I've recently finished a model of the Middleton Railway's Hunslet 22hp 4wDM, nicknamed 'Sweet Pea'. Allegedly the smallest standard gauge diesel in the UK! Which made it somewhat of a challenge to motorise... see size comparison photo with the Terrier. The roof hasn't printed perfectly but the rest of the body has come out pretty well. It's got a micro motor driving both axles, and a tiny flywheel that I'm not sure does anything to help. Runs a bit quickly but considering the space I had to play with (or lack thereof), I'm quite happy with it.