A student asked me about the LEGO differential housing last week. We talked about what it was for, and had a look at this excellent video.
I remembered a design challenge from Eric Wang's classic "Engineering with LEGO Bricks and Robolab", to create a south pointing chariot.
The south pointing chariot is a mechanical compass that was developed thousands of years ago in China and may have been one of the earliest uses of differential gears anywhere in the world. Typically, a figure stands on top of the chariot and always points in the same direction regardless of which way the chariot is pulled.
After some more research, I found a few different examples to draw on, and eventually came up with a working model.
I thought it might be useful to others to have some building instructions, so took this as an opportunity to reacquaint myself with MLCad and LPub 4. I've been wanting to get back into producing building instructions for ages - so that I can finally finish off a bigger project I started working on over two years ago... more about that later! In the meantime, here is the result of the current project...
Download Building Instructions for a LEGO South Pointing Chariot (pdf, 2.5mb).
I used parts from the LEGO MINDSTORMS Education NXT Base Set (9797) and the Education Resource Set (9648), but in fact all the important parts are widely available LEGO Technic parts.