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Initial Helicopter :

I chose a bi-rotor co-axial helicopter. This is a whell-known Lama V3 from E-Sky. I removed all useless parts : tail, cockpit... The co-axial helicopters are the most stable RC-helicopter. This behavior makes control loops even simpler.

The wingspan of a Lama-V3 is small enough for indoor flights. It is much more compact than quadri-rotors. I think that a small size is very important for indoor flights.

Motors :

I chose "Extrem Motors" that are more powerfull than original ones. The main disadvantage of these motors is that they create an unwanted magnetic field. This magnetic field disturbs the compass.

Motor Controller:

This is a "3 in 1" from E-Sky. This is originally designed for the "big lama" helicopter. It is compatible with 2s and 3s li-po batteries.

I chose a separated motor-controller, and not integreted on my custom electronic. My electronics sends "servo signals" to this motor-controller. I chose this because I wanted to have a flexible architecture : if I want to switch to brushless motors, I just have to put new motor controllers.

Batteries :

I put a 3s battery, instead of original 2s battery inside the Lama-V3, with the same capacity 800mAh. The motors (xtrem) and the electronics can accept the higher voltage.
The higher voltage gives more power, higher rpm. The UAV has a greater autonomy. Finally, the controll-loop is more robust, because the system is more linear. The throttle command saturates at higher level, higher rpm..

Blades :

I have tested "Xtrem" blades. These blades give more thrust with the same power, because they have a greater pitch. But they are much more flexible! During strong accelerations, the blades can collapse between the 2 rotors! In this condition, the UAV crashes very rapidly.
Therefore, I chose the original E-Sky blades. I bought plenty of blades, because crashes occur quite often during software development!

Landing Gear :

The landing gear is made with the original one. I put extensions made with carbon spindles. The spindles are assembled together with ligature technique : sewing thread plus cyanocrylate glue. This is very solid. The landing gear is more solid than the original one.

The landing gear integrates a position for the 3s battery (bigger than original one), and a position for the 2 electronic boards.
Leon | 28/08/2011