When you set up your flaps, do you use a travel setting of +100 (up) to -100 (down) (the figures do not have to be 100%, but are you using the full range of the servo travel), or are you at "0" at up and just using from 0 - 100 (down).

In other words, are you using the full servo travel, or half the servo travel for your flaps?

Thanks for the input.

Chad

Igenerally use 3 positions for the flaps and find it easier to mechanically set the middle position.

I then use whatever travel setting Ineed to set the up and down positions.

always use the full servo travel .
if you use half you only have half the strenght!
set to 100% flap 0 and make your linkage from there.

Is that true?My servo specs only give one torque figure, not one for half travel and one for full travel.

If you can get full flap travel with the linkage on the inner servohornhole then,IMO,reducing travel doesn't reduce strength. If you are notusing the inner hole,and increasing travel enables you to useto do so,then Iagree there is a strength benefit.

EDIT: This assumes that your control surface horn is a fixed length or already on the outer hole.

I think Sandor may be confusing power with resolution, the more you reduce servo travel with atv the more you loose resolution, but with flaps it doesn't matter.

m

What Sandor means is use as much of the available servo travel as you can & vary the horn length & hole position on the servo to get close to the needed flap movement. 

It's the same as short or long servo arms, it's easier to stall a servo if it has long arms on it so keep them short.

Likewise it's easier to move a control surface with longer horns on them so keep them long. 

By increasing the servo travel you can make the servo arms shorter & the flap horns longer. - John.

sorry for the confusion , yes this is what i ment.
always try to use full travel , otherwise why have a great TX and digital servo,s if you use only half the travel.
i indeed use most of the time the most inner hole for the flaps..

I think it is more important to ensure that on full flap deflection the servo arm and push rod are straight and in line with the ouput shaft of the servo to ensure mimimum load through the gears and motor, especially if you fly from grass and the flaps could get a hit on landing, but do use the maximum amount of servo movement and the shortest arm you can. All IMO

Mike</p>

In addition to better resolution you actually get more force at the flap surface if you use 100% of the available travel (+140 to -140 or whatever it is)

You get lower speed though, not a big deal on most surfaces, particularly on flaps

I always use a servo that will travel 180 degrees. Full up or full down are both in line with the servo splines with no load on the servo gear train.

Thanks for the feedback guys!

Chad

Just a quick observation. The force applied has more to do with the length of the servo arm compared to the length of the control arm, than how much travel is applied. Think of the bicycle example ... on a 10 speed it takes a lot less force to move the wheel if you have a small pedal sprocket driving a very large wheel sprocket. Same principle applies here.

So if you are concerned about torque, find the hole closest to the servo spindle on the servo arm that gets you the required movement of the flaps and you will have maximized servo torque by creating more mechanical leverage. It is multiplicative.

Loss of resolution is not typically a big issue for flaps, as it was pointed out here that people normally set three flap positions and don't look for a lot of granularity in between.

Following this along, if you have an internal flap horn (like a kingcat or a bobcat), you will actually lose servo torque as the mechanical leverage will work against you. The way to overcome this is to set the servo arm to point directly at the control arm when the flaps are fully deployed (see Ultra Bandit Addendums) so the force of the flap works directly against the spindle in a non rotational fashion. Throw now becomes how much servo travel is required to fully retract the flaps. Keep the servo arm as short as possible.

For more information, the formulas for computing servo torque requirements are in the Expermintal Regs ... believe they are AMADoc 520.

Keith, you're perfectly right and I would like to add a small thing.

The quote above is just to outline a small misconception:

The torque given for a digital servo is independant of the position of the servo arm. HOWEVER what is important for us is the torque LEFT AT THECONTROLSURFACE.

A servo torque of say 110 oz/in can become 30 oz/in at the control if the mechanical advantage law is not observed as explained above by Keith. So taking the best servos on the market is totally useless if a proper setup is not done.

This point has been already largely discussed on the FEJ F-18F thread where the elevator system is far from optimal.
It resulted in a very interresting "non mechanical" setup that optimizes the mechanical advantage on a pull-pull system. Look at Idleup1 posts on this page:
http://www.rcuniverse.com/forum/m_77...40/key_/tm.htm

http://www.modelaircraft.org/files/520-a.pdf
page 3 and 4

Here is a fantastic spreadsheet to compute leverage, servo torque required and much more by Craig Tenney ( once again, hat down to you Craig ):
http://www.geohei.lu/olin/data/model...calculator.xls