This was a project I more or less fell into accidentally, after shopping around for a mobile for my and my partner's new baby, and finding that most mobiles aren't made for babies, they're made for adults. That is to say, they violate the two main requirements for a baby mobile, which we may as well get into straightaway:
A lot of the makers of toy mobiles screw up at least one of those; in my shopping (in the San Francisco bay area) about two thirds of the mobile makers screw up the first one, and perhaps a quarter screw the second one up too.
The problem in visually stimulating a baby is that the visual processing in their brains is incompletely developed when they're born. At the very onset, their color perception is limited; they can't focus on objects; their eyes don't track together (limiting their stereoscopic vision, and hence their ability to perceive 3D space). Basically the ideal things to attract a baby's eyes are strong contrasts, bright primary colors, and faces (which, despite the lack of response to other shapes, babies can generally recognize -- which probably comes in handy, in evolutionary terms.)
Cut the dowels to approximately equal lengths. Don't stress if they're not equal, and if ovals seem more appealing, leave one length longer. Just keep in mind that very early on your baby can't aim his or her eyes, so it would help if the various colorful objects passed through roughly the same point in space.
Cut a pair of matching notches at the midpoint of each dowel; you'll be mating the dowels through these. Sand and/or file the notches smooth. If you're going to mount with a screw eye, drill a hole for it with the dowels mated but not glued.
Drill a small hole slightly in from the end of each dowel, perpendicular to the face of the notch in each. Measure these holes carefully, since you'll be hanging the CDs from them and errors will throw off the balance.
Mate the notches together with wood glue inbetween, and clamp them until dry.
I'm not sure about the proper term for these; the wikipedia definition of a mobile simply calls them "objects." At any rate, I'm referring here to the colorful objects your baby is intended to look at, being more or less the entire point of the contraption.
First of all, you'll need something visually interesting and stimulating to display. Using the photo editing or vector drawing program of your choice, sketch out some suitable designs. Adjust for the age of your baby, or make extra so you can replace them as your baby's visual cognition develops. Whatever designs you make, go back after and try to make them simpler -- it's hard for adults to adjust their visual thinking. Based on my reading, you're really aiming only for strong contrast early on, and color is a secondary consideration, so keep a lot of sharp light-dark boundaries in. This isn't the place for elaborate alpha-blending and antialiasing. Nor is is the place for all those pretty intermediate saturation levels on the color pallete -- you pretty much only want the bright strong colors over on the edges.
I made my visuals in Inkscape, and have put both the originals and PDF copies here if you'd like to use them as a starting point. In editing these, it helps to set your image editor to use metric display units and visual grids, since a CD is 12cm in diameter.
Once you've got the patterns made up, print them out on sheets of sticker paper. Modern color inkjet printers will do, or you can opt for the usual expedient of sneaking in to use the expensive color laser printer at the office. Printers vary in how close they can print to the margins, which affects the number of 12cm circles you can fit on the page; the one I used could only fit two without clipping, so the samples use that.
Cut out the visuals -- I found using a spare CD as a guide and working around its circumference with a penknife worked well, using scissors for a bit of cleanup after.
The only real trick here is to make it easy to suspend the CDs from a point vertically coaxial with their center of mass (or more simply, to give you something to hang them by so they'll be balanced.) We'll do that by making simple wire hangers, then gluing them to the CDs.
To make a hanger, cut off a roughly 3" length of stiff wire. Bend it in half, folding it almost closed but without quite crimping it at the fulcrum (it's more likely to break if you do.) Cut off the ends so they're even -- we're aiming for symmetry here. Bend the folded end sideways about 20 degrees, then unfold the entire wire while opening it at the fulcrum, so the legs are straight. Hold the thing against a flat surface to check; it'll take a bit of fiddling. You should be left with an essentially straight piece of wire with a V-shaped jag in it. Check for balance by hanging it from another piece of wire, and trim the downhill end if needed until it hangs level and balanced.
Mix up some epoxy, and use it to glue the hangers to the CDs. You have a choice here, design-wise:
Glue down the hangers, and leave the epoxy to cure. If you put the Vs through the holes, just keep the CDs level, e.g. by setting it atop two equally sized blocks -- so long as the CD was level, the hanger should naturally fall with the V perpendicular to the CD surface. If you kept the entire hanger on one side, you'll need to prop it up with the V properly positioned while the epoxy sets.
Repeat for four (or five) panels.
Peel off the backing from your visuals, and apply them to the panels.
Attach the panels to the frame, hanging them from the holes in the end of the dowels (and optionally put another in the middle) with thread, wire or monofilament (I tried both thread and solid-core copper wire scavenged from Ethernet cable to good effect). Try to use the same amount of line on each arm of the frame; excess will affect the mobile's balance. Use knots that won't come undone under strain.
Hang the mobile itself from its center, either by the screw eye if you used one, or by the center joint if not. A good simplifying hack here is to skip hanging by the center entirely, and instead use a coat hanger, either clipping or taping it to one arm of the frame.
Adjust the balance. First, level out the panels by putting bits of tape on the uphill edge of the upper (parent-facing) sides. If you were careful about attaching the hangers, you shouldn't need too much of this. Next, level out the entire mobile. If you used a center panel, check that its attachments aren't disturbing the balance -- lift its weight with the rest of the mobile still hanging to check. Next, if you left too much string/wire holding one panel and it's pulling down the mobile on that side, take some out. Finally adjust the balance by adding weight -- either wrapping the ends of the uphill arms in bits of tape, or adding an extra loop or two of string or wire.
That's pretty much that -- hang the mobile wherever you figure your baby will benefit from visual stimulation -- over the crib, the changing table, somewhere on the ceiling where you figure it'll spend its time, whatever. Enjoy.
Copyright (c) 2009, Devin Carraway <dyi-mobile/at/devin.com>.
This work is licensed under a Creative Commons Attribution-Share Alike 3.0 Unported License.