DIY Moving Head Spotlight PAR RGB-LED

There’s a small festival up in Uddevalla (Sweden) called Elinorspelen. It’s a non-profit festival with the goal to have fun and spread culture. Unfortunately the festival have a very low budget and can’t afford all the equipment that it needs, and lighting has especially been down-prioritized.

Two friends of mine, and I, decided to do something about it. We got together and started discuss what kind of stage light that would be possible to buy/make.

We all agreed on that moving head spotlights would probably the cheapest alternative that gave the most visual effect.


We started out to search for cheap LED-diodes to make our own spotlight.
But after a day or so we quickly found out that to just build the a LED-array would cost as much as a commercial spotlight. For example this LED PAR 56 black 151 LEDs RGB 16W for 296SEK.
We soon gave up the idea of making our own LED spotlights.

But we found out that all the cheap LED-spotlights had a very wide beam angle, and we wanted a very narrow beam.

Making an RGB spotlight on a tight budget

We got back to the idea of making an spotlight ourselves. Picking out narrow 10-13° viewing angle LED’s from

As I started to pick parts to the project, the list grew longer and the price were raised by big numbers.

I managed to find really cheap geared stepper motors from eBay for a really cheap price; 28BYJ-48 DC 12V, plus controller, for around 26SEK a piece. After some research it looked like that model i widely used in different DIY- and Arduino-projects.

After a few weeks of picking components forward and back I’ve come closer to a final budget on 450SEK per spotlight, and that excluding some material prices like polycarbonate. I suspect that the final price per unit will end up on 500SEK. That’s at least 3 times cheaper than any commercial light.

You can find the budget for the spotlights here (Google Drive).


I’ve just a basic idea of what components the electrical design needs. Some micro-controller based up on the STM32 series should work well.
Some mosfets to drive the LED’s.
The LED’s should be connected in series to 12V, and have the same pinout as the popular LED-strips that are so widely available now. This should make the testing very easy.

Designing the chassis and mechanics

The designing process were making its way alongside with the budget, a design-change could radically change the budget.

I had a pretty basic idea how I wanted the final product to look like.

A LED-array soldered on to a PCB, the PCB should be mounted directly on an axis that were attached in a U-shaped arm.
The PCB would make the LED-array really lightweight and it should not be a problem for the geared stepper motor to move it.

I also thought of having the cabling layed inside the axis, so why not make the axis into a tube instead of a solid rod?

Moving the U-arm

But how would the U-arm move? I knew that a central shaft would be the focus in this problem. It should be able to move a pretty heavy weight, PCB + Stepper motor + alot of polycarbonate.

I also think that the moving head spotlight should be able to be mounted in several ways; placed on a flat surface shouldn’t be a problem. But be able to hang upside in a ceiling, or hanging from the side of a wall, that’s tough.
The center-axis mus be able to take on forces from many directions.
One thing was for sure, we needed alot of bearings.

With the bearings a shape took form, centered around the axis.

4 bearings are used on the center axis. 2 axial bearings to make it spin easy upside down and standing. And 2 bearings up and down to make the center-axis stiff and prevent it from leaning.

And around the bearings, the framework took place.

Somewhere here the pieces started to place them selves in the big puzzle, it was much easier to design now.

Around the framework we needed a casing to hold out dirt and to keep it pretty.
It’s hard to make a nice chassis by yourself, so  I started to look around for a cheap case designed for another purpose.

I found this cheap water bawl for dogs for around 17SEK. It’s about 200mm in diameter and should house the mechanics and the framework nicely.

Designing in CAD

It’s one thing to have you design in your head and on paper, but it’s hard to grasp if it will fit or not. It’s here CAD-design comes into the picture.
I started to draw the different parts needed. As I draw the parts I could easily adjust lengths of parts to fit each other. Make puzzle-slots for the different pieces in the U-arm.

I try to make an easy design that could easily be milled out in our CNC-machine. The most parts are made so they could be cut out in X-Y-axis. I’m also trying to make as long and narrow pieces as possible, because long pieces are easier to fit narrowly on to a big polycarbonate-sheet.

The last part of the CAD-design was to put it all together, attach bearings to the shaft, build the U-arm.

