A pair of Robinson B4 hot air engines in 1:4 scale by William A Freeman photographed by Jason at the 2024 Midlands Model Engineering Exhibition. The original engines were normally coal-fired and used for pumping and light machine duties. The displacer is water-cooled by an integral tank under the power cylinder.

Power cylinder 1 3/8 bore x 1 inch stroke
Displacer 2 1/4 bore x 7/8 inch stroke
Flywheel 4 1/2 inch diameter
Overall height 7 1/2 inches.

Robinson drawings and castings may be available.