I noticed my son was more often playing with the glider by carrying it than by throwing it. With this in mind I decided to make a few more toys specifically suited for that. Now, if I was half the carpenter my dad is I would have used wood because it's more durable. Since I'm not I turned to cardboard again. I did not take detailed WIP photos of these but I will do my best to describe the process. If you have any questions, ask in the comments and I'll do my to clarify things.
Essentially, the design step was the same. I drew a design on the cardboard and then I cut it out. On the second helicopter and the biplane I ended up cutting the fuselages 3 times and then sandwiching them together with hot glue for more strength. The first helicopter just saw me going back and re-enforcing key sections (the tail, the rotor pivot point, and the skids with additional cardboard and hot glue.
To make the rotors and the propeller I stuck a toothpick into the fuselage at the pivot point for the moving blades. It was hot glued into place and then a small cardboard square was impaled on it and glued into place. This was essentially to make it so the blades had more of a contact point with the fuselage for added support and since I hot glued from below to ensure no glue would get on the rotors and cause them to stick. Next I hot glued 2 long, thin pieces of cardboard into a cross formation. This was then impaled on the toothpick as close to the the center point as possible. Another tiny square of cardboard was impaled on the toothpick over the rotor blades. The toothpick was then cut down to stick out just above the last cardboard square. And finally I finished this off by putting a glob of hot glue on the end of toothpick. This was for safety reasons. The result was a firmly fixed toothpick pole with a pair of rotor blades that could be freely rotated by hand.
And with that method I was able to create a helicopter and a biplane that are durable enough to be played with and cheap and easy enough to make that if my toddler should break them it's no loss at all. The final cost on this build came up to a whopping $0 since I already had everything I needed. These took a little more work than the original glider but still it was only about 20 minutes for each one.
My final thought on these is that the next time we need to add aircraft to our air force I will let my son color or paint these (after I draw the fuselage but before I cut them out) so he can be a little more involved.
Forces are the pushes and pulls of our universe. This neat little device can be built for almost nothing (I used plumbing off-cuts), but will let you measure pushes and pulls around you, as well as doing experiments with different-sized forces.
It is perfect for kids still at school as well; it can be made by dads-and-lads together, or by competent older children alone, and it can be calibrated in Newtons and used to do home experiments to reinforce schoolwork (any UK readers with kids in Years 6 or 9, this will help them get ready for their SATs).
As it stands, the force meter will only measure pushes. To measure pulls, you need a hook or loop. I'm adding a loop:
Thread the wire through the two unused holes in the inner tube and tie a knot to hold it in a loop.
The wire I used was quite smooth, so required three over-hand knots in opposite directions to lock. (I may still add a drop of glue to the knot, just to be sure.)
Your meter is essentially finished, but you cannot yet actually measure any forces with it. It needs to be calibrated.
Stick a piece of tape along the visible part of the narrower tube. Make a mark on the tape where the bottom edge of the wider tube is. This is your "zero" point.
Add a known weight. Either hang it off the hook or balance it on the narrower tube. It's a lot easier for you if the weight is sensible number (say 100g, 200g, 50g), as you will be using it to draw your scale. Make a mark on the tape.
If possible, repeat with a couple of other known weights, and mark those on the tape as well.
The Science Bit:
What you've been adding to the meter is not weight - it's mass. The weight is the pull on the mass due to the local gravity-field (i.e. Earth's gravity). A mass of 100g actually weighs a smidge under one Newton (1N). A mass of 1kg weighs 9.8N.
Label the marks you made in multiples of 1N. If a mark was due to a 100g mass, label it 1N. A 50g mark should be labelled 0.5N etc.
Either by eye or my measuring and marking, you should now be able to complete the scale on your force meter, filling in gaps and extending the scale to the end of the narrower tube.
The exact range of your meter will depend on the thickness, length and age of your band, and on the length of your tubes.
Hold the meter by the outer tube.
Objects can be hung from the loop or hook to find weights, or pulled with them to measure the force needed to move it (say, if you were investigating friction). Turn the meter round, and (still holding the outer tube) you can use the inner tube to measure the force of a push, or to weigh something that won't hang on the loop, such as balls or eggs.
You can also use the meter to investigate the effects of known forces, pushing or pulling until the meter reads a certain force and observing the effects. A fun one is to fire toy cars across the floor; how far will it travel when fired with a force of X Newtons?
Well, not hacking, as such, but variations on a theme.
You may find yourself needing to measure forces that are outside the range of any single meter, so you might want to make a range of meters, using different bands or pieces of bungee or shock-cord.
The materials may not be to your taste, so change them - you can make a nice meter with a piece of copper tube for the outer, and a length of dowel replacing the inner tube (which makes attaching a hook a lot easier, since it will simply screw into the end of the dowel, just make sure you don't screw it into the band).
Anyhoo, the exact materials you use don't really effect the operation of the meter, as long as they are stiff enough not to bend much when you use the meter, and you avoid rough edges that will saw through rubber bands.
Enjoy.
(Perhaps you would like to add a comment with ideas for other uses for this instructable?)
So force meter is a fancy term for a scale here? Should get the creative juices flowing for kids needing a project for school. Stating the obvious rubber bands deteriorate somewhat rapidly. Recalibration would be needed every time the bands are replaced. For the long term PVC pipe can be used to adapt a simple hardware store spring scale. _scale to measure both pulling and pushing force. I have been keeping an eye out for a hydraulic cylinder that has a bore area of exactly of 1 square inch. That way a simple pressure gauge can be used to indicate the force in pounds.
Strictly speaking a "scale" measures mass/weight only in respect to the to pull of gravity. A force-meter will measure will measure the amount of force needed to move an object along any vector. A scale will not work in micro-gravity but a force meter/guage will continue to function. A force meter responds to friction, moments of inertial etc.
A "scale" refers to a particular use of force-meters as weighing devices - yes, they measure the force placed upon an object by the mutual gravitational attraction of the object and the Earth, but the scale is graduated in whatever units the user finds convenient, be they Newtons, pounds or even kilograms.
I like this meter! Will build one (with a tensile property testing rig, see below) and post during December holiday!
Different Application:
Tensile property testing rig:
Referring to step 8, you mentioned using different materials for different measurement applications. This gave me the idea: the known mass (i.e. known force) and the resulting displacement between the 'spring' material's ends could be used to plot the stress/strain characteristics of that material.
This could give a good indication of which material is most applicable to which mass/force range by considering the linearity of the stress/strain plots of the various materials tested.
Slight modifications could make the forcemeter quite accurate: Use of vernier calipers with spring materials used in highly linear ranges ect.
Smile indeed! Good work, I will be making one of these with a mod of my own (see final paragraph for a possible modification)
Three comments:
Firstly, (as said below) the rubber band will change with use/age, replace rubber bands & calibrate often if you wish to use in a serious application.
Secondly, just to make sure:
F = m * a -> Force (caused by the weight of an object) = mass (grams/pounds meassured value ect.) acceleration (constant, g gravity = 9.81m/s^2)
Thus, 100g mass is pulled toward the earth by gravity with a force = 0.981N
Finally, your design could used to measure the max static force required to move an object and overcome the force it's friction with a certain surface can support, from which static friction constants can be derived. All you need to add is a slider that sticks to the scale. If you make the inner pipe steel you could use a small magnet, the idea being, as your measurement increases, the magnet slides, as the measurement decreases (due to the object sliding away), the magnet would remain at the maximum meassurement. (Simple Static/dymanic friction is quite interesting, fun to experiment with!)
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