Yesterday I went to Rail GWR Steam Convention 2003 at the STEAM museum Swindon - excellent. Hornby were demonstrating the new 4mm steam powered A4 model. It's quite an impressive engineering achievement, but the restrictions due to having the control of the heating of the water by varying the voltage on the track from 17V downwards rules it out for me. The maximum current is 5 Amps, which would have been deliverable from DCC, so why not go for that technology for the control? They have limited its appeal particularly in USA where DCC has really taken off. The control of the engine seems pretty good (it uses a skew wound motor, which the demonstrator thought was 3 pole, to control the input of steam to the cylinders). I thought that 2 of the attractions would be the 'authentic' steam sound but apart from the whistle this seemed virtually absent and exhaust steam from the chimney which again was only 'whispy' and unprototypical.
Although the superheater brings the steam temperature up to 280 (or was it208?) degrees C, there seemed to be no damage to bodywork or paint as the plastic is heat resistant and stable up to 400 deg C. The operator said that he could pick it up by the bodywork after running but would not care to hold it for very long.
The mechanism protrudes into the cab which contains an unprototypical lamp which flashes red/green to indicate the status of I assume the bolier temp etc.
My conclusions are that it is an impressive achievement to get controllable live steam in 4 mm but considering its non compatibility with DC or DCC locos (yes of course you could isolate it into a siding, change your power supply and controller and use your other locos but woe betide you if you forget and put your other locos on live track, but who wants this other complication?) is not something I would want. As it requires an electric motor inside it anyway, power to the track, a dedicated controller and doesn't give 'authentic steam sound', I would prefer to spend the 500 pounds it costs on upgrading my DCC system to put digital sound in my locos.