Introduction: Done Dirt Cheap 3D Foamy ( RC Airplane )
As a novice RC pilot, I have found myself needing a good training plane. I current own a couple of different store-bought planes, which I have crashed one too many times. To avoid the annoyance and expense in dealing with repairing higher quality planes, I created this bad boy.
Let's get started, shall we?
- 1 x Ginormous (calculate it yourself based on the template) sheet of foam core board, which can be found at an art or office supply store; should be paper coated not plastic coated
- 1 x Roll of scotch tape
- 1 x Flexible soft plastic baggy - small parts are usually sold in baggies made of this material; "Ziplock" style baggies may work
- 2 x 36" 3/16th inch OD aluminum or carbon fibrr tube - can be found at ACE hardware or art supply stores, or online
- 1 x 36" 5mm OD aluminum or carbon fiber tube - can be found at ACE or art supply stores, or online
- 1 x Foam safe super glue (though I used Zap-A-Gap, which isn't foam-safe, and it worked
- 1 x Roll of thread
- 1 x 36" music wire, minimum 1mm - make sure it fits in your servo horns
- 4 x servo horns
- 1 x 36" music wire, 2mm
- 2 x wheels - can be anything light and round. the bigger the better, as bigger wheels are able to roll over bigger bumps
- 1 x 20" velcro material (both hook and loop sides)
In addition to the above (cheap) construction supplies, you are expected to already have the following:
- 3 Cell, 11.1v, 1200mAh Li-Po battery
- 4 x Feather servos (7-9g)
- +/- 5400kw Brushless motor - likely labeled as "speed 370", though from my understanding it's the kw that matters
- Appropriate ESC, at least 20 amps
- Li-Po battery charger
- 12 inch slow flyer propeller
- 6.6:1 gearbox
Step 1: The Design
I began by 3D modeling the airplane. For this, I used Cinema4D, but almost any should do. One feature that is a huge plus is being able to export views of the model into a vector format, so that it can be printed out.
At the time of writing, C4D R14 was available as a student version for free:
You can find the printable AI file here:
Step 2: The Skeleton
After 3D modeling the plane, export it to vector and print each part out on paper. Tape the necessary pieces together, as the plane was too big to fit on one piece of paper. Of course...
Tape each piece of paper to the foam, and cut around the lines with a hobby knife.
Again, using tape, use a length of the wooden dowel to attach the two pieces of the elevators. Be sure that the horizontal stabilizer has room to fit between them without any resistance.
** NOTICE **
At the time of making, I used a wooden dowels instead of an aluminum or carbon fiber tube as the main strut on the body and wing struts. After the motor torqued a dowel too hard, breaking it, I switched to the stronger option. While these instructions refer to the body having a wooden dowel as a support, understand that we are actually using an aluminum or carbon fiber tube.
Cut the aluminum or carbon fiber tube to a length equal to the body section. Tape the upper and lower parts of the body to it, keeping it as flat as possible.
You will then need to cut out some rectangular pieces of foam as additional support for the wing. Glue them in place, again as evenly as possible. You want the wing to be perfectly perpendicular to the body.
Following the guides on the wing's template, cut out the slits for the support dowels. Tape them into place.
Glue some small strips of foam beneath and flish with the wing slit as supports for the wing. Glue the wing into place.
Feed the elevators through the horizontal stabilizer slot, then insert the horizontal stabilizer and glue it into place, being careful not to glue the elevators to anything.
At this point, the basic skeleton of the plane is complete. We can now move on to attaching the ailerons, elevators, and rudder.
Step 3: The Hinges
Creating a durable and highly effective hinge is easy -
Cut out two tabs of the plastic baggy material per hinge node. Each piece should be about 1cm by 3cm. There should be two hinge nodes per elevator, two on the rudder, and three on each aileron.
Tape one tab to one piece of foam, fold it through the joint, then tap it to the opposite side of the second piece of foam. Each node should have two tabs, each taped to opposite sides of each piece of foam.
Step 4: The Motor
In order to attach the motor you will have to create a strongpoint that is resistant to rotational torque.
To accomplish this, i glued several short pieces of the smaller diameter tubing to the main strut. I wrapped it in thread before gluing it for extra strength.
I then sanded the tubing until it fit snugly into the gearbox mounting slot.
To hold it in place, a little bit of masking tape worked perfectly.
Step 5: The Servos
To attach the servos, run zip ties through the foam and pulled them snug.
Attach the control horns similarly to the pictures using the appropriate method for your horns. Some are screw on some are glue on.
Cut the correct length of music wire and run it from servo to control horn. You will have to unscrew and adjust the servo side control horns once they are centered once power is turned on.
You will want to cut the wire slightly longer so that you can adjust it correctly and trim the excess.
To connect the wire to the control horns on either end, bend it first 90° Clockwise then about 3mm farther along bend it 90° counter clockwise. This will create a "stair step" looking shape that wont fall off of the control horn.
Step 6: The Electronics
Run a strip of sticky velcrow along each side if the body underneath the wing. You will need to stick the other side of the velcrow to the battery, receiver, and speed controller.
Specific positioning of the battery will need adjusting. Aim for the center of gravity being 1/3 of the way from the front of the wing to the back. You may have to adjust the positioning after the first flight.
Step 7: The Gears
Cut the length of 2mm music wire such that it is twice the length of the distance between the top of the front of the plane to 3 inches below the bottom of the propeller when oriented vertically. Cut off the excess.
Use the excess that was cut off as the main axle. Cut it to a fitting width. 7-9 inches would probably work.
Bend the first length of wire in half, then bend the ends outward into a Y shape beginning at the height of the front of the body of the plane.
Tack the axle to the gear supports eith masking tape. Ensure that when attached to the plane and wheels that the propeller is at leadt 2.5 inches from the ground.
Wrap thread tightly around the joints where the axle was tacked to the supports and glue into place.
Attach wheels how you see fit. I put them in between two washers and used tape as a barrier outside of the washers.
Once the glue dries, securely tape the gears onto the front of the plane. They top of the Y supports should bend over the top of the plane and each side should be taped onto the plane, splitting into a Y shape after they pass the bottom of the body.
Step 8: The Conclusion
- Stiffness in the body and wings is very important. More important than weight, to an extent. Using wood dowels was insufficient so i switched to heavier and more importantly stiffer and stronger aluminum. The motor was plenty powerful so i saw only positive consequence.
- I opted to tack the servos to the zip ties to prevent them from sliding slightly outwards.
- Adjusting the battery to the correct center of gravity greatly increased performance.
- The shorter your control rods are the better your plane will perform, as there will be less play.
- Use a lot of glue on your gears as they will be taking a beating.
* * * CRITICAL NOTICE: VERY IMPORTANT * * *
Have fun! ;]