Rotary motion is motion in a circle. As a mechanism rotates it turns about a fixed point. The speed of rotation is measured in revolutions per minute or rpm. This the number of complete rotations made in one minute.
Using Flash
It is the starting point for many mechanisms. Measurement: Rotary motion is measured in either angular velocity, the number of degrees turned in a given time, or in revolutions per minute (rpm). The direction of turn, either clockwise or anti-clockwise is also part of the measurement of rotary motion. The strength of rotary motion is known as the torque, the turning force. Torque is measured in Newton Metres defined as the force of one newton acting at a perpendicular distance of one metre from the axis of rotation.
Examples of mechanisms using rotary motion are wheels, helicopter blades, gears, volume knobs, steering wheel, washing machine drum and the London Eye
ConversionsRotary motion to: |
Transformations |
|||
|---|---|---|---|---|
| Linear Motion | Wheels. Rack and pinion. |
Increase / Decrease | Gears. Chain. Worm gear. |
|
| Reciprocating Motion | Piston. Geared mechanism. Cardan gear. |
Reflect | Gears. | |
| Oscillation | Crank. Quick return. |
Rotate | Bevel gear. | |
| Intermittent Motion | Geneva Drive. | |||
| Irregular Motion | Cam. |
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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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The rack and pinion is used to convert between rotary and linear motion. The rack is the flat, toothed part, the pinion is the gear. Rack and pinion can convert from rotary to linear of from linear to rotary.
Using Flash
This is the third draft on the rack and pinion animation. It should display in either Flash or HTML5 depending on which browser you are using and should be visible on a wide variety of platforms.
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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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The piston mechanism is used to convert between rotary motion and reciprocating motion, it works either way. Driving the wheel will move the piston back and forth, in this form the piston can be used to pump liquids for example creating the high pressure need in a good coffee machine.
Alternatively the piston can be driven back and forth commonly by steam (in a steam engine) or flame (in a petrol engine). In this form the piston is used to convert reciprocating motion into more useful and usable rotary motion.
Notice how the speed of the piston changes. The piston starts from one end, and increases its speed. It reaches maximum speed in the middle of its travel then gradually slows down until it reaches the end of its travel.
Using Flash
You can download and make your own working piston mechanism here and find out how it works first hand.
Thanks for your feedback about the previous post. It looks like Adobe Edge isn't ready yet, it's a shame because it is nice to use. I've gone back to creating animations in Flash, converting them using Google Swiffy and adding a snippet of home grown code to display either the Flash version or the HTML 5 version depending on which browser is being used.
Does that work for you?
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The piston mechanism is used to convert between rotary motion and reciprocating motion, it works either way. Driving the wheel will move the piston back and forth, in this form the piston can be used to pump liquids for example creating the high pressure need in a good coffee machine.
Alternatively the piston can be driven back and forth commonly by steam (in a steam engine) or flame (in a petrol engine). In this form the piston is used to convert reciprocating motion into more useful and usable rotary motion.
Notice how the speed of the piston changes. The piston starts from one end, and increases its speed. It reaches maximum speed in the middle of its travel then gradually slows down until it reaches the end of its travel.
You can download and make your own working piston mechanism here and find out how it works first hand.
I created this animation using Adobe Edge. Edge is a new tool for creating HTML 5 animations - much more standards compliant than Flash. It is currently a free download from Adobe Labs
I have put the animation up without a Flash alternative to see how it goes. I'd be grateful to hear feedback about if it works for you. If possible please could you also let me know your operating system and browser.Thanks!
(Just to be clear, there should be an animation showing a piston working just above the picture of the crank mechanism project)Keep up to date: Receive the latest blog post by email
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In the words of '68 The Outsider's song 'Bend me, shape me, anyway you want me" The perfect lyric for the poseable paper character. So it is that I'm experimenting with a joint to join hips and body together. Such a joint needs to be able to bend side to side and back to front and perhaps even allow the body to rotate. That's two, perhaps three axis of rotation.
I constructed this centre block using the same rotary joints as featured in the stick-man model. By adding the joints to two faces I add an extra axis of rotation. Left/right and front/back
...now I just need to add rotation.
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I've made a few small changes to the parts so that everything fits together better. Once done I printed out the bits, and put them together whilst watching Dr Who with #1 Daughter.
