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Old 12-09-2016, 09:35 AM
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Well this thread has officially stopped me from buying new savox1270 for my 73" laser ! Lol
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Old 12-09-2016, 09:41 AM
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Only Amateurs Measure First
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Im going to try NX588 servos on my 30cc plane.

The spreadsheet uses a simplified version of the true math required. I spent some time running out the physics myself and came up with 90oz-in for a 30cc plane doing IMAC flying. This takes into effect the lever arm effect of the control surface and several other factors that are not included in the spreadsheet. The spreadsheet gave me 50 oz in for the same scenario and recommends to double so 100 vs 90 is pretty close.
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Old 12-09-2016, 10:00 AM
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Another, and just as important, factor is geometry of linkage. The further away from servo center the weaker the servo is, the opposite for the surface horn. I typically can stay within the first inch of a servo horn and use the control surface to get distance of throw. Sometimes, on scale builds, I will even use a reducing or enlarging bell crank. This part is all about leverage.
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Old 12-09-2016, 10:03 AM
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Gimmie the sticks-I'll fly it.
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Quote:
Originally Posted by acerc View Post
Another, and just as important, factor is geometry of linkage. The further away from servo center the weaker the servo is, the opposite for the surface horn. I typically can stay within the first inch of a servo horn and use the control surface to get distance of throw. Sometimes, on scale builds, I will even use a reducing or enlarging bell crank. This part is all about leverage.
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Old 12-09-2016, 10:15 AM
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I wonder if this project would pass FAA inspection?
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Old 12-09-2016, 10:49 AM
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I wonder if this project would pass FAA inspection?
Being as I learned a lot of my linkage technique's from full scale I would assume so.
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Old 12-09-2016, 11:07 AM
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I ment, using rc grade servos and radios to fly a full scale from the cockpit.
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Old 12-09-2016, 11:14 AM
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Quote:
Originally Posted by KC0PPH View Post
Im going to try NX588 servos on my 30cc plane.

The spreadsheet uses a simplified version of the true math required. I spent some time running out the physics myself and came up with 90oz-in for a 30cc plane doing IMAC flying. This takes into effect the lever arm effect of the control surface and several other factors that are not included in the spreadsheet. The spreadsheet gave me 50 oz in for the same scenario and recommends to double so 100 vs 90 is pretty close.

That's good info I have these xq4013 I was hesitant to use cause they are only rated at around 200oz and the plane calls for 250 but I'm going to try them anyway , they seem pretty decent really!
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Old 12-09-2016, 11:58 AM
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Quote:
Originally Posted by KC0PPH View Post
Im going to try NX588 servos on my 30cc plane.

The spreadsheet uses a simplified version of the true math required. I spent some time running out the physics myself and came up with 90oz-in for a 30cc plane doing IMAC flying. This takes into effect the lever arm effect of the control surface and several other factors that are not included in the spreadsheet. The spreadsheet gave me 50 oz in for the same scenario and recommends to double so 100 vs 90 is pretty close.

Are you willing to share that math? I'd like to take a look....

One think to note in the spreadsheet is the author said to double for analogs. Its old (10+ years) and I dont remember where I got it from. maybe that old "geistware" website that had all kinds of tools.
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Old 12-09-2016, 12:21 PM
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The one I posted shows the math on that page. Make note of it's description of shortening the servos movement such as end point or dual rate. That is also why I use linkage geometry to obtain the throw without shortening the servos travel.
http://www.mnbigbirds.com/Servo%20To...0Caculator.htm
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Old 12-09-2016, 02:56 PM
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Why would this thread deter you from 1270s??
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Old 12-09-2016, 03:47 PM
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Now taking maneuver requests!
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While I fully agree with the correct flying style the servo torque used by some today is totally unnecessary.

Over all though it doesn't hurt to go ahead and buy 500 in/oz servos for a 30cc plane. My reasoning for this once you get into planes of that size 75+ of people just keep buying bigger planes and you won't find the limitations of that servo in any plane you may buy.
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Old 12-09-2016, 07:43 PM
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But you don't actually need 500 until you get up to 35% class rudders. If you fly IMAC pattern only you might never need that much at any scale.

Most guys don't keep just one plane and move their gear, when they get the itch to move up they buy a second plane.

Taken to its extreme this logic would have us putting BLS172s into glow 40 trainers
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Old 12-09-2016, 08:13 PM
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They're get'n lower mate.....
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Quote:
Originally Posted by acerc View Post
Another, and just as important, factor is geometry of linkage. The further away from servo center the weaker the servo is, the opposite for the surface horn. I typically can stay within the first inch of a servo horn and use the control surface to get distance of throw. Sometimes, on scale builds, I will even use a reducing or enlarging bell crank. This part is all about leverage.
Servo does not become weaker......it still produces a given tork at a certain voltage
Only the leverage application is altered
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Old 12-09-2016, 08:24 PM
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Originally Posted by rooman View Post
Servo does not become weaker......it still produces a given tork at a certain voltage
Only the leverage application is altered
And for those that don't understand the leverage principal, weaker fits the bill. Either way it is said the amount of oz-in at the control surface is the same, further from the servo center = weaker on the control surface side!! But I suspect you know what I am referring to and just don't like how I say it.
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Last edited by acerc; 12-09-2016 at 08:29 PM.
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