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The giraffe project is in need of a retractable head.
I need to be able to extend or retract the giraffe neck and for it stay in place. I had used a similar mechanism in the boxer projects to keep them in position but fancied that it could be made slmpler.
I've come up with this single part which doubles as an outer sleeve and a leaf spring combined into one piece.
The secret is this extra millimeter. Once the parts are folded round and glued together they make a small curve of card which acts as a spring.
If you are a member you can download the parts sheet and try it out. There are only two parts but it works remarkably well.
Fold up and glue the out tube as shown.
Give the spring part a gentle curve, fold up the valley folds then glue the tabs back on themselves onto the end of the tube. The spring is curved along the dotted lines.
Inside view showing the spring in place.
The inner tube is one millimeter smaller than the outer tube. It slides into place inside the outer tube and is free to move back and forth. The spring keeps it in position. The finished result will translate nicely into the giraffe project allowing the head to be pulled up and down and holding it into position.
It occurred to me that a modified version of the slider tube would work well holding an elbow type joint into position. The extendable slider tube would work in the same way as a muscle.
This is a smaller version of the slider tube in the download fitted into an elbow. It needs a little work but could be an interesting project!
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And so to Ambleside (my alma mater) to meet friend and website regular Smelter and his partner for pizza and chat. A very pleasant time was had by all but all to soon I was heading back to the car and home. I was briefly diverted by this intriguing mechanism on the side of a gallery near the famous bridge house.
You can have a virtual wander round the area on google maps here.
The water wheel is directly linked to a large gear which in turn drives the smaller pinion wheel. On the pictures I took I was able to estimate the number of teeth on each gear. The small gear has seven per quarter section, a total of twenty eight. On the larger gear seems to be thirteen teeth per eighth section making a total of one hundred and four teeth.
104:28 or roughly 3.7:1 so the smaller wheel spins at roughly 3.7 times the speed of the water wheel itself.
The smaller wheel has wooden teeth but the large wheel seems to be cast from a single piece of iron. I'm guessing (this is a guess mind you) that the mixed materials are so that if anything is gets jammed in the mechanism, tree truck, stone, tourist, that sort of thing, then the wooden teeth will fail rather than the iron ones. A broken wooden tooth would be much easier to fix. The miller could probably whittle a new one in their lunch break.
But what is this? A bicycle chain connected to the pinion wheel!? This isn't a real water wheel! It looks like the whole thing is powered by an electric motor hidden away in the wings. Putting on a show for the tourists? Fancy that.
The pizza? Delicious Zucchini & Chilli Pizza from Zeffirelis. Thanks Smelter!
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This project is an incremental improvement to the crank slider mechanism used in the sssnake model. The modified side pieces in the crank make it easy to change the the throw of the crank and hence the range of movement of the push rod.
These three animations show the three included crank sides. Once the model is assemble the throw can't be changed as the parts are glued together so you need to pick the correct size before you complete the model.
Perhaps a later project could include adjustable crank slide length. For now, this project includes crank sides length 8mm, 16mm and 24mm.
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| 8mm | 16mm | 24mm |
Print out the parts onto thin card. I've used coloured card here.
Score along the dotted lines, cut out the holes then carefully cut out the parts.
Fold the push rod ends in half and glue them down to make double thickness card. Once the glue is dry cut out the holes and then carefully cut out the parts.
Choose the length of throw that you want then glue up the two parts of that size, in this case the 24mm sides.
Glue together the push rod.
Glue the two push rod ends onto the grey areas making sure that they are lined up.
For each of the three pins; roll them round then glue up the end so that it lines up exactly with the point of the arrows and the edge of the grey area.
Assemble the crank shaft as shown in the picture.
The pin with the green arrows is slightly shorter than the other two. It fits in the middle.
Assemble the handle in three steps.
Glue the two square sections up. Fold one section into the other and glue. Roll round the long tab and glue it down.
Fold the tab at the bottom of the box to make a right angled triangle and glue it down.
Glue the two box parts together. Assemble the slider tube, Glue it to the tab in the box lid. Glue one edge of the box lid into place.
Slide the push rod up through the slider tube. Fit the crank shaft through the holes in the side of the box and glue the box round. Glue the box lid down.
Glue the base tabs into place and then glue the four long tabs to the inside walls of the box.
Complete the project by gluing the handle to the shaft. Use this as the starting point for your own character based projects. Send pictures of what you make!
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The hypocycloid mechanism is used to make a compact, simple gear box that reduces rotational speed. In the case of this animation the reduction is 7:1. Follow one of the lobes of the six pointed rotor with your eye and see how it advances one notch anticlockwise for each rotation of the blue rotor. By adding two similar mechanisms back to back it is possible to multiply up the the gear reduction ratio
Using FlashThe blue piece is an off-centre drive shaft connected to the main drive. The output of the drive would be from the front.
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The scotch yoke is a simple, effective mechanism for converting rotary motion (the handle round the back) into reciprocating motion (the yoke and slider at the front). This project allows you to make your own working mechanism and learn how it works first hand. Members can download the parts for free, non-members for £2.50
Find out more about the scotch yoke mechanism here and here
Print the four parts sheets onto thin card. Score along the dotted and dashed lines and cut out the holes before carefully cutting out the parts.
Fold round and glue up the axle and the pin. Fit them in place in their respective holes in the wheel piece.
Fold the wheel piece in half and glue it together to make double thickness card. Make sure it stays flat as it dries. One the glue is dry carefully cut around the circle.
Glue the pin tab to the wheel 1mm above the wheel.
Roll the tab round tight and glue it down to make a circular pin.
Glue the two box sides to the box body as shown above.
Fit the box inner into place so that it runs across the centre of the box on either side of the hole.
