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Old Jan 01, 2013, 02:16 PM
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Joined Oct 2012
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Mixer for sailplane with flaps and stabilizer

I have a sailplane "Ideal" from Topmodel (similar to Fascination), and I couldn't solve the way to move up the ailerons when you activate the flaps to airbrake the plane, using a single aileron channel since the EagleTree I'm using only provides a channel and is essential to route the aileron servo trough the Eagletree to have RTH function.

First solution was to route just one aileron servo to eagletree, sojust that servo is the one controlled by EagleTree. Since this sailplane is relatively slow in turns, taking away one servo reduced further the control by eagle tree, so the rotation for RTH was extremely slow and with strong wind there was times that he even couldn't turn.

I tried to fix it with a elevon mixer, but mixers outputs are reduced to 50% of the inputs, so the flaps and aileron movements was drastically reduced.

As a final solution I've programmed mixing function an Arduino-mini board, with the following features:
-Memorizes the maximum and minimum values of ailerons and flaps, and the percentage of mixture
-The mixture starts at the programmed minimum value of flaps, so a certain level of flaps may be left without activating brakes. This function allows you to slightly turn down the flaps to fly thermals without ailerons going up and breaking the plane
-When you move the ailerons up, it changes the slope of the mix in a way that both ailerons move to their extreme positions regardless of the state of the flaps. For example, if the ailerons are 50% deflected upward, one aileron has just 50% movement left, but the other has 150% to move. This mixer allows to achieve aileron limits when you move the aileron input to any end value
-Consumption is 14 mA (17 when the led is lit)

To operate you need:
- mini-arduino board or similar
-programmer STK-500 (I use Olimex), or using arduino tools (I've not used them)
-A converter rs232 to USB with TTL levels... There are cheap on ebay
-To set the values, connect the arduino serial port to a serial terminal, and put a jumper between terminals PC0 and PC1 before powering-on, and follow the instructions given on screen.

I have left the source program, and scheme connections, for anybody who has a sailplane for FPV and want to use flaps and ailerons for breaking.

Experts in Arduino will know how to use the bootloader function and not using the STK500 programmer (I don't).

Greetings and good flights
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