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[DPRG] Continuous rotation servo question

Subject: [DPRG] Continuous rotation servo question
From: Paul Bouchier bouchier at classicnet.net
Date: Sun Feb 6 20:24:30 CST 2011

Thanks to those who responded. It does not have a zero position adjustment
screw that I can find. I will try hobbypartz online chat support. I read the
sail winch comments, but to my mind, a servo which has say a 3-turn limit
from max to min pulse width is not a continuous rotation servo, so I
believed the label and assumed the sailors were doing something else as
well. Like maybe a boom angle feedback. Silly me. I'll let y'all know what
hobbypartz says it's supposed to do.

The reason I wanted to buy one is that I'm busy building the robot that's
part of our upcoming series of talks on how to use cheap or free tools to
build things out of electronics, firmware and mechanics. I was thinking we'd
offer to go buy a kit of parts for people who are interested in building the
project (which can readily be repurposed into any number of other projects).
Doesn't look like I've got a proven source for continuous rotation servos.
Maybe I will have to take Jose's suggestion & spend 10 minutes reading
Dale's excellent tutorial on the subject, then 2 hours doing it.

Happily, Doug lent me some continuous rotation servos, and they work like
they should, so I'm still in the ball game. However, the kit of parts might
need Randy's link.

Thanks everyone for confirming that I'm not crazy or ignorant - it shouldn't
be acting the way it does. 



> -----Original Message-----
> From: dprglist-bounces at dprg.org 
> [mailto:dprglist-bounces at dprg.org] On Behalf Of paradug
> Sent: Sunday, February 06, 2011 10:56 AM
> To: dprglist at dprg.org
> Subject: Re: [DPRG] Continuous rotation servo question
> Paul,
>   Does the servo have a small hole in the side that you could 
> insert a small 
> screwdriver? .  Some continuous rotation servos have a zero position 
> adjustment screw.
>  Also try hobbypartz's online chat support to see if they can 
> help. I have 
> had good luck with EXI servos and hobbypartz In the past, 
> though I have 
> never used the B1226.
>  Regards,
> Doug
> --------------------------------------------------
> From: "Paul Bouchier" <bouchier at classicnet.net>
> Sent: Sunday, February 06, 2011 9:49 AM
> To: <dprglist at dprg.org>
> Subject: [DPRG] Continuous rotation servo question
> > Does anyone know about these beasties?
> >
> > I understand how it works when you modify a regular servo to 
> > disconnect
> > the
> > sense pot from the output shaft, and you set up the sense 
> pot so that 
> > 1.5ms
> > input pulse holds it stationary, and if you give it say 
> 1.4ms it goes
> > continuously in one direction, and 1.6ms sends it 
> continuously in the 
> > other
> > direction, 1.7ms the same but faster.
> >
> > I bought a "continuous rotation servo" from hobbypartz - 
> the EXI B1226 
> > http://www.hobbypartz.com/12exiseb1.html
> > and it works differently. It looks like it's seeking to a 
> spot when I 
> > increase the pulse width: it lurches clockwise then stops with each 
> > increment of pulse width. Then when I start decrementing 
> pulse width 
> > it lurches counterclockwise then stops each time I decrement pulse 
> > width. When it reaches minimum pulse width I reset the 
> pulse width to 
> > 1.5ms and it does
> > about 2 turns clockwise then stops. It's almost as if it 
> has a delay and 
> > the
> > servo is driven by the difference between current input and 
> a delayed
> > version of current input. I can't even imagine how you 
> would use such a
> > thing. Or do you think it's faulty? (2 units do the same thing.)
> >
> > Are there different styles of continuous rotation servos? 
> If so, what
> > should
> > I look for to get one that is stopped at 1.5ms pulse width, 
> and goes one
> > direction for pulses longer than 1.5ms, and the other 
> direction for pulses
> > less than 1.5ms?
> >
> > (I'm looking to buy one - don't have time to make one.) Parallax &
> > sparkfun
> > both have "continuous rotation servos" but I don't want to 
> get burned 
> > again.
> >
> > Thanks
> >
> > Paul
> >
> >
> > _______________________________________________
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> > DPRGlist at dprg.org http://list.dprg.org/mailman/listinfo/dprglist
> > 
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