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[DPRG] Continuous rotation servo question

Subject: [DPRG] Continuous rotation servo question
From: Dennis Clark dlc at frii.com
Date: Sun Feb 6 17:04:06 CST 2011

Sounds broken to me.  If you set the pot to 1.5mS and vary the pulse 
width you will rotate at some speed until you the pot == location, which 
is never.  You can get about 6 speeds in each direction this way, all 
within about 10% of the center position.  Anything else means that your 
pot must be moving a little with the motor turns.  I'd take it apart and 
check the hack, it sounds poorly done.  The "hack" process is simple and 
VERY well documented on the web.  Just get normal servos and do it yourself.


On 2/6/11 8:49 AM, Paul Bouchier wrote:
> 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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Dennis Clark
TTT Enterprises

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