Presented for your entertainment, an animated picture of a paper Watt linkage complete with James Watt.
There are two Watt linkages one above the other which work together the keep the neck piece vertical.
I'll put it together into a download in the next day or so. I'm hoping to expand the mechanisms section so that each mechanism described has its own matching download.
"Ah - Grasshopper - when three bars are joined they can, like the eagle, make a straight line"
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The original steam engines used pistons that were powered in only one direction. As the piston pulled down, it pulled on a chain link over a curved rocker similar to the nodding donkeys seen in oil fields. When James Watt realised that he could dramatically increase the power and efficiency of the engine by powering the piston in both directions he set out to find a simple way of using the straight line motion of the piston to drive the circular motion of a drive shaft.
The Watt Linkage, shown here, is the solution he came up with. This mechanism is still widely used. The straight line motion is at the centre whole in the blue bar. It is not absolutely straight though in a mechanical situation it is probably straighter than the tolerances of the bearings. The figure of eight dotted line shows how the centre point moves over its full range of movement, not just the straight area.
I think we need a downloadable, make-able version of this nifty mech!
Using Flash
Hopefully this animation will work in all sorts of browser windows from Windows machines, Linux boxes to iPhones and iPads. Let me know how it's looking for you.
Make your own Watt Linkage here.
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A working Peaucellier linkage to download and make. The simple geometry of the linkages is used to convert rotary motion into straight line motion. Members can download the parts for free. Non-members can download for a small fee.
Print the two parts sheets onto thin card. (230micron / 230 gsm) Solid lines show where to cut. Dotted/dashed lines are score lines. Grey areas show where the glue goes. Use white school glue (PVA) to glue the parts together.
Fold the support round and glue it together.
Fold over the top and glue it down as shown. Notice the dotted, valley fold line on the front.
Fold up the base to make two triangular tube sections as shown.
Glue the stand to the base using the grey area for alignment.
Glue together the parallelogram as shown. Notice the 'Top' label.
Glue the parallelogram to the stand using the centre link. The 'Top' is at the top of the picture (as you'd expect)
Glue the lower linkage between the triangle on the parallelogram and the triangular area on the top back of the stand. Notice that it should be roughly one millimeter from the stand.
Glue the upper linkage into place. Make sure that you don't get glue on the creases.
Glue the post into place. You might need to rock it back and forth a little so that it lines up with the path of the end of the linkage.
Fold the handle in half and glue it together then cut out along the grey lines to make a curve.
Finish off the mechanism gluing the handle into place. Let the glue dry.
Move the handle up and down and the left side of the parallelogram will move in a straight line parallel to the post. Clever stuff Monsieur Peaucellier!
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Invented in 1864 the Peaucellier linkage (poo-selli-yeah) linkage was created as a way of making straight line from circular motion. It was used in steam engines to control valves without the need to guides. The peaucellier linkages, invented by, you guessed it, monsieur Peaucellier, is mathematics in motion. The four red parts are all the same length, the circle radius is the same as the green link and the two yellow linkages are the same length.
Using Flash
As long as these ratios are adhered too, the grey dotted motion line will be straight.
I've been helping #1 Son with his mathematics revision so I've been in a geometrical frame of mind. Inspired by the maths, here's my paper version of the Peaucellier linkage. The end of the linkage moves up and down maintaining the same distance from the vertical bar with the arrow on. Animation below.
I'll be doing this as a download then I'll have to find a use for it in a model. Something that moves up and down in a straight line. A meerkat? Groundhog?
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Further adventures with the Early Bird model. I've been trying different ways of of linking the worm to the bird's beak. Two ideas made it from the drawing board to the prototype stage.
First, I tried cutting a notch in the beak, wrapping a loop of card round the beak and gluing it first to the worm body then gluing the head on the other side of the beak. This made a flexible link which is what I was after but as I was testing it the loop slipped off the beak a couple of times. Not what I want in the finished model.
The second alternative, I've cut a slot in the beak and threaded a couple of back to back tabs through it and onto the worm's body and head. This works just as well as the other technique with the right balance of flexibility and rigidity but has the added advantage that the worm can't slip off the beak. Choice made. Box next.
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All sorts of family related chores to do today but I have managed to squeeze in a bit of work on the bird project. I was trying to change the way the head moves to give it a little twist as it moved up and down. The head is joined to the body using a four bar linkage. Keep the opposite pairs of linkages in a four bar linkage parallel and all the parts move in a regimented lined up fashion. Small changes to the alignment, however, can make for more fluid looking results. Check out the animation above. In the bird on the left horizontal bars are 50mm long and the vertical bars are 30mm. The result is a straight forward parallel movement. In the bird on the right the vertical bar joining to the head is only 25mm long, all other measurements are the same. The result gives the movement just a little kick and a little more realism. I've implemented that new linkage set in card and it works nicely. Pics tomorrow.
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This Much Robot, press down on the head of this delightful paper robot and the arms open wide. "I love you this much!" The arms use a simple concertina mechanism to open and close.
Print out the parts onto thin card, follow the instructions and make your own "This Much" robot. This model was originally published on the Workshop Notes blog and is free for members to download. Non members can download the file for a small fee.
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I've been polishing off the paper character that I was working on the other day. (No name yet, ideas?) The idea is straight forward. Lift the body and the tongue pops out. Initially I've had problems with the tongue catching on the lower lip and so not sticking out. Time to apply to wonder that is the four bar linkage.
The initial model used a simple four bar linkage with two sets of parallel bars. (Left hand picture) The result is that the tongue stays level as it moves.
What I really wanted was for the tongue to lift clear of the lower lip as it moved back. To acheive this effect, I've increased the length of the top bar by a small amount. The right hand picture above shows how this changes the movement.
Here's the resulting part, cut out and assembled. Just that small change makes all the difference.
Once it is in place in the box the tongue lines up nicely with the lower lip both in the forward and retracted position.
Sorted. Colour scheme next.
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East West. Turn the handle and while one character bows the other raises his hand to shake hands. Realising their mistake they switch greeting - an endless cycle of polite misunderstanding! Print this model onto thin photocopier card then all you need to make the model are scissors, ruler, PVA glue and a sharp knife.
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