Saturday, May 14, 2011

CrazyEngineers Forum - Other Engineering Trades

CrazyEngineers Forum - Other Engineering Trades

Making a Small Helicopter at Home! :)

Posted: 14 May 2011 03:59 AM PDT

Note: Before you build the actual helicopter you will need to build a simple bending jig (a board with some nails pounded into it) to twist the tongue depressors.

What you need:
2 1/2" long Finnish Nails
Finnish nails are thin and have a small head. They are the same as the one used to build the launcher. Here they are used to make the tongue depressor bending jig.

Small wooden board or short "2 by 4".
This will be the base that the nails for the bending jig go into. This could be just about any scrap of wood or plywood with a flat side that is is at least 3 1/2" by 3 1/2" by 3/4" thick.

Pliers or sturdy needle-nose pliers
These are for bending the nails over on the bending jig.

6" long wooden tongue depressors
These provide the frame of the helicopter. I prefer the wider "senior" tongue depressors because they seem a little sturdier, but I've used the "junior" size too. Look in the yellow pages under "medical supplies" and call around. They usually come in boxes of 1000 but they're cheap and useful for lots of things. You can also try craft stores.

Drill and 1/8" drill bit
If you don't have a drill, you could substitute a nail heated in a fire, held with pliers, to just burn a hole through.

Hot water
It's amazing how you can bend wood and have it retain its new shape by dunking it in hot water first. You will be twisting the tongue depressors so the airfoils have a slant, called an "angle of attack." I like to use water that is close to boiling--using a stove, hot plate or microwave oven--and pull out the tongue depressors with pliers, but you could use hot water out of a tap and soak it a little longer.

Cardboard
Using cardboard to make an airfoil shape makes the tongue depressors go dozens of times higher. I use old breakfast cereal boxes (or poster board of comparable thickness) or milk carton. Cereal box cardboard is easier to bend into shape but it has to be kept dry. It will wilt and weaken even after landing in dew covered grass. Milk carton can shake off water but it's a bit harder to bend and you will need to sand (scuff) the surface where it glues to the tongue depressor. It would probably be best to start with a cereal box.

Scissors, ruler

Electrical tape
This will hold various parts of the airfoil together. Although black is the most common, get red if you can because it shows up if the helicopter lands in tall grass.

Hot glue gun and glue sticks
I prefer the cool-melt kind with the thin glue sticks because you are less likely to burn yourself.

Non-hardening modeling clay.

The weights in the tips of the helicopter use momentum to keep it spinning. Paradoxically, adding weight to the center would just weigh it down, but weight at the tips makes the helicopter go dozens of times higher.

When the weights are spun fast, they are subjected to centrifugal force, (although that is not technically correct) and people underestimate just how strong it pulls on the weights. If not properly contained in the tips of the helicopter, the weights fly out. I use non-hardening modeling clay available from craft stores, mail order or perhaps you could get a little from a sympathetic art teacher.

I have to confess that I did not always use non-hardening clay and I am sure other people will rediscover using coins as weights. They provide a denser mass than clay, they are easy to put in, don't deform and they don't have to be weighed to get the right amount. However, if they are flung out they are really dangerous.

This is a true story. Back in the early days of making helicopters with classes of 9th graders the launchers did not spin the helicopter up above our heads, but rather right in front of our faces. So we used full face protection in the form of a clear face shield. One day, however, I was absent for part of the day, conducting science activities at a nearby elementary school. When I returned to the jr. high school, I saw drops of blood leading to my room. A student stopped me to ask if Eric was all right. I almost fainted.

I learned that although I had left instructions for the substitute teacher to only to show a video tape about flight, my 9th grade students had somehow talked him into letting them go outside and launch helicopters. Furthermore they assured the substitute teacher that no face or eye protection was needed. A coin in a helicopter launched by a student named Eric was flung out. It hit him in the thin skin right next to the corner of his eye. He required 3 stitches. Although the scar is virtually invisible and it was an unforgettable learning experience for everyone, I was so horrified by the incident that for years I didn't do the activity with students. It was only after developing non-hardening clay as a weight that I started it again.

Although we now accelerate the helicopters over our heads, flung out coins would still be a danger to other people nearby, not to mention a threat to windows. I think using coins as weights is a bad idea. Stick with modeling clay.

Triple beam balance (or other way of measuring weight to nearest gram.
This is for measuring 4 or 5 grams of clay for each tip of the helicopter. Science teachers always have at least one. They are fun to use. If you can't find one I'll show you how to make a homemade balance in step 7.

Due to some issues, I haven't posted the article here. Read the full article at BUILDING THE HELICOPTER

Sensor Selection Simplified

Posted: 13 May 2011 10:17 PM PDT
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