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Old Mar 15, 2010, 05:30 PM
Sink Stinks
Silent-AV8R's Avatar
Orange County, CA
Joined Aug 2004
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I am constantly fascinated by our fixation on speed and torque. The only thing I have ever flown where servo speed was a clear issue was helicopters. I have never flown a fixed wing plane, including precision aerobatic pattern planes or IMAC, where servo speed was an issue for me.

Torque can be interesting. 95% of the time I think we modelers overestimate what we need. In gliders the two most important things are flaps staying put on launch and if needed in a steep dive to come down fast, and elevator, especially is steep dives (high speed). Both issues were real with analog servos, but digitals went a long ways since early on we learned that moving torque and holding torque were two different things. And digital servos were vast improvements on both fronts over analog servos.

I know I still sometimes get amazed thinking that I have 2 tiny JR 241 servos on the V-tail of the molded Graphite. I can do full speed dives and pull out with never an issue. But every time I see those servos I shudder to think what I ask of them!!

But I guess if we can get faster stronger servos in the same size and weight package, then why not?? I've got big planes with servos that do 425 in-oz of torque so I guess I should shut up about torque!!
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Old Mar 15, 2010, 05:35 PM
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Woodstock 1's Avatar
Ireland, County Kerry, Kerry
Joined Dec 2005
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Quote:
Originally Posted by Silent-AV8R View Post
I am constantly fascinated by our fixation on speed and torque. The only thing I have ever flown where servo speed was a clear issue was helicopters. I have never flown a fixed wing plane, including precision aerobatic pattern planes or IMAC, where servo speed was an issue for me.

Torque can be interesting. 95% of the time I think we modelers overestimate what we need. In gliders the two most important things are flaps staying put on launch and if needed in a steep dive to come down fast, and elevator, especially is steep dives (high speed). Both issues were real with analog servos, but digitals went a long ways since early on we learned that moving torque and holding torque were two different things. And digital servos were vast improvements on both fronts over analog servos.

I know I still sometimes get amazed thinking that I have 2 tiny JR 241 servos on the V-tail of the molded Graphite. I can do full speed dives and pull out with never an issue. But every time I see those servos I shudder to think what I ask of them!!

But I guess if we can get faster stronger servos in the same size and weight package, then why not?? I've got big planes with servos that do 425 in-oz of torque so I guess I should shut up about torque!!
You see? If you type long enough, you end up answering your own questions, lol!
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Old Mar 15, 2010, 05:45 PM
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Tuomo, you know, your comments above are why guys have asked me why I did this build thread. Guys said that everyone will question every detail, and even when you respond with exact figures, that may not be good enough for folks.

Well, I have enjoyed the banter here on stuff, but when you asked that question and brought up specific data, I do my research, I know what is going into the ship and why. My rationale may have flaws, but I am using top of the line equipment on a top of the line ship. And you do too it sounds like.

Marc
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Old Mar 15, 2010, 05:47 PM
RIP MC
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United States, CA, Midway City
Joined Dec 2003
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Wouldn't the elevators of our all flying stabs, if designed and pivots in the correct place, put minimal requirements on ele servo torque?

Servo speed is a different issue, faster is really better. Mostly in dip/zoom. Depending on speed and dive angle it could translate to a few meters if everything else were equal. This is figured on a 40m/s terminal speed at 60 degrees, diving for .2-.4 secs.

I think it's even more important in a F3B zoom where speeds are reported at about 70m/s.
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Old Mar 15, 2010, 06:08 PM
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Originally Posted by fnnwizard View Post
Wouldn't the elevators of our all flying stabs, if designed and pivots in the correct place, put minimal requirements on ele servo torque?
That is my understanding too Wiz, but it may not always be the case.

Marc
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Old Mar 15, 2010, 06:34 PM
Daryl Perkins's Avatar
United States, VA, Falls Church
Joined Mar 2007
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Originally Posted by fnnwizard View Post
Wouldn't the elevators of our all flying stabs, if designed and pivots in the correct place, put minimal requirements on ele servo torque?
Ahhh... yes. Even a full flying stab is counter-balanced reducing the required torque. But there lies the problem... Don't assume the designer of your model did it correctly. It's not always an aero guy doing the structure....

D
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Old Mar 15, 2010, 06:48 PM
Sink Stinks
Silent-AV8R's Avatar
Orange County, CA
Joined Aug 2004
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Quote:
Originally Posted by fnnwizard View Post
Wouldn't the elevators of our all flying stabs, if designed and pivots in the correct place, put minimal requirements on ele servo torque?

Servo speed is a different issue, faster is really better. Mostly in dip/zoom. Depending on speed and dive angle it could translate to a few meters if everything else were equal. This is figured on a 40m/s terminal speed at 60 degrees, diving for .2-.4 secs.

I think it's even more important in a F3B zoom where speeds are reported at about 70m/s.

