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flip face

Flip Face Rack and Pinion


Average: 4.7 (7 votes)

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.


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

Flip Face - Latest Mechanism Variant

Average: 5 (4 votes)

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.

Two new modifications from Michael42er

Average: 5 (5 votes)

The prolific Michael42er has been at it again! This time he has modified the Paper Bird project and expanded on the Geneva powered Flip Face project. Nice work Michael!

Michael42er's Flip Face Mechanism

Average: 5 (4 votes)

Michael42er has contributed this ingenious device to the search for a mechanism for the flip face project. Nice work Michael!

Mech #4 in action

Average: 5 (3 votes)

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!

Flip Face - Mech #4

Average: 5 (6 votes)

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!

Using Flash

Flip Face Geneva


Average: 5 (3 votes)

First Flip Face prototype for members to download and try.


I'm trying out a few different mechanisms so see which works best and thought you might like to play along at home so if you are a member you can download the parts at the link and make your own. 

This is a successful mechanism. Turn the handle on the back of the box a full turn and the face turns 180°. The mechanism keeps the face in position when it is supposed to be stationary. The only downside I see is that turning the handle a full turn then stopping isn't the obvious thing to do. Ah well, you try it and see what you think.

Print out the parts onto three sheets of thin card (230 microns / 230 gsm) Score all the dotted lines, cut out the holes the carefully cut out the pieces. Dotted lines are valley folds, dashed lines are hill folds, solid lines show where to cut. Fold up and glue together the side pieces making right angled triangle sections top and bottom.

Glue together the drive stiffeners.

Glue the drive stiffeners to the drive wheel on the grey area.

Fold up and glue together the two axles.

Tightly roll up the two drive pins and glue them shut.

Thread the drive wheel sides onto the drive wheel axle lining them up with the two grey lines

Glue the sides of the drive wheel into place so that they are curved.

Expand the cross holes at the ends of the drive wheel with a cocktail stick then thread the drive pins into place.

Fold over and glue together the geneva wheel so that it is double thickness. When the glue is dry, cut out the piece then fit it to the second axle lining it up with the grey line.  

Assemble the handle as shown above.

Glue the two halves of the box together at one end only. Thread the geneva wheel and drive wheel into the correct hole using the picture above as guidance. Glue the washer into place. 

Glue the box closed then glue the washers into place on the back. Glue the handle to the axle then glue the face to the tabs on the drive wheel.

Done! Turn the handle a full turn and the geneva drive advances two quarter turns flipping the face over. Rack and pinion next.

flipfacegeneva.pdf (270.93 KB)

...and a forth

Average: 5 (1 vote)

The continuing adventures of the Flip Face Mechanism.


Here's another possible solution I could try. It is sort of half way between a rack and a gear. It has the advantage of going back to what I was originally aiming at, press down one hand for happy, the other for sad.

Three More Solutions

Average: 5 (3 votes)

Further adventures with the Flip Face Mechanism.

I've started off by adapting the bi-directional ratchet mechanism so that it turns a full 180° degrees for each cycle. I've done this by reducing the number of teeth on the wheel to four.

Here's the result. It works, sort of.  I could connect a pair of arms to the cross bar, (Under my finger in the picture.) which would then rock back and forth to rotate the face.

The downside is that it really is at the edge of what the mechanism will do, it works, but not easily, not smoothly. 

Two more mechanisms to try. A double ended geneva drive mechanism modified from this mechanism. I have the parts cut out for this, ready to try. I think it will be a good solid mechanism. I plan to put a handle on the back of the box and the face connected to the axle running though the cross piece on the front side of the box, one turn of the handle would make the face on the front turn 180°.

Alternative three, a rack and pinion drive. Also promising.  It could work quite nicely. The face would be attached to the gear with the rack running through the body as a set of arms with hands on each end. It would then just be a case of pushing the arms one way for happy face, the other way for sad face. Watch this space.

Back to the Drawing Board

Average: 5 (1 vote)

Progress on the Flip Face project.

Okay, so it sort of works. You press down on one arm and the place where the head will be mounted rotates 180° one way, press down the other and it does the same the other way. 

The trouble is, as soon as I let go of the hand the head bounces back perhaps 20°. You might think it would just look wistful but no, it looks crooked. Pah.

Also, the friction on the paper belts is a little high so it jams up very easily.

I think I'll mark this down as a dead end and try replacing the mechanism. I have a few possible ideas to try. Either a very short rack and pinion, some sort of long action ratchet or perhaps as Pookafletch suggested by email, some sort of adapted pop up mechanism. 

A happy mix of frustration and fun.

Expect to see a happy face in the thumbnail next time. :-)