Although popular with several European manufacturers, tender-drive has never been well-regarded in UK, possibly because of some rather poor implementations back in the 20th century. Nevertheless, it does have some advantages, when modelling prototypes from the 19th century. Locomotives of that period were generally quite small, with open cabs, and most passenger classes used single drivers until quite late in the century. These characteristics create two problems for the modeller: there is little space, where a motor can be placed out of sight, and single drivers give poor adhesion.
Some time ago, I found that I could place a Tenshodo SPUD power unit within the front bogie of a Tri-ang Dean Single but, if I were tackling the same problem again, I think I would go for a powered tender, even if a little less elegant as a solution. The disadvantages of a powered tender are the lack of 'daylight' under the body and, in some cases, a rather visible power-train. It is also necessary to provide a high coal load to conceal the motor, though I have several prototype photos to show that this is not as unrealistic as sometimes supposed.
When I converted a Mainline Dean Goods to a representation of a 'Stella' 2-4-0, I initially accepted the rather noisy tender drive motor but then began to explore alternatives. Hornby produce the X9105 drive unit (available from suppliers of Hornby spares), which has a smooth-running, 5-pole motor and a reasonably quiet drive train. It also has the 7' 6" + 7' 6" scale wheelbase, used by many types of GWR tender. My first trial with this unit was to see if one could be fitted into the tender provided with the Dapol (ex-Airfix) 'City of Truro' plastic kit. This approach avoided 'butchering' the Mainline tender, while providing a similar outline from more easily manipulated components.
Fitting the motor proved quite straight-forward. I had to either cut away or file down several protrusions on the inside of the tender side mouldings and also cut away the 'coal'. The rear part of the top and most of the sides could be retained, with a little filing to increase clearances. I then eased the motor unit into the body from below, with some thin black polythene sheet (cut from a waste-bin liner) to hide the top and provide a base for a 'coal' load. I fitted a miniature computer-style power connector to the front of the tender so that it could be used with different locomotives.
My first application was to the 'City of Truro' kit, in which I replaced the plastic wheels with Gibson extended-axle drivers. Pick-ups on the locomotive were wired to a matching connector, for coupling to the tender. The result was a smooth and quiet running locomotive
The Dapol tender is not too bad but does have irritations, such as raised panel mouldings that have to be removed with a scalpel, and it represents a later type, with filled-in side-sheets. I found that a white metal kit of a Dean 3,000 gallon tender, with etched coal rails, is available from Scale Link, so my next step was to try and adapt one of these in the same way. Although I had managed to squeeze the Hornby motor into the Dapol plastic body without modification, the protruding metal 'lugs' were too wide for the Scale Link kit. After carefully wrapping the motor itself in plastic sheet, to protect it from swarf, I skimmed off part of the lugs with a rotary cutter on my mini-drill - do not forget to wear eye protection, as swarf does fly about.
I stuck strips of electrical tape on the inside surfaces of the white-metal sides to prevent any electrical 'shorts' and then assembled the kit around the motor unit. The end result is quite an attractive coal-rail type tender which, because of the weight of the white metal body, does not need traction tyres to perform well.
I am now working on plans for some more Dean locomotives, which will be powered by these tenders. I am sure that there are several other tender drive units, with different wheel spacings, which could be used for other prototypes. It would be helpful if suppliers could indicate the wheel spacings or, perhaps, others could contribute a list of suitable modern units, to help in adapting these to different models.