coal hopper wagon

Nothing British. Remember that a working mechanical trapdoor also requires the building or bridge with mechansism to operate the trap which Rovex Triang Hornby of course did provide. I cannot ever recall seeing anything European so you may have to look to the USA. Rovex designers did like their mechanical working toys and it is a design skill that now seems to have been lost as the world has gone electronic.

I wonder how todays designers would design a Corgi James Bond Aston Martin ejector seat?

And would it be possible to apply DCC technology to a hopper wagon?

Happy modelling
Gary