Continuation of my FX-61 Phantom build configuration. (this part has the BoM at the end)

The other wing is just stock. Look at that horrible stock servo, it’s transparency only serves to taunt me by showing the horrible plastic gears that are dying to eat each other to bits. I would like to change them ASAP – safety-wise I really think they are the weakest point in the whole system.

The 433 telemetry radio antenna folds flush with the body. Extending it does not increase the RSSI but it looks cool, and looking cool is just as important as flying well when you’re impressing people at the park.

As much as I dislike adding weight, fibreglass tape definitely buys its way on-board! It seems that every single edge that I didn’t tape now has a dent on it :\ Taping the wingtips and rudders is essential. I always seem to bash them during transport. I laminated the LE (Leading Edge) with strips of A3 hot laminating film using a household iron. It’s not easy to get it on without damaging the foam with the heat (it bubbles up like orange peel if it gets too hot). For that reason I only did the straight sections, and will fibreglass tape the curved outboard LE section.

Ideally, about 20% chord from the LE is laminated with film and then the LE radius is covered in fibreglass tape. Alternatively, don’t crash.

The TE (Trailing Edge) never gets damaged on my aircraft.

I use a second hand Futaba FP-T8UP, and I love it. Great build quality. It only has 7 custom mixers, but I have not run out yet.

I don’t have a 3D printer or CNC mill so thought I would have to settle for a sub-optimal hack to attach my tablet to the transmitter. Surprisingly, a headrest mount attaches easily to the Tx handle and works very well. An hour of chin scratching whilst surfing the web can sometimes pay off it seems – the mount works great and was only £5.99 delivered.

I don’t take a laptop to the field. I plan my mission at home, then use an Asus Nexus 7 tablet for telemetry while flying. Droidplanner is okay, but annoyingly it disconnects when the signal is too low but doesn’t try to reconnect. I have to manually spam the connect button, and it’s getting annoying now. Is there a solution?

The plane balances nicely. CG is very sensitive to placement of the huge battery, but there’s plenty of space. Velcro is not enough to secure the battery, so I use squares of grippy pad on the tray to firmly stop the battery from slipping. With everything in (autopilot, video gear, no payload) it weighs 1350g.

Grippy pad is the rubber-like material marketed as a dashboard phone holder. It is truly amazing, you should get a bit just to play with it if you have never felt it. When it’s clean it sticks almost as well as sellotape when used on a smooth material like plastic. I use it to attach the radio to my tablet, because it’s not permanent and leaves zero residue.

I like to leave space in front of my battery so that in a crash it can slide slightly allowing the grippy pad absorb the impact rather than crunching into the nose and killing itself.

The phantom has a stupid bell shaped moulding around the motor. I cut the bell shape away. The purpose of the bell is unclear to me – the aerodynamic effect of its shape is to promoted radial flow across propeller, but that reduces efficiency. Plus, it blocked the root portion of the blades.

I balanced the motor using the trim balancing technique, using a laser plus a portion of DVD taped to the tip of the rudder to measure vibration amplitude. I have not seen any videos of trim balancing being used for RC models, it seems to be reserved for gas turbines despite being rather simple. Perhaps a video tutorial is in order.

I found the stock propellers to be impossible to balance. I thought I was being an idiot, but on closer inspection I found that the plane of rotation of the blades is not orthogonal to the axis of the hub, causing dynamic imbalance. In other words, the blades can be statically balanced to perfection and the prop CG can be bang in the middle of the hub, but the blades will teeter when spun and cause vibration. I’m not just being picky, the dynamic imbalance in my blades is very powerful!

At the moment when I come in to land I have to stop the prop on approach, and hope for it to stop in the horizontal position to avoid hitting the ground, otherwise I have to tweak the throttle until it does. The sooner I switch to a folding prop the better. I will also be switching to a 10” prop in hope of reducing noise, because at the moment this model is far too noisy for it’s power.

Okay, here's the most important bit: Money! 

I worked out the cost of the drone (just aircraft, no ground equipment) as described in the above build log to be £540

The breakdown below includes some of the hardware, but also other tools and consumables. The full breakdown of absolutely everything is available upon request if you really want it.

