To bring a little motion to the boxes, it’s worth having a few motorised components, like turntables. But they need to turn slowly, which is a challenge. Since I’ve never done the Exploratorium’s workshop personally I just assumed they’d made their own, but compiling this page I’ve realised they seem to be using jewellery display turntables, like these or this.

Since I didn’t know that, I ended up reverse-engineering something which didn’t exist in the first place. Hmm.

Well, I’m proud of our turntables. They turn slowly (about 1rpm) and despite looking pathetically fragile have proven quite robust in use. The old exhibit standby of ‘if it looks fragile, people treat it with care; if it looks solid, they’ll whack the heck out of it’ seems to apply. They do tend to fall apart in transit, but a minute’s ministrations with a glue gun solves that.

The core is a geared 3–6V motor, driven off a single 1.5V cell. There’s enough torque to work reasonably well, and undervolting it slows it down even before you get to the gearing. The drive pulley is a short length of plastic tubing with a cardboard end-cap. A slot in the cardboard cap fits tightly on the motor shaft, then hot glue poured into the tubing fixes it well enough. Gaffer tape wrapped around the plastic tube provides enough friction for the edge drive to the turntable itself.

Since we hand-cut the turntable discs they vary in diameter somewhat. The pivoted chopstick and elastic band tension spring keep the drive pulley and turntable in contact. The main turntable bearing is a short M10 bolt glued to the frame – ridiculous overkill, but it’s what we had lying around.

Things we’d do differently next time

• For such a simple design, the turntables are surprisingly fiddly to make. There are a lots of components, many being slightly-hidden bits of wooden chopstick used as supports or guides. Each of those pieces needs to be cut, sanded, and glued in place.
• I’d simplify further. A better bearing would allow for tighter tolerances, and you could then probably laser-cut ply to give a geared drive rather than the tensioned friction drive we used. You’d lose some of the charm of ours, but you could likely finish dozens in a day.
• Tempting as it is to go to a stepper motor and variable-speed controller, the unit cost would go way up. Also, the power consumption of these things is impressively low; they’ll run all day on a single AA cell.
• While the maximum payload is quite low, in some ways that’s a benefit as it forces participants to find creative solutions. As ever, we push against limitations and come up with inventive work-arounds. Completely ‘open’ play, without constraints, can be less creative.
• One common approach from participants is to fix objects to the drive pulley directly, not just the turntable. They then have two rotation rates to explore. Another example of finding creative utility from apparently-poor design.
• One advantage of this design’s rustic approach is that it can become a talking point itself. None of the components is unfamiliar, which helps it feel accessible; there’s a sense of ‘I could have built that’ about it. Yet it’s seen by a wide range of ages as ‘clever.’