There are always interesting side projects to work on; some are for clients, some are used to develop new techniques. The thermistorcator, for example, was developed to see how cheaply and accurately temperature could be measured, and wound up being used as a piece of test equipment for a client project.
Most of these are small scale ‘test’ projects, but they provide insight into how we solve larger problems. The art/engineering projects are sometimes the toughest. Not only must we grapple with the classic issues of ‘better, cheaper, faster’, but the projects have to fit within a certain aesthetic, and many times the artists themselves want to be able to modify or at least understand the mechanical, electrical, and programming elements of a solution.