Thanks for reading, and if anyone in Bristol wants to fly then let me know!

This is a description of the configuration of my FX-61 Phantom FPV Flying Wing EPO Airplane 1550mm (PNF) V2

The whole reason for me to get this plane was to get started with autopilots. I have chosen the HKpilot32, a pixhawk clone that comes with the same accessories as the pixhawk and a 4GB microSD installed. 

The GPS + compass module is mounted on an anti-vib polymer that is marketed by Specialized as ‘Bar Phat’, a vibration damper for bicycle handlebars. The Mobius camera lens module is also loosely secured using bar-phat for anti-jello, and not fixed firmly so that it can pop into the fuselage if hit.

The embedded nuts are used to fasten a tray that goes over the pixhawk. I should have used metal nuts because if the nylon threads are stripped, I am screwed since the nuts are epoxied in.

The PLA plastic is marketed as Polymorph, and is a granular plastic that melts into a malleable mass when submerged in hot water. Great for making funny shapes like antenna root clamps. The radio PCB is floating, supported by the antenna. I tried fixing the PCB using 3M VHB tape and leaving the antenna floating, but the tape kept detaching.

Note on 3M VHB: it is a spectacular double sided tape, but the full strength is only realised if your apply about 15psi pressure for a few hours – I'm too cautious to clamp a PCB to some foam with that much pressure.

The carbon tray was freehand cut with a dremmel clone. It opens up a lot more space, leaving the whole rear volume clear. In my opinion, it’s important to have the payload area at the centre of gravity, so I don’t waste time balancing the plane when I add or remove a payload.

The VTx (video transmitter) is powered straight from the balance port, which I learned is a great way of RUINING your battery. I crashed into a tree and everything stayed intact, so the VTx carried on sapping power and drained my battery down to a few mV, since it doesn’t have undervoltage protection. So that battery is now a flammable paperweight.

I also learned the hard way that the arming switch will become gummed up with glue and seize if you just throw it into a gluey hole. So after a number of years with a scalpel I picked all the glue out, wrapped the switch case in tape then glued it again. It’s fine now.

The fantastic Mobius camera has been a very pleasant surprise, especially considering the cost. The fact that you can extend the lens module out of the main camera is very nice! I have the camera set up to start recording & outputting video as soon as it receives power, which is ultimately from the pixhawk power module which I trust far more than the horrible noisy stock ESC.

The Phantom v2 now has detachable wings, but the attachment solution is not elegant at all. In fact, it’s horrible! The screw is hard to align, plus it’s made of rubbish playdough steel. Needless to say, the blind nut which the screw goes into became detached, sigh -.-’ I will replace it with a chunky nylon screw ASAP.

I made quick connects using a bundle of servo extenders. It works okay-ish. The connectors are too tight to disconnect 3 at once, so I have to manually plug/unplug each one. It’s no big deal, but it’s not the simple snap-in dream. There are good multiplex quick-connects out there, but they don’t have enough contacts for a servo and a VTx. Next time I will try DSUB connectors with a locking latch.

Note the connectors are loosely held in place so they are free to move in order to survive wing-off crashes.

The VTx is cable-tied to an embedded carbon rod on the suction side. It does not lie straight on the foam, there are spacers to create an air cavity. I thought I would build an air cavity in in case I discovered the VTx gets too hot. If that turns out to be the case I could vent the cavity for some cooling flow.

The circular antenna protrudes, but not lower than the wingtip skid so it shouldn’t be a problem. I actually spent a long hangover-ridden Saturday thinking about antenna placement. I wanted to protect the antenna. The wing suction side must stay clean to keep me happy, so I thought about putting the antenna near the tail to keep it protected, but that would be too close to the other electronics. I decided the current location was the best. I chose the spanwise distance by figuring out the maximum rolling moment I could balance with just the offset battery, because I hate adding unnecessary weight (i.e. balance weights on the other wing tip).

Instead of digging a cavity for the VTx, I simply cut a whole chunk out of the wing, cut that core to the right shape, then glued it back in. I am pleased with how clean the VTx installation is, the only protrusion is the cable tie.

(reached image limit - see part 2)

High-res .pptx version