39: motion studies

Here are some of the motion simulations that are possible in the computer.

The first one is an extension of the eccentric motion I posted a while back. This time, the main and side rods have been put in place and the crossheads (and the hidden pistons) are now in motion.

Some notes to observe:

  • The motion simulates the engine running at about 2.5mph
  • The offset of the two pistons is more obvious when watching the two crossheads move relative to each other
  • The tendency for the lifting shaft, link, and the reverser bar (out of view) to nudge or swing “forward” as the wheels spin. This is why the reverser bar arc is notched. In the animation watch the lifting shaft carefully for this effect
  • The mechanical lubricator link can be seen in the upper half of the animation. It’s driven off the left valve stem
  • The empty slots at the crosshead/piston rod junction will receive the piston/crosshead key

Next simulation is the throttle valve linkage. The throttle bar (left) is linked to a valve at the top of the dry pipe (L-shaped rising pipe, right). The valve is inside this pipe and when the throttle is closed, the valve sits snug in a seat in the dry pipe. When the throttle bar is pulled, the linkage causes the valve to “pop” open and allows steam in the steam dome to enter the dry pipe, then onto each cylinder and piston.

The yellow vertical pipe immediate behind (left) of the dry pipe is the header pipe, which takes steam from the steamdome into the cab to run appliances.

And speaking of throttle, the next animation shows the throttle quadrant in action. The quadrant is notched, and a spring-loaded block with teeth “grabs” the notches to hold the throttle in place against the steam pressure acting on the throttle valve.

It all looks simple, but there are a number of subtle movements, such as the moving quadrant and the pivot of the throttle bar.

Note that to actually move the throttle, the engineer would grab the handle at the end to release the spring-loaded latching block from the quadrant. That action is not in the animation. The latching block simply slides along the edge of the quadrant instead. I used this motion to ensure that the latching block is concentric to the quadrant.

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