This series of small industrial Critters are designed to fit on a single Bachmann 44ton truck , from the first series of production( later ones used a single central motor).

 Other mechanisms of roughly 24mm wheelbase  can be used as well.

 They are all freelance to a greater or lesser degree, but are inspired by various prototype locos from the US, UK, Germany and Japan and in some cases other models!

 This one was inspired by a Whitcomb Prototype