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Big servo for use in Elevator Trim Tab Ultralight Airplane

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Big servo for use in Elevator Trim Tab Ultralight Airplane

Old 07-01-2011, 01:33 PM
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Isaac F
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Default Big servo for use in Elevator Trim Tab Ultralight Airplane

Hello Guys,

I am looking for a BIG servo that I can use for a Elevator Trim Tab on a Ultralight Airplane.

One thing that I need is that when the servo move to the position I want, it keep and hold the trim tab in the position I want it (something like the way a Digital Servo work) but without having to keep giving power to the servo

Any ideas or advice?

THX

Isaac
Old 07-01-2011, 06:17 PM
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pkoury
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Default RE: Big servo for use in Elevator Trim Tab Ultralight Airplane

The servo will draw power to remain in the position you want wheter it is digital or not, in fact the digital servo will draw more power. If the servo does not have power then it can be moved by external forces.
Old 07-02-2011, 08:37 AM
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Default RE: Big servo for use in Elevator Trim Tab Ultralight Airplane

I would update my life insurance policies prior to this attempt !

Certainly there are some RC servos with some impressive torque numbers but they are not and never were intended for craft your size, - even if it does qualify as an "Ultralite".
You will also require the control mechanism which routinely is a Tx and Rx set .

NOT recommended for man carrying craft . BUT, it's your neck.

Old 07-02-2011, 09:15 AM
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Default RE: Big servo for use in Elevator Trim Tab Ultralight Airplane

The Seiko PS-050 deliver almost 1000 oz-in of torque on 12 volts. It will continue to draw some current even when the surface has finished moving. I suspect the holding current would be less than one Amp. This current would depend upon how much pressure is being applied to force the servo back. You'd have to find a servo with a worm gear in order to minimize the current draw in the "holding" position. The R/C field does not typically use any worm-gear servos, but maybe someone else would chime in here.

Have you calculated the force needed to move and hold the trim tab? I suspect it is a lot less than people (e.g. previous poster) think.
Old 07-02-2011, 10:36 AM
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Default RE: Big servo for use in Elevator Trim Tab Ultralight Airplane


ORIGINAL: DMcQuinn

The Seiko PS-050 deliver almost 1000 oz-in of torque on 12 volts. It will continue to draw some current even when the surface has finished moving. I suspect the holding current would be less than one Amp. This current would depend upon how much pressure is being applied to force the servo back. You'd have to find a servo with a worm gear in order to minimize the current draw in the ''holding'' position. The R/C field does not typically use any worm-gear servos, but maybe someone else would chime in here.

Have you calculated the force needed to move and hold the trim tab? I suspect it is a lot less than people (e.g. previous poster) think.



_____________________________________________

This has nothing to do with it !

There are untold numbers of Ultralights in the world and I'm quite certain that a simple mechanical trim mechanism
has long been available .
Similar to the ones we used in WWII .

You may also drive a nail with a shovel . It simply is the incorrect tool .
Ditto here .
Old 07-02-2011, 11:09 AM
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Default RE: Big servo for use in Elevator Trim Tab Ultralight Airplane

Using a servo to set the trim tab is not a new application. I saw one installed on a homebuilt more than 20 years ago.
Take a look at Servo City (Google for URL). They have many special servos that could be used for this. I am considering one to use to apply the brakes on my towed vehicle from my motor home.
Old 07-02-2011, 11:37 AM
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Default RE: Big servo for use in Elevator Trim Tab Ultralight Airplane

ORIGINAL: dirtybird

Using a servo to set the trim tab is not a new application. I saw one installed on a homebuilt more than 20 years ago.
Take a look at Servo City (Google for URL). They have many special servos that could be used for this. I am considering one to use to apply the brakes on my towed vehicle from my motor home.
________________________________________

And I repeat: It was the wrong tool then and it is the wrong tool now !

What you saw 20 years ago means what ?
Simply a half baked solution then and it still is .
Old 07-02-2011, 12:44 PM
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Rodney
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Default RE: Big servo for use in Elevator Trim Tab Ultralight Airplane

A much more reliable and simple solution is just a motor activated jack screw with limit stops. You power it up (selective polarity for direction of travel) to move it; remove power and it stays where you left it. You can use a very small (weak motor) and with the proper screw pitch you can power almost any size surface.
Old 07-02-2011, 01:56 PM
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Default RE: Big servo for use in Elevator Trim Tab Ultralight Airplane


ORIGINAL: Rodney

A much more reliable and simple solution is just a motor activated jack screw with limit stops. You power it up (selective polarity for direction of travel) to move it; remove power and it stays where you left it. You can use a very small (weak motor) and with the proper screw pitch you can power almost any size surface.
__________________________________________

Now, that's more like it !
Old 07-02-2011, 02:33 PM
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Default RE: Big servo for use in Elevator Trim Tab Ultralight Airplane


