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Tutorial 8: Add your plunger lane

This is part of our Getting Started guide.

The guide starts here.

It's been awhile since this tutorial has been updated. If you find anything that is no longer relevant, please let us know, or better yet, edit or update it yourself!

In this step we're going to create your plunger lane (or shooter lane or ball launcher or catapult or whatever you want to call it).

This is the device that holds the ball after it's been ejected from the trough or drain where it sits waiting for the player to put it into play.

It's important to understand that a ball device is anything that holds a ball, even if that's just a divot in the wood with no switch where the ball sits waiting for the player to pull back on a spring plunger.

MPF's ball tracking only works if MPF knows where all the balls are at all times, which is why it needs to "know" about the plunger lane, and you let MPF know about a plunger lane by configuring it as another ball device.

1. Add your plunger/catapult/launcher/etc.

Like the trough, there are several different plunger designs. Some are purely mechanical, some launch the ball with a button which fires a coil, and some have both options. Also, some plunger lanes have a switch which the ball sits on while it's waiting to be plunged, and others don't.

Visit the Plungers & Ball Launch Devices documentation for pictures that show each option and step-by-step guides which walk you through configuring each type for MPF.

2. Revisit your trough/drain device and add it as source_device to your playfield

Even though this is mentioned in the how-to guides, once you have your plunger device set up, be sure to go back to your trough or ball drain device and add the new plunger lane as an eject target, like this:

eject_targets: bd_plunger

Of course you'd add the name that you gave your plunger device, which could be something like "bd_catapult" or whatever you called it.

Also, if you have a two-stage drain (like a System 11 machine), you'd add this to the second device (the one that feeds the plunger).

Tell the playfield to use the plunger for new balls:

#! switches:
#!   s_plunger:
#!     number: 10
#! ball_devices:
#!   bd_plunger:
#!     ball_switches: s_plunger
#!     mechanical_eject: true
    tags: default
    default_source_device: bd_plunger

3. Check out the complete config.yaml file so far

Again, our example config will probably diverge from yours since you might have different types of drain and plunger devices, but we do have a complete machine conform for Demolition Man for this step which you can view in the mpf-examples/tutorial/step_8 folder.

You can run this file directly by switching to that folder and then running the following command:

C:\mpf-examples\tutorial>mpf both

4. Fire up your game and test

Unfortunately there are a few more things we need to configure before you can play a full game, but if you want to test what you have so far, you can launch MPF and drop a ball into your trough and you should see some cool things in your log file. To do this, launch the MPF game engine with the -v command line options so it shows the verbose information in the log file, like this:

C:\pinball\your_machine>mpf -vbt

You don't have to launch the media controller this time since we're just looking at the console output of the MPF game engine, which is why we added the b command line option too. (The b option tells the MPF game engine not to use the BCP protocol and not to try to connect to the MC.) You also have to add t to disable the text ui to see the verbose log. Otherwise, you would only see the verbose output in the logfile in the logs directory of your machine.

Note: For more information about command line options take a look at MPF commands and mpf game (command-line utility).

Once your game is running, drop a ball into your trough and you should see a whole bunch of trough switches changing between active (State: 1) and inactive (State: 0).

If you don't have a physical machine, you can run MPF with the -v option and see a bunch of stuff in the log too by hitting the keyboard keys for the trough switches which will add and remove balls.

Now quit MPF and open the MPF log file (which is in your machine's /logs folder). Grab the latest file with "mpf" in the name (if you ran mpf both then you'll have separate log files from MPF and the MC).

Search (or filter) the log for the name of your trough or drain device, and you should see all sorts of interesting things. Here's a small snippet:

2016-11-18 03:54:06,103 : DEBUG : ball_device.bd_trough : Counting balls by checking switches
2016-11-18 03:54:06,103 : DEBUG : ball_device.bd_trough : Confirmed active switch: s_trough1
2016-11-18 03:54:06,103 : DEBUG : ball_device.bd_trough : Confirmed active switch: s_trough2
2016-11-18 03:54:06,103 : DEBUG : ball_device.bd_trough : Confirmed active switch: s_trough3
2016-11-18 03:54:06,103 : DEBUG : ball_device.bd_trough : Confirmed active switch: s_trough4
2016-11-18 03:54:06,103 : DEBUG : ball_device.bd_trough : Confirmed active switch: s_trough5
2016-11-18 03:54:06,103 : DEBUG : ball_device.bd_trough : Confirmed inactive switch: s_trough_jam
2016-11-18 03:54:06,103 : DEBUG : ball_device.bd_trough : Counted 5 balls
2016-11-18 03:54:06,103 : DEBUG : ball_device.bd_trough : Switching to state idle

What if it doesn't work?

If you've gotten this far and your trough, drain, and/or plunger isn't working right, there are a few things you can try:

If your log file shows a number of balls contained in one of your devices doesn't match how many balls you actually have, that could be:

  • You didn't add all the ball switches to the ball_switches: section of the device's config.
  • Your trough uses opto switches but you didn't add type: NC to each switch's configuration.
  • A a switch isn't adjusted properly so the ball is not actually activating it. (Seriously, we can't tell you how many times that's happened! We've also found that on some machines, if you only have one ball in the trough that the single ball isn't heavy enough to roll over the top of the eject coil shaft. In that case we just add a few more balls to the machine and it seems to take care of it.) Either way, if you have a ball in the trough, the switch entry in your log should show that the switch is active (State:1), like this:

<!-- -->
2014-10-27 20:05:29,891 : SwitchController : <<<<< switch: trough1, State:1 >>>>>

If you see State:1 immediately followed by another entry with State:0, that means the ball isn't activating the switch even though it might be in the trough.

If you get a YAML error, a "KeyError", or some other weird MPF error, make sure that all the switch and coil names you added to your ball device configs exactly match the switch and coil names in the switches: and coils: sections of the machine config.

Also make sure that all your names are allowable names, meaning they are only letters, numbers, and the underscore, and that none of your names start with a number.

Finally, make sure your YAML file is formatted properly, with spaces (not tabs) and that you have no space to the left of your colons and that you do have a space to the right of your colons. See our Debugging YAML Parse Errors guide if you got YAML errors. At this point your trough is ready to go! Next we have to configure your plunger lane.

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