Building techniques

[Kovu]

Yea rice works perfectly, had my ipod go swimming put it in a cup of rice, it worked the next day.

[kjhsscioly]

Would the silica gel packs you get in shoes work too?

[illusionist]

Would the silica gel packs you get in shoes work too?

Yup those work great as well. I would suggest throwing some of those in with the rice.
Luckily in Michigan, our humidity levels aren't that bad yet...

[kjhsscioly]

Ours are awful, and the day of regionals was somewhat overcast, so the weather has been shifting drastically. State shouldn't be an issue now, but the humidity is high is April.

[New_Albany_Eagle]

What is the best design for the wings? My partner and I are new. We want to make wings curved out of balsa wood.. is this a good idea?

Olive

[kjhsscioly]

Take a look at the picture gallery - it will give yo an idea of what to do. I don't think it is recommended to start with curved balsa, you would be better off using 1/16 sticks to build. You want a twisted shape on the rotor, which you would do by building a jig to support the angled pieces while you build. Once you have the long pieces in place, then the ribs can be fitted in.

[illusionist]

From jander14indoor:

The conventional solution is a dual rotor copter; both rotors mounted coaxially and counter rotating. One is attached firmly to the motor stick; the other rotates free on a wire shaft. In flight, BOTH turn in opposite direction as one end of the motor torques on the 'free' rotor, and the other end torques on the 'fixed' rotor attached to the motor shaft.

Let’s start with the 'fixed' rotor.
• We'll start with the axis of the rotor which is the motor stick itself. It should be about 12 inches long and weigh about 1.5 gm.
• Select two spar sticks for the rotor. These are long straight stiff pieces of wood. Just fewer than 40 cm long, probably 1/16 by 1/16 and weighing 0.3 to 0.4 gm. These pieces are key, select them carefully.
• Now, glue the first spar to the rotor, oh say 2 inches down from what will be the top of the motor stick. Glue it so it is centered on the motor stick, opposite side from the rubber band. Make sure it is SQUARE to the motor stick. A jig is handy here. Don't try to do this free hand. You won't be accurate enough.
• Now, measure up the motor stick, say 1 1/4 inches. You are going to attach the second spar here, again centered on the spar.
BUT, you have to rotate this spar around the axis so the tips of the spars are separated about say 4 inches when looking down along the length of the motor stick. A little trig gives me about 28 degrees of angle rotation. And that's clockwise looking from the top of the stick, by convention. It only matters because the free rotor you build next MUST rotate the opposite way. As long as you wind correct, either can work.
O Now, to attach the spar at an angle with good glue joint, you'll need to sand a shallow angled notch into the motor stick on the same side as the first spar at the marked location. The angle is of course 28 degrees in the direction you want. Glue the second spar into this notch, again SQUARE to the motor stick, but angled to the first spar when looking from the top. A jig of some kind is handy.
• The next step is to put some ribs between the spars to define a twisted surface to put tissue or Mylar covering on. Measure and mark along each spar 5, 10, and 15 cm from the motor stick. Using light balsa cut and fit a rib between the spars at each of these locations and at the spar tips. Make sure you don't cause the spars to bend!! These ribs can be straight, or have a slight curve like a wing. This is finicky hand work, cut, fit and reject if not perfect. Once you are sure the rib is right, glue it in place. Of course a jig is handy, be creative.
• Now, cover the rotor from the 5 cm rib out to the tip. The inner 5 cm theoretically adds thrust, but as a practical matter, most of the work is done at the tip and the inner area just adds drag and weight. Covering is just like covering a Wright Stuff wing, except the surface is curved in three dimensions. It can be done in one piece, but treating each section on its own might work better.
• Voila' you have a rotor.

The 'free' rotor is almost exactly the same except for the axis. For the free rotor the axis is the shaft (think prop shaft wire on a Wright Stuff plane). The spars are selected the same and are just as critical here. You glue them to a very long prop shaft (rubber hook at one end, locking hook at the other). Same spacing, same rotation difference, but in the OPPOSITE direction as the fixed rotor. It’s a little tough gluing to the wire securely, so you may want to cut two 1/16 square spacers about 1 ¼ inches long to slab alongside the wire and glue between the two spars. You also want to glue the locking hook to the top spar VERY securely. Everything else is the same.

Hope that helps there are other methods, but I've already taken a lot of space.

Note, the dimensions I gave are approximate!! They should give you a good flying copter if you keep the overall weight to 4.0 gm. MAX. The ideal is for YOU to determine. But don't be too surprised if you find the best thrust is with the lower rotor at a slight higher pitch then the upper! And maybe a three or four bladed rotor is better. Only testing will tell.

[kjhsscioly]

the above instructions sound really good, but I have a few things to add. I noticed that illusionist said to glue the spar to the motorstick straight off on the fixed rotor, but I find that it is easier to build both rotors off the motorstick, then mount them so they are exactly the same distance from the motorstick. When I build, I draw out a diagram, the cut basswood sticks to support the far ends of the upper spar, with one one spar lying flat on the board. The other will be diagonal to it, but a few cm above it, so it needs to be supported. Putting basswood as a support ensures equal pitch.

[illusionist]

Just saying, those were Jeff Anderson's instructions. Not mine. I just quoted them!
If you are using a jig, then obviously build it off the helicopter. If not, you can build it on there.

[aubrey048]

Take a look at the picture gallery - it will give yo an idea of what to do. I don't think it is recommended to start with curved balsa, you would be better off using 1/16 sticks to build. You want a twisted shape on the rotor, which you would do by building a jig to support the angled pieces while you build. Once you have the long pieces in place, then the ribs can be fitted in.

Curved balsa . . . *sigh* How is this accomplished, exactly?