[NSRCA-discussion] Futaba and pattern ( A plus for Futaba)
Earl Haury
ejhaury at comcast.net
Sun Dec 23 13:16:50 AKST 2007
Jim
Valid point if it's actually providing hysteresis. I haven't looked at it with a scope and wonder exactly what these settings are doing. Initially, a setting of 3 or so seemed more comfortable - now I prefer the lowest number and really dislike anything else. (The higher setting gave a "feel" similar to a 9ZAP - the lower setting seems tighter.)
Earl
----- Original Message -----
From: James Oddino
To: NSRCA Mailing List
Sent: Sunday, December 23, 2007 3:21 PM
Subject: Re: [NSRCA-discussion] Futaba and pattern ( A plus for Futaba)
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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