[NSRCA-discussion] SD-10

Tue Aug 25 12:02:18 AKDT 2009

Measuring the latency has already been done by the heli groups. I fly  
a fair amount of heli also and follow the heli forums. I don't really  
remember the results as I do believe it is all down in the noise  
anyway. But I'm sure if you did a search on RunRyder or HeliFreak you  
can find the info.

Tony

On Aug 25, 2009, at 8:14 AM, John Pavlick wrote:

> Yes I understand that. I guess I oversimplified a bit. I was  
> assuming that their tradeoff decision took into account the frame  
> rate of the data. As you know, you can get more bits at a slower  
> frame rate or have a higher frame rate with less bits - given a  
> fixed bandwidth. As all servos are now pretty fast, it would seem  
> that increasing the frame rate would work in your favor AND make the  
> control system more responsive, especially in a Pattern setup. A  
> "fast" servo that is being updated with a position signal at a  
> "slow" rate is not a good thing.
>
> I remember when PCM was becoming popular, a few guys took some  
> measurements of the different systems (Futaba, JR, etc.) comparing  
> frame rate, resolution, latency, etc.. This was really interesting  
> stuff. Now that we have 2048 resolution and 2.4GHz systems in  
> widespread use, I think it's time we did this again. :)
>
> John Pavlick
>
> --- On Tue, 8/25/09, Anthony Frackowiak <frackowiak at sbcglobal.net>  
> wrote:
>
> From: Anthony Frackowiak <frackowiak at sbcglobal.net>
> Subject: Re: [NSRCA-discussion] SD-10
> To: jpavlick at idseng.com, "General pattern discussion" <nsrca-discussion at lists.nsrca.org 
> >
> Date: Tuesday, August 25, 2009, 10:12 AM
>
> 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
>>
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