Quadcopter build: DJI F450 + Pixhawk

After training with a Hubsan X4, I wanted to build a more hackable quadcopter. After a lot of research, here’s what I ended up assembling.

My DJI F450 with Pixhawk  inside. You can also see some basic telemetry on the Taranis' display.
My DJI F450 with Pixhawk inside. You can also see some basic telemetry on the Taranis’ display.

Equipment

As mentioned above, I wanted to build a hackable quad, so I didn’t want to go with a Ready-To-Fly (RTF) model, least of all one that comes with a limited/cheap transmitter, battery charger etc. Building models is fun anyway, even if putting together a quad is not quite the same experience as building a plane out of balsa wood.

The DJI Flame wheel F450 shows up in many places around the internet, and it seems to be a reasonably-sized frame, which I hope will offer some payload capacity without being too big, bulky and slow. I decided on the 3DR Pixhawk flight controller for its flexibility and open-source software; I also expected it to be a reasonably mature platform, since I had seen a friend of mine fly a quad with the previous generation APM flight controller. For the transmitter and receiver, I went with FrSky products. Compared to Spektrum it’s a less well-known brand, but their transmitters can run open source software, and appear to provide a lot more value (features, channels etc) for money. This comes at a cost – apparently there’s a steep learning curve, but I figured that as an electronics/computing enthusiast that should not be an issue.

Parts list

While I had some past fixed-wing model flying experience, all of my previous equipment was unfortunately outdated (40MHz transmitter, NiMh batteries), which meant my shopping list was a bit longer than originally expected. I did however avoid buying a dedicated telemetry radio system (such as this one) and FPV gear for the time being; I can always add those later. In retrospect, I also could’ve considered the OpenPilot CC3D platform as a low-cost alternative to the Pixhawk.

I believe that omitting the FPV gear is actually an advantage in some ways: my quad should not qualify as Small Unmanned Surveillance Aircraft (there’s no way it could possibly do any form of surveillance), and therefore fewer legal restrictions should apply to it here in the UK (see the BMFA guidance on Multirotors with cameras). Disclaimer: I’m not a lawyer, and this should not be taken as legal advice.

The build and first impressions on the ground

Assembling the quad was actually surprisingly straightforward, thanks to all the articles on this topic available on the internet. Don’t forget to configure the failsafe options.

When I went through the Pixhawk setup process, I had some issues calibrating the accelerometer. This turned to be caused by a faulty accelerometer/IMU, similar to the issues described in this thread on diydrones.com. After a somewhat lengthy RMA process with 3DR, a new Pixhawk arrived in the post.

The Pixhawk flight controller and the Taranis transmitter both run pretty cool open source software, which facilitates some interesting setups: For example, I can use the FrSky telemetry to get vital data about my quad to the transmitter, where it can be displayed and logged to a SD card. This means that I can land before the battery dies, and if I’m unfortunate enough to crash my quad in a field with high grass, at least I’ll have access to the last known GPS coordinates. I can also read the current flight mode from the telemetry data (it’s encoded in TEMP1), and whenever that changes, play a sound file announcing the new flight mode, similarly to the ground control software! (see my post on the ardupilot forums for more details)

One thing I noticed is that the Pixhawk does not send any PWM signal to the ESCs when it is disarmed. This causes the E300 ESCs to continuously beep the “no signal” tone, which is quite annoying. I might flash them with the BLHeli firmware (see this and this thread) or try to find some other solution to this problem.

Flying

Stay tuned for pics & flight logs… 😀

Reading material

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