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Old Sep 02, 2009, 09:41 AM
Deniable plausibility
Shedofdread's Avatar
Derbyshire, UK
Joined Aug 2008
2,307 Posts
Question
Twisty wing servos

Hi Everyone,

What servos are people using for twist wing aeroplanes?

I'm in the process of puting together a little (2M) twist wing thing and servo recomendations would be welcomed. I'm thinking digital and really 'play free' mechanicals but which to go for? Also, they can be standard size items.

Thanks for reading and hopefully suggesting,

S
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Old Sep 02, 2009, 10:49 AM
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slopemeno's Avatar
United States, CA, Mill Valley
Joined Jan 2003
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Well, I have two HS-645MG's in my Shredder, which is a pitcheron.

That servo is probably at the upper end of its abilities on 4.8 volts, and at speeds above 100 mph (on radar) it does start to have a bit of lag/hunt. Banging turns on the frontside the'yre great, though. The price is really good considering the specs too.

For my next Shredder I'll want something with pretty massive torque/precision/speed. I'll probably go 6.0 volts too, since the plane needs a ton of noseweight it might as well be in the form of receiver batteries.
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Old Sep 02, 2009, 10:58 AM
TD- F3K- Slope - What to fly?
Dale Thompson's Avatar
Cupertino CA
Joined Aug 2005
1,465 Posts
JR 8717's

196 in oz and .07 speed on 6 volts

snappy!!
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Old Sep 02, 2009, 11:10 AM
Go fast, turn hard
Tailslide UK's Avatar
Berkshire, England
Joined Aug 2006
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For high perfomance FS, go with a minimum of 2X wingspan. For example a 78 inch span would want 156 oz-in on each wing.

Look for digitals with two ball bearings. I prefer karbonite or synthetic gears to metal because of reduced slop. If the choice is nylon or metal, go metal.

Another consideration is your linkage on these type of servos. Us the heavy arms and helicopter type rod ends. There is no point having 200 oz-in of torque if the linkage flexes or breaks at 100.

Finally, make for abloute certain that your battery can handle the current load that two of these servos can impart. Big diameter cells of lower capacity are always better than AA's. Even on 5 cells, AA's can drop too much voltage if a wing binds a little at high G.

Let us know what you do!

Tailslide
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Old Sep 02, 2009, 11:14 AM
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Milwaukee G Mitchell, Wisconsin, United States
Joined Mar 2002
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JR 8611, http://www.horizonhobby.com/Explore/...ArticleID=1450
260 to 280 oz/in of torque

JR 8411, http://www.horizonhobby.com/Products...odID=JRPS8411R
150 oz/in

or for slop free (nylon) gears
JR 8411sa, http://www.horizonhobby.com/Products...dID=JRPS8411SA
150 oz/in
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Old Sep 02, 2009, 12:15 PM
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bcc1955's Avatar
San Mateo
Joined Aug 2004
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I can not imagine needing nearly 200 oz/in torque servos for a 2M. I am running a pair Hitec HS5245s (about 60 oz/in) on my 60" Shrike. I bet even these would work on a 2M if one was seeking to make a lighter weight one. If you want a high wing loading or need more weight to balance anyway then going for larger servos makes a lot of sense. But I think it depends on your application.

I second point. It is standard practice to put very strong servos in pitcherons. When you think about it why is this necessary? I understand that there is a fair bit of mass to the wing but the resistance that needs to be overcome against the wind is probably LESS, since the air itself actually assists the rotation of the wing. I am guessing it is probably needed to hold the entire wing steady during high stress maneuvers like tight fast loops.
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Old Sep 02, 2009, 12:42 PM
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Pacific Palisades, CA
Joined Jul 2004
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Quote:
Originally Posted by bcc1955

I second point. It is standard practice to put very strong servos in pitcherons. When you think about it why is this necessary? I understand that there is a fair bit of mass to the wing but the resistance that needs to be overcome against the wind is probably LESS, since the air itself actually assists the rotation of the wing. I am guessing it is probably needed to hold the entire wing steady during high stress maneuvers like tight fast loops.
Bigger surfaces equal more force against the surface, not less.
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Old Sep 02, 2009, 12:44 PM
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Milwaukee G Mitchell, Wisconsin, United States
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For a TW plane I'd use the largest servos that are appropriate. Bigger servos give more holding power, stronger gears and power to overcome friction or binding.

