Tuesday, June 14, 2016

Building a 280mm Quadcopter out of spare parts (FC, RX, PDB)


Part I – The Frame

Part II – Motors and ESCs


        After the frame assemby and ESC calibration was complete, it was time to work with the heart of the quadcopter: the flight controller (FC), the receiver (RX) and the power distribution board (PDB).

        Most builders tend to use standard components that practically connect to each other without much trouble; in my case, this is not 100% possible due to the FC used. Some reverse engineering was needed as documentation for the BigFlyShark FC I have is – to say it gently – not available and a lot of time was spent on searching for schematics in order to replicate the missing components functionality (mainly the USB port). In the end, everything worked, including the USB port (with tricks).


The BigFlyShark Flight Controller

        The BigFlyShark (or SharkX6 as they call it now) package consists of three (or four if you include the OSD capability) modules: the first module is the FC board that features the main SoC (ARM STFM 32-bit), the barometer, gyroscope and accelerometer sensors. The second module is the GPS board which has the uBlox Neo 6m GPS receiver and the magnetic compass. The third module is the PDB board which provides regulated voltage of 5V to the FC board and also includes some auxiliary USB circuitry. The OSD module provides telemetry capabilities to the system; in my case (I was using the guts of a broken Flying3D X6) the telemetry functionality is programmed into the receiver board (RX).

        As Flying3D X6 has the FC and RX boards ‘naked’, some sort of casing is needed in order to provide some minimum protection. I do not have a 3D printer so some creativity was needed: I’ve used an empty TicTac box to make a case for the FC, after ‘trimming’ it a bit in order for the board to sit firmly inside. To secure the board in the plastic box and to minimize the amount of vibrations towards the sensors, some double-sided adhesive foam tape was used.


       From left to right: the FC case (with the FC board inside) from above, the front side of the FC case where the adhesive foam tape is shown underneath the board (it holds together the board to the bottom plastic part of the case) and the final picture is the case from the side. The case fits perfectly inside the frame.


The Receiver Board

       For the RX board (the FY-X6 FY-Q7 receiver together with telemetry module), one plastic MicroSD case was used to make a house for it. Below is a picture of the RX board right before soldering the two antennas. Just enclose the RX between the two plastic surfaces and secure it with some scotch tape. The RX connects to the BigFlyShark FC via a 3-pin PPM line (the three-coloured cable in the picture below) and the telemetry module via a single pin cable (the white one).



The Power Distribution Board

           Initially, I planned to simplify the build by powering the Flight Controller using the 5V BEC from one of the ESCs. This however was proved a wrong idea, as the 5V line from the BEC is not guaranteed to be regulated; this was discovered when I was performing an initial test and upon throttling-up the quad, the 5V BEC voltage dropped under 4.92V which in turn rendered the FC inoperable (i.e it rebooted mid-air). So, I went for the Matek MicroPDB option that fits on the frame perfectly (it is 32mm * 32mm) and provides regulated 5V and 12V lines.

          The FC telemetry module has a pin that is used to monitor battery voltage and provide that information to the TX. This pin is actually ‘fed’ from a voltage divider circuit, where Vin is the input battery voltage and Vout is the measured voltage scale required by the FlyShark FC.


         The FlyShark FC pin layout is this:


Front side


Back side


        The only thing missing is the USB connection port. Unfortunately, I could not manage to get it working using off-the-shelf parts, so I ended up using the broken PDB USB circuit.


This concludes the build log for the Tarot TL280H RoboCat quadcopter using FY-X6 parts.

Feel free to contact me for any questions about it.

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