Introduction: Solar Airplane Mobile
Step 1: Parts and Materials
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Ball bearing snap swivel (South Bend ASST BBS-A)
Propeller (BLH 3603 MCP X/2 tail rotor) - fits perfectly on motor and spins mobile nicely
30ga magnet wire (Radio Shack 278-1345)
Solar cell 20x23mm
Solar motor 6x10mm - motor and solar cell EBay item #280561903011
Carbon fiber tube 3mm OD 100mm length cut in half
Brass tubing 5/16 inch OD (3mm ID)
10-32 brass machine nuts (qty 2)
#6 brass washer (qty 2)
Black polypropylene scrap - King starboard marine outdoor grade 9mm thick
clear rigid clamshell package plastic
Insulation spray foam - Touch 'n Foam Max Fill worked well
Plaster of Paris
Plastic molding box
Squadron white putty
Krylon Fusion white matte spray paint for plastic
Stay-Brite Silver solder
Outdoor grade silicone seal
#31 or 3mm drill bit
5/8 drill bit
1/8 inch end mill bit
Drill press with cross vise or small milling machine
Small lathe or carving tools
Soldering Iron, solder
10-32 threading die
Step 2: Mold Plane
We wanted to make multiple copies so we decided to make a plaster mold from a clay master. Injecting wall insulating foam worked quite well, the surface was smooth, but you have to be very light on the trigger or the mold will blow out even if you have it tightly wrapped.
Support the clay with toothpicks and mix the plaster of paris according to directions. Pour plaster in mold box (plastic container with sloping sides) halfway. Create registration bumps by pushing a finger in the lower mold in a couple places before it dries.
After the plaster dries, Applies a couple coats of paste wax to the lower plaster and stick a drinking straw into the body (for filling the mold) then pour the upper mold half plaster.
Unmold the clay and dust the two cavity halves liberally with cornstarch so the spray foam will not stick. Clamp the two halves together with rope or elastic bands and insert the spray foam applicator tip into the hole left by the straw. Fill with the expanding foam. It takes a light touch to get just the right amount. Too much blows out the mold and too little leaves voids. Spray some on a piece of newspaper to get a feel for how much it expands after you stop spraying. You can unmold pretty quickly - as soon as the foam gets hard. Small voids can be filled with putty and extra flash can be trimmed so it doesn't have to be absolutely perfect out of the mold.
Step 3: Assemble Plane
Cut wing templates out of cardboard. We used heavy clear plastic sheets (recycled annoying clamshell plastic packaging) for the wings and tail.
Sand, cut off flash, and fill divots with white putty to make the body smooth. Cut slots for wings and super glue them in place.
Cut teeth on the end of a brass tube of the same diameter as the motor and put tape on it at the length of the motor. Spin the tube into the nose to the tape mark and pull out the cut foam plug to leave a perfect motor sized hole!
Find the balance point of the plane after temporarily putting the engine and prop in the plane. I used a long needle right above the wing to find where the plane wanted to stay flat and level. Hand spin a #31 or 3mm drill at this balance point deep into but not through the plane body perpendicular to the center line. This hole will be used for the 3mm carbon fiber support rod.
Hand spin a drill diagonally from the engine hole to the support rod hole through the body. See that it is visible in the support rod hole and pull loose foam out of the holes. Take a short length of brass rod and gently push two pieces of 2.5ft long 30ga magnet wire through till just flush with the end. Push this brass rod with wires through the diagonal hole and fish them out the support rod hole. You will never be able to feed the bare thin wires through the body loose. Remove the brass rod leaving just the wire going through the body of the plane from the motor hole to the support rod hole.
Solder the magnet wire to the motor leads and insulate the joints from each other. I just use a trimmed pinch of electrical tape. I didn't have heat shrink tubing that tiny. Pull the wire as you fit the motor in the plane. Mine was a snug fit so I didn't glue it.
Push the wires carefully through the carbon fiber support rod without kinking it and push the rod into the side of the plane. Superglue the carbon rod to the wing for strong support.
Step 4: Hanging Ring
To hang the mobile, I made a short length of brass rod with an ID of 3mm and silver soldered 1 or 2 brass washers to it. Use two washers if you want to stack two planes for a wilder dual plane mobile. The planes can counter rotate or go the same direction in a race, just make sure they have enough string to not collide. I gave the dual mobiles away before taking movies, sorry!
Slip the tube and washer assembly onto the carbon fiber support rod but don't glue it yet.
Step 5: Counterweight
To fine tune the balance of the plane to the solar panel, I added a short length of threaded rod with 2 brass 10-32 nuts. I made the solar panel slightly underweight so the counterweight goes on the solar panel side of the support rod to leave the plane by itself for a nice clean look.
I happen to have a Sherline lathe that I could take a 2" by 0.25" by 0.25" plug of the black plastic and turn it down to a cylinder diameter of 0.200 inches (a bit more than the greater diameter of 10-32). I then center drilled it with a #31 (3mm) drill and put the drill in the hole to keep it from collapsing while running the 10-32 die down about 7/8 inch. I cut it to 3/4 inch length.
Push the threaded plastic counterweight with two or three 10-32 brass nuts (depending on weight needed) onto the carbon support rod.
If you do not have a small lathe: you can drill it out first, then leave the drill in for support and hand carve the plastic with woodworking tools until round. Chuck the drill and carved plastic it in a drillpress then CAREFULLY sand it down to 0.200 diameter.
Step 6: Solar Cell
The solar panel needs a bracket to hold it to the support rod and counter balance the plane. I found some scrap outdoor grade black plastic that was perfect at Tap Plastic.
Cut a 30mm square of the 9mm thick plastic.
Mill a rectangular pocket for the cell to fit in snugly flush with the surface.
Cut a 5/8" hole through the center to lighten and leave a place to solder the magnet wire to the solar panel.
Drill a #31 (3mm) hole in the side that goes through to the large center hole beneath the solar panel. Make this as centered as possible top to bottom so it doesn't want to flip the whole mobile upside down (my only mistake).
Test fit the solar cell holder and solar cell on the support rod to check for balance. Cut off corners of the support until everything balances out. You can slide the counterweight nut assembly and turn the nuts for fine tuning.
Silicone seal the solar cell in place after cutting the magnet wire to length and stripping insulation off it.
Touch the wires in bright sunlight to first check polarity so the plane flies forward. Solder with electronic solder then silicon seal over the contacts after checking operation to weather seal it. Silicon seal the solar cell and holder to the carbon support rod - facing up!
Step 7: Paint and Enjoy
The planes need paint of course. Mask off the parts you do not want painted. A couple light coats of matte white spraypaint for plastic makes a nice undercoat (acrylics will not stick to the shiny plastic). You can sand and fill any further imperfections at this time too.
Paint with your favorite color scheme.
Attach to black woven fish line with the fishing swivel and slide the carbon rod back and forth along the hanging ring until everything balances just perfect. Slide the counterweight and turn the brass nuts for fine tuning the balance. Super glue the brass support hanging ring with the plane nice and level and balanced. You are ready to go when sunlight hits it!
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