[dorkbotsea-blabber] Looking for help with a motor controller circuit (or a cheap full-rotation servo)

[Eddie Lloyd]

Is there a possibility I could get my email address REMOVED from this list?
I keep getting email after email about robot parts. BORING.

-E

On 5/15/07, claude <bronzenose at hotmail.com> wrote:
>
> I am working on a sculpture in which 25 to 100 rotating robot heads will
> watch passers by.  I have finished a preparatory sculpture with four heads
> which watch TV, you can see it here (1 minute long):
> http://www.youtube.com/watch?v=1cCMXl3k1sA
> That one used hobby R/C servo motors and a phidget controller.
> The problems I need to fix for the next sculpture are:
>         (1) Hobby servos (generally) turn only up to about 180
> degrees*.  I
> need more than, say, one and a half complete revolutions, but preferably
> arbitrarily many revolutions /without losing absolute positioning/**.
>         (2) I need to control many, many more devices.
>
> Buying something pre-built would be ideal - any suggestions?
>
> Failing a pre-existing solution, I found a cheap (about $7) DC motor
> w/gearhead and encoder***.  What would it take to build my own servo
> controllers?  I figure I'd need:
>         a) A reversible motor controller
>         b) Something to keep track of the signals from the encoder
>         c) Something else electromechanical to occasionally detect the
> absolute orientation of the output shaft (a switch and an index on the
> output shaft at "zero" degrees?)
>         d) Some logic to coordinate those three functions and accept an
> input for the desired position.
>
> This seems complex to my level of electronics knowledge but it also seems
> like the sort of standard circuit that must be designed and redesigned
> over
> and over every week.  Can you point me at a ready-made circuit I can
> reuse,
> or can you help me cobble something together?
>
> Ultimately the whole shebang will probably be controlled by a PC or a PIC
> microcontroller (so long as I get the hang of the demo board).
>
> Any pointers appreciated.
>
> Thanks in advance,
>
>
>
> Claude
>
> PS -- tips on locating multiple humans in a horizontal plane at distances
> of
> 6" to 10' also appreciated.
>
>
> * I found sail winch servos from HiTec which rotate 3.5 times for about
> $50
> which seems a bit spendy, or from GWS for $20 which will rotate once, only
> once isn't really enough -- I don't want the heads to have to whip back
> mid-turn while watching someone walk around the sculpture.  It seems
> obvious
> to rearrange the sculpture so it doesn't need more than 180 degrees of
> rotation but it is important that it be "in the round".
> ** gearing up the output from a standard servo is also a possibility but
> between the price of the gears, shafts and housings and the labor to
> assemble it all it seems like an expensive way to get a low resolution
> limited rotation compromise.  tips in this direction would also be
> appreciated, though.
> *** 6v 20mA, 2-channel encoder 1 cycle per motor rotation, 141:1 gearhead
> on
> output
>
> http://maximumrobotics.com/store/index.php?main_page=product_info&products_i
> d=98
>
> ........................................................................
> .........dorkbot: people doing strange things with electricity..........
> ..........................http://dorkbot.org............................
> ........................................................................
>



-- 

Any man's death diminishes me, because I am involved in mankind, and
therefore never send to know for whom the bells tolls; it tolls for thee.
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