I am particularly fond of the eccentric and the steering system.
The eccentric rods swing the toggle to work the steam inlet piston, the reversing lever lifts the eccentric toggle and would reverse the steam input and engine movement (via a pose of the eccentric armature).
The steering wheel turns according to a curve path thus winding the chains around the «winder» and pulls the wheel tub to turn the front wheels.
Well that’s how it works in the real world, in the model it is the wheels turning that control the chains and wind them round the winder via a curve modifier.
It’s funny how animations seem to work the reverse of the real world, the engine has the same reverse logic, instead of the steam pushing the piston and driving the crank shaft, in the model the rotation of the crank shaft drives the main piston!
The model follows a curve and all the mechanics ect will turn and follow accordingly, the wheels turn into the corners ect. I did this with an instance of the model in another scene, the instance follows 2 bones that wiggle around a curve via a drive control object, if I reverse the drive control object’s movement the mechanics also reverse. One bone controls the position of the engine along the path, the other points to the direction of the oncoming bends and controls the steering wheel and the front wheels rotation.
The drive control object only moves on one axis, this was useful as it got rid of an annoying problem in which when the model simply followed the path curve the wheel rotation would stop and then reverse when the model goes over 180º. The movement on the y axis of the drive control object controls the bones, which in turn control the rigs for the wheels, motor and steering system via drivers. The method I used is based on this discussion:
And last but not least the steam!
The video is a test, not final and could do with more work… yes, I know there is no real enviroment, the grass sucks, and there is no driver!
So it is a 10ton run-away steam engine – better keep a distance!
I decided to use a particle system for the steam instead of a smoke sim, that way I can go around with the engine and it will leave a trail (or it would if I gave the particles more lifetime!). Also if you reverse the engine, the trail will reverse and do corners etc. If it was smoke I would be limited to a domain, with particles the engine can go for miles and round bends etc leaving the particles behind.
The particles are a cube with a volumetric material. In the end I used two emitters one with more vertical velocity than the other so some smoke goes up and some drags more. I prefer subtle smoke with very few steps, if I crank up the steps the steam gets denser and more detailed but I decided not to. All in all I think the steam works ok, I am not going for photo-realism, and it was «painless» to render in eevee.
The video was done with Eevee because to render the volumetric particles with cycles I would need a farm myself, (or another lifetime).
Thats all…for the moment!