Although Himself's in no hurry to begin the Robex Gelert project he couldn't resit having a fiddle to see how the Fleischmann chassis would fit within the 3D printed body, and I couldn't resist giving it a test run to check whether the chassis (which has been sitting in a drawer for more years that I care to remember after being bought on German ebay) actually worked.
The short answer is that it did, and made a very ghostly sight running around Bron Hebog.
Now, anyone who's ever modelled one of these Bagnall tanks will know that the design is very rear heavy, even in featherweight 3D form, and the pony wheel is essential to keep the front driving wheels on the rails.
Well yet again Himself's hoarding of 'bits that might come in useful one day' has come to the rescue.
In his former life working on pianos he saved some little cylindrical lead weights (they're used to counter-balance the keys) and it turned out that one of these was a perfect fit inside the hollow smokebox, and also the perfect weight to balance the loco on the track without a pony wheel in place.
So remember that the next time someone near and dear to you is ordering a clear-out and tells you: "you're never going to use that stuff, you know......."