I've been working on the Nessie project. I've changed the design of the sleeve so that the main slider sits in a U shaped channel rather than being using a tube. This is mainly as a way of keeping the slider tube in position. I was concerned that the old design which was spaced away from the box by a narrow rectangular tube could easily move up and down. I've left the top of the channel open as the rack is held in place by the two wheels. This leaves plenty of space for the head and tail mech. 

The slide fits over the top of the rotating pin to complete the scotch yoke front and centre. The two hump wheels then fit over the slide completing the double rack and pinion and holding the slide into place. 

From the front you can see the axles supporting the wheels and the handle which drives the scotch yoke.

Turn the handle and the humps rock back and forth, the head and tail will move up and down.

Head and tail mech next. Not sure whether to use a bell crank or a cam surface on the top of the slide. I'll probably end up trying both and see which works best.

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Further progress on the Nessie project...

I've reduced the number of pinion teeth from eight to seven. The dimensions of the zig-zag piece that make the teeth have stayed the same but the extra spacing now gives the sides of the teeth more of a slope.

I've changed the way the hump wheels are constructed. The wheel is now made from two donuts and a rim. This extra space makes construction much easier.

The axle support pieces are then glue into place and the axle added.

The finished hump wheel.

Two humps will then sit above the main slider which is, in turn, driven by the scotch yoke.

From the front it will look something like this. I'll be adding a Loch Ness surface just above the level of the axles and there will be a handle attached to the drive shaft in the front centre of the box.

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The Nessie model will have two humps which will be rocked back and forth using a rack and pinion.

This is the latest draft of the hump part. The pinion teeth run the length of the bottom quarter of the hump. These will engage with teeth on top of the main slide, driven it turn by the scotch yoke.

I had originally planned to add a cross piece in the centre of the wheel. You can see the tabs where it was to be glued into place. In the end the piece was unnecessary so I've left it out. 

Gluing the rim of the wheel into place is quite tricky, especially the last stage where I just can't get my fingers in. To get round this problem I'm going to try using two ring donut shaped pieces to make the wheel. Once the wheel is complete I'll add the white axle side piece. That should make construction a lot easier.

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Flip Face! Pull one hand for a happy face, the other way for a sad face. Members can download and make this rack and pinion powered model at the link. Non-members can download the parts for £2.50ukp

Print out the parts onto thin card (230 micron) Score along the dotted lines and cut along the solid lines before carefully cutting the parts out.

The teeth of the rack fit to the arm lining up with the grey areas. The red blocks are at the top of the teeth. Be as accurate as possible gluing the teeth to the arms.

Fold over and glue together the body front and back, the head and the pinion to make double thickness card.

Once the glue is dry carefully cut out the body front and back including the axle hole.

Glue the guides carefully to the curved grey line on the back of the body parts.

Assemble the two parts of the box as shown left then glue the body back to the back of the box leaving a small 1mm gap between the box and the guide.

Assemble the four parts of the pinion as shown. Note that the tabs on the washers are facing inwards towards the centre.

Fit the arm under the guide.

Slot the pinion into the axle hole with the two tabs facing forwards..

Glue the front into place so that the guide holds the arms into place but doesn't stop them moving.

Cut out the double thickness face and glue it to the tabs on the axle so that is is vertical when one of the hands is pulled through almost as far as it will go. Use the grey circle of alignment.

Fold over and glue together the two end stops to make double thickness card.

With the head in its vertical position, glue one of the end stops into place so that it is just touching the body. Pull the arm through to the other end so that the head is in the other vertical position and glue the second end stop into place. Let the glue dry completely.

Done. 

Pull one arm for happy :-)  one for sad :-(

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Part of the process of making the revised Big Gear experiment is this long flexible rack. It got me thinking about yet another possible mechanism for the flip face project.

I constructed this box with a curved top and a slot...

...fitted a slightly shorter rack into the slot...

...and added a pinion. (With involute gear teeth of course)

With a second side in place holding the pinion, it is just a case of pulling either hand to rotate the axle.

Next, a redesign of the flip-face artwork. As I may have mentioned, it was beginning to creep me out.

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More on Flip Face: Mechanism #4.

Here's my implementation of mechanism #4 as per the previous post. It works a treat!.

From the back you can see how the parts fit together. The pinion wheel, with face attached, is a ten tooth wheel, the rack gear is a section from a fifty toothed wheel. The mechanism as a whole, needs tidying up, with spare space being removed and parts aligned properly. I might re-do the face as well as it is beginning to freak me out!

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More Flip Face Fun: Animation test for mechanism #4.

I've jumped past the original Rack and Pinion idea straight to this. The lower gear is a six tooth section from a forty tooth gear. The pivot point at the bottom is where the centre of the gear wheel would be. The top gear is an eight tooth gear with one tooth missing. The top gear rotates a full 180 degrees as the bottom gear is moved. This'll be a fun mechanism to implement in card!

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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.

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.

Download and make your own Rack and Pinion model in the shop

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Here's a quick experimental animation I created using program called hype that helps create animations in HTML 5 and CSS3. All things being equal I'd carry on creating animations using Flash but Steve Jobs, in all his infinite wisdom, has taken against Flash for some reason. The end result is that users of iphones and ipads can't see the animations on my site.

The question is, then, can you see this animation okay? If you can (or can't) please let me know by comment below or by email letting me know which computer and which browser you are using. Thanks!

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An animated paper tortoise to download, print out and make. Press down the lever on the from of this model and the tortoise peeps out from inside her shell to see what is going on.

The download includes all the parts and instructions to make the model, just print it out onto thin card and away you go!

Interested in finding out how this model was made? Follow the design process from start to finish here.  

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