The first design is now complete. We’ll have to make several adjustments to the design in iterative steps.

But for now, I’m thinking it’s starting to look good!

Hot bending the polycarbonate-sheet for speaker backpack

Here we have placed our hotbending machine on the joint that is to be bent.

We used aluminum-foil and paper to isolate material that we didn’t wanted bent.

The corners seems to match!

Vilse removed some plastic left from the CNC.

We used our laser-cutted acrylic angeles to bend the polycarbonate-sheet in to the right angle.

We placed this böp to let the joint cool down

15 seconds left of our 4:25 timer, the heating of the polycarbonate is almost ready.

We used straps to hold the last bend

The last bend is a round corner, the radius is 200mm. We knew it would be very hard to bend it.
We heated like 100mm of the polycarbonate with both hot air gun and the heat bending machine. We heated the area for at least 20 minutes, it wouldn’t bend.

At last the polycarbonate was bending, but it turned out ugly as hell. A lot of bubbles and ugly artifacts, at least this side won’t be that visible.

Our heating machine turned out to be far more superior to the hot air gun.
Lesson learned, never make round curves in polycarbonate!

This is what the backpack will look like. The 12kg weight of the polycarbonate didn’t feel heavy at all. I think the weight will be ok.

To hold the corners of our speakerbox, we use a two-component poly-urethane glue (3M Scotch-Weld Urethane Adhesive DP-610). We got a test-sample from KA Olsson and it worked really great. It’s quite expensive, but we got it a little bit cheaper thanks to KA Olsson.
We used straps to tighten the polycarbonate around the corners. We also applied tape at the edges to stop the glue from seep out.

Laser-cutteed acrylic angles for bending polycarbonate in to fixed angles

For my and Vilses speaker-backpack it’s really crucial that we bend our angles straight and in the right angle.
We developed our own heat bending machine to make straight bends, but we needed a fixed angle to bend it in the correct angle.

So we extracted all the angles from our CAD-drawing and placed them on a new drawing. We had this idea about a multi-angeled hexagon, containing all the angles needed.
But we couldn’t fit all angles on one sheet, so we had to make two sheets.

After that we cut the angles with the laser-cutter, we also wrote the angles on top.

Here is the result:

DIY Heat bending machine

As me and Vilse were picking up our CNC-milled polycarbonate sheet for our speaker backpack we noticed the heat bending machine they used at Plastmästarn:

We asked them how it was working, apparently it was a heating wire set for a fixed temperature. They didn’t know how it worked, just how to work it.

The profile on the bottom was set for 210° Celsius, and the one on top for 180°.

They placed a polycarbonate sheet around 5mm on the heat bending machine for about 4 minutes, after that it was ready for bending.

Here is two other commercialized heat bending machines:

It’s really hard to bend stright angles in polycarbonate with a heatgun.

Me and Vilse started to think of a way to make our own heat bending machine.
We bought some Nikrothal from Elfa

2.83 Ω/m

We angle-grinded a steel-profile to a U-shaped profile.

We cut holes in to the profile and placed isolated plates to hold the nikrotahl-wire from shorting.
The isolator plates were found in a old salvaged heatgun, you could find equivalent in a old toaster.

We placed the wire in a U-shape inside the profile. Half way in to the U-shape we attached a spring to make some tension on the wire. As we heat the wire the spring will retract around 20mm due to the expanding wire.

A total of 1,54 meters of wire give us 4,36Ohm. At 30V it will give us 220W of heat energy.

To make a even distribution of the heat we made two heating beams, on for the bottom and one on top.

We tested out the heating properties and it turned out pretty good. We got about 200° Celsius under the material.

It turned out great! We tested out different kind of thickness of polycarbonate, it was very bendable. It’s much easier to get a straight lines with this method compared to the heating-gun method.

One important factor to get the bending look clean is the timing. If the timing is too short it will be hard to bend and the plastic might break. If it’s to long bubbles will appear.

Material Heatingtime [minutes:seconds]
Polycarbonate 8mm 4:00
Polycarbonate 8mm with V-milled 90° angle 3:45
Polycarbonate 10mm 4:30
Polycarbonate 10mm with V-milled 90° angle 4:25
Acryllic plastc 3mm 1:30