I need a large throw for a giant scale 1: 5, Dee Howard 500 Fowler flap. When I do the math it says 239 in.oz. at each of the two servos per flap, not a problem with todays power digital servos. But when you have to move it 6.3125" in a 60° throw you end up with a arm ±4.5" long and a mechinical disadvantage of 5:1! So I need aboth ±1500 in.oz. at the servo device output. Servo City makes a neat device that will do it but it weighs 11 oz, times the 4 is way to much. They also sell gears and all the hardware one would need to build your oun. I got it all figured out mechincially, but I have not a clue on how to figure out what to do for the follow pot. I can couple it to the output arm, but the size (resistence) and the like it a mistery. I once knew of a site that had such informatiom but I have had a senior moment and can't find the http! Any help would be greatly appreciated!

how about using the hitec robot servos and setting endpoints with your transmitter, go to robot.com or the likes ...FWIW

??? HiTec does not manufacture a servo with 1500 in.oz.??

As I see it, your problem is that the movement starts with the small torque of the motor of the servo spinning at high rpm.
At the output of the servo, the torque is high (~50 for standard servos, ~100 for high-torque servos, and ~275 for digital servos), but spinning only 1/6 of a full turn.
From that point, you need to reduce the torque back and to increase the speed up the rotational speed, so you satisfy the 6" of displacement.
That 1/6 of a full turn happens in just 0.25 seconds.
If you transfer that speed to the flap, it would be too much.
To make the speed scale, you need to slow down the motor of the servo, which reducing the torque

Work = Force x linear displacement = Torque x angular displacement

Power = work / time = (torque x angular displacement) / time

In simpler words, in order to move from ground level to the 10th floor, you are using the elevator to go from ground to floor #20, just to descend inmediately to floor #10.
From minimum torque to the torque required by the deployed flap (240 in-oz), going up to 1500 in-oz is a waste.

I would try to mimic the real mechanism of a full size plane.
Spanwise, there is a shaft that spins at high rpm driven by a motor, transmitting the work to the slidding flap, which moves slowly.
In order to achieve that, I would liberate the servo from its angular limit.
The shaft of a standard servo can rotate 1.5 turn in 1 second (0.25 sec/60°), or 90 rpm.
The key is finding out the reducing gear to convert those 90 rpm into 6" per the scale time of the flap deployment.

The pot should be installed independently to sense 60 degrees of total rotation, actioned by the flap.
An alternative is to install two limit switches for full retraction and full deployment positions of the flap.

Check this mechanism out:
http://www.freepatentsonline.com/6010097.pdf

For continuos rotation servo, see:
http://www.seattlerobotics.org/guide/servohack.html

Check these videos out:
http://www.youtube.com/user/ScaleAero

Thanks there is some good material there! I have the Fowler guide track and drive tracking figured out, it is getting the servo set up with the outside pot for a 5:1 gear drive. I'll take a look at that flap PDF, but at first glance it is way more the I think I want to get into.

You are welcome, ByLoudDesign.

Here you have three more links that I have found:

http://www.seattlerobotics.org/guide/servohack.html

http://www.nextcraft.com/highlift_rc_setups.html

http://www.freepatentsonline.com/res...ch=top&search=

An all-thread powered by an electrical motor can excert great linear force on a slidding nut, which will move the flaps slowly.

Your project is as interesting as complicated.

Best luck!

Thanks again!!! I spent about 4 hours looking for a like application on the last web site with the patent documents. The KISS principle wasn't in operation in most of them. One of my problems is there are no appendages, everything is kept within the foil. It travels about 80% back without much downward movement and then the last 20% or travel it deploys to a -35°. I have the tracks working. I would not mind using a servo to drive a screwjack but I have seen no control hardware to allow control?

I was also checking the patents (PDF formats), and yes, many are really complicated.

I have seen the one I described above in operation while flying in Boeing passenger jets.
The sliding guides are covered by those aerodynamic shapes under the trailing edges, and the action mechanism is driven by that spanwise rotating shaft.

I have found references to articles describing a similar system to yours published in Model Airplane News Magazines of June 1993, February 1995 and May 2008.

http://www.modelairplanenews.com/Me2...94682A2B3FCDB8

http://www.modelairplanenews.com/Me2...+February+1995

http://www.modelairplanenews.com/Me2...News+June+1993