I've recently completed another two little projects - one Mechanical Horse and trailer -
a small 3 ton capacity 3-wheel tractor and trailer affair that were very common in our cities from the thirties to the sixties,
and also a 14mm gauge 'steam' crane to help with duties on 'Denton Brook'.
Both are fully functional, and run off a single lipo (each).
The Mechanical Horse has a flat 650mAh battery under the trailer bed, which gives a two-day exhibition duration,
and the Steam Crane has a 1000mAh battery, which gives it a one day exhibition duration.