A belt drive with two drive wheels is useful for transmitting rotary motion from one place to another. By changing the size of the wheels it is also possible to change the speed of rotation. I've put together a couple of new pinions for the Belt Drive model, one with four teeth and one with twelve teeth.
I fitted these into a box and joined them with a belt. I've added the drive handle to the twelve tooth wheel. Turn the handle and the small wheel spins round three times as fast (12/4) as the drive wheel.
I could have fitted the handle to the other wheel and had the speed reduced to a third.
I've added these parts to the belt drive download. If you have already downloaded it, re-download now to try this model out. The instructions for construction are basically the same for both projects.
I'm pleased with the way that this mechanism is working, time to start fitting it into a character based automata!
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Belt drives can be used to transmit power from one place to another. The typical belt drive set-up has at least two wheels and a belt connecting them together. In a mechanism using stronger materials such as wood or metal it is possible to stretch an elastic belt between the two wheels and rely on friction to make them turn. In a paper model this is not possible. To link the belt to the wheel in this project the wheels are fitted with paper studs which match up with holes in the belt. As one wheel is turned, the belt is pulled round and this in turn drives the second belt.
Print out the parts onto thin card (230 gsm / 230 micron)
Score the dotted and dashed lines, cut out the holes and carefully cut out the parts.
The completed project in action.
Glue the studs to the wheel using the grey areas for alignment.
Fold round the wheel and assemble first one side with the tabbed end (Arrowed) then the other side to close the wheel.
Fit the axle into the wheel lining up the faces of the wheel with the two grey lines on the axle.
Fold round and glue the flaps on the box top and bottom to make triangular section tube sections. These will add strength to the box.
Join the two ends of the belt pieces together to make a closed loop.
Assemble the handle in three steps. Fold up the two square sections. Fold one section into the other. Roll the long tab round and glue it down.
Wrap the belt round the two wheels.
Fit the wheels into the holes in the side of the box.
Wrap the box round and thread the other end of the axle into place.
Glue the box closed and glue down the four flaps top and bottom.
Glue on the four washers using the grey areas for alignment.
Glue the handle onto the shaft to complete the project.
Now includes to mkII belt drive with different size wheels!
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A paper butterfly for you to download and make. If you are a subscriber (thank you!) you can download the model at the end of this blog post. None subscribers can download the file for a small fee. You'll need three sheets of thin card (230gsm) and two sheets of 80gsm printer paper.
Print out the parts onto the card, note that the first six pages are marked front and back. Print out the front onto card, flip the card over and return it to the printer then print out the back. Let the ink to dry completely before proceeding. Dotted and dashed lines show crease lines, solid black lines are the cut lines. Score all the dotted lines and cut out all the holes except the push rod ends while the sheets are still whole then carefully cut out all the parts.
This is the completed model, this is what you are aiming at. Turn the handle and the crank slider / belt drive makes the wings flap vigourously.
Fold the push rod ends in half and glue them down to make double thickness card.
Once the glue is completely dry cut out the holes in the centre and cut out the two push rod ends.
Make up the crank shaft parts in two stages. Fold the diagonal into place and glue it down, this makes the tube rigid and strong. Fold the remaining flap round and glue it down.
Glue one of the crank ends to the crank centre as shown above. Don't glue the second one down yet.
Glue together the main push rod and glue on the push rod ends using the grey area for alignment.
Fold the slider tube round and glue it down. Use the small tab to join the two top ends of the slider tube together to make a roof like point. Glue the adjacent ends of the slider to to the ends of this roof.
Roll round and glue together the two wheels as shown above. Use the thin grey line to line up the piece that goes across the diameter of the wheel.
Assemble the two wheel supports and glue then to the top of the slider tube.
Gently curve round and glue together the end guides as shown.
Glue the end guides to the slider tube. There should be a gap under the end guides where the belt will thread.
Glue the tabs on the wheels to the supports. The wheels should be free to roll back and forth.
Fold round and glue down the tabs on the bottom of each of the box parts to make a triangular tube.
Fold round and glue together the box top stiffener. Glue it to the box top so that it lines up with the crease line where the tab sits.
