I know how to drive a servo using PWM.  My question is how does
the servo work internally?  Is it a DC motor?  I presume there
is some sort of active driver inside to perform the feedback
function and interpret the PWM.  Does anyone know the history
of development of these devices e.g. why did they settle on this
1-2ms pulse thingy?  Just curious...

> From: Clyde Smith-Stubbs <clyde@HTSOFT.COM>
> Thus spake Jean-Francois Joly (jolyal@CAPITALNET.COM):
>
> > But the PIC can supply enought power to send pulses to the pulse pin?
> > And then I can connect the power and ground pin to a battery or something?
>
> Yes, the servo can be run off the same 5V supply you use for the PIC. It needs
> 4.5V-6V as a rule.

Would one have problems with commutator noise etc?

>
> > Can the TS-51 be easly converted so it can fully rotate? (365 degrees)
>
> No standard servo can rotate more than 270 degrees, most are only
> set up to rotate a maximum of 180deg, and normally only about 90deg
> of this is used. The fundamental limit is that the feedback pot
> inside is coupled directly to the output shaft, and the pot has
> an carbon element with a maximum range of 270deg.
>
> You can get things called "sail winch" servos that will rotate multiple
> times. I don't know if they are directly compatible with standard
> servos for control. I assume they drive the feedback pot via a reduction
> gear.

Perhaps some units 'gear the pot down' as you intimate so one can
achieve several output rotations for one pot rotation.  This would be
useful for screw drives (ever sat in a 747 and watched how the flaps
are extended?  Reminds me of a lathe leadscrew, sounds like a windscreen
wiper motor is driving it!).

Regards,
SJH
Canberra, Australia