Project summary

In this project I made a quick-and-dirty 2 DOF robotic arm with an LED as the end effector. We were given two 9g metal gear servos and an ESP32, and the rest was up to us. I made a little laser-cut box using my go-to Onshape laser joint tool and two little arms out of 3mm plywood.

Our first task was to draw some “wild” shape using only forward kinematics (specifying an angle position and hoping for the best), and a long-exposure camera app. I ended up with this:

It looked pretty cool! (perhaps not all that wild though)

Our next task was where things got interesting. We were tasked with drawing the letter “M” and an animal of our choice – I choose a fish. We could no longer specify random angles and be happy with the results, we had to go backwards and get the angles from the x, y position coordinates we wanted – inverse kinematics.

I drew out the general shape I wanted for the M and the fish in Onshape, did some trial and error until the points fit into the “work envelope” of the robot, and recorded the x,y coordinates manually into an array (there probably was a less tedious way to do this).

Readjusting the points of the fish until all could be reached by the center of the second circle. The two sets of two lines represent the two possible ways the arm can reach a given point.

Then, using some basic law of cosines and inverse tangents, I was able to get the angles I needed. I then experimented with different speeds of running through the angles, and ended up with this:

Red lighting to see the robot spasming

All in all, they turned out really nicely! I love the way they glow against the dark backdrop.