[NSRCA-discussion] SD-10

Tue Aug 25 07:35:33 AKDT 2009

Ditto on the hanging weight deflection meters..I have them in my field box
for emergencies at the field.  A good laser pointer (Budd) setup will easily
show 0.1 degree at the control surface, and I suspect the digital deflection
meters will as well.  I think having better than 0.1 degree of resolution
matters (and this is easier to do with 2048 as shown in examples previously
given), assuming the rest of the control system (servos, linkages, hinges)
are that good - and if they aren't, then my opinion is fix the servos,
linkages, etc.

My recollection is that the best possible human reaction time in a simple
situation is something like 100 ms, with the average reaction time being
about 200 ms.  This is actual reaction time, not anticipation (you can't
anticipate a wind gust that rocks the wings, but you can anticipate the end
of a rolling maneuver or snap maneuver).  Reaction time in a complex
situation is a different animal because time is required to see, process,
and then react to the situation - ie, a driver may not actually hit the
brakes for a panic stop until 1 - 1.5 seconds after the need arises (the
additional time beyond 200 ms is the processing/analyzing).

Without starting a brand war..there was (is) a very popular radio that is a
little slow in terms of latency (and that could have been adjusted to), but
the latency deviation (minimum compared to average, maximum compared to
average) was pretty severe...and that made the radio unflyable (for me).  I
much preferred a slower radio (or a faster radio) with a narrower range of
max/min latency.  Predictability and consistency in the control system is
very important - even if it is slow, if it is consistent, it can be adapted
too.  With all the changes in radios the past 20 years in terms of
resolution and processing speed (FM to PCM, 512 to 1024, 1024 to 2048, early
2.4 systems, 2.4 add-ons, newest 2.4 systems), I've noticed faster response
and better resolution.

I think the best radios today are all under the previously quoted (Tony)
40-50ms.  It would be interesting to note if that study included an analysis
of max/min latency.  For me personally, when the latency min/max range
exceeds about 20ms, that is the point at which I can notice the
inconsistency (ie, 20-40ms ok, 30-50ms ok, 20-50ms annoying).

Regards,

Dave Lockhart

Team JR 

  _____  

From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Anthony
Frackowiak
Sent: Tuesday, August 25, 2009 10:13 AM
To: jpavlick at idseng.com; General pattern discussion
Subject: Re: [NSRCA-discussion] SD-10

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
<http://us.mc805.mail.yahoo.com/mc/compose?to=nsrca-discussion-bounces@lists
.nsrca.org> 
[mailto:nsrca-discussion-bounces at lists.nsrca.org
<http://us.mc805.mail.yahoo.com/mc/compose?to=nsrca-discussion-bounces@lists
.nsrca.org> ] On Behalf Of Atwood, Mark
Sent: Monday, August 24, 2009 4:19 PM
To: 'nsrca-discussion at lists.nsrca.org
<http://us.mc805.mail.yahoo.com/mc/compose?to=nsrca-discussion@lists.nsrca.o
rg> '
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

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To: 'General pattern discussion' <nsrca-discussion at lists.nsrca.org
<http://us.mc805.mail.yahoo.com/mc/compose?to=nsrca-discussion@lists.nsrca.o
rg> >
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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