Inspiration
In class we learned all about mounting motors. This was super exciting for me because I’ve had some experience working with motors for various projects and it generally was always a crap shoot. After some brainstorming, I decided I wanted to put my skills to the test and build a waving machine. The final iteration of this project will be make of acrylic, have a long metal arm, and interchangeable “gloves” with different hand symbols.
Drawings
To translate the rotational motion of a motor into a waving motion you need to create a four bar linkage. I used this handy tool to figure out what dimensions I needed for the movement I was looking for.
Dimension drawing
Planning and more dimension scribbles
Joint hardware stackup
Laser cutter drawing
Laser cutter drawing
Materials and Tools
Tape measure
Laser cutter
Utility knife
Screw driver
Wrench
Drill
Sander
Cardboard
Wood and plywood
Wood glue
Motor mount (comes with screws)
6 mm hub coupler (ONLY comes with set screws)
9V battery and barrel jack
x4 m3 screws for the coupler
x3 32 screws for the joints
x3 32 nylon locking nuts
Washers
Process
Once I had all my materials in hand I started this project by laser cutting the links for the mechanism. Following the simulation from above I made sure the screw holes were the correct distance apart. I also made a set that was scaled by half just in case I wanted a a movement that was half the size or I needed extra pieces.
Next I wanted to put together the base for my motor. I knew I needed to make sure that the motor was high up enough so that the surface it was sitting on wouldn’t interfere with link AB. I glued together some scrap wood to make a platform. Then I screwed in my motor mount. I’ve never used wood glue before but it dried quickly and the joint feels sturdy.
I also needed to get my motor ready. I soldered some leads onto the motor terminals and attached the battery to a barrel connector I got from the shop. If you’re following along, just be sure to check that the battery connector works with a DMM because the one I originally grabbed was broken.
It had been smooth sailing up until this point but this is where my build process hit some friction. I was trying to put all the parts together when I realized the motor shaft couplers didn’t come with any mounting screws. I’ve run into this issue before where I don’t know what screws or hardware I need. I was tipped off to go to the Tandon Makerspace and figured out that I needed m3’s for the hole size. And they also had the matching tiny nuts to go with them!
With the new screws and nuts sticking out of the back of link AB, my mechanism was encountering a collision. I cut out some extra spacers out of the cardboard so that link BC could clear the hardware sticking out but then the screws I got for the nylon nuts were too short. I found some longer screws of the same size (32’s) in the shop that could accommodate all my parts.
Another thing to note is that I’ve always been afraid of nylon nuts. Turns out they’re not permanent! You just need to hold down the nut with a wrench and use a screwdriver to remove or tighten the screws. Good info for future projects!
Lastly I needed to create my point D for the fourth link. I cut this simple mount on the laser cutter. I tried my best to get the height to match with the motor shaft. The wood platform ended up being a little short so my AD link is actually 4.5 inches and not 5 inches. This did change the acceleration of the wave.
Final Product
Conclusion
I’m really happy with the first iteration of this project. There is something so satisfying with the movement and the sound. I also loved learning about and implementing the four bar linkage. I feel a bit like a mechanical engineer!
Next steps:
Reinforce point D. Is it in the right spot?
Add a switch to the circuit. Where could I mount it?
Attach metal rod
Decide if the movement is correct
Do I need a slower motor? Do I need to revisit my link lengths?
Re-cut links using acrylic
Create different hand “gloves” using some material?!??!
Resources
Special thanks to Ben Light for fabrication guidance and sharing hardware with me. And thanks to Josh for taking me to the Tandon Makerspace to pick out my missing hardware.
https://mechanicalexpressions.com/explore/kinematics/4-bar-linkage.html