This short film of 1911 just took my interest some years ago when I thought about modelling a Claughton. These pictures are stuffed with interesting prototype information. But the most exciting object is the rotating dumper. I have seen some US prototypes before on youtube and thought about the Walthers model, but I find, it looks more like a toy and produces a horrible noise. So I started thinking about how to get the Crewe dumper to model size. The key moment, when I decided to start this project, was an Arduino starter kit, I ordered for the summer holidays. To rotate the dumper and return it exactly to the starting point can be really easily solved using a stepper motor. Here the positive points of stepper motors:
- No need for a reduction gear, because steppers have a good torque
- No endstops. The working angle or rounds and speed can be programmed absolute exactly
- In hi-res mode absolutely quiet. Listen to my video!
The Arduino can control servos aswell. On this project I used two to lock down the wagon during dumping.
The whole model is a two part 3D print: The revolving drum and the base. The conveyor in the background is printed and driven by a bigger NEMA stepper. The coal wagon is a 3D print on a Dapol-chassis.
The unloading process starts with the engine pushing the wagon into the dumper. On the far end there is a bumper with a magnet inside, that catches the metal hook of the coupler. So the wagon is and stays exectly positioned. On my shunter, there is a Märklin DCC decoupler (This action I will show later, when the dumper is installed into the diorama). The dumping will be started by a push button: Like on the prototype the bars were lowered down on the wagon. The guy fastening the chains is simulated by two servos mounted under the track. After having locked down the wagon, the Arduino controller starts the stepper making 3800 steps that equals appx. 160°. The controller waits three seconds and brings back the wagon to its starting position. Then the servos release the bars and the engine can come back to grab the empty wagon.
The rotating drum is sitting on and is driven by four gears. Just gravity was not enough to keep the drum sitting well on the gears, so I fixed two of these strong micro magnets under each of the two big rings and painted the surface with ferro-mgnetic paint. I never belived it will work, but this paint is really magnetic.^^
Compared to the prototype you might realize that my model looks a bit bigger. The small H0 scale Preiser guy in the front is not the only reason. The two servos had to be hidden under the track, so their size was the minimum factor for the radius of the drum.
-> Watch it in motion on youtube.