Electronic Tilt Bob for Pinball Machines - Part II

At this point in time, the core software emulation is functioning as expected which leaves only fine tuning to be completed.  The only firmware changes I am making at this point are to add new features as people suggest them.  One of which is to to be able to zero the tilt bob between players (ie tournaments).


Phase 7:  Installation

Have you ever designed a product only to say, "Ooops, I didn't think of that at the time"?  Well, this happens to be one of those times.  Two things jumped out at me the second I tried to install the PCB.

1.   The board is just slightly too large
2.   No holes for mounting

The whole idea of making this project was to replace a mechanical tilt bob with minimal changes to an existing pinball machine.  Ideally, the PCB should have fit between the top and bottom metal piece of the existing tilt bob ... in other words, no changes to the existing setup and the ability to quickly switch back if required.  My measurements were close, but not close enough.  The board was about 3~5 mm too big to fit within the space.  Unfortunately, this required the removal of one half of the tilt bob bracket which can be seen by the holes between the board and the ball and under the tie-wrap.

The other issue I ran into was I didn't think about mounting holes.  In the back of my mind I was thinking velcro would work, but I'm sure the board would come loose over time.  Luckily there were a couple of spaces on the PCB I could drill into.


Phase 8:  Connecting to the Existing Tilt Mechanism and Power

The two white wires connect to the existing tilt brackets using spade connectors.  Again, the whole idea was to quickly and easily tap into the existing wiring without any major modifications to the machine.


Power connects on the top left

Phase 9:  Staying on the Level

The first thing that needs to be done once the Electronic Tilt is installed, is to fine tune the levelling of the device.  This is really no different than ensuring a mechanical tilt plumb bob is centered within the bracket however, instead of a physical adjustment, we do an electronic one.

By clicking on the green buttons, we can bring the values of the X and Y axis as close to zero as possible in real time.  We can also adjust the Z axis to bring as close to +/- 1.0000 as possible.

The values are immediately saved in non-volatile memory allowing them to be loaded the next time the machine powers up.  In addition to saving the values in non-volatile memory, I've also included the option to backup/restore the offsets to the internal file system.

Phase 10:  To Tilt Or Not To Tilt.  That Is The Question.

A mechanical tilt bob is electrically equivalent to a switch which opens and closes so an electronic version should act in a similar fashion.  I could have used an electro-mechanical relay which physically opens and closes, but anything mechanical is subject to wear.  Instead, I chose to do this electronically.  As such, my first test was to verify I could trigger the tilt in the machine.  Instead of shaking the machine to cause a tilt, I included a test button to manually trigger the tilt ... much easier.

In order to understand how a pinball machine detects a tilt condition, I need to introduce you to the TILT HOLD setting.  In other words, how long is the tilt switch closed for.  Every pinball machine has a switch matrix which scans (polls) through rows and columns to check the state of the switches attached to it.  This happens continuously but requires a certain amount of time in order to read the state correctly.  Based on my research, 10 ms was a good starting point ... and based on my initial testing, this number appears to be correct.  I could set it to a higher number (seconds vs milliseconds), but this could have the potential to cause issues with tilt warnings being detected multiple times as the switch polling period repeated.

Phase 11:  Zen and the Art of Tuning an eTilt

Accurately simulating the movement of a mechanical tilt bob requires us to first understand the characteristics of its movement.  Newton's Laws of Motion cover the majority of this topic and since they are basic scientific principles, I'll spare you the details.  These are controlled by the following user settable variables:  BOB DIAMETER, PLATE DISTANCE, HOLE DIAMETER and CENTER OF MASS.

The remaining characteristics of movement involve friction.  The video link (~3:05) shows what we need to accomplish.

https://youtu.be/E4ZZT2nvgkg?t=182

In the video, the fore/aft movement came to a rest after about 7 cycles while the right/left movement took around 42.  With that in mind, let me introduce you to X DECAY and Y DECAY.  These parameters affect the settling time of the tilt bob.  I'm using a bit of reverse logic in my calculations so a value of 1.000000 is no decay/friction while a value of 0 represents full friction.  I've allowed 6 digits of precision in these variables, so really fine tuning is possible.

Numerous decay values were tested in order to achieve the 7/42 swings of the tilt and my visual representation of the tilt plumb bob was an excellent means of observing this.  From these tests, I came up with a starting value of 0.999 for the X axis and 0.996 for the Y axis.  I like to point out that my eyes sometimes confused the sixes and nines so I ended up using 0.999001 and 0.995999 respectively ... not only did this prevent my misreading of the values, but it also served as a reminder that I have 6 digits of precision instead of 3.

EDIT:  It was difficult trying to bump the table consistently after making minor changes to the decay values.  Sometimes I hit harder than I did previously and so my results were inconsistent.  The latest firmware revision now has test buttons to start the tilt at its maximum.

