The architecture section decided to create an automated, “haunted” Ouija board that appears to move on its own, creating the illusion of an invisible presence guiding the planchette. At the core of the system is a CoreXY gantry mounted beneath the tabletop. This gantry carries magnets that track along the X-Y plane under the board. Permanent magnets embedded in the planchette couples it to the motion of the gantry, so when the electromagnet moves, the cursor glides smoothly across the engraved letters and symbols on the board. The motion is fully programmable, allowing us to script specific words, patterns, or behaviors that match different storylines or user prompts.
I was on the end effector team and was a floater in the gantry team to help get the custom components printed. Below summary is what we had done in our subteam (same written in our machine week page).
Initial Magnet Testing: Our original plan for the end effector was to use electromagnets. Gert gave us the electromagnet that was used by the architecture section last year, we were concerned it wouldn’t be strong enough. Anthony gave us electromagnets that still used 5V, but it was stronger due to the steel core. We tested both electromagnets using a power supply. We tested using metal scrap and different strengths of magnets. We tested different thicknesses of wood to see if the design team would be severely limited by the thickness of the board. We found that the electromagnet worked with ½ inch thick wood and a weaker magnet.
Electromagnet Prototyping: The end effector mounts to the top of the carriage and we chose to use two electromagnets to limit a degree of freedom so the cursor does not spin. Our first prototype used the existing holes in the carriage design to mount the electromagnet on the side of the carriage. This design wasn’t very stable, but we originally tried it because we weren’t sure there would be enough space to place the 4-inch electromagnet on top. Once we confirmed there was enough room and the gantry team provided an updated carriage CAD, we modified it to add an electromagnet holder. Our next design included an inset for part of the electromagnet and steel rods and prongs to hold the electromagnet in place.We opted for prongs because Anthony advised leaving the blue portion of the electromagnet exposed to avoid overheating. However, the prongs were not as stable as we had hoped and required a zip tie. In the next iteration, we switched to a top piece that bolted onto the carriage and enclosed the top and one side of each electromagnet. We offset the side walls from the electromagnet to try to avoid overheating.
Magnet Testing V2: On Tuesday, after receiving the acrylic ouija board we did a second round of magnet testing. At first we had a mini panic attack because the electromagnets were not working with the Arch Shop power supply. We’re unclear what the issue was, but we went to the EECS shop to test with their power supply. The electromagnets worked on the EECS power supply through the acrylic board on 5V which corresponded to ~ 1.21 Amps of current. We also discovered that using the strong permanent magnets worked through the acrylic and could serve as end effectors. We originally chose electromagnets so we could reverse the current to let go of the cursor and move to the candles, but since this feature was later removed, electromagners were no longer necessary. We also did not have a clear plan for powering the end effector. For these reasons, we switched to using two permanent magnets. As the magnets don’t need power, it was a simpler solution with one less failure mode.
Magnet Holder Design: Switching to permanent magnets required a new addition to the end-effector assembly. Because the magnets were shorter than the steel rods, we needed to raise the end effector so the magnets could be as close to the underside of the board as possible. We also found that the magnets repelled each other when placed less than 4 inches apart, so we needed to increase their spacing. We first printed a quick test piece and then we printed a two piece adapter which attaches to our existing end effector design and holds the magnets at the correct height and spacing. We ended up using the steel rods to stabilize our end effector. We also updated the spacing of the magnets on the cursor piece to match the new 4 inch spacing between the magnets.
Final Design: Our final end effector consists of three 3D-printed PLA pieces, two permanent magnets, and two steel rods. The bottom piece bolts into the gantry carriage, the upper pieces connect to the bottom piece with steel rods and super glue. The top piece holds the two magnets, which control the cursor through ¼-inch acrylic.