Exercise is good, so I'm told. But if you don't have time for it you can always create a paper avatar to do it for you. Hence the push-ups model I'm working on now. Soon I'll have the vicarious physique of a seven stone weakling.
So on to the mechanics! Sometimes with mechanisms the best way to create a movement is not to mirror reality. When I'm doing pushups (ha.) The muscles in my arms, chest and shoulders contract to lift my body from the ground. In this project I'm actually lifting the body via the feet.
I see two main competing ways to achieve this, via a cam or using a crank. Cam first. I fitted a cam to a drive shaft and threaded it into the box. The cam rests against a cam follower linked directly to the feet. Turn the handle and the body lifts up and down.
It works reasonably well, the plus side of the cam is that you can create any movement profile you want within the limits of the cam follower. In this case I was able to add a little dwell at the top and bottom of the travel, a slight pause at each extreme of movement. The downside - there is always a downside - is that the movement is only driven up and relies on gravity for the return. Not a huge problem but it does give a slightly floaty feel to the movement.
The red writing on the side is where I measured up for fitting a crank.
Onto the crank. I used the crank template I'd created in the recent crank slider project with the throw set to 9mm. Everything fitted together nicely, I simply needed to turn the box top round so that the feet were at the other end away from the drive handle.
Looking good! I must say I was surprised just how much more satisfying the movement is using a crank. Very positive in both direction and the lack of dwell doesn't seem to be a problem. Yep. I'm going with that.
It'll look better with two arms and a head. I'm still not sure about the character though. Robot? Pirate? Gentleman in a top hat and tails? Hopefully inspiration will strike soon.
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This project is a cam powered T.Rex automata. The head and lower jaw are driven by separate cams which can be interchanged to change the way the T.Rex moves and so tell a different mini-story.
The T.Rex is a fascinating project to make with students aged twelve and up. By building this model, students will be improve their skills in accurate cutting and scoring. Students will also learn how cam profiles can be used to create movement and how these movements can be used to act out a story.
The project parts come as a downloadable file. Members of robives.com can download the file for free. Non-members can download the file for a payment of just £2.50.
Print out the parts onto thin card. (230 micron 67lb). Score along the dotted lines and cut out the holes before carefully cutting out the pieces.
Make up the base and the top in the same way as shown in the picture above. Make sure that the edges are at right angles.
Glue together the four parts of the body.
Assemble the lower jaw.
Glue together the head.
Fold round and glue together the head inner.
Glue the head inner into place so that it is lined up with the crease across the top of the head.
Glue the two tabs on the lower jaw to the top back of the body. Make sure that the lower jaw is free to move up and down.
Glue the head tab into place on top of the lower jaw tabs.
Fold the legs and arms into half and glue them together to make double thickness card. Once the glue is dry carefully cut out the pieces.
Glue the lower legs to the grey areas on the body. Note that the legs bend forwards at the joint, use this to get the right leg on the right side.
Glue the two arms into position as in the picture above.
Thread the jaw push rod up through the body and glue the tab to the grey area on the underside of the jaw.
Thread the head push rod up through the body and glue it to the head support piece as shown.
Glue on the feet and glue the feet to the box top so that they are one on either side of the hole with the back of the foot just touching the back of the box top.
Fold up and glue together the two cam followers. Notice that the triangular section at the end of the cam follower use valley folds.
Glue the cam followers to the grey areas on the front of the box top.
Glue the end of the push rods to the cam followers.
Assemble the two parts of the box.
Glue the box body to the base. Make sure that it is straight and square.
Glue the top to the box again making sure that it is straight and square.
Glue together the drive shaft tube. Glue the washer to the end.
Thread the drive shaft through the holes in the box and fix the second washer into place. the drive shaft must be free to turn.
Assemble the handle in three steps. Fold over the two sections and glue to make square section tubes.
Fold on section into the other and glue them at right angles.
Roll round the long tab and glue it down.
Glue the handle to the drive shaft.
Making the interchangeable cams.
This project features easily interchangeable cams. Make a set for each story you want to tell. There are two cam sets already included in the pack as a well as a blank set of cams for you to design your own.
Fold round and glue together the cam shaft. Line up the stop with the grey line and glue it into place.
