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[mahrgell]

Hi, somehow my attempt at building a watergun is failing right now for strange reasons. There is not even water in the system yet, but it looks as follows:

sideview:

The 3 blue carts sit there, with the hatch closed. When I pull the lever to start the system, the first cart drops down, onto the ramp. And then... it stops... the 2 carts on top of course follow right away(as they are sitting on impulseramps), and close the gaps... But now nothing moves. If i now close the hatch, the stuck cart suddenly starts moving again, rolls off the ramp and drops down then pit and cycles through the system.

I tried a few variations, with various results:
When using only 2 carts, there is no problem at all... first cart drops down, rolls off the ramp down into the pit and continues, second cart follows right away...

When removing the ramp below the hatch, and moving the pit one to the right (so it is directly under the hatch) result gets even weirder...
Now when I open the hatch, nothing happens at all. The cart on top of the hatch is now simply floating above the opened hatch, not dropping down at all....

Can anyone explain me that behavior?

[Di]

Firstly, you should have used image links provided by hosting.

Spoiler (click to show/hide)

Secondly, minecart physics is weird and buggy as hell.

If you want a working watergun you'd better use a single cart per route (or, as you've discovered, two carts).

Or you can have a little bit of dwarven science.
I'd say it's the second cart hitting first from above that prevents it from going left immediately and it's the third cart resting on the impulse-ramp that prevents second cart yielding a little to the left, so first cart could continue along the ramp. When you close the hatch you break the contact and first cart can move unobstructed by the rest.
When you have two carts, first one falls, second moves off the ramp, and even if it entangles with first one, the state doesn't last.
When the pit is just below the hatch, second and third carts press the first firmly into the green one.

Also, the order of cart creation is important since it determines the order game evaluates them. If you've changed carts' positions between first and third test that could explain the difference in their results.
You can determine cart priority by looking for them in stocks menu (relative for the same material, I believe) or by examining them with gui\gm-edit function of dfhack (absolute number).