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Servo torque convension?????

Old 04-04-2004, 08:36 AM
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C 130
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Default Servo torque convension?????

hi all ppl
i had some strange question in mind.
when i read some specs for servos i see torque, but the problem is that it is written some times in units such as (xyz oz/in)
what does this mean ???? does this mean that the servo can apply torque for its rotation equal to xyz oz on each inch square or what
and how can use this fact in my pane calculation. i mean like if i have a servo that operates my rudder for example should I (not should in the have to sense...) but to calculate the required servo torque. i calculate the space or span of my rudder and see how much wieght applied on it or what ????
can any one help
thanx guys
have a nice day
Old 04-04-2004, 09:18 AM
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LesUyeda
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Default RE: Servo torque convension?????

xyz oz inches, means that at 1 inch out from the center of rotation, the servo would provide xyz ounces. At 2 inches out, it would provide 1/2 xyz. At 1/2 inch out it would provide 2 xyz. As far as calculating the amount of torque required for rudder; near impossible. Depends on the size of the rudder, the deflection, the speed of the aircraft at that deflection, and how quickly the tail moves around in response to rudder. Best bet is to look at the recommendations for an airplane similar in size and performance.

Les
Old 04-04-2004, 09:33 AM
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The PIPE
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Default Here are a FEW tips to get you started...

Dear C 130:

The PIPE Here yet again...and those torque figures are NOT so "confusing" when you look at them THIS way...

Imagine you had a servo that can put out 153 ounce/inches, like the big Hitec 5945 digital servo does. That means at a distance of one inch from the center of the servo rotary output post, from a hole on the arm EXACTLY one inch (25.4 mm) from the center of that post, you WILL have a maximum thrust figure of 153 ounces, or just OVER 9-1/2 POUNDS of force from that hole (153 oz/16 oz. per pound).

Now suppose you used a hole on that same servo arm that was only 3/4ths of an inch from that same center of rotation...you would NOW multiply 153 oz. times the RECIPROCAL of 3/4ths (1/ (3/4)), which you can figure out with the Windows calculator (in the "Scientific" mode) by dividing 3 by 4, and than clicking on the button marked with the "1/x"...you'll get the reciprocal number as a result. Since the reciprocal of 3/4ths is 1.333 (the same as 4/3rds), just multiply 153 x 1.333 and you'll get about 204 ounces...about 12.75 pounds...which SHOULD tell you that the thrust force you can get from the servo WILL be greater "further in" on the arm towards its center of rotation!

And for what your CONTROL SERFACE will see for an applied force...well, I sure someone else can help you with the math to figure out the air density, AND the speed your model will be going at...it's important to know BOTH those things to get the "whole picture" of what servo would best fit your needs, "math-wise" anyway...but as for the "projected area" of your control serface, if you know the area OF the surface you're concerned about, it's the SINE of the angle your deflected surface's area is at (depending on the angle it's deflected out into the air) that determines how much of that area the "wind is going to see" !!!

Say, you were operating a HUGE aileron on an aerobatic model with that 5945 servo (if dual aileron servos were in use on it) of about 90 sqare inches in area. If you were going to have it deflect at a 30ΒΊ angle, the SINE of 30ΒΊ...findable with your Windows calculator in scientific mode, with the "sin" button, AND that "degrees" circle "dotted" right UNDER the number display of the Windows calulator, the sine of 30ΒΊ turns out to be 0.5, or ONE HALF. If you multiply the area by 1/2, you'll get the area that "the wind sees" when your aileron is deflected AT a 30ΒΊ angle, (it ends up being 45 square inches) and figure out , with the proper air density calculations AND the speed of your model, how MUCH servo torque will be needed to deflect your control surface the amount you want it to go.

There USED to be a nice servo calculator at the Multiplex USA site to REALLY help you out with this task, but since Hitec took over Multiplex, the usual address to find that online calculator...at http://www.multiplexrc.com/calcservo.htm ......is NO longer effective. However, some RCers, in Colorado, at both http://www.csd.net/~cgadd/eflight/calcs_servo.htm AND at http://www.coloradogliders.com/servo...calculator.htm , look like they DO have just what you can use!

Just hope I've "cleared up" some of nthe things you were looking to figure out...and with the two VALID online servo calculator links I came up with, you SHOULD be all set!

Hope this helped!

Yours Sincerely,

The PIPE!
Old 04-05-2004, 02:56 AM
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C 130
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Default RE: Here are a FEW tips to get you started...

hello ppl
well Mr. The Pipe just made it clear . thanx for both of you reall. i can get the idea now and by experimenting with the calculator links you gave i will undertstand more.
thanx alot guys
have a nice day
Old 04-05-2004, 09:07 AM
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Red B.
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Default RE: Here are a FEW tips to get you started...

Imagine you had a servo that can put out 153 ounce/inches
Just nitpicking :-)
Torque is force times lever and the imperial unit is oz.*in. NOT oz./in.

/Red B.

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