Plywood construction using common A2212 brushless motors and Hobby Power 30A ESC’s with 1045 propellers. Servos are high speed metal geared standard sized servos. And lastly the flight control board is the simple to use KK2.1.5 board.
Step 1: Design and Build
The construction of this model is mostly covered in the
Tricopter build. It uses the same servo arm as the tricopter but uses two of them on a special twin hub.
The video shows a few more details about the arm construction but it is a very simple build. The tricky bit was getting this thing to fly!
But let’s start with the construction. As with most of my builds I design on a free cad program running on my raspberry pi, I then save the drawings as pdf’s and print out using a scale of 100%. Then I stick the plans to the 3mm plywood and double up all the parts. Again this model easily fits on a piece of plywood 300mm by 600mm.
Once all the bits are cut out then clean up the edges and stick all the bits together but like the tricopter don’t stick the arms into the hub. (Mainly because I wasn’t convinced this was going to work so wanted to use the arms as spares for my tricopter) once all the bits are glued together you can add the servos and wire up the speed controllers and add the flight control board. As you can see in the video my first attempts at flying this machine didn’t go well! I persevered for 3 evenings and most of a Saturday before finally accepting that the weight was all wrong.
Following a quick redesign I added the vertical battery holder and now the machine was able to fly and be controlled! This extra bit is shown in the 4th and 5th PDF’s. this kind of messes up the fitting onto one sheet of plywood 300 by 600mm, but if I get time I will see if I can make it fit.
Step 2: Electrics
Nothing really fancy about the wiring. The motors were soldered directly onto the ESC’s. And the power cables were lengthened and soldered together into the battery connector.
The Back motor ESC (more by mistake) is connected to channel 1 and the front motor ESC is connected to channel 2. The back servo is channel 3 and the front channel 4.
Step 3: Setting Up the Flight Controller. KK2.1.5
So there are two ways this machine could be flown. The first is with both propellers in front. This is the standard dual copter configuration. I started with this layout and instantly found i had to make adjustments, firstly to the servo offsets which needed to be at 50 and then the rudder needed to be reversed in both the two servo channels.
Or if you wish you can fly this like a Chinook with one propeller in front of the other. To make this change I had to move the fight controller around by 90 degs and change the settings on the mixer.
Whilst testing I quickly discovered that the motors were fine and the flight controller was able to control the motors to allow changes in direction. However the servos were not working well and because of this I had to separate the PI channels so the Aile and Elev were adjusted independently. This was obvious after all in one direction the motors change and in the other axis it’s the servos so it really was daft to have them set to the same values in the PI settings.
So where next? I think I will revisit one of my early bicopter designs, but move most of the weight to the bottom, which means moving the servos to the bottom and the esc’s and anything else I can lower!
In hindsight I think the dualcopter/bicopter is one of the least desirables models due to the pendulum effect of the required weight below the propellers and whilst it is fun to make these machines and even more rewarding to get them to fly I don’t think it is worth pursuing anymore!
Settings Flown As Chinook.
Self-Level : Always
Link Roll Pitch : No
|Roll (Aileron)||P Gain : 80||P Limit : 100||I Gain : 50||I Limit : 80|
|Pitch (Elevator)||P Gain : 48||P Limit : 100||I Gain : 8||I Limit : 80|
|YAW (Rudder)||P Gain : 30||P Limit : 95||I Gain : 2||I Limit : 2|
|Channel 1 (back motor ESC)||Throttle : 100||Aileron : 0||Elevator : -100||Rudder : 0||Offset : 0||Type : ESC||Rate : High|
|Channel 2 (front motor ESC)||Throttle : 100||Aileron : 0||Elevator : 100||Rudder : 0||Offset : 0||Type : ESC||Rate : High|
|Channel 3 (back servo)||Throttle : 0||Aileron : 50||Elevator : 0||Rudder : -100||Offset : 50||Type : Servo||Rate : Low|
|Channel 4 (Front servo)||Throttle : 0||Aileron : -50||Elevator : 0||Rudder : -100||Offset : 50||Type : Servo||Rate : Low|