Week 14: Mechanical Design
Download the code
- Hand mount Fusion 360 file
- Hand mount STL files for 3D printing
- Lady Hand Illustrator file for laser cutting
- Man Hand Illustrator file for laser cutting
- Monster Hand Illustrator file for laser cutting
- Smoothed belt clip STL
- Smoothed belt clip Fusion360 file
The first checklist
Design a machine (mechanism + actuation + automation), including the end effector, build the passive parts and operate it manually.
The second checklist: Learning outcomes
- Work and communicate effectively in a team and independently
- Design, plan and build a system
- Analyse and solve technical problems
- Recognise opportunities for improvements in the design
The third checklist: Has your group
- Shown how your team planned and executed the project
- Described problems and how the team solved them
- Listed future development opportunities for this project
- Included your design files, 1 min video (1920x1080 HTML5 MP4) + slide (1920x1080 PNG)
Dmitri, Xavier and I chose an "analogue" karaoke machine. That is, a machine that displays lyrics for a karaoke song without a screen. After much discussion, we settled on a form where a scroll of lyrics is slowly unwound (or rewound), and a hand on a horizontal axis points to the word to sing.
Here are images of the keywords that everyone created for generating ideas, Xavier looking adorable, and our form sketches from discussing the design.
We divided tasks. Our scheduling put pressure on our availability. I was only available until Friday, Xavier would be working separately in Brussels, and Dmitri would be working later. Dmitri has a good feel for the form, so he was tasked with designing the frame of the machine, I would design the pointing mechanism, and Xavier would construct based on Dmitri's designs, at his lab in Brussels. We all use Fusion 360, so we would make use of its sharing abilities.
We determined that the hand module would run along a horizontal bar, pulled by a belt controlled by a motor at the edge of the machine. I examined a similar mechanism from an Ultimaker, and designed a new part according to our needs.
Some things: we have access to 6mm timing belts, also known as B300MXL or GT2 belts. I determined that we would have a changeable hand, with a length of 10 cm from base to fingertip. The module would clamp to the belt, and also clamp in the base of the hand, and would glide along the rod on a linear bearing. I used calipers to determine the diameter of the bearing and made the hole the same size. There would be nothing fancy like flexure clips. I would use screws to squeeze the components into place. After all, we weren't building anything that required precision or was going to be under any real stress. This simple design in Fusion 360 took FOR EVER. I am obviously still an amateur with this.
I printed the part on the Printrbot Metal Plus in PLA, using the default settings (layer height .1mm, shell thickness .8mm, speed 40). The result of the first print was fine, so I didn't see any need to alter and reprint. The hand clamped in as expected, though the screws screwed into the plastic, which worked well enough that I didn't use nuts to secure the screws. And the linear bearing fit in just great.
Here are some photos of the parts being designed, printed, and together with a test hand in cardboard. The aborted print there had to be stopped because I had to leave the lab to go home (there's a lesson there about time management and starting digital-fabrication jobs).
The hand would be laser-cut out of MDF or plywood. I found free SVG files of pointing hands, added a base tab to them in Illustrator, and cut them out on the laser cutter. After some experiments, it turned out that etched plywood had a greater contrast, so I went with plywood instead of MDF. Three hands: a lady's hand, a man's hand, and a monster's hand. Monster hand from here, and man's and lady's hand from here
While laser cutting, I kept having an problem where midway through etching the pattern would "glitch", producing a shifted pattern with a hard horizontal edge across it. I could not find the cause of this, but restarting the computer and the laser cutter made the problem go away. Here is a picture of editing the hand in Illustrator, the laser-cutting problem, and all three hands with the mount.
I downloaded a belt clip from Thingiverse to attach the two belts together. I printed it using our Printrbot Metal Plus in PLA using the default settings (layer height .1mm, shell thickness .8mm, speed 40). In the video from the group page you'll see that the belt clip kept catching on the hand mount. To fix the belt clip that kept catching on the hand mount, I redesigned the file in Fusion 360 to include tails on either side that would guide obstructions around the clip. I printed it as I printed the original clip. See the design here, and the actual printed clip:
I also uploaded my modification to thingiverse, maybe it will be of use to someone.
Meanwhile, Dima finished his full design: