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# Bending the light

A lasersculpture which uses a certain mathematic geometry so that the light appears bent in the middle of the room.

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In 2010 I was helping the artist Rainer Plum to create a lasersculpture in the german national library in Frankfurt (a.M). I did some calibration work and developed a custom interactive projection software for this lasersculpture. (see: http://rainerplum.com/index.php/de/laserinstallations/2010-eine-sonderbare-wiederholung-eines-traumes/)

While doing development I looked up some formula on the network. Accidentially I stumbled upon this arcticle: https://de.wikipedia.org/wiki/Hyperboloid

While sitting in front of the lasersculpture I was shocked. Using this mathematical fact should make it possible to create a lasersculpture which is "bent" right in the middle of the room. So we built this lasersculpture in our maker space "Digitales Aachen e.V.".

In 2010 I was helping the artist Rainer Plum to create a lasersculpture in the german national library in Frankfurt (a.M). I did some calibration work and developed a custom interactive projection software for this lasersculpture. (see: http://rainerplum.com/index.php/de/laserinstallations/2010-eine-sonderbare-wiederholung-eines-traumes/)

While doing development I looked up some formula on the network. Accidentially I stumbled upon this arcticle: https://de.wikipedia.org/wiki/Hyperboloid

After sitting in front of the lasersculpture I was shocked: Using this mathematical fact should make it possible to create a lasersculpture which is "bent" right in the middle of the room.

The problem with classic "laser shows" is that all light is emitted from one center which is the center of the scanner module where the galvanometer mirrors are joined together. To get a bright sculpture inside the room you'd need a really powerful laser. In small rooms maybe 1W of laser power is enough. Outdoors you will need 5W or more. All at all laser projections are really dangerous toys and you should really know what you are doing. You have only one try. One false blink and you could end up blind.

To maintain a sculpture which is opened at both ends we needed a completely different approach. We cannot start with a central powerful laser source to create a ring of light. We introduced an alignment which has some benefits: If you want to achieve the "same" brightness like with scanners you need to distribute the power to a couple of laser modules. We also want to keep the number of revolutions low to have better control of the centrifugal forces. We decided to go for somewhat like 3-5rev per minute. To get a clean and smooth image we calculated that 10 lasers should be enough to trick the eye - which works perfectly.

To avoid any danger we decided that the total power of laser light should not exceed 20mW. Therefore we used 10 times a 2mW laser diode to maintain the maximum power of 20mW. For indoor usage this is absolutely bright enough and the danger for people is not so high. However: Do measurements before showing this sculpture to anyone!

(The picture above shows the calibration of the first version from 28th April 2012)

To avoid static beams we attached the power connection of the laser diodes to a centrifugal switch. Two metal blades are arranged in the middle of the wheel. One metal blade was glued to the wheel while the other blade is being bent by the forces which occur by the rotation. If the revolution speed is high enough the blades touch each other, the switch is closed, the laser diodes are turned on!

An e-bike motor maintains the rotation so that we can start the sculpture by just pushing a button next to our audio mixer.

To get the nice "bended light" we just needed to adjust the lasers to a virtual circle on the wall. Think of the 10 laser beams being wires which are connected to virtual wheel on the wall with the same diameter like the bike wheel. Rotate the virtual wheel a litte bit and see how the wires follow. The more you turn the virtual wheel the more narrow the sculpture becomes.

The second version of the "Bending the Light"-device with the centrifugal switch a wallmount and sliding contacts (which you can see in the video and the image above), was built by Uwe Reisinger at Digitac. If you visit Digitac in Aachen you can see it wall mounted and in action.

If you like to see a video of the sculpture in action, see the end of the following video:

About the video: I've got feedback about that video. Some people have been confused about the style. Last year we did a small "partyprod" at the demoscene party "Evoke". The category was "wild animation". The video is a parody of old eighties demos which mimics "roto cubes" and other geometry with real life objects. It won the 3rd place in this category. We used the video here because it's already on youtube. The hyperbolid is to be seen after the break in the middle. Unfortunately it's hard to...

• 10 × Laser modules, 2mW
• 1 × Bike wheel
• 1 × e-bike motor
• 10 × Clamping material for the lasers
• 1 × centrifugal switch
• 1
Step 1

We created a small prototype using a bicycle wheel and 10 of 2mW laser modules in October 2010. Unfortunately the prototype was stolen and never came back.

At 9th July 2015 we decided to recreate the project. Uwe, Cersten, Micha and a couple of other Makers from our club "Digitac" helped us to create this stunning laser sculpture.

First of all you need a wheel with a ball-bearing in the middle. We used an old bicycle wheel.

• 2
Step 2

Attach 10 Lasermodules equally distributed around the wheel.

Uwe prepared strong plastic plates with a hole in the middle. The laser modules where put into wooden spheres. Cable ties were used to clamp all of this together. This construction made it possible to adjust the lasers later. If you want to recreate this project better us another construction. The centrifugal forces destroy the adjustment after some time.

• 3
Step 3

Connect all cables together by soldering them. Connect all red cables and all blue cables (or whichever colour the laser module cables have). We want to achieve a parallel connection of all lasers so that we can turn them on using a centrifugal switch. Solder one side of the cable to the centrifugal switch. The other side of the cable goes directly to a battery-pack wich is attached in the middle of the wheel. (We later used some self made grinding contact to be able to use external power supply).

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