ORIGINAL: onewasp


ORIGINAL: Rodney

A much more reliable and simple solution is just a motor activated jack screw with limit stops. You power it up (selective polarity for direction of travel) to move it; remove power and it stays where you left it. You can use a very small (weak motor) and with the proper screw pitch you can power almost any size surface.
__________________________________________

Now, that's more like it !
And that, is a simple servo.
Old 07-07-2011, 05:22 PM
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dirtybird
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Default RE: Big servo for use in Elevator Trim Tab Ultralight Airplane

A motor with a jackscrew is an open loop servo. If you were to use it in an aircraft you would quickly decide it is unsatisfactory, just as the modeling community did. Our early reed system used open loop servos for elevator trim. They proved hard to use, A closed loop servo is much easier to use.
If you are afraid of the reliability of model servos, get one designed for UAV's. It will cost you a bit more though.
Old 07-08-2011, 05:36 AM
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Default RE: Big servo for use in Elevator Trim Tab Ultralight Airplane


ORIGINAL: dirtybird

A motor with a jackscrew is an open loop servo. If you were to use it in an aircraft you would quickly decide it is unsatisfactory, just as the modeling community did. Our early reed system used open loop servos for elevator trim. They proved hard to use, A closed loop servo is much easier to use.
If you are afraid of the reliability of model servos, get one designed for UAV's. It will cost you a bit more though.
Exactly what you want for this, open loop. You are the feedback loop in such device, you stop the input when the trim is where you want it. The KISS principle.
Old 07-08-2011, 01:40 PM
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Default RE: Big servo for use in Elevator Trim Tab Ultralight Airplane


ORIGINAL: dirtybird

A motor with a jackscrew is an open loop servo. If you were to use it in an aircraft you would quickly decide it is unsatisfactory, just as the modeling community did. Our early reed system used open loop servos for elevator trim. They proved hard to use, A closed loop servo is much easier to use.
If you are afraid of the reliability of model servos, get one designed for UAV's. It will cost you a bit more though.
__________________________________

You have taken "servo' to a new level. We were talking about RC MODEL servos.
Any driven mechanism is a "servo" the discussion was about the use of an RC model servo !

In short you are talking in circles as the suggestions have to do with reliability not whether or not it could be defined as a servo.

The point is a "model servo" is NOT a reasonable choice . It wasn't at the beginning and it isn't now .
Old 07-08-2011, 03:01 PM
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Default RE: Big servo for use in Elevator Trim Tab Ultralight Airplane

The Seiko servo is a model servo as well as a UAV servo. See troy built models.
The trouble with a jackscrew open loop servo is you never know where it is unless you include a mechanism to read its position. Then you are very close to a closed loop servo. You might as well complete the loop as the electronics to complete the loop are well developed and practically failure proof.
With the open loop servo and no position indication you could get into serious trouble. It would be like flying a new aircraft for the first time every time you take it off.
Old 07-08-2011, 05:15 PM
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onewasp
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Default RE: Big servo for use in Elevator Trim Tab Ultralight Airplane

Strange, we used your, 'non indicator type' through WWII and much of Korea on trim tabs.
We were so dumb we were happy when we felt what it was we were after . No indicators needed !
Apparently we had much more sensitive 'arses' then .

BTW, UAV's like RC models have no passengers soooo I really do not feel that is is anything of note .
Today the FAA calls them sUAS .

Old 07-08-2011, 05:56 PM
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Default RE: Big servo for use in Elevator Trim Tab Ultralight Airplane

ORIGINAL: onewasp

Strange, we used your, 'non indicator type' through WWII and much of Korea on trim tabs.
We were so dumb we were happy when we felt what it was we were after . No indicators needed !
Apparently we had much more sensitive 'arses' then .

BTW, UAV's like RC models have no passengers soooo I really do not feel that is is anything of note .
Today the FAA calls them sUAS .

Right, they were used when we did not have the technology for better systems. They were also a cause for accidents.
Old 07-11-2011, 06:25 AM
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Default RE: Big servo for use in Elevator Trim Tab Ultralight Airplane

http://www.aircraftspruce.com/catalo...anstrimsys.php
Old 07-13-2011, 06:05 AM
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Default RE: Big servo for use in Elevator Trim Tab Ultralight Airplane

This would work well. I made this jackscrew drive for retracts for a 1/4 scale FW190. Made from an electric screwdriver using the planetary gear system for reduction, then going into an 8-32 screw driving a brass dog.You would only need a switch in the cockpit to drive it. For flight, set the surface to neutral before you take off. Stick load will tell you where you are. Much of the mechanism can be eliminated as the micro switches on the ends are for the stops for the retracts.The aluminum plate is off the side to show the mechanism.
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