Building a Working Mechanical Model

This midterm assignment was both very enjoyable and fulfilling. It was nice to work with a partner to make a functioning device as well as have the liberty to be as creative (or not creative) as desired. Using all of the skills that we developed through the class and compiling them in one device was very satisfying and gave me a good overview of how the prototyping and manufacturing processes are done in the professional world.

Brainstorming and Low Fidelity Prototype 

The project began with my teammate (Garrett French) and I brainstorming for a solid two days before coming up with the idea of making a person bench press. We searched through the 507 mechanical movements until we noticed number 131 which immediately caught our eye. The movement made sense to both of us that it could easily imitate a person lifting weights. We began sketching on a piece of paper until we both agreed on a layout we liked.

Mechanical movement 131 converts rotational motion to translational motion, as shown in the link attached here. Our idea was that we could attach a dowel rod to the translational motion part of the gear system (red) in a way that would stick out of a box, imitating a barbell going up and down. We would create this motion by attaching a handle to the rotational motion part of the gear system (blue) that would stick out the back of the box. The neat thing about this movement is that the translational motion is faster in one direction than the other depending on which way you turn the handle. We used this to our advantage by making the bar go up slowly as if the person is struggling to move the weight, and then fall quickly, much like a weight would when you stop pushing up on it.

We broke the project down into three main parts, the box, the gears, and the man. As we began constructing our low-fidelity prototype, we used makeabox.io to cut our box design out of cardboard. Additionally, we used human proportions that we measured from our own bodies to construct a man on Adobe Illustrator. This process was rather simple since we planned on just doing a side view of our person with not a lot of detail, as this was purely for aesthetics. We then used a gear generator to create gear teeth and Adobe Illustrator to make the frame of the gears and then combined the two.

In the images above you can see two interactions of the person we made out of cardboard, one wider than the other, which we ended up going with since it fit our design better. On the right, you can see the initial box that we cut out of cardboard, at the time of this image it was not assembled yet.

Medium Fidelity

In reality, our medium-fidelity prototype was a minor improvement to our low-fidelity prototype. The largest jump in improvement is from our medium to final prototype. In this stage, we created our person and gear out of wood, as well as began constructing our box. We did a test cut to see if our kerf was correct in our cut, and it was. We then cut out the box, but after assembling it we realized it was too wide for our liking, so we made a note to make it less wide in our final iteration. We also realized we needed to scale down the size of our gear system.

Test cut on the left.  Medium-fidelity gear system on the right.

Final Prototype

After perfecting our gear mechanism after multiple trials, we began the final assembly of our device. We cut out our final design for our box as well as our person. After making sure our gear teeth worked we began attaching our gear to the inside of the box. We glued in wooden constraints on either side of where the translation motion of our gear would take place. In doing so we got rid of the possibility of the gear moving in the horizontal direction. We used dowel rods to fasten the gear to the side of the box as well as to make the handle that would stick out through the back which you can see here. After this was done, we attached a dowel rod to the translational movement part of the gear, which would function as the bar with weights on it.  After attaching the face of the box, we were ready to stain and finish our project.

As you can see in the image above, we went with a dark wood finish. We made sure to tape off the parts we wanted unstained. After allowing the finish to dry, we applied a glossy clear coat and let it sit overnight. The next day we glued the person to the front of the box. We found that the box did not fit together perfectly because some of the wood was bowed, so we went ahead and applied wood glue to the connections that were not touching and clamped them down for 30 mins. For the vinyl requirement, we decided to clothe our person and made him an outfit, and stuck it on him. Additionally, we added an arrow on the handle on the back to indicate which way the handle should be turned. We then created our nameplate and the weight plates to attach to the bar. We got the inspiration for the weight plates from actual weights we have seen in the gym.

Finally, we had our finished product.

Videos Explaining What Exactly is Happening and Our Final Movement:

https://youtube.com/shorts/IF5eWB09_Qs?feature=share

What We Could Have Done Better

I would say that we were both very pleased with our final product. We did not choose an overly complicated design because we knew how much time and effort would go into even the simplest movement. The only thing I would have changed was recutting our box so that glue would not have been necessary to make all of the edges flush.

Cost Analysis

Time: Approximately 15 hours a person x 2 people x $25 an hour = $750

Laser Cutter: $20 an hour to rent at some places x 3 hours of use total = $60

Vinyl Cutter: $20 an hour to rent at some places x 1 hour= $20

Adobe Illustrator: Free trial

Plywood: 1x Sheet of plywood from the ODEK= $5

Cardboard: Free

Stain and Finish: Approximately $5 dollars each = $10

Woodshop tool rental: We used a miter saw and belt sander to cut and even out our dowel rods, assuming it would cost about $10 an hour to use a woodshop x 30 hours = $5

Total = $850

Obviously, this is the most expensive thing we have made in this class and that mainly being because this was the most time-consuming. I now have an even deeper understanding for the prototyping and fabrication process and see why some things are the prices they are.