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How to balance a mobile... and attach its parts? Answered

I've always been interested in making mobiles, or at least making the various parts that I would like to balance in a mobile. I've only really made one, which was a real hack job. I want them to look nice, so...two questions: 1) Is there a scientific method for achieving balance in a mobile apart from guessing? In the one that I did make, I used a fairly thick flower-wrapping wire, tied the parts to each end, and then found the fulcrum by balancing it on my finger. This is an awfully rough approach and is only so accurate. It worked okay, but I'd like to know how you've found success in doing this. 2) As far as attaching the parts to the end of the wire, how do you do it? I'm not very happy with the flower-wrapping wire because it's so tender and warps so easily. It's impractical for shipping or moving the mobile. Not at all durable. So what material do you use for the wire portion, and HOW do you attach your parts to it? I've tried twisting loops into the wire, but it really messes up the general straightness of the wire. I've tried tying fishing line onto the wire and adding a dollop of glue. But that's just ugly. If you have a good online source for making simple mobiles, and the materials one should use, I'd love that too!



7 years ago

Calder's answer to balancing was:

"Start at the bottom and work up."

If (as I assumed in my reply to caitlinsdad, below), you are making a Calder-style mobile, then you want to use very stiff support rods. Wire coat hangers are excellent for the task. Cut off the rounded corners and the twisted hook at the top, and you're left with three very nice straight pieces of stiff wire. To attach your decorations, use a file to cut notches at each end, and tie them on with fishing line or sewing thread. Put a little dab of glue (I'm partial to two-part epoxy, but whatever...) over the tied loop to secure it to the wire.

I guess if you did not design your mobile using a computer, finding where the center of gravity and the line that passes through it would be more trial and error if you did it without weighing, measuring and calculations. Try anyplace that has a fishing dept to use snap swivels of various types or other hardware to go along with your fishing line. They do make these parts pretty small and can be used to detach the parts that hang off the mobile for shipping and allow them to spin freely when attached.

Hi, caitlinsdad (there's got to be a better greeting than that :-). I think svirden is wanting to build Calder-style stacked balance-bar mobiles, rather than a flat plate with decorations around the rim. In that case (as you know, but I'm posting for others), the center of gravity lies along the one-dimensional support rod, and can be determined (see below) from the relative weights at the two ends. For the case of a decorated plate, as you describe, there is a reasonably accurate method of finding the suspension point. First, attach the decorations directly to the central plate. Don't have them hanging from strings, but tie them off directly, perhaps using short (and equal) bits of trash-bag twist ties. Next, hang the plate by its edge and draw a vertical line down from the suspension point. Turn the plate 60 degrees or so, and hang it from the new point, drawing a second line. Turn the plate another 60 degrees or so, and repeat. You should have three lines, all of which cross at a single point (yeah, right :-). That's the suspension point for the plate.

If you have a precision scale, then it's simple :-) Weigh what you're putting at each end of the rod (separately). Each rod is simply a lever, and balancing simply means the moments of inertia are equal. That is, m1×L1 = m2×L2.

Here's a simple numerical example:

            10cm   |         20cm        +----------+--------------------+        |                               |      100g                             50g

If you don't have a precision scale, then you'll have to do what you've been doing (though you can make a decent first guess just from approximate weights).

use cotton thread punch the parts in the air with 2 message board pins to make it kinda on pivot. play with it and feel their balance point. build the mobile from the bottom up