People have been asking about the measuring Turtle and I realized I didn’t explain the thing. This is a sort of sensing “LOGO Turtle“, which reads how far the wheels have turned and then uses that data to plot a bar graph. The concept centres around understanding of what a stright line is. Although the notion of “what is straight” seems rather obvious, trying to describe it in geometrical or mathematical terms is a bit tricky. Especially when we move from 2D to 3D worlds. One way of thinking about it is that a straight line is as a path of symmetry.

The “turtle” (okay, it is a turtle with wheels!) demonstrates this in the 2D plane or on a 3D sphere. As long as both wheels are turning at the same rate, the turtle is moving in a straight path, which is symmetrical. By moving the turtle manually across a plane or sphere, the movement of the weels can be observed and compared to to determine straigtness or curvature. This is a way of embodied learning about fundamentals of geometry, which we are using on the Spot-On project. We’re taking the turtle into secondary school classrooms early next week to see what the students think of it. To demonstrate using the turtle on a sphere, we;ve procured a couple of giant (1 metre) sports balls for kids to roll the turtle upon!

The underside of the “turtle” shows the gearing mechanism for transferring the rotations of the independent axles to the sensor wheel. Rather than using an optical encoder - which is basically just too expensive - the sensor wheels pass through the slots of two IR emitter-detector pairs. These TTL logic devices pull up digital pins on the Arduino and this signal is passed to a Processing sketch. The wheels do generate consistent data on the whole, which is what we were aiming for.

The tracking turtle is almost complete. I’ve added the bluetooth arduino board (Arduino BT), though with a bit of trouble getting it to communicate with Processing via firmata. Serial port keeps getting “clogged up”. However, the sensor wheels and IR slot sensor are working as planned.

Resistors for the IR emitter+sensor combo are visible in the undercarriage.