We decided to base our final project on a previous ENGI 210 project, which used a version of mechanical movement 138/507. This mechanical movement is a camshaft/lifter system that converts input rotational motion into linear motion, and uses a combination of 6 lifter arms in offset linear motion in such a way that the tips of the legs form a rotating slanted 2D plane in 3D space. When a plate-like object is placed on top, bounded only at its center from moving laterally, the plate is observed to ‘wobble’. We then harnessed that wobble and used it to roll a few bearings around the rim.

To begin, we created an initial 3D design in Fusion 360 in order to confirm that the motion produced would in fact be as we expected. In our first design, the legs driven by the outermost cams were placed directly above the cams. Due to the geometry of the design, this meant that the four inner legs had to extend outwards, but also ‘twist’ relative to the plane of the wood being used. 

In order to counter this, we came up with the idea of rotating the base plate relative (with cams in a straight line) to the upper plate (with cams in a hexagon), and then extend the legs out such that they are perpendicular to the line that bisects the holes in the base plate. This shift resulted in all six lifters being slightly offset but none of them having to make an angled offset to find their position on the top plate. 

Once the correct distances had been worked out, we cut the legs out on the laser cutter. Each leg consisted of two sheets of wood superglues together, with the feet at the base of each leg cut out separately, such that the legs are able to be inserted into the base plate. This worked great in theory until Oli glued the feet on before putting the legs through the support plate, negating the idea of cutting them separately. We then recut the legs. 

Following this, we cut the support plates on the laser cutter. We originally tried the design out with cardboard support plates, however the friction was significant and greatly impeded the movement of the legs. To counter this, we decided to use acrylic for the plates to complement the wooden legs in an effort to reduce friction. This ended up working very well, and it was easy to cut the acrylic with the same Adobe Illustrator files that we had used before. 

 

Once we had glued the legs together and inserted them into the base plate. There was minimal kerf on the acrylic, so the holes were tighter than we expected. To solve this issue, we lightly filed the inside of each hole until the legs could move completely unrestricted. 

Next, we built the cam shaft. This consisted of laser cutting individual circles with offset holes and then attaching them to the dowel. Each cam offset was chosen in such a way to create the desired motion through the lifters. This meant that the 6 cams were offset by 60 degrees from each other, but it wasn’t a consistent shift from one end to the other. Due to the circle we were trying to achieve the cams had to be offset in a particular manner. 

The support structure for our project was two circular base layers of wood attached to two vertical pieces of wood with holes cut out for the dowel. These were easily laser cut and then post-processed using a clear coat. 

We then assembled all of the pieces using super glue, using the setting time to ensure that the alignment was correct and that the legs could still move in the desired way. 

The only part that needed to be cut out following this was the top rotating acrylic plate. This consisted of an acrylic disc of roughly the same diameter as the support discs, as well as two rings to provide a constrained path for the metal spheres that were placed in the top. The rings were cut out of a much thicker acrylic than was previously used, so even after 2 passes on speed 2, the laser cutter barely cut all the way through. The rings were joined using super glue, although in hindsight, it would have been better to use acrylic glue. 

Overall the project was a series of failures and design changes, however through those changes we learned a great deal about working with 2 dimensional materials. Our laser cutting and test fitting skills greatly improved, as well as our CAD modeling skills. Our project may not have reached the level of post process completion that we may have wanted, but I do feel like it was overall a success. 

Cost: 

Materials:

• Wood:
  • 2 sheets ($5 at oedk per sheet)
• Acryllic
  • 1 sheet ($14 at oedk per sheet)
• Cardboard 
  • Approx 2 sheets (free)
• Super glue 
  • 15 tubes ($20)
• Total: $44

 

Time spent: 

• 12 hours each
• 24 hours total at $15/hour
• Total: $ 360

Grand total: $404