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RC Radios, Transmitters, Receivers, Servos, gyros Discussion all about rc radios, transmitters, receivers, servos, etc.

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Old 04-14-2013, 04:22 PM   #1
GaryJ
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Question servo arm travel limits

I'm using 2 dynam micro servos on a 1909 wright military flyer.My concern is that servo arms don't seem to move control surfaces far enough.Don't know how many degrees of travel supposed to get from cunnards or rudder,but what there is seems to be a little shallow to me.Is there any way to extend this travel length?Do all micro servos pretty much travel the same radius?Are there micro servos that travel a longer radius.Is there some kind of linkage set-up that would allow control surfaces a bit more travel?
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Old 04-14-2013, 04:45 PM   #2
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The standard way to increase travel is to use a longer arm on the servo and/or move the pushrod to a position closer in on the control surface horn.

You can also get more movement from the servo if you have a computer tx that allows you to program servo travel.

PS.. the thing at the front is a 'canard' (French for duck because canard planes look a bit like a duck in flight)
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Old 04-14-2013, 05:42 PM   #3
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Longer arm on servo
Shorter horn at control surface

Digital programmable servos... Many can be programmed for 180 deg instead of the standard 100 to 120 deg.

"ATV" (adjustable travel volume... sometimes called endpoints) in computer radios.

The computer radio can be safely programmed to 120% travel (rotational... often about 110% actual response at the surface) with most servos.
Note that Parkzone ultra micro servos can not be pushed past 100% (100% reference is Spektrum DX6,7, 8, 18 default travel) safely.

"full flying" control surfaces (no fixed surface) need appx 1/3 the deflection angle of the conventional fixed + moving control surface. 10 deg (each way) is a lot for a "full flying" Canard such as on a Wright Flyer. The rudders may still need up to 30 deg (each way) available due to being so close to the main wing and CG.
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Old 04-14-2013, 05:48 PM   #4
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and I thought I was smarter than a 5th grader.Ok..spelling lesson noted ( I already knew it meant duck ) I thought longer arms will have to make some and xperiment,thanks
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Old 04-14-2013, 05:52 PM   #5
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Time to dust off the protracters and angle guides
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Old 04-14-2013, 06:04 PM   #6
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Generally with servos - it's best to stay with the standard lengths - why ? Torque and stress on the servo. Micro servos especially cannot take increased loads and strip out very easily.

The Tx EndPoint Adjustment (EPA or ATV as some call it) ... is in my opinion a dangerous item when called to EPA more than 100% ... why ? If you have combined surfaces ie elevons, ailervators etc - pushing EPA to 120% can lead to servo trying to move further when other command made simultaneously. This leads to burnt out servo motors. Ask me how I know !!

The best way is geometry ... moving clevis OUT on servo arm, IN on control surface horn.

My opinions ...

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Old 04-14-2013, 06:12 PM   #7
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We all recognize 90 deg pretty easily... (close enough without even having a corner of a sheet of paper to compare)

Fold that corner of a sheet of paper to get 1/2 the angle... 45
Fold again.. appx 22
Fold again ... appx 10

No tools needed... just a sheet of paper.
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Old 04-14-2013, 10:11 PM   #8
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I have found that a canard type plane, can be very sensitive to surface deflection.

In my case, I had too much movement and I crashed the plane, so be cautious.
The movies of the Wright's plane show the front bouncing up and down so maybe it would be scale flying if a model did that.

Dave R, Proud PGR rider.
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You become a master at repair.
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Old 04-14-2013, 11:08 PM   #9
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Originally Posted by GaryJ View Post
I'm using 2 dynam micro servos on a 1909 wright military flyer.
My concern is that servo arms don't seem to move control surfaces far enough.
Don't know how many degrees of travel supposed to get from cunnards or rudder,but what there is seems to be a little shallow to me.
Is there any way to extend this travel length
?Do all micro servos pretty much travel the same radius?
Are there micro servos that travel a longer radius.
Is there some kind of linkage set-up that would allow control surfaces a bit more travel?
Post #6 +1
A pity Tx model not named but further information is available under:
. EPA, ATV, Dual & Triple Rates, Expo Differences & Caution includes ESC / BEC Set Up. and
. Servo - FAQ : Throw, 100% Tx setting is best, 125% is mechanically poor
and as a last resort:
. Servo - Horn Arm Extension - DIY Alloy, FRP, CF & Nylon

Much more information available under sub sections
"Glitches & Jitter in Receiver, Servo & ESC - Causes and Cures"
"Servo - Alterations, Calculators, Databases, Leads, Repairs, Convert to an ESC or winch & FAQ."
below
"Radio Systems, Accessories, Alterations and FAQ" at
Alan's Hobby, Model & RC FAQ Web Links

Alan T.
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Old 04-15-2013, 12:18 AM   #10
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Re-read the instruction sheet and found where the designers recommend the canard throw to be 7/16ths up and down measured from the leading edge of the canard.Got out a piece of paper,protractor and small angle and drew this full size the way I read this is the canard throw works out to be about 25 degrees.That looks a little steep on paper.Cannot raise leading edge of canard to that degree anyway as the trailing edge would contact the pushrod
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Old 04-15-2013, 12:39 AM   #11
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Originally Posted by A.T. View Post
Post #6 +1
- FAQ : Throw, 100% Tx setting is best, 125% is mechanically poor[/URL]
Alan,

I didn't read that thread entirely that way, here's a quote from one of the better posts in the thread:
By increasing servo throw and using a shorter servo horn and/or longer control surface horn you can increase output force and reduce stress on the servo.
While there are trade off's (arent there always) increasing throw to greater than 100% is often a better option for getting more deflection compared to doing it mechanically with longer arm or shorter horn, because it maximises the force transmitted to the surface and minimises the stress on the servo gear train.

Like most things it needs to be done with some caution and knowledge of the potential pitfalls.
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Old 04-15-2013, 01:58 AM   #12
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Originally Posted by Wildflyer View Post
I have found that a canard type plane, can be very sensitive to surface deflection.

In my case, I had too much movement and I crashed the plane, so be cautious.
The movies of the Wright's plane show the front bouncing up and down so maybe it would be scale flying if a model did that.

As a WWI bipe model flyer, beware wishing for accurate flight characteristics.

Ask me why your DX5e is doomed... and how to fix it.
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Old 04-15-2013, 05:59 AM   #13
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Originally Posted by CNY_Dave View Post
As a WWI bipe model flyer, beware wishing for accurate flight characteristics.
Aint that the truth !!

Nigel

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Old 04-15-2013, 06:39 AM   #14
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Love the Fokker Dr1... but its a beast to fly.
Even the "tamed" versions sold as ARFs can be a challenge.

If you want it to look scale... its going to get some of the habits of the full scale.
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