Phase 12:  Do the Shake

Somebody was asking me for video of the Electronic Tilt in action.  Here's a short clip of what happens when you shake the machine.

I'm happy to say that the device has performed as expected.  The individual tuning parameters (ie DECAY, DIAMETER, etc.) could be played with a little more to help zero in on the "ideal" settings, but that brings up to the question of 'What are the ideal settings?'  This is where I'd like to see one of of my devices in the hands of the players ... both real and virtual pinball players since there is an application in both markets.  That way, a consensus can be made on standard settings for home and tournament use.


To be continued ...

Introducing: Electronic Tilt Bob for Pinball Machines - Part I

Some time around 2003 I came up with the idea of using an accelerometer to simulate a pinball tilt plumb bob.  I had been working with gyroscopes and accelerometers since 1993 and it seemed like a good crossover to my hobby of pinball.  I recall my biggest challenge at the time was creating a simple user interface to customize the internal settings ... a task that would require adding a whole new layer of interface electronics such as a display and keypad.  After researching a few microcontrollers I had a basic design, but unfortunately I lacked the will to complete the project due to other commitments.

Fast forward to 2012 and the birth of the Raspberry Pi.  MEMs devices have become mainstream and I decided to revisit my Tilt Simulator project and learn Python while I'm at it.  The simulation worked ok.  And by ok, I mean it worked but it really didn't work entirely as anticipated.  Python is not the language for anything in real time and the Raspberry Pi is not the ideal substitute for a microcontroller.  Proof of concept was achieved, but the burden of requiring ancillary equipment once again put my idea on hold ... I called this prototype #2 and relegated it back on the shelf where it belonged.

Fast forward again to 2015 and I find out about a microcontroller called the ESP8266.  This device had built in WiFi and that combined with a smartphone, solved all my interface challenges.  It was then I realized that the Tilt Bob Simulator was once again a viable concept.

Phase 1:  The New Plan

Basic System

- A device which accurately mimics the movement of a pinball tilt plumb bob

- Usable in both Electro Mechanical (EM) & Solid State (SS) pinball machines

- Usable in Virtual pinball machines

- Length, size, distance, diameter, etc. in the simulation must be user customizable

- Independent decay rates (ie friction) in both X & Y axis to mimic a mechanical setup

- Accelerometer 6 point calibration to get consistent data output across multiple machines (ie tournaments)

- Mountable in any one of the 6 major axis and self aware of its orientation

- Offset tuning to correct for minor alignment errors

- WiFi connection via Access Point and Station

- mDNS support for ease of access

- Tuning/setup done via web and/or MQTT server

- Utilize power already available in the machine (5V~12V DC)

Additional Considerations

- Variable tilt hold time to accommodate for different switch matrix read times

- Tilt warnings.  So older machines can act like new ones.

- A second 'Simple Force' simulation to emulate modern systems

- Setable force threshold

- A visual indication of current force or tilt bob position

Crazy Ideas
- variable gravity (have you ever played pinball on the moon?)

UPDATE:  All features implemented except variable gravity

Phase 2:  The Test Circuits

Prototype #3 and Prototype #4

The plastic box was originally the packaging from an Intel camera however, it was the perfect solution for performing a six point calibration.

Phase 3:  The Software

I remember the days when I used to code in Assembler and wondered why you'd ever code in anything else ... Those days are now gone but not forgotten.  Coding languages may have changed but methodologies do not.  I won't go into details on how a PID control loop works or the mechanics of how to calculate the current position of the tilt bob.  I have no intention of teaching you Calculus, Physics, Electronics or Software Programming.  Just be confident in the knowledge that I've been curious about all of them at one point of time in my life.

I held off learning javascript for the longest time and finally 'bit the bullet' for this project.  It was very easy to pick up however the whole time I couldn't help but think that someone slapped this language together and said 'good enough'.  Anyways, I shouldn't complain ... it talked XML to me and made communications much simpler to implement.

Phase 4:  The Web Interface

General Setup

Fine Tuning and Levelling

Classic (Tilt Bob) Tuning

Modern (Simple Force) Tuning

Phase 5:  The Supporting Cast

Bally PLAYBOY

Here's the perfect candidate ... well, yes and no or yes.

Pros:
Has damaged tilt mechanism so it needs replacing anyways.  A few bulbs may have come loose but it is otherwise functional.

Cons (or Pros in disguise):
Display buzz ... you know the sound, it's common for machines of this era.  Despite the potential doom and gloom, it's secretly a 'pro' since it helps test the robustness of taking power from the machine.

Phase 6:   Time To Get Serious

I had to use a hot air gun to solder some parts.  Since the soldering was successful, you could technically say that I'm good at blowing hot air 😏


Installation is next, but it's a long weekend in my part of the world so hold tight for a couple days.

To Be Continued ...