The paper model is made from two separate modules. The Geneva Drive in one box and the Watt linkage in another. They are connected together with a drive pin. I've glued the two parts together then added a couple of elastic bands while the glue dries. The egg sits on the top.
The egg is a little small for the box so I'm going to remake it 20% larger. After which I'll be fitting a dinosaur into place.
This side view shows the Geneva Drive. The output from the lower drive shaft is connected to the Watt Linkage in the next box.
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Two corrections and a modification for you to try:
Firstly, I always thought that the Geneva mechanism was named for the Geneva cross, so when I was looking up images to use in the blog and found that the Geneva cross is the same shape as the cross of the Red Cross I was a little taken aback. The cross I was thinking of was the Maltese cross. It turns out that the Geneva part of the mechanism is named for the city of its invention. I've now corrected that on the mechanism post here.
Second correction. The drive mechansim that I have been experimenting with is not a Geneva Stop, its a Geneva Drive. Makes sense. The Geneva Stop is the mechanism originally invented in Geneva. It is used in clocks and watches to stop the main spring from being over-wound. Again, the mechanism post has been updated here.
And for you to try? I have put together a file for members to download with a couple of alternative stop pieces. These parts interchange with the slotted wheel in the Geneva Six project.
The slotted wheels are made in the same way as those in the Geneva Six model. Fold the wheel piece in half and glue it together to make double thickness card then cut out the outline. Glue together the axle. Slide the wheel onto the axle lining it up with the grey line in the centre of the axle.
The new Stop Wheels fit into the project in place of the slotted wheel. This wheel lets the handle turn five full turns in each direction before the drive wheel stops as it touches the outside of the stop wheel.
In this alternative layout, the pin collides with the missing slot stopping the drive wheel turning any further. The handle in this model can turn five and a half turns each way, a half turn extra which may or may not be useful in your project.
So just to be clear, the model shown here is a Geneva Stop or Geneva Stop Works. The model with the fully slotted wheel is a Geneva drive. Sorted.
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Turn the handle on this Genava drive mechanism and the slotted wheel turns one sixth of a turn for each turn of the handle. This model uses a slightly different construction design to the four slot Geneva drive from earlier. Try them both out, see which you prefer.
Members can download the parts for free, thanks for signing up! Non members can access the parts for a modest fee.
The model comes in two forms, one colour and the other mono. Print the parts onto thin card 230gsm/230 micron.
Score along the dotted lines, cut out the holes and then carefully cut out the pieces.
The completed model in all its animated glory. Notice that for most of the turn of the handle the slotted wheel is stationary, moving only at the last arc of the turn. the stationary angle is known as the dwell angle.
Fold the slotted wheel in half and glue the two halves together to make double thickness card. When the glue is completely dry cut out the six slots with a sharp knife...
...then cut out the rest of the piece with scissors.
Assemble the two axles. Slip the slotted wheel onto the shorter of the two axles. Line it up with the grey line then glue it into place.
Glue the drive wheel body to the drive wheel back as shown.
Starting from one end, glue the tabs of the drive wheel edge to the drive wheel front face.
The completed drive wheel edge.
Slide the axle into place. Line up the red arrows with the face of the drive wheel. Make sure that the parts are straight and square then glue down the four tabs.
Make the drive wheel cut-out by glueing the remaining piece to both the drive wheel edge and the axle as shown above.
Roll the drive pin up as tight as possible and glue it closed.
Enlarge the cross shaped holes in the drive wheel with a cocktail stick then thread the drive pin into place and fix it with a small blob of glue.
Fold round the tabs on the two box parts and glue them down making right-angled triangle tubes.
Glue the two halves of the box together.
Fit the drive wheel and slotted wheel into place. The drive wheel fits in the hole closest to the end of the box.
Fold the box round and glue it shut. Glue on the washers, then glue down the tabs top and bottom.
Make the handle in three steps.
Glue up the two sections to make square section tubes.
Fold one section into the other and glue.
Roll round the long tab and glue it into place.
Complete the model by gluing the handle to the drive wheel. Turn the handle and the slotted wheel advances one sixth of a turn at a time.
Use the Geneva drive to learn how mechanisms work or as the starting point for your own design.
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