Fold the box round and glue it together.
Make up the two box ends, thread the bushes through the holes in the box sides and glue them into place.
Thread the wheel through the box. Fix it into place using the washer. It must be free to rotate.
Fit the yoke vertical to one of the two shafts. Use the grey area for alignment. Repeat the process with the other half of the yoke.
Glue the two ends to the yoke vertical...
...and complete the yoke.
Fit one of the box sides into place on the end of the box. Line up the tab edge with the edge of the box to make sure that it is straight and square.
Thread the yoke into place as shown.
Fit the other end of the box into place making sure that it is straight and square.
Assemble the handle in three steps. Fold the two halves round and glue them to make two square section tubes. Fold one tube into the other and glue it down. Roll the long tab round and glue it down.
Complete the project by gluing the handle into place.
Turn the handle and the yoke/slider will move back and forth! Scotch yoke!
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By adding a cut out to the yoke of the scotch yoke mechanism that is the same shape as the locus of the pin it is possible to make the yoke stay still for a portion of the wheel's travel. This stationary time is know as dwell. In this case the dwell at each end of the yokes movement is 90 degrees. This changes the characteristics of the movement and has all sorts of possible uses.
Using FlashMixing both the dwell scotch yoke and the standard scotch yoke in one mechanism adds an extra layer of interest. The way the ends of the two yokes move differently could be harnessed to create a secondary movement. Perhaps a grabbing hand or a lifting flap.
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The scotch yoke is a very simple mechanism for converting rotary motion into reciprocating (back and forth) motion using an absolute minimum of parts.
Using FlashThe dark blue pin, sits in the slot in the yoke. The pin is as close to the width of the slot as possible. As the wheel turns the yoke is forced back and forth with in its two bushes (dark orange). The speed of motion follows that of a sine wave with the speed reaching a maximum at the middle of the travel and momentarily coming to a complete stop at each end of the travel.
Scotch yokes have the advantage of being very simple and direct but the disadvantage of having a lot of parts rubbing together which can cause wear and friction.
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We have a weird plug in the bathroom basin. It doesn't lift out of the sink but stays over the plug hole. Press and release it once and the plug hole seals. Press and release it again and it lifts allowing the basin to empty.
Recently the basin has started to take a long time to empty. I reckoned it was probably time to give it a clean out.
The plug assembly came out of the basin easily by unscrewing it revealing this interesting looking unit. I could make it work by pressing in and releasing the brass body to the right of the picture. Squeeze once to shorten the assembly, squeeze again to restore it to full length. Time to take it apart and see how it works.
I unscrewed the grub screw then removed the spring clip which released a steel pin. The pin was approximately 20mm long with both ends bent over at 90°. It was located inside the body in the position of the pink pin in in the picture above.
With those parts removed the main body came apart easily.
This heart shaped groove is, as its shape suggests, at the heart of the mechanism. The pin sits in the groove and controls how the body of the plug moves. To work properly, the pin has to keep moving round the groove in the same direction and not back-track on itself. This is the clever bit. As the pin moves round the groove it falls down little steps, these stop it returning in the direction from whence it came. Neat!
You can see how the pin and groove move in this animation.
I put the plug assembly back together and returned it to the basin where it now works beautifully again. Even #Truelove is pleased with this latest tinkering as the sink is now sparkling clean!
How does this relate to paper engineering? I think it could be a really useful mechanism for a variety for different automata but my first thought was that I could extend the Logic Goat range!
The flip flop is one of the core logic gates used in computer circuits. Apply an input once and it turns on, apply it again and it turns off. The Flip Flop Logic Goat would work in the same way. Just like with the plug mechanism , press the button and it would nod, press it again and it would raise its head. If I could connect a series of them together I could make Goat counting device!
And all that from cleaning the sink. Sometimes cleanliness pays off!
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Like gears, chain and sprocket drives are used to transmit rotary motion from one place to another and just like gears the ratio of speed between two sprockest is the same a the ratio of the number of teeth. In the example below there are two wheels, one with twelve teeth one with twenty. 12:20 is 3:5
Unlike gears however, the direction of rotation for any wheels within the chain is the same Any sprocket on the outside pressing up against the chain will rotate the other way.
Using FlashAlso unlike gears, the wheels do not touch, they can be as far apart as the chain allows. Any number of sprockets can be driven by a a single chain. In complex mechanisms, such as car engines, the chain often loops round several different sprockets driving them and keeping them synchronised.
Rather than using a chain, which can be rather noisy, a toothed rubber belt is often used in car engines to drive the camshaft and valves.
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In a clock the minute hand runs at one sixtieth the speed of the second hand. The clockmaker could connect the two with a 60:1 gear but even with a small 10 tooth drive wheel she would still need a 600 tooth main wheel!
To make the mechanism more compact horologists (clock and watch makers) connect more that one gear pair together.
Using FlashIn the example above there is an 8:30 gear connected to an 8:40 gear pair. To calculate the final gear reduction it is just a case of multiplying the two together. (8 x 8) : (30 x 40) which is 64 : 1200 or simplified 1 : 18.75
Simply put, turn the small gear or the right 18.75 times for each turn of the large gear.
In the example of a clock the clock maker is looking to create a 60:1 reduction. Rather than using the 60:1 gear shown above, our hypothetical clock maker could add another gear to the animated gear train at the top of the page, this time with a ratio of 1: 3.2 to complete the conversion to 1 : 60. In the gear train below the four gears can be make much more compactly than the 600 tooth monster meaning that the whole mechanism can fit into a smaller case.
In the lower right of the picture above I have scaled down the gear train so that the ten toothed gear wheel is the same size as the one matched with the 600 tooth gear in the other picture. This shows just how much space is saved!
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