Designing an Enclosure
From Open Source Urbanism
I rode my Spoke-o-dometer through a torrential downpour last week, it didn't miss a beat; I think the spinning of the wheel prevented water from pooling on the circuit board. But electronics and water are generally not a good combination, it's not just the wetness, corrosion is a major concern. The solution of course is some kind of protective case.
Design Ideas
I set my Mod Mania class the task of generating some design ideas, a stipulation of the design being that it needed to be suitable for the owner-builder. i.e. a design that others can replicate. They came up with a diverse array of responses.
Sam designed an aerodynamic case for the circuit and a 'kinetic battery' to power the device.
Carson's solution involved a match box and a whole lot of gaffa tape to create a disc wheel.
Darby and co. decided a condom would provide the perfect combination of protection and transparency.
Bao proposed mounting the arduino board to the bike's frame. The LED strips are mounted to the spokes using the clear body of a Bic ballpoint pen.
Mohamed suggests creating a pdf download to assist in laying out the various components and then pressing Sculpey or a similar modelling clay over the components to create the enclosure.
Other suggestions included using a tennis ball wedged in the spokes to house the circuit, vac-forming directly over the components, and embedding the circuit in resin. All this activity made me realise there doesn't need to be a single design solution. Diversity is good and there should be as many enclosure designs as there are Spoke-o-dometers in the world. Currently there's only two Spoke-o-dometers and neither of them have enclosures - but I'm working on that.
Prototype III
One of the students came up with the idea of mounting the Spoke-o-dometer on the bike valve.
Initially I was sceptical, I thought the device would be too heavy, but after building the Really Bare Bones Board (RBBB) I have changed my mind. With the batteries mounted separately the RBBB and LEDs are light and small, they could easily be designed to fasten to the bike valve.
The RBBB has a row of pins running along either side of the board; the LED's, sensor and save button are connected to these pins. Using the pin assignment outlined in the previous section (Doubling the LEDs) the left and right hand side LED pins are concentrated on either side of the board. This means the LEDs can be easily placed on two separate boards. Each board can be connected to their respective row of pins, creating 'wings' on either side of the main circuit board.
This arrangement produces a very compact design with an open channel running through the centre of the object. The channel is the perfect size for a bicycle tube valve. I placed a piece of heat shrink tubing over the bicycle valve to insulate it from the electronics, fitted the circuit around the valve, and filled the cavity with hot glue. The glue bonds with the heat shrink tubing and once it has cooled the whole contraption can be screwed off the valve. This works well with my valves because they have a thread that runs their entire length - it may not be as successful with the chunky car-tire valves you see on many bikes.
With the circuit removed, the hot glue can be easily cleaned up. The glue provides the circuit with some water protection, although the main board is still exposed. This style of mounting seems very secure and with the battery compartment located closer to the wheel hub (and on the opposite side of the wheel) the wheel maintains a good balance.
