Making a baby mobile (out of old CDs)


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:

Requirements

  1. Visually stimulate baby in a way compatible with the state of their sensory and cognitive abilities
  2. Be visually interesting from underneath, where the baby actually is

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.)

Materials

CDs
This project was more or less predicated on the thought that CDs are about the right size and shape, come in a highly standardized size, and most households probably have plenty of disposable ones around. Don't go picking through your music collection for sacrifices -- just root around in your desk drawer and pick out everything with the word "drivers" on it.
Dowels
For a simple mobile with a single X-frame, all you'll need is a single dowel, suitable for cutting into two lengths 15-18" long. Remember, this isn't going to be an elaborately balanced four-level mobile with delicately painted biplanes or seabirds on it -- those are for adults. This is just going to be a single-level structure, able to hold four or five visuals. The diameter of the dowels isn't especially important; slightly thicker dowels are sturdier and a bit easier to work with, thinner dowels offer you the option of mounting the CDs directly on the dowels rather than hanging them. More on that later.
Sticker paper
This is how we're going to get the patterns onto the CDs. You could probably use CD labels or fancy inkjet contraptions that can print directly onto a CDR, but don't bother. You aren't going to need the hole in the CD anymore, and all you're looking for is bright contrast. A few hundred sheets of white sticker paper should run you $10 or less at the office supply store of your choice. If you can't find sticker paper, ordinary paper and some light-duty spray adhesive can be used, though the result doesn't look quite as good (not that your baby will care.)
Stiff un-insulated wire, roughly 16ga
This is how we'll enable a CD to be hung from a single point. You want wire that's stiff enough to hold a shape it's bent into, but not so rigid as to be annoying to work with. You could cut up a coat hanger in a pinch, but that's probably too stiff. Unbending paper clips would do better, though it adds a bit of extra tedium.
Monofilament (or fishing line, or strong thread, or fine string)
Chances are you've already got at least one of these around.
Screw eye (optional)
Useful for hanging the mobile, although not essential. You can tie an extra loop in your knot to balance it, but attaching via a screw eye makes it easier to get the balance right and strengthens the (one) join.

Construction

Frame


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.

Visuals

The Graphics

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 panels

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:

  1. Keep the entire hanger on one side of the CD, with the V pointing upward and away from the CD's surface. This leaves the entire visible side smooth and avoids an unsightly lump across the visual. However, it also means the joint is only as strong as the epoxy, which in turn depends somewhat on your mixing and application technique. If you're comfortable working with epoxy and you've got nice flat hangers to work with, this should be quite strong enough.
  2. Keep the flat side of the hanger on one side of the CD, and poke the V through the hole (do not emulate the horrible epoxy job I did on that particular panel). The visual then sticks onto the flat side. Gravity will work in the epoxy's favor, and the whole structure will strong, but you'll have the lump to contend with.

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.

Assembly

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.