How to get into writing software for more physical things?

In my spare time I enjoy writing lower level software for things that move around or have more of a physical nature to them. I would like to pursue this as a career and transition away from writing web services which I currently do as my day job.

This is proving to be difficult as I do not have formal experience in this field and only have my personal projects to talk about in interviews. Has anyone made a transition like this in the past? If so, how did you do it?