[NSRCA-discussion] SD-10

Tue Aug 25 06:12:38 AKDT 2009

Some good points, but I must correct a misconception. There is system  
"latency" and then there is servo speed. These are two different  
things. Reduced latency does not make the servo faster. It only very  
slightly reduces the time between stick movement and when the servo  
begins to move. It doesn't make full travel servo speed any faster.  
This is a subtle point but an important one in this discussion.

Also, when I want my control throws measured properly I never use the  
hanging weight devices. They are not accurate enough. I use a 7"  
protractor and pointers on the surfaces. This is much better and lets  
me detect even a single digit of travel adjust.

I still feel that improved resolution is better for pattern flying  
then a slight decrease in system latency. But that is just my opinion!

Tony

On Aug 25, 2009, at 6:40 AM, John Pavlick wrote:

> Good point Jay. Remember, no matter WHAT people say (or would like  
> to have us believe), we live in an analog world. Trying to digitize  
> an "analog" motion is best accomplished with the largest number of  
> bits that bandwidth (and memory) allows. But there's more to our  
> control systems than meets the eye.
>
> One thing to keep in mind is that Pattern setups are almost totally  
> opposite from "3D" setups. Pattern strives for maximum control  
> precision with the least amount of surface travel whereas "3D" does  
> the opposite. What this means is that our linkages are configured to  
> give the servo maximum mechanical advantage. This is like putting a  
> transmission in low gear. You have lots of torque but not a lot of  
> speed. It also means that the "resolution" of the control system  
> (meaning servos and encoding process) does not play as large a part  
> in the total positioning accuracy as it does with a "3D" setup. Not  
> that high-resolution numbers are "bad" - they're certainly not, but  
> in a Pattern setup they're not as important as you might think. If  
> the servo has a 3:1 mechanical advantage over the control surface  
> (as opposed to a "3D" setup which may be close to 1:1) then a 1  
> degree "error" at the servo only gives us .3 degrees at the control  
> surface. Can you even measure that with one of the "standard"  
> weighted-pendulum deflection gages? On the other hand a "slow" servo  
> will become very noticeable in this case. When the servo must rotate  
> to it's extremes while only moving the control surface a slight  
> amount, it will take a noticeably long time if the servo is slow.  
> When you look at the mechanics in detail it becomes apparent that a  
> good Pattern control system could actually compromise on  
> "resolution" and instead look to improve the "speed" + "response".  
> So maybe the Airtronics Engineers hit the nail on the head. I'm sure  
> if you told them to build the BEST control system possible they  
> would throw in 2048 resolution if they could, but in this case they  
> had to make a decision and it looks to me like they made the right  
> one. As long as you're a Pattern pilot anyway. :)
>
> John Pavlick
>
>
> --- On Mon, 8/24/09, Jay Marshall <lightfoot at sc.rr.com> wrote:
>
> From: Jay Marshall <lightfoot at sc.rr.com>
> Subject: Re: [NSRCA-discussion] SD-10
> To: "'General pattern discussion'" <nsrca-discussion at lists.nsrca.org>
> Date: Monday, August 24, 2009, 7:58 PM
>
> A liner, non-digital system such as PPM, has infinite resolution and
> therefore the ultimate "smoothness". I agree, however, that you  
> probably
> can't "feel" a 1/2048 digital step. I suspect that the major  
> improvements
> have been in less latency.
>
> Jay Marshall
>
> -----Original Message-----
> From: nsrca-discussion-bounces at lists.nsrca.org
> [mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of  
> Atwood, Mark
> Sent: Monday, August 24, 2009 4:19 PM
> To: 'nsrca-discussion at lists.nsrca.org'
> Subject: Re: [NSRCA-discussion] SD-10
>
> I'll take a stab, and I'm blind copying Mike Greensheilds (don't feel
> comfortable putting his email out on the list) who is the product  
> manager
> for ATX here in the states.  He may chime in with additional  
> background.
>
> My understanding is that when Sanwa was evaluating speed vs  
> resolution,
> speed was deemed a much more critical factor.  1024 resolution is  
> already to
> the limits of our ability to "feel" any difference where as the
> speed/latency was much more noticable.   Cost does come into the  
> equation
> such that for a $500 radio, they couldn't do both.
>
> 1024 resolution provides better than 1/10deg at 90 deg of rotation.   
> That's
> less than 1/1000" on a 1" servo wheel.
>
> The speed on the other hand is just now approaching our limits of  
> "feel".
> The faster systems clearly feel more connected and are noticable  
> when flying
> Snaps and other rapid input maneuvers and especially flying 3D with  
> the
> helis.
>
> So the choice was to invest in a fast response system with 1024  
> resolution.
>
>
> Does anyone know the tolerances of our servo accuracy?  I'd be  
> curious to
> know how high a resolution they can accurately replicate.
>
> Mike?  Any input from the source?
>
> -Mark
> --------------------------
> Sent from my BlackBerry Wireless Handheld
>
>
> ----- Original Message -----
> From: nsrca-discussion-bounces at lists.nsrca.org
> <nsrca-discussion-bounces at lists.nsrca.org>
> To: 'General pattern discussion' <nsrca-discussion at lists.nsrca.org>
> Sent: Mon Aug 24 15:30:03 2009
> Subject: [NSRCA-discussion] SD-10
>
> Hi Anthony, Jim, Mark , and Others who Responded,
>
>
>
> Thanks for your valuable input. I've read that this radio's  
> resolution is or
> is among the very  fastest; so much so that even digital servos  
> can't keep
> up with it. I understand  that the system is 1024 , but can't help but
> wonder why it isn't 2048. I'm sure I'll get past my  hangup, but would
> appreciate everyone's insight's on that one.
>
>
>
> Thanks,
>
> Frank Imbriaco
>
> _______________________________________________
> NSRCA-discussion mailing list
> NSRCA-discussion at lists.nsrca.org
> http://lists.nsrca.org/mailman/listinfo/nsrca-discussion
>
> _______________________________________________
> NSRCA-discussion mailing list
> NSRCA-discussion at lists.nsrca.org
> http://lists.nsrca.org/mailman/listinfo/nsrca-discussion
> _______________________________________________
> NSRCA-discussion mailing list
> NSRCA-discussion at lists.nsrca.org
> http://lists.nsrca.org/mailman/listinfo/nsrca-discussion

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.nsrca.org/pipermail/nsrca-discussion/attachments/20090825/5b34ef85/attachment.html>