This helicopter uses coaxial or contra-rotating blades instead of a main lifting rotor and smaller anti-torque tailrotor, because this design is easier to make and is more practical for rubber-power. I have also made "normal"-looking rubber band helicopters but they require more parts and time to make. They also do not fly for as long as this design can and they don't work without an auto-stabilizing flybar system, plus you have to add a pulley system to spin the tailrotor and this creates a bigger probability of a part not working from over-complication of what should be a much simpler machine.
Throughout this instructable I include dimensions (in brackets) of parts on this helicopter but your scale will probably be different to mine so provided you keep your scale correct to the photographs your helicopter should work just as well as mine.
To make one like this one, you will need:
- A bamboo chopstick (or other strong, light wood if you prefer)
- Thin wood offcuts (I used balsa)
- Aluminium from a can (make sure the can you use is aluminium first, you can do this with a magnet because aluminium is not magnetic under normal conditions.)
- Foam sheet(s)(I use the kind of polystyrene found in food packaging)
- 2 Pins
- A paperclip (You won't need the actual paperclip, just the plastic insulation around it. If you don't have a paperclip with this insulation on it, then you will need to find a small tube that one of your pins can easily fit through without too much wiggle-room.)
- 4 Small Beads
- Plastic (From an ice-cream or yoghurt container)
- An Elastic/Rubber Band (I find that many small ones strung together works better than one bigger one)
- Tape (Most types of glue dissolve the polystyrene foam)
- Craft knife/scalpel
This is a fun toy to use and does not take much time to make (and it will cost you virtually nothing since most people throw away the majority of materials needed).
Step 1: Frame/Body
Next come the joins/separators on both ends of these beams. One is just a wooden rectangle, the other is composed of 2 smaller wooden rectangles and a tube which I will explain how to get now. "Un-bend" a paperclip and use a sharp knife to make a circular cut (through the plastic insulation) around any point on it. Pull on both ends of the insulation until one part of it comes off the paperclip. Cut this tube to size and use it for this step. (the tube I cut for this helicopter was cut to 7 mm)
Cut a rectangle (mine measured 10 x 6 x 1.6 mm) from a piece of wood for the bottom end of the helicopter frame. Then cut 2 smaller rectangles from the same thin piece of wood (either of the two on mine measured 4 x 6 x 1.6 mm) for the top end of the frame.
Glue the bottom separator to the "inner" bottom edge of one of the frame beams, also glue one of the top separators to the top of this beam. Then glue the paperclip tube onto this top separator.[See picture 4] Glue the other top separator onto the other main beam and then glue this onto the existing frame construction [See picture 5]
Now, to strengthen the 2 ends of the frame and the joins there, you will use some aluminium from a can. The bottom end is simple, just cut a rectangle from the can (mine measured 14 x 16 mm) and bend it in half, in a sharp-cornered "U" shape. [See picture 6] Then glue it over the BOTTOM separator. [See picture 7]
Then for the top, cut a strip of aluminium (mine was 35 x 6 mm) and wrap/coil it around the top part of the frame and then glue it on there. [See last two pictures] Be careful not to get any glue into the tube or you will have to start from there again.
Step 2: Drive system
Next, you will need to make the 2 mirror-image rotor hubs. For this, you will use that plastic from a container. Cut out 2 rectangles from it (mine were both 15 x 4 mm) and determine the middlemost point of both of them by drawing 2 corner-to-corner lines and their intersection is the point you will need. Prick a hole through this point. [See picture 2 to see how I got this point and approximately where other lines will be] The best I can tell you about how to find where the new lines will be is to look at pictures 2 - 6 and try to copy that. (On this model I cut 2 strips off each hub but that isn't necessary.)
I have included a Google Sketchup 3D model containing both the top and bottom hub, so hopefully it makes understanding the next step a little simpler.
The red lines in [Picture 2] are the axes for bending the blade-to-hub attachment. The inner two must have everything outwards of them bent down. The outer two lines must have everything outwards of them bent back up. Once you have made the one hub, follow the same process to make the second, but remember that it must be the mirror-image of the first one because it will be spinning the other way.[See picture 6]
Cut a small rectangular piece of wood (Mine was 5 x 8 mm) and prick a hole in the centre. Glue this piece of wood under one of the hubs and make sure that the holes in the plastic and wood align.[See picture 9]
Thread 2 beads onto the top end of the shaft and make sure no glue gets on them because they must be able to turn freely. Place a third bead onto the shaft, but this time glue it in place. Slide the hub (with the wooden part attached) onto the shaft and glue it both to the shaft and the glued bead. Slide a fourth bead onto the shaft and glue it to the shaft and hub for an extra bit of strength.
Next, make the bottom elastic hook. Clip the head off the other pin and bend it into a "G" shape [See picture 12]. Put this around the bottom part of the helicopter frame and make sure it is in the centre of the bottom separator before gluing it in place. [See picture 13]
Next, add the bottom hub for the bottom set of rotor blades. Because there is a pin around the bottom of the frame, it will probably not be flat enough to glue the hub to. Fix this problem by cutting some thinstrips of wood and gluing them around the bottom of the frame [See pictures 14 and 15]. Glue the bottom hub to these wooden parts and make sure it is not skew.
(Keep in mind when choosing pins that a longer one will stick out further above the blades so if you plan on using your helicopter indoors it will stay in a small space on your roof like a spinning top.)
Step 3: The Blades and Elastic Installation
Start with a sheet of polystyrene foam from packaging or similar and cut 4 equal rectangles out of it. (Each of my blades measures 160 mm x 35 x 2 mm)
Make a small slit into the base of each blade [See picture 2] so that they can all fit onto a hub attachment nicely. Slide each one onto an end of a hub and add tape afterwards to keep the blades from being pulled off while it flies.
(For the elastic band powerplant I find that strings of a few narrow elastics work better than one or two broad ones. Also, for better flight duration the elastic should be longer than the frame so that the bottom end can be held by hand while the top end is wound, causing the elastic to "shorten" then it can be hooked onto the bottom hook of the frame.)
Hook your choice of elastic/rubber band around both hooks and wind the top set of rotors backwards. (You can tell which way is backwards by feeling the air above and below the rotors when you let the elastic unwind, the air should blow downwards when you let it do this.) Your helicopter is complete!
Release the hand you were using to wind the helicopter and the other hand from the frame and it should stabilize and fly by itself. How much you wind it up is up to you, but don't overwind the elastic or it will snap.(Mine is good for about 75 revolutions)
Do not try launch it away from you, it will flip back around and fly at you with a spinning pin sticking out towards you. This is very dangerous. Release it with the body vertical for best results.
If your helicopter does not fly in a very stable manner or rotates on its side or upside-down, bend the top set of rotor blades upwards to form a slight "V" shape.
Step 4: Update [For Extra Fun :)]
Above are some pictures of it and I have also embedded a video of it. The LED doubles the weight of the helicopter and it only has about 2 fifths of the flight time. Stronger elastics are needed to compensate for the additional load.