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Gear train for learning about ratios - designed in South Africa, made in USA

Rating: 3 votes, 5.00 average.
My daughter Reka and I made this in the C-U FabLab last week:

The design files are at this link:

The design

How we got the design is a fun story. At the FAB6 conference last month I met Pieter Tolmay from the Potchefstroom Fab Lab in South Africa. During the showcase on Thursday night, he was showing some things that they'd made in their lab to help teach mathematics to local kids:

I was particularly interested in the little gear train with the rack and pinion mechanism. Reka has just started middle school, and it seemed like something her school might be able to use when teaching mathematics. Pieter and I exchanged cards, and he sent me the Corel Draw design files for the gear train. This really of exemplifies the spirit of FabLabs worldwide - we design something useful, share it with each other, and something designed in South Africa will end up in my daughter's middle school in central Illinois, USA.

I wanted to make sure that future kids at Reka's school would be able to appreciate that it was designed half-way around the world for kids just like them. So I etched the following text on the base:

It says "Designed at the AMTS FabLab North-West, Potchefstroom, South Africa. Made at the Champaign-Urbana Community FabLab, Urbana, IL, USA September 2010". Then Reka added "From Reka" in a sharpie, to sign her gift.

Making the gear train

Anyway, once I had the file I imported it into Inkscape and made a few minor modifications (etched where the "hub" pieces should attach on the base, etched out some text, and added etched dots on each gear to help keep track of where the gears are). Those modified files can be found at this link. I made a few small changes at the lab, namely rounding the corners of the base plate and breaking all the gears out into different files so I could cut them out of different colors.

The base is made out of 3/16" frosted acrylic, and the gears are made out of various colors of 1/8" clear acrylic. After everything was cut out, I super-glued small pieces to the base so that the gears would have something to rotate on:

Once we had it together and played with it a bit, Reka made some really good suggestions for how we could improve it even more. The first one was that we cut some small cylinders out of the 3/16" acrylic to act as handles on the gears (held on with more super glue):

The second one was to put some feet on the underside of the base, since it was really hard to pick the base up off the table:

Using it to teach math

I'm not a math teacher, so I don't know how to write a lesson plan for this (any volunteers?) but Reka spent some time playing with the gear train, and offered up this starting point (she will show this to her class on Tuesday, when she gets to school).

Arrange the gears with the dots on the two smaller gears right next to each other, and the dot on the yellow gear touching the orange gear, like so:

Move the blue rack gear until the dot on the smallest gear has gone all the way around once, like so:

Now, why aren't the dots lined up any more? What has happened to the dot on the yellow gear? And most importantly, why have these changes occurred?