Flight loads aren't where the servo is likely fail. Landings can sometimes be abrupt and smaller servos with weaker gears might give where a larger ones won't.

For the Vector2's I'm building I'll use one of the three I listed.

davidk
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Old Sep 02, 2009, 12:49 PM
TD- F3K- Slope - What to fly?
Dale Thompson's Avatar
Cupertino CA
Joined Aug 2005
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A Wingeron and a Pitcheron have very different servo loads.

Wingerons are more balanced on the servo load with each wing rotating with opposite loadings ( one goes up while the other goes down)

A pitcheron servo resists what ever twist loading each wing half experiences.
That's where the OMG torque is needed. As the mass of the plane increases and the speeds go up so do the loadings.

A 2M TW plane can weigh up in the 80oz range with Ballast for a big day.

I would want as much horsepower as possible on the wingrod when pulling out of a high speed dive.
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Old Sep 02, 2009, 01:03 PM
I want it to go fast...
c0dem0nkey's Avatar
San Diego
Joined Sep 2006
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The engineer in me wants some sort of equation...

Wing area * wind speed * mechanical advantage / weight = torque

The test pilot in me says...just put somethin in and fly...

I think the Shrike is a good starting point to determine weight and wing span need a what type of servo.

I need help finding servors for

Snipe
Shredder
Spyder

I would be interested if people could chime in on what servos have failed for them in twisty wings.
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Old Sep 02, 2009, 02:44 PM
Yes, ALL your money...
winchdoc's Avatar
A hut in the woods in Oregon
Joined Jan 2003
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I've always wanted better resolution in my TWF linkages. Every time motion in transferred, there is an opportunity for play in they system.
A common weak link is the servos themselves.

First is a good geartrain

My old kitbash hornet rotor has had several different sets of servos over it's lifetime. Each time I would replace a pair of servos, the plane flew better.
This was probably as much new gear trains as it was improved digital amplifiers.


I like those lighter nylon gear servos in my Shrikes.

More's theory (more is better)

I'm running the biggest digital servos I can fit in my performance TWF planes
So far they all seem to work equally well. the airtronics 94258's seem to be the quickest, although the JR DS8711's can follow the stick movement when you 'boink' the springs.

The other thing we want in TWF servos is some sort of holding power, especially for pitcherons, where the servo's performance shows up in ability to hold roll AND pitch headings without perceptable deadband. This is where digital servos get my nod, but with a bad (loose) gear train, the holding power is wasted, and centering is compromised.

Oh yeah, centering. Real important!
Be sure your servos and linkages return to the same zero point when bench flying them.
I mount Robart incidence meters on the surfaces and wiggle the sticks. The Robart meters are accurate enough to show any hysteresis in the control system.


WinchDoc
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Old Sep 02, 2009, 03:37 PM
Deniable plausibility
Shedofdread's Avatar
Derbyshire, UK
Joined Aug 2008
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Wow, thanks everyone for the input.

It may be 2M span but it's only 0.27m2 wing area and the section has a low pitching moment. Roll and pitch will be controlled by wing twist. Also the wing will probably (not decided whether to bother or not yet) be mass balanced.

The conclusion would seem to be digital, as large as practical, double ball race, good centring, fast and probably metal gears.

Indarotor - 80oz!!!!! I think your slope may be a little larger than the one I usually fly at. If it weighs half that I'll be dissapointed.

Thanks again and keep the info coming - I'm sure many will benefit from the input.

S
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Old Sep 02, 2009, 03:54 PM
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Tailslide UK's Avatar
Berkshire, England
Joined Aug 2006
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Thanks for posting more details of the model you are working on. Everything in the thread is spot on. Just remember that when you say pitcheron around here it cojures up a certain image in peoples mind.......

"Start with a solid block of high density Carbon fiber/epoxy matrix. Mill away everything that does not look like an airplane. Add ballast and radio......"



Tailslide
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Old Sep 02, 2009, 04:11 PM
Yes, ALL your money...
winchdoc's Avatar
A hut in the woods in Oregon
Joined Jan 2003
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Quote:
Originally Posted by Tailslide UK
"Start with a solid block of high density Carbon fiber/epoxy matrix. Mill away everything that does not look like an airplane. Add ballast and radio......"

SHHHhhhhhhhh!!!!
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Old Sep 03, 2009, 05:34 AM
Go fast, turn hard
Tailslide UK's Avatar
Berkshire, England
Joined Aug 2006
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iiiiiiiittttttt!

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