Accelerator 22: science fiction table-hockey

directional electromagnetic accelerator

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This is the latest phase of the 'Kinetic Surfaces' project : - creating sci-fi inspired retro-futuristic game systems in which players remotely control the movement of objects placed onto the surface of a table-top. This could be described as 'simulated telekinesis'.

Kinetic Surfaces are complex and expensive, so the aim of this phase is to build a simplified accelerator with maximum 'bang for your buck'. Using just a few low-cost components, Accelerator 22 detects and repels a magnetic puck at high speed.

The key to this invention is the shape of the Accelerator's electromagnet (EM); it is difficult for a player to direct the puck using a conventional cylindrical EM - due to the shape of its magnetic field. I found that using an EM with a square cross-section makes the Accelerator remarkably directional - by creating a large enough 'sweet spot'. The jolt of recoil felt in your hand when the EM activates adds to game excitement.


Accelerator 22 is the latest phase of my 'Kinetic Surfaces' project - creating retro-futuristic  'simulated telekinesis' game systems. Players remotely control the movement of objects placed onto the surface of a table-top, as they might have done in old science-fiction movies/books/comics. (In early sci-fi, advanced technologies were assumed to be physical (e.g. jet packs, hover-boards, teleportation systems), rather than virtual technologies in 'cyberspace'.)

How It Works

The Accelerator is essentially a 555 timer, a power MOSFET, a Hall sensor, and an electromagnet. The Hall sensor triggers the 555 when it detects the magnetic puck - the 555 activates the MOSFET and the electromagnet for a brief period - creating a magnetic field that repels the puck

Structure of Accelerator 22 and platform

Figure 1 (below) shows a simplified vertical cross-section through the Accelerator and the game platform, showing: Accelerator (1), electromagnet (2), copper coil (3), iron core with square cross-section (4), Hall sensor (5), clear acrylic sheet (12), magnetic puck (6), magnetic poles of the electromagnet (7,8) and the puck (9,10).

Figure 2 (below) shows a view from below the Accelerator (1) at the moment the magnetic puck (6) is detected by the Hall sensor (5) and then repelled away from the Accelerator in the direction indicated (13). Note that directional control is best achieved when one of the four corners (14) of the square iron core (4) overlaps the magnetic puck (6), as shown in Figure 2. The square shape of the iron core (4) is one of the most important aspects of this invention - it seems to deliver both power and directionality. With a cylindrical core it is very difficult for a player to direct the puck with any accuracy, particularly during high-speed game play. It would be interesting to explore the effectiveness of other core shapes, such as triangular cores.

How the electronics works

Below is an example circuit diagram for the Accelerator.

The 555 (IC1) is essentially acting as a switch de-bounce circuit - once the Hall Sensor (HS1) detects the presence of the magnetic puck, it switches on the current through the MOSFET (T1) and the electromagnet (EM1) for a few milliseconds. (The activation period t = 1.1 x R2 x C1, so for a pulse length of 30mS, R2 = 270k, C1 = 100nF.)

Note that, if you don't have the 555, then when the electromagnet activates its magnetic field interferes with the operation of the Hall Sensor.

I have suggested components in the component list, but I don't want to be too prescriptive; the performance of the system is governed to a great extent by the geometries of the electromagnet, magnet puck, air gaps etc. In other words, when I built this I decided on the basic geometries of the system to get the aesthetic and game-play that I was after, and then evolved the system by seeing what worked.

If you would like further advice on how to build an Accelerator, please message or email me, or write something in the comments. Thanks.

Other Kinetic Surfaces I have built

  • 1 × IC1: NE555 Timer IC
  • 1 × HS1: Hall Unipolar Switch For example, AH3366Q
  • 1 × T1: N-channel Power MOSFET For example, IRLB8721
  • 1 × EM1: Home-made electromagnet
  • 1 × R1: resistor 10k

View all 9 components

  • Other electromagnet core geometries

    andrewfentem04/23/2022 at 14:38 0 comments

    The square shape of the electromagnet's iron core is one of the most important aspects of this invention - it seems to deliver both power and directionality. With a cylindrical core it is very difficult for a player to direct the puck with any accuracy, particularly during high-speed game play. It might be interesting for someone to explore the effectiveness of other core shapes, such as triangular, rectangular, or U-shaped cores...

  • Updates - how it works, circuit diagram etc

    andrewfentem04/22/2022 at 11:34 0 comments

    I've just published lots of details about how the Accelerator works - components, circuit diagram, physical structure etc.

  • Retro-futurism and sci-fi

    andrewfentem04/07/2022 at 10:48 0 comments

    These projects originate in my interest in retro-futurism (i.e. past visions of the future), and sci-fi. I wanted to build game systems that you might see someone playing in an old-school science fiction movie - like Metropolis, Flash Gordon, Buck Rogers, or Tron.

    Below is a very old video of one of my earliest projects of this type:

  • Kinetic surfaces

    andrewfentem04/07/2022 at 10:32 0 comments

    In case anyone is interested, here's a bit of background info about this project:

    Accelerator 22 is derived from a longer-term project looking at what I've been calling 'Kinetic Surfaces' - in other words, ways of moving and tracking objects at high speed (usually small balls) across the surface of some kind of graphical display screen - see video below.

View all 4 project logs

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francisco.campos wrote 05/28/2022 at 16:09 point

Hi, after having a look at this project I got really interested in you previous work. While this project seems to use a minimal set of hardware, your other works seem somehow  more challenging. I have been thinking about just the same kind of kinetic surfaces that you devised and watching your videos made me wonder about what goes on under the surface...

Would you care to explain a little bit? In you 'virtual football' I figure there must be an immense array of solenoids under the table that are switched on and off as desired. To build such hardware must have been a daunting task?

Your Robo-breakout looks amazing! And all I could get was the old youtube video, but still it really rocks! In this case you used a planar robot under the hood that carries an (electro) magnet? For such a system, the speed you get is fantastic.

Well, I would like to know more about these past works, if any info can be made available! - I believe these may be commercial products, so I suppose there is a line you can not cross.

All the best!

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Inne wrote 04/07/2022 at 13:33 point

In case you are still looking for an aesthetic, I think the disk mini game from "Beyond Good and Evil"  would make for a cool kinetic surfaces game.

example of the game:

Though think a bit more about it would probably fit less well with the Accelerator 22 as input. Your previous experiments/projects reminded me of it. And though the mini game is a bit boring in my opinion (really selling it here I know XD), I think that could be negated with a fun input/control scheme.

Anyway good luck in the contest this Accelerator looks awesome and I would love to see how it is build.

  Are you sure? yes | no

andrewfentem wrote 04/09/2022 at 13:54 point

Thanks, Inne! 

That mini disk game looks cool. I've never seen it before.

I'll add some more info about how to build the Accelerator system (and some of the Kinetic Surfaces) over the next week or so...

Cheers, Andrew

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McGruffff wrote 04/06/2022 at 17:17 point

Geez Louise! The execution both component wise and aesthetic wise is *chef's kiss* excellent. Keep up the good stuff!

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andrewfentem wrote 04/07/2022 at 10:01 point

Thanks! :-)

  Are you sure? yes | no

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