Limits and abilities of the Parallax servos....
GSUIndiana
Posts: 8
Heres hoping that I am not out of bounds!
Being my first post I am eager to impress,
so naturaly I am probably completely out
of line!.
So on to my question!
I· have ·4· Continuous· rotation·servo and
one standard servo,· I am curious of a few
things that I have been unable to discover
on my own.····· Can the continous rotation
servos be reverse enginnered to standard
servos and then back again, (depending on
the application) And also can I get the servo
to stop and hold a load steady?· Such as on
a robot arm?
Thanks for any help! GSU
Being my first post I am eager to impress,
so naturaly I am probably completely out
of line!.
So on to my question!
I· have ·4· Continuous· rotation·servo and
one standard servo,· I am curious of a few
things that I have been unable to discover
on my own.····· Can the continous rotation
servos be reverse enginnered to standard
servos and then back again, (depending on
the application) And also can I get the servo
to stop and hold a load steady?· Such as on
a robot arm?
Thanks for any help! GSU
Comments
Having never needed to do it, this is just a guess. I say probably not easily, or not at all without a good deal of work.
Parallax sells the continuous rotation R/C servos for $6.95 (web special) and standard R/C servos for $12.00, so there hardly seems a need to reverse engineer them. I've seen the standard servos for even less when they're on special elsewhere. Just by way of example, here is a web site selling the Hitec HS-311 for $8.99:
http://www.servocity.com/html/hs-311_standard.html
As far as the holding power is concerned, so long as an R/C servo is being pulsed on a regular basis, it will hold its position. Shortly after the pulses cease, the ability to hold a position is lost.
Regards,
Bruce Bates
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
<!--StartFragment -->
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Truly Understand the Fundamentals and the Path will be so much easier...
Why?
You have to de-link the mechanical feedback system AND you have to remove the stopping block from the servo.
These are done by a combination of simple removal and cutting away key areas on existing parts.
Additionally, a lot of people remove the potentiometer and put in a pair of resistors. Again, it is not so easy to find an identical potentiometer.· The Parallax continuous rotation servo's pot is positioned 90 degrees from the axis it would have to be on for a sucessful modification to a positional servo.
Without the feedback system, trying to use continuous rotation for positional uses requires setting up an external feedback system. And such a system usually needs to recalibrate each and every time you power up the device.
Stepper motors really offer more choices in holding power while being able to do both rotation and position in software.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)
······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
Post Edited (Kramer) : 3/13/2006 3:51:12 PM GMT
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
From···· ·Northwest· ·· Indiana-
Where·· the · introverts · stare
at··· there·· ·shoes··· and·· the
extroverts stare at your shoes!
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Jon Williams
Applications Engineer, Parallax
You'll use the same commands (PULSOUT and PAUSE) for either type of servo.
For the standard (unmodified) servo, these will dictate to what POSITION the servo will move. Values that indicate a pulse width of greater that 1.5 ms (on the BS2, this is represented by 750) will move the servo output various "distances" away from center one way, while pulse widths less than 1.5 ms will move the servo output various "distances" away from center the other way.
In the case of a continuous rotation (modified) servo, using the "centering" value (again, a pulse width of 1.5 ms which is equal to 750 on the BS2), will cause the servo to stop. Values less than the "centering" value will cause the output shaft to rotate one way, and values greater than the "centering" value will cause it to rotate the other way. In either case, the SPEED will be dictated by the difference between the value used and the "centering" value...greater differences = greater speed.
The "What's a Microcontroller?" text does a much better job of explaining this than my blurb...
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Truly Understand the Fundamentals and the Path will be so much easier...
Post Edited (Tom Walker) : 3/15/2006 2:12:01 PM GMT
C/R will stop at 1.5 ms pulse and rotate in one direction when going low, the other direction when going high.
Where they stop is entirely dependent on when the command is issued and cannot really be easily repeated in software code.
Positional servos never really 'stop' in a true sense, they hold a position. At the 1.5 ms pulse, it will hold at center. From there you go one or the other direction, but the pulse works with the internal feedback link to hold at a new position. If you were to force the rotor to move, it would move back.
Where the hold is can easily be repeated by using the same code.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)
······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
From···· ·Northwest· ·· Indiana-
Where·· the · introverts · stare
at··· there·· ·shoes··· and·· the
extroverts stare at your shoes!
Hi,
I was just curious why the continuous rotation servos have almost doubled in price ($12.95)
www.parallax.com/detail.asp?product_id=900-00008
Thanks
In the past we had a massive (tens of thousands) excess of continuous rotation servos. Excess inventory·is a tremendous risk. Dated inventory has a decreasing inventory value, and accountants want to see it removed from the books quickly. So, we discounted them deeply and below our cost to get them out of our inventory as quickly as possible.
After two years, Mission Accomplished. We're·now·managing normal inventory levels and selling servos for a small profit at the $12.95 price you see.
These are based on Futaba S-148s, by the way.
Sincerely,
Ken·Gracey
Parallax, Inc.