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[Roger in France]

Thanks all of you. Very, very helpful......as always on this forum.

Roger in France.

[malcolmfrary]

I followed the link to Prestwich Models, and contacted them.  They very kindly replied (many thanks to Randy Carr), which I have pasted below -

"Malcolm, you can use digital servos anywhere you would normal servos, but you just have include other things with them (about calibrating them, etc.).

I think for boats, it might be a waste of money.  The only benefit would be that the sheer accuracy of positioning the output arm and some performance benefits.  For helicopters and other flying machines that need the best in return-to-center capability and other things like non-linear travel, digital servos are your best bet, if you can afford them.

I actually don't use them in any of my aircraft.  I experimented with them, but couldn't find any direct benefits from using them in the type of flying that I've done."

[cbr900]

All radios are I understand digital proportional, therefore will run any servo with no problems....


Roy

[Tug]

I am thinking somethings afoot here,

digital servo's? are they not the coreless motored ones

and being coreless they must be ac,  derived from somewhere? Yes/ No?

[CAD2]

Tug
No, sorry mate - they aren't the same thing at all ( and God knows, I've been all over the Internet researching this since Roger started this thread!). Think of a digital servo as like a high-frequency version of a "normal" servo, in much the same way as we can buy "normal" and "High-frequency" electronic speed controllers. The signal from the receiver is just the same for both types and so is the motor and gear train; it's the electronic bit in the middle that's different. A digital servo has an extra gubbins inside which takes the slow signal pulses from the receiver and ramps them up to about six times as fast. This makes the servo respond much more precisely to changes in the input signal. You can also program a digital servo to respond in the way you want it to e.g. total travel angle, linearity, centre position etc whereas you're stuck with what you're given with an analogue job. Overkill for model boats, in my humble opinion (if not then why do we have proportional controls?).
A coreless motor - as you say - needs a different input signal to one with an armature. This is a sexily "chopped-up" DC signal which is generated by another electronic gizzmo inside the servo and acts - as far as I can see - rather like an ignition distributor in pointing the current sequentially to different segments of the motor.
There may now be digital servos which also have coreless motors in them, but I'll stick with my cheapo Perkins analogue lump if that's OK with everybody.
CAD2

[Tug]

Thanks for that CAD2,

I was off frequency a bit there  :-\  Tug