Large Autonomous RC Plane

I have build quite a few rc planes out of foam in the past. And I have crashed pretty much every single one of them (hint). This time I wanted to go bigger than ever before.

It should have a wingspan of over 2 meters (78 inches) and a flight time of over 30 minutes with two batteries. And thanks to the APM 2.6 it should fly waypoint missions on its own. But it also needs to be able to break down in to smaller pieces for transport.

So I started designing it in Fusion 360 and 3D printing the parts...

Supplies

- Foam sheets (I used depron 1000mmx800mmx3mm)

- A bunch of M3 nuts and bolts

- Tape

- BBQ-skewers

- 4x 8mm rods

- 1x 15mm rod/tube

- The 3D printed parts

- Lots of hot glue

-1.5 mm wire

- 2x XT60 connector pairs

- Small connector pins

-14AWG wire

-Servo wire

The electronics I used:

- APM 2.6 (It is old and outdated but does its job fine)

- Neo6m GPS

- 90A current Sensor

- MinimOSD

- 5V bec

- 2x 30A ESCs

- 2x cheap NTM 900kv Motos with 10x5 props

- 2x 4000mah 4s LiPos

- PDB Board

- Video transmitter

- Orange RX reciver

- 4x 9g Servos

Step 1: Printing the Parts

There are many parts to print. Most of them are desgined to not need support when printing. The only ones that do are the motor mounts. The pin grip needs to be printed 3 times and the motor mount with cover is needed twice.

Step 2: The Wing Frame

I drilled out the 8mm holes of the 3D printed parts and glued them on with epoxy. Even spacing of the ribs and their alignment is very important. After the glue dried I glued in the servo and the connectors. One connector is a XT60 plug. The other one is a custom one for the servo and the ESC. It has +5V, GND, servo data and ESC data. I soldered two wires to the ground pin. One for the ESC one for the servo. I made sure that the wires do not interfere with the mounting rods of the wing.

I then covered one side if the foam with tape and made little grooves where it is going to be foldet later. Then I used hot glue to glue the frame on the foam.

I added a foam wing spar to increase the stiffness of the wing. I would recomend to use more than I did. (At least 3 per wing)

Step 3: Folding the Wing

This is the most stressfull part of the build.

At first I added a hole for the ESC wires and fed them through. Then I punched out the mounting holes for the motor mount.

After that I added hot glue to the ribs and spar and folded the wing over, making sure to pull the foam tight. This is much easier if you have someone to help you out.

Then I glued it completely shut and trimmed the foam at the end. Then I cut out the aileron. I had mine just a tiny bit too large. But that is fine.

Step 4: Finishing the Wing

I cut a hole around the servo to mount the servo horn, making sure to center it before. Then I closed the hole with little pieces of foam and tape.

After that I taped on the aileron and installed the servohorn (I found it on Thingiverse) and the metal wire connecting the two.

Then I reinforced the wing with duct tape on the underside. I then mounted the motor and ESC on the motor mount and punched holes on the top of the wing to put in the screws for the motor mount. I covered the holes with some more tape. The motor mount cover is secured with some short screws that just screw in the plastic.

I finished it off with some tape on the edge of the wing.

Step 5: Do It All Again

Now that one wing is finished the other one needs to be done.

I actually build four wings in total. I failed twice by not using the right glue (I tried using gorilla glue but failed) and using no further reinforcement other that the 8mm spar and other major design flaws.

One could call it stupidity, but I call it iterative design ;)

Step 6: Building the V-tail

I wanted to go fancy and use a v-tail instead of a traditional tail.

I started by drilling out all the holes of the 3D printed part and gluing in the BBQ-skewers. Then I cut out the shape of the tail out of foam and made grooves for the skewers and the antenna of the reciver. I then glued it to the tail mount and glued another plate on the other side. Just like a sandwich.

After that I repeated the process for the other side. Then I cut out the actuating surfaces and taped them on the v-tail.

After that I cut the servo wires in the middle and istalled the servos in the mount connecting them with the servo horns and the 1.5mm wire.

I soldered the servo power wires to the receiver. Then I used some very long servo wire and fed it through the mount up to the receiver (5 wires in total). The wires are +5V, ground, servo 1, servo 2, and the reciver signal. I used a PPM reciever so I only need one wire for the receiver.

Finally I covered it all with some foam and tape.

Step 7: Mounting the Tail Boom.

The 15mm tube can simply be glued into the v-tail mount and the main frame of the plane.

But I wanted the plane to be compact for transport so i made it detachable.

I started by gluing the cut off servo wires into the tail pin. I then soldered it to the wires coming out the boom and glued it in the boom making sure it is oriented in the right direction.

The 3D printed tail pin is not very strong so i do not recomend making the tail detachable.

Step 8: Building the Main Frame

I split the main frame into two pieces because my 3D printer is too small to print it in one go.

I started by gluing in the pins that connect to the tail wires and also gluing in a big pin to take of the load of the data pins. It also sticks out further than the data pins so that I can not smash them with the tail boom. The first picture shows the tail pin inserted in the first halve of the main frame.

The wires coming out must be glued in at an angle so that a 8mm rod for the wing can pass thourgh the frame later.

Then I drilled out the holes for the supporting rods on each side of the big hole and glued the two frame halves together.

Finally I made the connectors that connect the wings to the main frame.

Step 9: Finishing the Body

First I installed all the electronics: PDB, APM, BEC, OSD, Current sensor and so on.

Then I cut out some long strips of foam and glued them on the frame leaving the bottom open. And I cut out a hole for the VTX on top of the main frame. I then cut the foam body to lenght.

Then I glued in the connectors for the wings and made holes for the 8mm rods in the foam.

After that I cut out two small aluminium plates and glued them in the slit of the main frame. These later secure the wings on to the main frame with pins. I later put on the wings and drilled through the holes in the first wing spar and the aluminium plates.

I then made a cover for the APM and a big hole at the front for the batteries. After that I closed the bottom and attached the APM cover. I used the back plate to keep the cover closed but if you decide to glue the tail boom in, you can use velcro.

I made a GoPro mount out of foam and used it as a nose for the plane.

Step 10: The Last Step

I made a lid for the batteries that is secured with velcro.

Finally I made 3 sercuring pins. One for the tail and two for the wings. I printed the small grips and bent the end of 3 small pieces of the 1.5mm wire. Then I glued the wire into the grip.

The plane is assembled by sliding in two 8mm rods through the main frame and pushing the wings over the rods. This also connects all the power and data pins to the wing. The wings are secured with pins through the first rib of the wing. Tail can be pushed it the main frame and is also secured with a pin through the top of the main frame.

Step 11: Final Assesment

I am extremely happy with how the plane turned out. It is exactly how i imagined it to be. The wings are a bit flexible but that is ok. It is very compact when taken apart despite its final wingspan of 208cm.

I later changed the angle of the v-tail (I also updated the STL) for better flight characteristics.

The autonomus features are pure magic and things like return to launch are amazing.

The flight time is over 30min with two batteries.

Step 12: Crash It!

Welllllll ... I did it again ... oops!

This step is not necessary ;)

It was only the second flight of the plane and I crashed it. It got stuck 10 Meters above the ground in the middle of a tree. There was no way of climbing up there. The nose of the plane was between two branches so even throwing up a rope with a counter weight did not help at all. The next morning I cut off a bunch of bamboo in my garden and duct taped the bamboo into one loooong uncontrolable bamboo noodle. After hours of trying and punching the plane I pocked it to pieces, causing it to fall down.

Luckily all the electronics survived. Now I just need to build a new plane.

I already have ideas for a new design :)