Thread the head cam into place on the shaft. If you are experimenting with cam profiles, don't glue them on yet. Thread the lower jaw cam onto the shaft. Make sure that the read line on both are lined up so that the parts are in sync with each other.
Once you are happy with your cam design glue them to the shaft.
Lift the cam followers out of the way and thread the cam shaft into the drive shaft so that the stop butts up with the box.
This cam pack makes the T.Rex eat. Nom nom nom!
Don't forget to complete the model by gluing the eyes into place otherwise it won't be able to track down its prey!
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I've found another project that I had originally posted on the Flying Pig website many years ago. If you are a member you can download it at the link. It is one that I am particularly fond of so I'm a little surprised that I'd forgotten about it. I reckon it could make an interesting pendulum powered model...
A model to bridge the gap between the precision of the cardboard engineer and the philosophy of the Zen Monk.
Consider the sound of the one hand clap.
Through the crank and the cam the cardboard engineer can stroll through the garden of enlightenment and dip a toe in the pool of infinity. Print out the model and follow the instructions for construction.
Enlightenment awaits.
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A free mini-zine for everyone to download and make. This pocket size booklet is a guide to using cams in your paper animation projects.
Skip to the end of this post to find out how you can receive one of the limited edition signed and printed versions!
(Only 20 available ) All gone! Look out for the Lever-zine coming soon!
Download the file and print it out onto ordinary printer paper. Set the print-out to "Scale to fit" so that it prints as large as possible on the page. If you are using an inkjet printer let the ink dry completely.
Carefully cut out the page along the thin black border line.
Fold the page in half along the shorter centre line. Make sure that the crease is accurately lined up with the centre of the page and that it is crisp and sharp.
Open out the page then fold the two edges into the centre crease, again paying attention to accuracy.
Open out the paper again then fold and crease along the long centre line. (Accurately!)
Take a sharp knife and cut along the centre black line starting at the point arrowed above and stopping at the end of the line.
Fold the paper in half along the long centre then scrunch it up to make this cross shape.
Fold the pages round as shown. Place the completed mini-zine on a flat surface and rub over the creases to make them crisp and sharp.
Done!
The result should be like this where black lines are cut lines, dotted lines are valley folds and dashed lines are hill folds.
Learn all about cams by reading the booklet!
I have printed out twenty copies of the Using Cams Zine which I will be signing and numbering. If you would like to receive one of these mini marvels I'm asking for a donation of at least £2ukp / $3usd after which I will be delighted to post one out to you anywhere on earth! Click on the donation button above and fill in your details. All gone!
Let me know what you think of the zine format in the comments below. Thanks!
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The heart of many automata, both traditional and the paper variety, is the cam. The cam is perhaps the most flexible way of driving a mechanism. By changing the shape of the cam profile all sorts of different movements can be described.
But on its own, a cam just goes round and round. To use the movement the mechanism needs a cam follower, the part that runs along the cam's surface. In more traditional automata, made from wood and brass, it is quite possible to run the cam follower so that it is perpendicular to the cam, as in the first picture above. In paper based models this doesn't work so well. By their nature paper models have more flex and tolerance. A perpendicular cam on a paper based model will tend to flex and bend rather than running smoothly up and down, not what you want! Paper is at its strongest when it is under tension (being pulled) To use this strength, cam followers in paper models tend to drag across the cam surface (above right)
Using Flash
The design of the part of the cam follower that touches the cam is important. There needs to be a finger shaped end to closely follow the surface of the cam. More complex curves need a narrower finger but, as is often the case with engineering and design, there needs to be a balance between fineness and strength. The animation above shows how well the narrow cam follower follows the cam compared to a stronger wide one.
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I've been working on the Early Bird model. I've repositioned the bird further along the base and hooked up the worm.
I think I'll have to extend the box a little further so that it fully encloses the worm's hole.
I've made up a snail cam with a 15mm drop. Next step is to fit the cam into the box and add the ratchet. Fingers crossed that there is room!
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Which Came First? Something of an engineer's joke just in time for Easter. Turn the chicken shaped cam and the egg pecks back and forth (!?) Originally published on the Flying Pig website I've made a few minor updates and re-done the photography. Paid members can download this model for free, none members can download it for a modest fee.