Honestly Tuan, you are telling me that if I gave you a plane with a 0.2 second elevator servo and then one with a 0.16 second servo you would be able to discern a verifiable improvement?
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Old Mar 15, 2010, 06:57 PM
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I know that I couldn't, but I'm sure not a DP (just received & read your interview in AMA last night. Thanks, but too short. )
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Old Mar 15, 2010, 08:06 PM
RIP MC
fnnwizard's Avatar
United States, CA, Midway City
Joined Dec 2003
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Originally Posted by Silent-AV8R View Post
Honestly Tuan, you are telling me that if I gave you a plane with a 0.2 second elevator servo and then one with a 0.16 second servo you would be able to discern a verifiable improvement?
No, of course I wouldn't be able to. Sometimes, I wouldn't even be able to tell if I was +- 3ft from the nail in the landing zone. Daryl would know as I over flew the "nail" at SWC, even when I was right over it .

But, how I got the "few meters" is simple math in a not so simple equation.

In a dive at 40m/s (some good launchers do 50m/s). Assume your servo is .20 sec to 60 degrees.

In the zoom, you need to move say 30 degrees for the dive and another 30 the other way for the pull out all else being the same, the.20 sec servo would cost you 3.46 meters in height on the downside if you were to dive at 60deg. (.10sec*40m/sec*sin 60) when you .think you need to pull out vs. a .10 sec speed servo.

This assumes you move the servo 60 total which probably you don't. It depends on how short your arm is and the linkage of the ele, ect. I just use a total of 60 to keep it simple.

By over diving it would also cost some speed so the zoom would not be optimal as well. But that's much harder to calculate since we don't have drag numbers.

Radio response time will add to this. It all adds up.

Of course the top guys would probably know how to correct for the "slop" and they anticipate... flying ahead of the curve.

Now, given a .20 sec vs .16 sec, I would say few if anyone can tell, but from .20 to .10, even I can tell. Of course underload, it could be well that the .20 servo may end up being faster, I don't know, but that's my next step in testing these suckers.
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Old Mar 15, 2010, 08:18 PM
Sink Stinks
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Orange County, CA
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Originally Posted by fnnwizard View Post
No, of course I wouldn't be able to.
Which is my point. Of course there is a absurd reductionist point at which anyone could tell, but for the range of servo that we commonly use I doubt that most of us can really feel any difference. Some of the top pilots perhaps.

Just because a thing can be measured or calculated does not mean it will have a real world effect.

Human reaction time for college age people averages around 160 milliseconds (0.160 seconds). Keep that in mind when we are thinking about the differences in servo speed of 0.0015 seconds per degree of rotation. (0.1 sec/60 degree = 0.00167 sec/degree 0.20 sec/60 degrees = 0.00333 sec/deg)

This is sort of a fun site. It lets you test your reaction time. Of course there are some other factors like computer speed and Internet connection speed, but still sort of fun:

http://www.humanbenchmark.com/tests/...time/index.php

My 5 test average was 227.6 ms (0.2276 seconds). Just a bit slower than the servos I use need to go a full 60 degrees. Perhaps this explains a lot!!

Here is another with 4 different tests: http://www.reactiq.com/index.php
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Old Mar 15, 2010, 08:45 PM
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United States, CA, San Luis Obispo
Joined Aug 2006
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Without getting too far into this discussion. If you have equipment that makes you feel more confident, then you will fly better. Having said that, I really doubt that any zoom mechanics that can be attributed to a faster servo will net a higher launch. You are trying to get spring-back from the line and a smooth technique will get you a higher launch every time. Some jerky "oops" maneuver will scrub off speed and result in less altitude.
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Old Mar 15, 2010, 08:48 PM
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And thank you Mr. Valdes for that great comment. May wear B/O, but I go with the aero-engineer everytime!

Marc
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Old Mar 15, 2010, 09:02 PM
Sink Stinks
Silent-AV8R's Avatar
Orange County, CA
Joined Aug 2004
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Originally Posted by Avaldes View Post
Some jerky "oops" maneuver......
Aaron has seen me fly so he speaks with absolute authority with this statement!!!

I'm pretty sure I could use a reed radio and not really feel much of a difference But as long as it had a big screen TV on it and lots of bells and whistles I'd be a happy camper for sure!!!
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Old Mar 15, 2010, 09:16 PM
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United States, TX, Weatherford
Joined Nov 2002
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Hey, Marc... If you think folks second guess you on a radio install... try posting a build thread for a model you designed... I can't tell you how many PMs I answered as to "why" this was this way or that was that way... I had one insinuate that I was stupid and the Journey would never fly correctly... I didn't bother to answer that one...

Keep up the good work. Pay no attention to those behind the curtain...

Jack
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Old Mar 15, 2010, 09:35 PM
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Joined Jan 2004
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Jack,

you need to add winglets on your X that will start something

sj
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