The gondola.
It dangles, hence a gondola. Clip the two lengths of beaded cord into the hooks on the gondola, and hang them over the sprockets.
If you need to build your gondola, or it falls to pieces, then have a look at this video:
Counterweights: These can be anything slightly adjustable. Use a bag of change, or that foreign money you don’t know what else to do with, or a bunch of washers strung on a nut and bolt.
But you should use the little hooks. This cord is a pest to try and tie knots it.
The weight should be enough so that the gondola falls naturally in the upper-middle of your machine. Mine are about 120g each. The object is to balance the forces so that the motors never have to try too hard to move the gondola to any particular point on the machine.
In practice, the exact weights of these isn’t that critical. If you consistantly find that you’re unable to make it up to the top of the surface, then it might be worth adding a bit more weight. If you find your cord skips down at the bottom, then it might be worth removing some weight.
Note that sometimes I add a bit of extra ballast to the gondola itself – usually a bag full of nuts or bolts, taped to the pen lift motor. This is sometimes nice with a very fine pen, to pull the whole thing a little more taut. Sharper corners. If you’re doing this, you might need to add a bit extra to the counterweights too, and reduce your top speed.
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