High Resolution: A few questions about servo precision - RC Groups
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Apr 06, 2017, 07:34 PM
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High Resolution: A few questions about servo precision


Hi!

So Hitec's air Tx units in 7, 8 & 9 now broadcast to 4096 samples end-to-end. Those are pretty decent gimbals! (Here I was, totally happy with Futaba's 8U giving me more than 500 samples on either side of center - if the servos were precise.)

One.... If... I'm using the 9X, and broadcasting to a Maxima Rx with Hitec digital servos, what can one expect for precision, for actual delivered servo positions - 4000+?

Two.... What sort of servo precision can one expect from a Spectra module (now in my 8U) through an Optima 6?

Three.... What range of servos will deliver the best resolution/precision with my 8U's Spectra & Optima 6?

Thanks for your thoughts!

Ran
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Apr 07, 2017, 01:47 PM
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Angular Precision, Accuracy , Total Travel & Deflection Error


By way of update re servo resolution:

I can not find anywhere a manufacturer's statement of potential angular precision nor of angular accuracy. (Precision and accuracy - related but different metrics.)

One can find "deadband" sure... a related metric, though not the same thing. Surely a 1 or a 2Ás servo is potentially more precise than one who's deadband is 8Ás? Tells us a lot about the electronic control, though in meaning, that's like describing "intent" in response to a question about "action."

Not only are those missing, but try and find a statement of full angular travel?

Then there's deviation under load - let's call it 'deflection error'. Digital servos are far less susceptible than analog here - but no numbers, no curves...

So I go and look at the specs published on a $3 feather servo from Hong Kong - nice! digital! coreless! 2Ás deadband! Uh-huh. It's a three dollar servo. In the real world, just how many angular positions will this puppy hold over its full travel, and at what loads? Over what travel? And over how many cycles?? Sure, for a park flyer or a fun plane, hey! It's three bucks!

(This goes to another reason why I now appreciate name-brand equipment, even at three times the price, especially on planes I want to keep - a discussion for another day. Right. Where were we? Ah, yes... )

Servo angular precision and accuracy, total travel, deflection error and service life. Experience tells yours truly that one can expect far better performance in these metrics with a Hitec (or Futaba, etc.) than one can from a 'bargain' servo with similar published specs - but just try and get some actual numbers!? (Hey, we didn't even ask about servo arm slop due to gear-fit tolerances. )

Cheers guys!

Ran
Apr 12, 2017, 10:55 AM
Team Hitec, Customer Support
Xpress..'s Avatar
To simplify this all for you:

Our newest systems are capable of operating at 4096 resolution, or 4096 steps total. That does not mean that your servo will travel a full 4096 steps, the servo itself dictates what resolution you will actually see. Most digital servos are 1024 steps (analog 512), higher resolution digital servos are 2048 steps, and our D-Series, 8XXX, and 9XXX series digitals are all a full 4096 resolution.

Our brushless 9XXX series servos have a deadband of 0.008Ás, so you will see very close to 4096 steps in its total travel.

Your Spectra module has a max resolution of 2048 with Optima series receivers, any of our 7XXX series servos (I.E. HS-7955TG, HS-7950TH, etc.) will match it perfectly, though you can use any of our higher end servos and still see the same resolution.
Last edited by Xpress..; Apr 13, 2017 at 03:46 PM.
Apr 13, 2017, 01:37 PM
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Originally Posted by Xpress..
To simplify this all for you:

Our newest systems are capable of operating at 4096 resolution, or 4096 steps total. That does not mean that your servo will travel a full 4096 steps, the servo itself dictates what resolution you will actually see. Most digital servos are 1024 steps (analog 512), higher resolution digital servos are 2048 steps, and our D-Series, 8XXX, and 9XXX series digitals are all a full 4096 resolution.

Our brushless 9XXX series servos have a deadband of 0.008Ás, so you will see very close to 4096 steps in its total travel.

Your Spectra module has a max resolution of 2048 with Optima series receivers, any of our 7XXX series servos (I.E. HS-7955TG, HS-7950TH, etc.) will match it perfectly, though you can use any of our higher end servos and still see the same resolution.

Real eye opener!! That is great performance, and the kicker is the fair price, backed-up by a lot of available spare parts. (I was surfing through Tower's Hitec servo inventory. I felt like a kid in a candy shop.) I hope I don't sound like a sales guy here. I make my living in industrial design.

Hearing that the Spectra-Optima set-up, driving 7XXX servos has fine resolution is interesting - and much better than I had expected. It could be a real selling point for the system. That's a thousand points either side of center. Boggles.

Thanks Xpress! Most appreciated.

Cheers!

Ran
Last edited by Xpress..; Apr 13, 2017 at 03:46 PM.