Mobiles are kinetic sculptures. We have a few, but without a slight breeze, they are stationary and aren't all they could be. For years, I have wanted to find a way to rotate our large mobile. I found it in a Hankscraft motor, made in Reedsburg, WI. It is a 1.5 volt DC, 0.5 RPM per motor. 1/2 rotation per minute was perfect, since our mobile is about 4 feet across, it would still look like it was moving pretty fast with the slow RPM. It could be powered by a battery, but I didn't want the hassle of having to change it out. So, I decided to make it light powered. This way it would only be on when there was light. This instructable goes over my process in making our light powered mobile spinner. I would be interested in any comments or suggestions to improve it.
Step 1: Design
Since the ceiling does not get direct sunlight, I had to get solar cells with excellent low light effect. I tried two types of cells, thin-film and regular. I wanted to try the thin-film since it was flexible and I could potentially wrap the cell around a cylinder making the support design super easy. However, it's low light performance was 6X worse than the regular cells, so they were put aside for a later project. Then, I had to figure out how many cells I needed. I started with a single 26 x 39mm cell. It's output was rated at 0.5V and 400mA in full sun. However, in the room with the mobile, it put out 0.4V at 2 mA. The voltage was close to spec, but the current was far off. Then I had to find out what the motor needed to turn. At 1.5V, it needed 12 mA to keep running, and a little more to get started. This would mean at least 24 mini solar cells. Then, I searched online for mini solar panels that were 1.5-2V with long rectangular dimensions. Nothing suitable was found, so I started making my own panels with the mini 26 x 39mm solar cells. I bought a kit of 40 of these for $13 from Ebay. This included a flux pen, tabbing wire and bus wire. Four were combined in series to increase the voltage and mounted onto a plastic backing then encased in epoxy. These resulting mini solar panels produced around 1.5V at 2mA each with indirect light.
Based on the size of motor and how I was going to hang it, I had about 4 inches of vertical space. I also looked around for the largest diameter light bases in our house and they were around 9 inches. So. I decided to keep my design envelope at approximately 4 inches of height and 9 inches in diameter. I had the size of my mini solar panels and started to sketch out the design to see what would work. I worked out designs of 6, 8, and 10 mini solar panels, set at a 30 or 45 degree angle. The 8 panel set at 30 degrees fit my design envelope best. I also liked that the extra solar panels would give me a bit of margin for error.
I started designing the enclosure in 3D starting with the panel layout. I drew the bottom and top profiles, then lofted a solid shape between them. A shell was formed from this solid for form a wall of .300" thickness. A rectangles cut was extruded down at an angler from the top surface to hold the solar panel. Then a slightly smaller rectangular extrusion cut was made for the panel opening. Once this looked good, I patterned these two features to cut to the remaining 7 sides. For the motor inset, I took the motor dimensions, added ,005-.010" and extruded a cut into the base. Next, I added two features for securing the enclosure to the hook. This involved extruded 8 posts from the base up to the top of the motor. At the top of these posts is a ring with 8 holes for securing the hook assembly to. Finally, I rounded any edges the best I could, both for aesthetics and strength.
The mobile is currently hung from ceiling from an eyelet that is bolted into a joist. I wanted to use the same eyelet and designed a hook to slip into it. The top of the hook is centered over the axis of the enclosure so the entire piece will be balanced. It was designed with a little clearance to fit into the eyelet of the bolt. The hook is part of a disk that will attach to the enclosure with screws and nuts. I have found that with some 3d prints, it is easiest to join internal components with screws and nuts, so the tolerances for assembly are not as crucial.
The parts were printed by a new service called 3D Hubs. Through this, I found someone in my neighborhood and he printed both parts over the weekend in white PLA at 150 microns for $101. This is one of the wonders of the sharing economy. The part had some rough edges and layering, but for the size, speed and cost, it was a pretty good deal.
Step 2: Assembly
Cleaning up the 3d Prints: Most 3D prints are pretty rough and usually need some extra work after they are printed. PLA printed parts are usually the roughest. It was a good choice for this project due to the larger size, lack of features with fine details and cost. However, the layering is very evident and there is a bit of sanding and filing to remove rough and high spots. The solar panels slid snugly into the slots. I did not account for the wiring on the panels, so I had to snip out a slot for the wires to slide through. The holes for securing the hook were also tight, but these were easily opened up with a drill and .165" drill bit. One note on cleaning up the prints. Depending on your size and thickness, these my be printed with an internal honeycomb shape. In this case, you can't be too aggressive with sanding or filing or you may sand through the top layer into your honeycomb.
Motor: The motor has a small rod that spins. This rod is slightly flattened on one side. I used a hole punch to make a small divot centered on the flat. Then I started drilling through the rod, starting with a .020". I then used a .039, .060" then .080" drill to cut a centered hole in the rod. Through this, I placed a .050" figure-8 shaped wire. I pulled this from an IKEA curtain ring clamp. The motor is then placed into its slot in the enclosure.
Wiring Solar Panels: Each of the panels will produce 1.5V at 2 mAmps. Since the voltage is where I want it and the current needs to be increased, the panels were wired in parallel to increase the current. All of the red wires were connected to the positive terminal of the motor with a twist-on wire connector, while the black wires were connected to the negative terminal of the motor. At this point, the motor should start to run. If it doesn't, double check all connections.
Hook: I drilled two extra holes on the side of the hook for the motor wires. The hook is attached to the enclosure with the use of 8/32 x 3/4" pan head screws and bolts. Although there were 8 holes, I only used four for securing the hook to the enclosure. Make sure to move the wiring away from the opening of the hook. You don't want to get any of the wires stuck while hanging the enclosure.
Hanging: The opening in the hook has enough space for the eyelet hook to slip in place. Align the opening of the hook with the eyelet and raise the enclosure to the ceiling. If it does't go in or is to far down, you will need to adjust the depth of the eyelet in the ceiling. When in place there will be about a 1/4" gap between the enclosure and ceiling. Hang an S shaped wire from the figure-8 motor wire. Hang the mobile from the S-shaped wire. Enjoy your spinning mobile! If there is not enough light, you may need to jump start it with a strong flashlight.