Kinetic Creatures

Elly the Kinetic Creature

A Christmas gift that I received from my lovely wife is a kinetic creature. This is a cardboard model animal — mine is an elephant named Elly — that through clever design can walk. The walking mechanism is based on a simple crank shaft paired with cleverly designed legs that act as linkages. Here’s a slide show of the construction and a video of it in action:

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One exciting thing about this toy is that you can replace the hand crank with a motor. They sell a kit for this but I plan to make my own.

Laser Cut Windmill

Laser Cut Windmill

I’ve been learning how to use the laser cutter at NextFab over the last few months. I’ve already posted about the laser cut Christmas ornaments that I made, but I also took on a larger project for the Holidays: I decided to make a toy windmill for my nephew who loves anything that spins, especially fans and gears. This turned out to be quite the design challenge, requiring several different versions and iterations – some of which never made it out of the computer.

Roughly speaking, I specified what I wanted in the design, created it in SketchUp, exported and touched it up in Illustrator, laser-cut it out, and finally sanded and glued pieces together. I actually went through the full process twice, but many steps required several more passes.

Windmill Design Goals

  • It is a wooden toy
  • It can be assembled by hand by a young child
  • The windmill blades spin
  • The tower looks like a windmill tower
  • The gears are functional
  • The windmill blades turn with the gears

SketchUp

I used SketchUp to design several versions of the windmill. This was a great way to iterate quickly and create the gears (there’s a very simple plugin). I don’t have the pro license so exporting was tough. Luckily, NextFab has a copy of Rhino which can import a SketchUp file and export it to Adobe Illustrator (just make sure it is a 1:1 scale factor).

Here are sample snapshots form various versions of the windmill. I think the box at the top of the windmill and the base were the pieces that changed the most.

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Illustrator:

After exporting from SketchUp to Adobe Illustrator, there’s still a lot to do. I found that first joining the line segments together into a single path made the cutting much more consistent; instead of jumping around to cut segments, the laser cutter followed a complete path which eliminated gaps in the cutting. SketchUp exports circles as a series of line segments, which is OK, but for cleaner looking pieces I redrew them in Illustrator as actual circles. Because the laser cutter has a color-coded preset cutting order, I recolored the pieces to make sure the pieces were cut in the right order (black cuts first, then red, then blue, etc.). Finally, I grouped the pieces and distributed them on the artboard (which maps to my wooden board) to maximize the number of pieces I could cut on one board. Because I often needed multiple copes of a single piece (e.g. a gear), I usually made copes from one finished piece in Illustrator.

 

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Laser Cutting

Once the files were done in Illustrator I loaded them onto the laser cutting computer. A laser cutter works a lot like a really large printer. You press print in Illustrator, adjust some settings and it opens a program dedicated to the laser cutter. Before sending the file you put the wood in the laser cutter.  You raise up the bed of the laser cutter so that the laser is in focus on the wood. You move the laser left and right to position it to where you want to start on cutting on the wood. Then you send the file from the computer to the laser cutter.

Here’s a video of the laser cutter in action:

You can’t actually see the laser beam since all of its light is going straight down to the wood where it very quickly burns through. The fan blows air in to clear the smoke away. The big plastic cover is darkened to protect your eyes from the laser.

Sanding and Glueing

The laser cutter can leave behind some unwanted smoke marks, but they are easily sanded off. The most important pieces to sand were the gears designed to meet at a 90 degree angle at the top of the tower. Laser cutting is limited to two dimensional shapes, but to fit gears together at a 90 degree angle the teeth have to be angled to a 45 degree. My solution was to shape flat gears on a sanding belt until they ran together smoothly.

90 Degree Gears

These gears are sanded to fit together at 90 degrees

 

I chose to round the edges a bit since they were a bit sharp for a toy. I also sanded the tabs and holes a bit to narrow and widen them respectively. This made the parts more forgiving during assembly. I glued some of the pieces together to reduce the number of assembly steps and to make the gears turn with the axles. For some of the last gears I made, I added a flat side to the axle hole in the center of the gear to act as a key. I didn’t need to glue the axle to these gears to get them to turn together. I just needed to sand the axle to match.

The flat edge in the hole grabs the axle

The flat edge in the hole grabs the axle

Laser Cutting Version 1

The first version I cut was nice, but because it was in 1/8″ Birch plywood it was too fragile to be a toy. There were some other issues too: the weight of the blade tipped the tower over so I needed to add a counter balance, the box at the top kept falling apart so I used a rubber band to hold it together, and the axle didn’t really stay straight with just an 1/8″ of plywood in the base or the gear (1/4″ combined), which led to a lot of friction in the gears. Initially I used a friction fit to get the gears and axles to turn together but after repeated use it became apparent that they needed glue.

Overall the pieces were just too complex and needed a lot of simplification; building this version in the real world revealed a lot of issues that I couldn’t see in SketchUp.

Here is the first version:

Windmill Version 1

Windmill Version 1

Laser Cutting Version 2

Having learned form the first version, I cut out this final version (after sever computer-aided iterations) of 1/4″ plywood to make it sturdier. The base is triple layered with the gear holes extending through two layers. This solves the axle alignment issue and keeps the axles from marking the table underneath, and I added some spacers to increase the thickness of the gears. In total, each axle now has a whole inch of material to keep it in aligned. The base and the box panels are greatly simplified and hold together on their own. The extra thickness made the tower pieces difficult to fit, so I sanded them to a shape that worked which improved the tolerance when putting it together.

Here’s the sequence of pictures that I used to make the assembly instructions for my nephew and his parents:

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Here’s the final product (with overly dramatic music):

Next Steps

The windmill was a big hit and I was actually surprised with how fast my nephew could get it spinning. Right now he has to turn the gear directly so I’m working on a crank to make it easier to spin.

Overall I’d say this project was a success.