LED Pendants on the Trotec

A write-up of something I did using the laser-cutter to help show the love to Trotec.

Idea

I wanted to make something to give away at Burning Man this year.
I decided to find something that could be done with the Trotec lasercutter and also had some blinky lights. Because blinky lights are a good thing a Burning Man. Also not too big and preferably not too costly since I would make a lot of them.

Background

I have made some light up pendants before but using arduino-based controllers and expensive but that wasn’t going to scalable (either in terms or effort or budget) so went to Google and came across this:

Glowing Lasercut Pendant

I liked the coin-cell battery and magnet method of switching it on and off as it eliminated the need for a switch and also the need to choose between a permanently installed or hard to replace battery or a bulky complicated battery compartment. However it looked a little fiddly with multiple layers or acrylic creating a void in the centre for the LED which put me off but a further modification by someone else in the comments section (can’t seem to find them now) which made it a single layer of acrylic made me consider it.

Prototype

I ordered the parts. 100 slow colour changing 3mm LEDs for under £4 made it appear to fit the low cost requirement (more on that later). A small sampling of magnets and a pot of the conductive glue. 4mm and 5mm acrylic as I wasn’t sure what thickness I would need for 3mm LEDs and the cast acrylic varies quite a bit in actual thickness.

I changed the design aesthetically but stuck largely to what had been already done to modify the original by one of the commenters. Front piece from 3mm ply, centre piece from 4mm cast acrylic and back piece from 3mm ply.
Using the conductive ‘glue’ (it really doesn’t glue in any sense of the word) and trying several different magnet sizes I actually ended up with a working prototype:

Pendant prototype video

It worked but I hated the conductive ‘glue’. Also the led was near the bottom and shone down so it wasn’t really lighting up as much as it could. So back to the drawing board.

Final design

I changed the sizing of the holes for the magnets so I didn’t need glue at all. Fortunately they were already quite tight in the original prototype (I’m a numbers guy so tend to go literal for sizing) so it wasn’t a huge intellectual leap for me to get there. That worked.
I found the magnets actually attracted the LED legs so just bent them a little to assist and and that worked.
No conductive glue needed for LED to magnet and no glue needed for magnet to acrylic. Glue 2 pieces of wood to one piece of acrylic, bend an LED, push in 3 magnets and you’re away (or so I thought - more on this later)
I rotated the battery/magnet/led portion 180 and shifted the LED so it was similarly position 3 quarters of the way down but now shining up to get more light. Pushed my meagre Inkscape skilsl to the limit. This was as a result of a conversation I had with someone in the space while working on the prototype but for the life of me can’t picture who it was was - sorry but thanks.
Etched then man cutout shape into the acrylic to try and catch more of the light.

The lasercutting

I spent what turned out to be a whole morning in the space on the Trotec cutting out the pieces. I had 100 LEDs (less a couple broken in prototyping) and decided to go the whole hog and make 100 pendants. Since it was also now 2 days before I flew out to head to Burning Man I also did a few more than needed since I would have to assemble them in Chicago where I was staying for a week before heading into the desert. Probably should have planned this a little earlier in the year but I was determined not to fail now.

The bulk lasercutting of the front face:

Cutting the acrylic:

Assembly

I had to piece all these together in Chicago. It took longer than I hoped to do each piece even with the reduced glueing requirement and I used Gorilla superglue which was way quicker then epoxy. Not a huge amount of time but even a few minutes per pendant adds up when you’re doing 100. Plus since I was visiting family you don’t have a lot of spare time. The lesson from this is don’t start a project with a week to go before you hit the road. I’d like to say I’ve learned my lesson but…

Step 1 is glue the front face to the acrylic. 6 drops of superglue (Gorilla brand that came with a brush whcih I think helped)

Step 2 is bend one LED leg (make sure it’s the correct one). I used a Leatherman for this since I was on the road but it actually worked quite well. A jig to bend them may have been an idea but I got it pretty much correct 95% of the time by hand.

Step 3 is get the LED into the cutout in the acrylic. You can hopefully see the bend I had the legs so it didn’t lie ‘flat’ and help ensure good contact with the magnets.

Step 4 is insert the magnets. Again the Leatherman pliers were really helpful but after a few hundred you start to get a little tired of gripping the pliers.

Step 5 is glue on the back face and drop in the battery. I don’t have pics of this for some reason so will have to find or take some.

Conclusion
These worked pretty well. I got a little lucky assembling them away from home and doing all this at the last minute. With just a couple of prototypes I could have ended up with 90-odd duds in Chicago and no way to fix them or adjust the design. But it worked. people liked them and I’ll probably make them again.

Lessons learned:

Start earlier. Last minute is a pain and a bad idea. After deciding on final design and magnets size the bulk order of 300 magnets literally arrived at my door an hour before I left for the airport.

I also discovered during assembly that the cyclindrical magnets under the battery need to stick out about 1mm or the circuit doesn’t close reliably. Not sure why yet. The magnets I had were 4mm long and the acrylic 4mm thick so I had to leave then proud when assembling. If someone pushes down on the battery it will push them in and the circuit will be intermittent. Ideally figure out why this is needed or ensure the magnets are 1mm longer then the acrylic is thick. This may be harder than it sounds as the magnets don’t come in 1mm increments. Some design tweaking is needed.

A stronger square magnet is good but too strong and it pulls the battery across and turns itself on.

There are a few things I would like to improve in the next version including a better way to attach a cord or chain. The pendant s too thick to put a ring through. I made do with leather cord and some knots which meant it sat correctly but it can be done better.

This was not as cheap as I thought. The LED is cheap, the wood and acrylic is cheap, the magnets are expensive, the battery can be cheap but then it also tends to be rubbish (not work or fail after few hours) and surprisingly the cord I used ended up being expensive as well. Hopefully I can get the cost down.

I really enjoyed making these.

They were a bigger hit than I expected.

7 Likes


Could always add one of these under the existing magnets

I can well imagine. Doing things in bulk completely changes the game.

These are really cool! Good project, thanks for sharing! I am sure they were a hit on the playa!

That’s a good idea thanks.
I’m going to try 3mm acrylic with the 4mm magnets. The led’s are 3mm with an almost 4mm shoulder so I’m hoping that although the shoulder will stick out a little the battery will still clear. I have all the bits so worth a punt.
Otherwise it’s off to the magnet store :slight_smile: