High speed train driving

[DaveMcW]

I am using this function to "manually" drive a train.

Code: Select all

function on_tick_driver(driver, direction)
  driver.riding_state = {
    acceleration = defines.riding.acceleration.accelerating,
    direction = direction,
  }
end

It works great for vanilla train speeds. But for very fast trains, it is possible to drive past several branches in a single tick. Is there any way to queue up several riding commands in a single tick?

If not, what is the theoretical max train speed I can handle before this breaks down?

[DaveMcW]

If not, what is the theoretical max train speed I can handle before this breaks down?

I did some investigation into this, and found three limiting examples. Let me know if I missed any!

Example 1

In this example, driving north, the three possible paths are:

• Left
• Straight + Left
• Straight + Straight + Left

If a manually controlled train wants to take the middle path, it must hold straight for exactly 2 tiles, then left. This becomes impossible at speeds over 2 tiles/tick.

3-left.jpg (273.72 KiB) Viewed 500 times

Example 2

In this example, driving northwest, the three possible paths are:

• Left
• Straight + Straight + Left
• Straight + Straight + Straight + Straight + Left

Diagonal rails are only √2 tiles long, but there are two of them between each turn. If a manually controlled train wants to take the middle path, it must hold straight for exactly 2√2 tiles, then left. This becomes impossible at speeds over 2.8284 tiles/tick.

3-left-diagonal.jpg (317.82 KiB) Viewed 500 times

Example 3

In this example, driving northwest, the three possible paths are:

• Right
• Straight + Left
• Straight + Straight + Right

If a manually controlled train wants to turn left, it should hold straight for exactly √2 tiles, then left. Correct? Wrong! It can hold left the entire time, because left is not an option on the first straight track! This reduces the problem to the previous case, where it only becomes impossible at speeds over 2.8284 tiles/tick.

right-left-right.jpg (316.15 KiB) Viewed 500 times

Conclusion

The minimum limit is Example 1. Manual driving works perfectly at speeds up to 2 tiles/tick (432 km/h), and after that it starts to fail. On diagonal tracks, you need to start turning 1 track early at speeds over 1.41 tiles/tick (305 km/h).