BOE (board of education)?
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> basic stamp and the BOE (board of education)?
<http://www.parallax.com/detail.asp?product_id=28107>
--
Enjoy,
George Warner,
Schizophrenic Optimization Scientists
Apple Developer Technical Support (DTS)
The signal you send to the servo is not necessarily the actual
position of the servo. Once the signal is sent, the servo TRIES to
position itself accordingly but if 'the loop is too short' or the
servo gets stuck on something it will not reach that position. It
will stop before. This means that in reality the pulsout you send can
never be trusted to indicate the correct position of the servo.
That's why it would be nice to get feedback on the position from the
servo. Unless the PSC uses a variable to store the position (and not
the actual position of the servo) is seems the servo is able to send
a signal back to whatever is controlling it with its position. Then
it should be possible to read this signal with just the Basic stamp
aswell right?
Hope that explained my question a bit better [noparse];)[/noparse]
the key lies in something jon Williams wrote:
"The variable will tell you where the servo is (supposed to be)."
"supposed to be" explains it very good. Once a signal has been sent
to a servo it is up to the servo to reach the given position. If it
gets stuck before getting there any variable storing the supposed
position will be inaccurate. In reality the signal sent has nothing
to do with the actual position of the servo.
To get the real position i guess I would need some feedback from the
potentiometer in the servo.
the PSC (Parallax Servo Controller) apparently has "Position
Reporting" that gives back the position of the servo, but i don't
know if this is done using a variable stored in the PSC or with some
kind of feedback from the servo. If it is feedback from the servo I
guess this signal could be read with the basic stamp directly which
would give an accurate position for the servo.
I just got interested when reading about the PSC but if it uses a
variable for servo position then I just misunderstood what it could
do.
Anyway - I hope someone can help me clear this out [noparse]:D[/noparse]
thanks.
/patrik
> Reporting" that gives back the position of the servo, but i don't
> know if this is done using a variable stored in the PSC or with some
> kind of feedback from the servo. If it is feedback from the servo I
> guess this signal could be read with the basic stamp directly which
> would give an accurate position for the servo.
It appears to just returned the "remembered" position. There doesn't seem to
be any feedback from the actual servo.
> To get the real position i guess I would need some feedback from the
> potentiometer in the servo.
It's relatively trivial to solder a wire-wrap wire to the center pin of the
servo's pot and feed that back to a A/D converter. Saved my butt a few times
when I needed position on a non-driven joint; I just yanked the motor out of
a dead servo and just read the pot voltage. ;-)
As someone will probably note if I don't, some servo's (digital?) don't use
a pot but use optical encoder's & up/down counters instead. This trick won't
work on those servos. Most hobby servo's are not of that type.
--
Enjoy,
George Warner,
Schizophrenic Optimization Scientists
Apple Developer Technical Support (DTS)