What is the smallest N guage drive mech out there?

I need to find the smallest 2-axle drive mechanism for an HOn30 micro layout I want to build, but other than a N guage Bachmann 0-4-0 Dockside Switcher I cant think of anything else that can handle ludicrusly tight corners (like 4" R) that I like doing on Micros. Any ideas?

Thanks for any offerings Vic[8D]

This is the smallest I’ve found

http://www.reynaulds.com/Trix/temp.asp?item=12212

Arnold used to make the littte Swiss Tm 2/2 switching tractor in N scale - it was about the same wheelbase as an EMD F unit truck but still had a motor and all wheel pickup shoehorned in. Saw one running on a friend’s layout and have wanted one ever since, though as Arnold were part of the Lima group (now bought by Hornby) it might take a while. If you take a look around on ebay and other sources you might find someone selling one. There’s a few photos of the real thing here: www.railfaneurope.net/pix/ch/SBB_CFF_FFS/diesel/Tm_II/pix.html - should help with identifying the model. Hope this is of use!