Building a Deadcat SK450 Quadcopter

This was my first quadcopter build. I ordered that parts from Hobbyking and waited anxiously for 3 weeks for them to arrive. I have previous experience with RC cars, planes and helicopters, I was keen to branch out into drones – more specifically for aerial photography.

The kit arrived, the frame, 4 brushless motors, a 4 in 1 ESC, KK2.1 flight controller and some hardware bits and pieces. As there are no instructions on these builds I turned to the online community, its all up there you just have to find it! I used this instrucatable as a rough guide: http://www.instructables.com/id/A-SK450-Dead-Cat-Quadcopter-to-Call-Your-Own/

I began by building the frame and installing the ESC. The Q-Brain is a neat way to send power to the 4 motors. It allows 1 unit instead of 4 individual ESCs. It is cheap and reliable and keeps soldering down to a minimum. It also allows you to centralise the weight distribution by mounting it at the centre of the frame rather than having ESCs strapped to each arm.

qbrain

I soldered on an XT60 battery plug to the ESC and fixed it to the frame with a 2 sided foam sticky pad. I calibrated the ESC using a programming card I bought separately (details in instructable).

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I then attached the motors and installed the KK2.1 board and radio equipment as per the guide mentioned earlier.
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I updated (flashed) the KK2.1 software to the latest firmware version. I downloaded the updater and the patch for free online. I purchased a USBASP programming cable to connect the board to my laptop and install the update.

IMG_4063

Once this was done I powered up the model (with props off!) and calibrated my radio to control the KK2. The KK2 board itself has a built in display and buttons to allow you to make quick easy adjustments. I found it relatively easy to use.

Once this was done the I balanced the model and tried it out in the garden on a blustery evening. I used a 3S 2200 mAh LiPo from Hobbyking to power it. I couldn’t wait! It took off and wobbled around as if it was drunk. No matter how I tried to dial in the gains following numerous suggestions from the online community I could never get it to fly just right. One of the better set up guides I found is here :

https://www.youtube.com/watch?v=OMBUkaezjns

I believe there is something inherently wrong with the Deadcat frame / KK2 board combo. The KK2 only works if it knows exactly where the motors are positioned. Due to the asymmetric shape of the quad this is difficult. As I researched further I found others were having similar issues. I even tried to calculate the motor positions myself and entered the results into the board with no major improvements. I got fed up and eventually decided to switch to a more traditional X-frame configuration and the model flew much more accurately right away. I wouldn’t recommend the Deadcat frame as a first quadcopter, it looks cool but doesn’t fly as well as a more traditional set-up.

image (2)
KK2 board should theoretically be centred at the yellow cross. No mounting options were available.
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