Print out the parts pages onto thin card. (230 micron / 230 gsm) Score the dotted lines and cut out the holes before cutting out the parts.
Fold the chicken on half and glue it back to back to make it double thickness. Fold the tabs out so that they don't stick together.
Once the glue is dry, cut out the chicken.
Fold up the cam shaft and glue it together.
Slide the chicken onto the cam shaft using the letters on the tabs for alignment.
Glue together the two parts of the box.
Assemble the cam follower as shown above.
Thread the end of the cam follower with the three tabs up through the hole in the top of the box. Glue the single tab to the front of the box. Glue the three tabs to the box top in the grey areas.
Thread the chicken into the box so that it is facing forward.
Glue the egg inner together and glue it to the back of one of the egg pieces as shown.
Glue the other face of the egg into place.
Assemble the handle by folding the the two square section tubes. Fold it in half and glue it together.
Glue on the two washers. Glue on the handle.
Finish the model by gluing the egg to the top of the cam follower assembly.
Once the glue is dry, turn the handle to see the egg peck!
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This question was posted on the cams page of the mechanism pages. It's interesting so I thought I'd re-post it to the blog where more people would see it.
Hi Rob, found the site this week and really like it, nicely done!
I was trying to envision a cam that could be used to make the cam follower appear to pause at both and upper end and lower end (in your animation it pauses at the lower end).
To do that, would you just draw two circles of different dimensions, connect their outer edges, and spin along the center of the bigger circle? I added to picture to show what I was talking about:http://www.tooz.us/cam.jpg
I realize that the pause and the top and bottom will be of different lengths of time, but that seems necessary to get the cam follower to roll along nicely.
Thanks and keep up the great drawings!
A cam is, at its simplest, a surface describing a movement, all wrapped round in a circle. The highs and lows of the surface create the highs and lows of the cam follower's path.
To create a flat area in a cam, an area where the cam follower doesn't move up or down, you need an area that follows the circumference of the circle centred on the centre of the cam.
In this cam there are two quarter turn flat areas. In a mechanism this would give you a cam follower that stayed high for a quarter turn, drops down, stays still again for another quarter turn then rises again. It should do what you are after.
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Downloadable interchangeable cam model. Build the model and learn first-hand how cams work! If you are a member, first of all, thank you - I couldn't do this without you! Secondly, as a member you can download the parts at the end of this blog post. None members can download the file for a modest fee, for which, thank you as well. Print the parts out onto thin card (230 micron / 230 gsm is perfect)
Score along the dotted lines and cut out the circular holes before cutting out the pieces. (Don't cut out the square hole in the box top. Follow the instructions below to complete the model.
The completed Interchangeable Cam model.
Fold round and glue down the box top as shown above. Make sure that the end touches the crease line at the point arrowed. Set it to one side to let the glue dry completely.
Fold over the cam and glue it together. Make sure you don't get glue on the four tabs.
Cut out the cam.
Make up the cam shaft and glue the cam in place, make sure that the orientation is the same as in the picture.
Fold round and together the two box stiffeners. Glue them to the inside of the box parts so that they are just above the circular hole.
Glue the two box halves together as shown.
Retrieve the box top, carefully cut out the square hole through both layers of card.
Glue the top and bottom of the box to the box, use the grey areas for alignment.
Make up the cam follower and and the push rod.
Thread the drive shaft through the two holes in the box. Note the square grey areas are to the back of the box. Glue on the washers making sure that the drive shaft is free to rotate.
Assemble the handle in three steps. Fold round the handle parts to make a square section. Fold one section into the other and glue down. Roll round the long tab and glue it down.
Glue the handle to the drive shaft.
Glue the cam follower to the box top then glue the push rod to the cam follower.
Complete the model by slipping the cam into the drive shaft.
That's it! Turn the handle, the cam turns and the cam follower moves according to the shape of the cam. Find out more about how cams work in the mechanisms section.
The kit comes with four different cam profiles shown above as well as a sheet of blank cams for you to design your own. Use the model to help you design cams for your own models!
Part of the Paper Mechanisms Multi-Pack - Buy and save!
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All done, I've completed the interchangeable cam model, complete with interchangeable cams!
All I need to do is write the instructions. Tomorrow. I promise.
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