[NSRCA-discussion] Futaba and pattern ( A plus for Futaba)

Sun Dec 23 12:21:51 AKST 2007

Earl,

I don't think we want hysteresis.  That would mean we'd have to move  
the stick in the opposite direction to get the servo back to neutral.   
Draw yourself a typical stick position vs. servo position curve with  
hysteresis on an x-y plot and see what happens.  You go up one slope  
but when you reverse stick direction nothing happens until you come  
down the other.  I can't imagine why we'd want that in a control  
system?  Something helicopter guys want?

Jim O

On Dec 23, 2007, at 12:24 PM, Earl Haury wrote:

> Jim O
>
> On the 14MZ, go to system, H/W, Stick Settings and you are able to  
> globally set the Response & Hysteresis for each stick. You might  
> find this easier than using the spline for setting a deadband. (Be  
> interested in the actual pw / bits difference with each setting if  
> you measure it.)
>
> Earl
>
>
>
> ----- Original Message -----
> From: James Oddino
> To: NSRCA Mailing List
> Sent: Sunday, December 23, 2007 12:08 PM
> Subject: Re: [NSRCA-discussion] Futaba and pattern ( A plus for  
> Futaba)
>
> Bob,
>
> I would think that 256 resolution would mask poor stick centering.   
> Think about 3 step resolution. Right, neutral left.  When you select  
> neutral it is always the same unless you move the stick to the  
> extreme where you get right or left.  The problem is you can't trim  
> neutral unless you do it with another channel like folks did back in  
> the reed days.  Move the servo with another servo.
>
> You had many factors affecting trim in your 8 bit system starting  
> with drift in the servos and an AM link that introduced large  
> changes in pulse width to the servos as signal strength changed.   
> You could adjust linkages everyday and not keep up with everything  
> that was fighting you.
>
> So if low resolution masks poor stick centering then more resolution  
> must emphasize it.  This has always bothered me.  I learned long ago  
> that the servos can resolve pulse widths that would appear to be in  
> the servo deadband.  In the early dual rate schemes we had to adjust  
> the neutral if we changed the dual rate setting.  I tried using a  
> servo to do this.  Adjust the pot until the servo didn't move as I  
> switched the dual rate    switch back and forth. Go fly.  Every time  
> I threw the rate switch the trim would change.  Went home looked at  
> it on a scope and sure enough the pulse width was changing.   
> Adjusted it so it didn't and the trim didn't change with the  
> position of the rate switch when I flew.
>
> This week I got a Futaba 14MZ.  I checked the stick centering with a  
> scope.  Not perfect.  Plus or minus a few bits.  Now a bit in a 2048  
> is only about a half of a microsecond change in pulse width to the  
> servo so most folks don't care.  However I found that with the line  
> or spline curve programming of the control sicks I can put in a plus  
> and minus .5% deadband in the stick.  Now the centering is perfect  
> no matter how I return the stick to neutral and I can trim it in .5  
> microsecond increments.
>
> I love this high tech stuff.
>
> Jim O
>
>
> On Dec 23, 2007, at 5:37 AM, Bob Richards wrote:
>
>> Jim,
>>
>> You may be correct, the stick centering depends on the quality of  
>> the stick. But, throw in 256 instead of 1024 resolution, the step  
>> size is now 4 times as much and it would be much more noticeable.
>>
>> Ok, if we were flying the 4 channel Conquest transmitter (cheap  
>> plastic gimbals) with 148 servos (non-ball bearing) in a slow  
>> moving trainer, we probably could not tell the difference between  
>> 256 and 2048 resolution. So, would I be better to fly a Conquest  
>> radio in pattern? That seems to be the type logic I would get from  
>> people that say 256 is "better than most servos".
>>
>> Oops, I forgot the Conquest is an analog radio. No steps  
>> whatsoever. ;-)
>>
>> Bob R.
>>
>>
>> J N Hiller <jnhiller at earthlink.net> wrote:
>> Guys I don’t believe the mechanical stick centering is absolute  
>> enough especially on a somewhat used radio at least on less than  
>> top of the line transmitters. The detent design and pivot bearings  
>> are less than shall we say industrial quality. Bob, I had the roll- 
>> centering problem you described with my super 7 and felt it was due  
>> to stick centering not being equal from either left or right. I  
>> think my 9-C is better but not absolute. I wish I had one of those  
>> little devices that displayed the signal count to verify my  
>> suspicion.
>> Jim Hiller
>> -----Original Message-----
>> From: nsrca-discussion-bounces at lists.nsrca.org [mailto:nsrca-discussion-bounces at lists.nsrca.org 
>> ]On Behalf Of Bob Richards
>> Sent: Saturday, December 22, 2007 3:37 PM
>> To: NSRCA Mailing List
>> Subject: Re: [NSRCA-discussion] Futaba and pattern
>> Ron,
>> All I can say is, I flew the Micropro with every intention of  
>> competing at the '93 NATS with it. I had trimming issues with my  
>> plane that I could not tune out. Some flights would be good, some I  
>> could not trim the plane for level flight (slight roll left or  
>> right). And, yes, I had taken out all the throw I could  
>> mechanically so I had 100% throws programmed into the radio.  
>> Frustrated, I decided to put my 7UAP in the plane, and it  
>> immediately felt good. That is when I decided to do a little  
>> digging and discovered the resolution issue.
>> Whenever I mention that 256 is not good enough, I hear all sorts of  
>> reasons why 256 should be sufficient. Yes, once the stick is moved  
>> away from center, 256 probably is good enough. But when the stick  
>> is at center, the darn servo better go back to the same position  
>> every time. And you need fine resolution at center so the neutral  
>> position can be varied in small enough amouts to arrive at  
>> precisely the desired position.
>> With a slightly worn stick or pot, the neutral position might be  
>> bouncing between two adjacent steps. With 256 resolution, this can  
>> be VERY noticeable. With 1024 or higher resolution, not nearly as  
>> noticeable, if at all.
>> Given the outcome of the '93 season with my old 7UAP, I'm glad I  
>> switched out the radios.
>> Bob R.
>>
>>
>> Ron Van Putte <vanputte at cox.net> wrote:
>> Hmmmm, I never thought of blaming my radio's resolution for my bad  
>> flying.  Let's see now..........
>> Ron Van Putte
>>
>>
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