How to: Blade mCPX Tail extension mod

1:18 AM giovanni 0 Comments

A very common problem with the Blade mCPX and with all the helicopters with a separate motor driven tail is the tail blowing out. 
Tail blow out, or TBO, happens when the thrust coming from the tail rotor is not enough to counteract the torque coming from the main rotor during fast pitch changes, resulting in an unintentional pirouette. 
This is mainly caused, in the case of the mCPX, by the motor not responding quick enough to the inputs of the gyro.

TBO is a major cause for crashes when the pilot steps up from hovering and wants to try to flip or roll the helicopter: sudden pitch variations will cause the tail not to hold anymore, the heli will spin, the pilot loses control, and down she goes...

There are a few solutions to this problem: 

- you can add a second motor on the tail to double its effectiveness, like shown here

- you can swap the stock motor for a bigger one, such as the tail coming from the Blade 120SR
- or you can extend the tail boom

I preferred the third option as I found it the easiest...and the cheapest.

What you need to perform this mod is:

- a length of 2 mm carbon fibre rod (I used fiberglass because I couldn't find any carbon around)

- cutter / X-acto knife
- mCPX tail case and motor
- some CAT 5 wires (optional, I use them because it's a relatively thick copper wire which prevents any voltage drop. It is the wire you commonly find in Ethernet cables.)
- Soldering iron
- Some heat shrink

First thing is to cut the rod to a length between 140 and 150 mm and to shave a flat spot on both ends to be able to insert the new boom both into the frame and into the tail case. NOTE: the flat spot must be aligned

Check if everything fits properly

Now, be brave and peel the heat-shrink off the motor wires. You will expose a soldered connection. Go ahead and desolder it to expose the red and blue wires from the motor. Strip the ends, and strip your CAT 5 wires as well.

Solder them together, remember that the red wire is positive and the blue is negative. Heat-shrink the joints properly and wind the CAT 5 wires around the boom. You could also run them along the boom and save some weight, if you prefer.

To protect the tiny wires coming out the motor I use the old trick of inserting the motor and motor mount in some 7 mm heat shrink. This way in an impact the assembly is well protected.

I then removed the connector from the 3 in 1 and inserted the other end of the wires in the holes. This is to reduce the voltage drops to a minimum. 


And remember, the negative wire goes towards the outside of the board.

Last thing I added was to cut the wires behind the main shaft, strip them and re-solder them together  so that if I need to take the tail apart I won't have to work on the motor or the 3 in 1.