Charlie Lockyer and Travis Dowd
The inspiration for our design came from the “Penguin Stairs” toy, which is battery powered and uses an inner set of stairs that move up and down to allow penguins with thin arms to move up the stationary outer stairs. We created this same up and down mechanism by employing a user-powered crank:
The most difficult mechanism of our mechanical model was getting the inner stairs to slide when moved from outside of the outer stairs and allow for an object to be moved up the stairs in the process. We Therefore first made a proof of concept prototype out of cardboard to ensure this mechanism would be possible. We laser cut the inner and outer stair sets out of wood and bolted them together to find that the sliding mechanism worked and was able to move objects up and down, meaning that the dimension ratio of the inner and outer stairs was correct!
From our low fidelity cardboard prototype we found that we needed larger stair sides to fit gears on the sides and incorporate a mechanical movement to drive the up and down motion of the inner stairs. We also learned that we would need more stability through the stairs at different points to keep them in line. We expanded the base and height to 9 inches and added extra stability in the form of more moveable slots with screws through both sets of stairs. We then cut this larger-sized stair structure, which ended up being our final structure, out of wood. This prototype initially lacked a base, so it could be hand driven, but required lots of force. After discussion with Dr. Wettergreen and Douglas, we determined that this was due to excess movement since the outer stairs weren’t fixed and therefore didn’t align well with the inner stairs. We super glued this model’s outside stairs and it moved much better! The inside stairs move downward with only gravity (I needed my hand to hold them up as the picture shows), which demonstrated improved stair alignment!
After ensuring that this up and down movement mechanism worked on our wood model, we went ahead and began plans to incorporate a mechanical motion into driving the stairs. After looking at using mechanism 85 and other possibilities in our early low fidelity prototyping, we ultimately decided on mechanism #92, which converts rotational motion (driven by the user in our machine) into translational up and down motion of the inner stairs. Rotational movement of the crank, which is attached to the inner stairs that we intend to move up and down, drives the crank’s up and down motion in a periodic fashion, regardless of the direction of crank rotation:
The successful fixation of our initial wood prototype told us that it would be extremely important to fix the outside, stationary stairs in place. After realizing that we needed to fix the outer stairs to improve alignment, we made a press fit base for the outer stairs with finger joints. This worked well and provided a secure base and the model worked well with unfinished wood. We did not incorporate the live axle into this design, however, which goes through both the inner and outer stairs. This initial attempt at our final prototype ensured us that we would be able to create a working final design as the wooden stairs moved well once we fixed the outer stairs. We provided additional alignment by adding triangular press fit finger joint supports on the tall end of the outer stairs.
After testing the friction of wood on wood, wood on acrylic, and acrylic on acrylic, we found that wood on wood provided the least friction, especially after sanding. We therefore decided to incorporate our final live axle design of the gears using laser cut wood. We assembled this newer version and ensured that it worked. The inner stairs moved very soundly against the outer stairs! We then placed gears, dowels, spacers, and cranks into our design. We connected the live shaft to both sides of the outer stairs because we found that the stairs lifted more easily when lifted from both sides, however only one side needs to be cranked by the user since the live axle couples the two sides as shown in the below photo.
The placement of the crank on the gear and therefore the length of the crank was determined by the range of motion on the inside stairs. Specifically, we needed a 1.8” vertical climb of the inner stairs to allow the owls to climb the outer stairs. We connected the gear moving the crank to a gear powered by the user in a rotational motion. The final design of the side of each stair looked like this:
We decided to finish the wood with a dark walnut and clear colored beeswax (shown in bottle and applied to a gear below) finish in different places to create contrast and make our design aesthetically pleasing. We also applied oil to the ¼ inch spacers and slots to reduce friction as much as possible. We gave all exposed parts of our machine a clear coat to add longevity.
Finally, we wanted a cool shape to climb the stairs. We needed a long, light shape for this purpose as this design would be most effective. What better way to do this than using owls! We used different stains and finishes on different owl “barbell” shapes. We laser cut the owls, used 400 grit sandpaper (as we did on the other parts of the mechanism) to smooth them, then applied finishes to get their color. We added wings using the vinyl cutter so that the owls can fly up the stairs! We secured them on either end of a dowel to allow for balanced waiting and easy climbing of the stairs as the crank is turned. The owls are super cute and we were able to use vinyl in an aesthetically pleasing fashion:
Our mechanism is a bit hard to turn because the turning must account for the weight of the inner stairs that they lift, however, it is relatively easy to turn, and the owls move up the ladder well! Here is our final product and a video of the mechanism:
Here is a video of the final machine working! (liked below)
Here is our presentation with a condensed version of the above summary of our project experience:
https://docs.google.com/presentation/d/1j4D1J0pZx3o9Ux4ns2OT1G_LOX4rdy2LsziSUWtkAJE/edit#slide=id.g118c708bfeb_0_35
Cost analysis:
Between us, we spent about 70 hours working on the project and have some skill with the machinery, so we assume a pay rate of $15.00 an hour. This amounts to $1050 in labor costs. We used about four full sheets of 1/4 inch wood sheets to laser cut the materials of our box. These cost about $10.00 each, for a total of $40 in wood [1]. We also used about about a full can of clear gloss finish on all of our parts, amounting to about $7.00 [2]. The total amount of staining material and spray paint, which was done on just the small owls, was negligible. We also used lots of tape to prevent wood burn, amounting to about 1 full roll of tape, or about $6.00 [3]. To glue together the dowels with the spacers and machine parts, we used about a full tube of epoxy, which is about $7.00 [4]. The use of the vinyl cutter was also minimal (only for the owl wings), so this cost can be assumed to be negligible as well. The power consumed. Machine costs such as the laser cutter, vinyl cutter, and bandsaw may also be factored in, although we already had access to these materials, so have chosen to neglect them in the large cost of the overall product. The wooden dowel cost would also be around only $1.00 as we only used 2-3 of the 1/4 inch wooden dowels [5].
As expected, this project was our most expensive to date, with most of the costs coming from labor. The total cost is $1,111. These costs will be reduced by practice we had during the project, so the time taken to finish the product would be less.
References:
- Lowes.com. [cited 2022 Mar 9]. Available from: https://www.lowes.com/pd/1-4-in-Lauan-Plywood-Application-as-2-x-4/1000068895?
- Homedepot.com. [cited 2022 Mar 9]. Available from: https://www.homedepot.com/p/Deft-1-Aerosol-Gloss-Interior-Clear-Wood-Finish-Lacquer-01013/100204936?
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Lowes.com. [cited 2022 Mar 9]. Available from: https://www.lowes.com/pd/J-B-WELD-Clearweld-Clear-Epoxy-Adhesive/501496365. 1/4″ x 36″ wooden dowel [Internet]. Woodpeckers Crafts. [cited 2022 Mar 9]. Available from: https://woodpeckerscrafts.com/1-4-x-36-wooden-dowel/