Glue the box parts together and glue on the box top.
Thread the crank through the holes in the push rod ends. Complete the crank by gluing on the remain crank part.
Glue the slider tube to the tab on the box top using the grey area for alignment.
thread the push rod up into the lider tube.
Fold the box round and fit the crank through the holes in the box sides.
Glue down the lid.
Glue down the two tabs on the base.
Fold the vertical tabs inside the box into place to make triangular tubes.
Make up the handle in three stages. Make up the two tubes, fold them one into the other, finish off by rolling the long tab round and gluing it down.
Glue the handle into place
With the wheel level as shown, glue the end of the paper belt to the top of the wheel in the position shown. Use a thin strip of glue.
Thread the bolt down through the end guide and back up again. Glue it to the belt where it joined the wheel, you may need to cut it down to length.
Tricky bit. Move the wheel so that it is at its lowest point point (top arrow)
Apply a dot of glue to join the belt to the push rod right at the top near the top of the hole in the slider tube. Make sure you don't get any glue anywhere except where it joins the belt to the pushrod.
Repeat the process on the other belt.
Glue the two belt guides into place as shown in the picture. They will hold the belt out of the way but the belt should be free to slide through the gap.
Complete the model by gluing on the wings and body. Let the glue dry completely then give it a try!
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I've been working on the colour and layout for the butterfly model. The picture here is of a rather large painted lady butterfly.
The art work is made up from several photographs of painted ladies manipulated in photoshop and stitched together.
Having made one wing I simply flipped it to make the second. I then printed the wing out onto paper rather than card. In this model the front and back of the wings will need to be aligned accurately. Alignment printing is always difficult so I think I'll suggest printing the front and back separately onto paper then gluing them together.
I'm hoping to finish most of the layout tomorrow.
After that, I have an interesting idea for a cam based model ;-)
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I've done some more work on the combination crank slider / belt drive mechanism that I started yesterday and I must say its looking good!
The pulley wheels in the model that I made yesterday where a little bit too far apart, (above left) so I started off by remaking the top of the shaft with the wheels closer together. (Above right)
To fit the pulley wheel in place I had to taper the top of the shaft. Then it was just a case of making a narrower shaft.
To tidy up the belts I've made a simple guide to hold them up against the shaft. This picture is from yesterday's prototype where I was trying the guide out.
I've also changed the diameter of the pulleys. The originals were 14mm, these are reduced to 12mm. For the same belt movement the wheel turns a few extra degrees. The result works really well, the movement has a different feel compared with push rod driven wings, much brisker and more positive.
Here's what it looks like with a body and head :-)
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I've been experimenting with the crank slider mechanism today.
I think I mentioned before that one of the problems with using push rods to drive wings up and down is that the effective range of movement is only around 90 degrees. If you want to get closer to 180 degrees you need to use a different technique.
In the belt bot model I used a paper belt drive to move the arms the result was a range of movement close to 180 degrees. I thought I'd try the same technique but this time connected to a crank slider model.
This is my second draft.
There are two pulleys at the top of the shaft, each connected to a paper belt. The pulleys are fixed to the top of an extended slider tube. The belts are glued, through a cut out in the side of the slider tube, to the main push rod. As the crank is turned the main push rod goes up and down pulling the belts back and forth. This turns the pulleys and flaps the wings. It'll all be much clearer when I've made a model for you to try out!
At the moment the wing still only moves about ninety degrees but by making the pulley smaller in diameter I should be able to fix that. I'll see if I can get a completed prototype up for you to try in the next day or so. I like the pulleys and belts, they give a nice Heath Robinson/Steam Punk look!
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I've spent most of the day adding models to the www.flying-pig.co.uk web site. I'm in the process of converting said web site from static pages to database driven, which, unfortunately means I have to spend ages and ages moving data from static pages into a database. Once it is done its done though. And I'll be glad.
I've found time this afternoon, to put together a more complete belt driven robot. If you can imagine him with rivets and textured colouring I think you'll agree that he is coming along nicely.
I reckon I might be able to use belt drive for a butterfly model I've been thinking about for a while...
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