>
> Andy Kunz answers me:
> > I make a living driving these servos, believe it or not.
> >
> > Center on "new" Futaba servos (connector on servo is a female) is 1500uS,
> > with other limits at 1000uS and 2000uS.  Don't know where he came up with
> > 1520.
>
> My servos are the "new" ones.
>
> I must be misunderstanding how these servos are supposed to work.
>
> Unless I've misinterpreted you, you're saying that the 1ms-2ms pulse
> width range is where the servo has linear response.  I thought that it
> was the whole range of the shaft (i.e. just over 180 degrees).  For my
> application[*], I don't care too much about linear response, but I do
> care about having a large range of motion.  Can I feed the servo my
> over- and under-sized pulses, or do I have to add some gearing to avoid
> harming the servo?
>
I would also like to know the answer to this question.  I have
always been told that most servos have 90 degrees of rotation
(except for the ones mentioned below), and that I should stay
within the 1-2ms spec.  I assumed that giving them out of spec
signals was not a good idea.

> I also figured the "center" was the middle of the shaft's output range,
> but you're saying that the center is wherever the shaft is when you're
> feeding the servo 1500uS pulses (which, since the output is linear in
> the 1000uS-2000uS range, is the midpoint of the linear range).
>
> Thanks for the help,
> Brian
>
> [*] For what it's worth, my application is a camera platform with two
> servos mounted at 90 degrees to each other (left-right and up-down).  I
> can put the camera against a wall so that there's nothing behind it,
> but I still want it to be able to look all the way to the left and
> right, so I need a full 180 degree range of motion.
>
I do robotics research and I need greater than 90 degrees of
rotation on my servos.  I found one commercial servo that has
170 degrees of rotation: the Airtronics 94739 proportional
retract servo.  There are also sail winch servos that have
rotations of multiple revolutions, but their positional
accuracy is poor (they add internal gearing to get more rotation).
I have been told that many connercial servos can be modified
to achieve a greater than 90 degree rotation.  The people at
FMA Direct will modify their servos to do 160 or 180 degrees
(depends on the servo) for an extra $10--a great deal since
their servos are less expensive than most anyway (the nature
of the modification is "a change to the amp").  I haven't
purchased any yet, but I probably will in the near future.
You can contact FMA Direct at:

FMA Direct
9607 Dr Perry Rd - Unit 109
Ijamsville, MD 21754
Email fmadir@fmadirect.com
Sales (800) 343-2934
Technical service (301) 831-8980
Fax (301) 831-8987
http://www.fmadirect.com/


Keith

Keith D. Kotay
kotay@cs.dartmouth.edu
http://www.cs.dartmouth.edu/~kotay