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Helmet breakaway lights DIY with magnets

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Helmet breakaway lights DIY with magnets

Old 09-10-19, 05:12 AM
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tomtomtom123
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Helmet breakaway lights DIY with magnets

I previously used headlights meant for strapping directly to your head with a headband, and wrapped it through the holes in my helmet. But this adds risk of injury in a crash if the lights or band get caught in something. So I decided to make my own breakaway lights using magnets.





I took a pair of Topeak Headlux lights, removed the rubber cup, filled it with polyurethane Seam Grip, stuck a 20x3mm neodymium magnet into the wet urethane, let it dry overnight, and then taped it over.

However, the magnets became loose after a few weeks. It seems that the urethane shrunk and formed a concave surface, which detached itself from the magnet. Or else the urethane doesn't really stick to metal. Although it did help form a socket. I cleaned the magnet with alcohol, and then put 2 component epoxy glue into the socket, reinserted the magnets, and let the glue dry overnight. Hopefully the magnets won't fall out again.






For a few times, I accidentally placed the magnets in my hand near metal objects, and they quickly flew into my fingers. Luckily, I had kept the knives and scissors far away beforehand. I wanted a way to store the lights safely when they're off the helmet, so I 3D printed thick plastic cups, with male and female chamfered edges to keep them from sliding off each other. It forms a 10mm gap around the magnets. Small and light metal objects still have a slight magnetic attraction, but the force is very weak.

If you want the 2 lights to attract each other, you'll need to have one magnet with north facing down, and the other magnet with south facing down (polar opposites). Otherwise if both magnets have the same polarity, they'll repel each other.



On the helmet, I also used Seam Grip to attach 24mm diameter washers to areas that were directly above voids in the helmet that aren't in direct contact with my skull (in case the lights smash through the helmet). I then used some Tenacious Tape over the washers, but duct tape probably works too. Since urethane doesn't really work with metal, the washers will probably detach in the future. When they do, I'll just use double sided tape, applied with concentric layering in order to achieve a sort of dome shape to adhere to the convex surface of the helmet.

The washers need to be larger than the magnets, otherwise the magnets will not center themselves to the washers. If the washers are smaller, then the magnets will move to the edge of the washers.



Although the magnets are rated at around 4kg perpendicular pull force, it's more like 1kg vertically, and 250g horizontally. If I orient the helmet sideways and place a 300g saddle on the edge of the lights, the magnets will slide off. It's probably weakened from the 0.5mm gap from the 2 layers of tape, and maybe the hole in the middle of the washer (not sure about this). It's not as strong as I would like, but the lights haven't fallen off yet during rides. If I shake the helmet lightly, the magnets will not detach. However, if I grab the helmet in my hands above my head and throw it very hard toward the ground without letting go, the magnets will slide off.

I could increase the magnetic force by double stacking 2 magnets together, but there is a higher risk of injuring my fingers against sharp metal objects that become attracted to the stronger magnetic force. So I decided to use only 1 magnet per light.

One way to increase the sideways break force is to make the 3D printed cups with protruding lips that surround the edges of the washers, to capture the washer. But I didn't want to peel back the tape that I already placed on the washers, which help to keep them from detaching from the urethane. I also didn't want the residual solvent from the urethane to seep into my hair when it rains.

Attaching anything to the outside of your helmet has a risk of injury or death. I am not endorsing it. You do so at your own risk.

Last edited by tomtomtom123; 09-11-19 at 07:03 AM.
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Old 09-12-19, 10:52 AM
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wojowojo16
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looks great. can you "glue" or put something in middle of magent to sit in in the indent on the washer..........to keep it from sliding off?
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Old 09-12-19, 11:42 AM
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It's possible, but I originally filled the center hole of the washer with Seam Grip to help keep it in place. I had thought about gluing a smaller washer onto the magnet and having it sit in the hole, but then I'd have to cut the tape and try to remove the Seam Grip from the center of the hole. I didn't want the risk of delaminating the urethane from the washer, so I left it alone.
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Old 10-31-19, 07:02 PM
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I have a new helmet and this time I did not use glue to attach the washers to the helmet. I simply used double sided tape under the washer, but I cut a hole in the tape about half the diameter of the washer so that the outer edge would rest closer to the surface of the helmet since it is a spherical surface. I then added the clear tape on top of the washer.

I noticed that these Topeak lights don't work in the cold. When the temperature outside falls below 15C, the lights will dim a little. When it's below 10C, the lights only last about 30 minutes before they're really dim. Below 5C and they die after a couple of minutes. I don't know if it's simply because they're using button cell batteries, or if the power management is poorly designed for cold weather.

Edit: I think the problem is with both the battery and the power management of the hardware. I searched and found a CR2032X extended temperature range battery from Murata, but it's difficult to know whether or not it actually works better in cold temperature without trying it. It doesn't seem to be available in Europe. Alternatively, I have a cheap $5 6 mode rear tail light that has both red and white lights and has worked fine in the same cold temperature without dimming, although it only lasts for about 1 to 2 hours. It runs on lithium polymer rechargeable battery so it is probably more resistant to the cold. It has a low and high brightness setting for the red light on the dual red/white version, or low and high brightness for the single white light version, so the low setting would probably extend the battery life or reduce the battery resistance in the cold with better power management. It mounts with a screw through the back, so I might get 4 sets from aliexpress and attach them to a 3D printed stem with a magnet glued to the bottom of it. I'll post an update in a month when I get them in the mail.

Last edited by tomtomtom123; 11-01-19 at 09:07 AM.
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Old 11-01-19, 04:43 AM
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Very clever solution.
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Old 11-13-19, 02:14 PM
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So I received the lights from Aliexpress yesterday and proceeded to build my magnetic breakaway helmet lights. Here they are.




As previously mentioned, I got a new helmet and this time I used double sided tape underneath the washer instead of gluing it. I cut a hole in the center of the double sided tape wider than the diameter of the hole in washer (not shown), so that as much of the outer edge of the tape would contact the domed surface of the helmet. I then covered the washer with tape. This time, the 3D printed part has a small cup edge that fits around the washer to add some resistance against sliding off. It does work as intended, but I didn't factor in the thickness of the duct tape over the magnet, so it's a very tight fit and takes a few extra seconds for me to blindly find the center when reattaching the light to the helmet. If I had made the cup a few millimeters wider, it would have fit much better.


Just like the old lights that I built, the new lights also have a male and female 3D printed part that fit together to prevent them from separating when stuck together. The new lights are heavier though, 70g each pair for a total of 140g (including magnet and overly thick 3D printed part). The old lights were 40g each for a total of 80g, but because of their smaller batteries and lower light output. Just like the old lights, the new lights have 3D printed parts that are over 40mm in diameter even though the magnet is only 20mm in diameter, to serve as a protection buffer around the magnet to make it more difficult to unintentionally attract metal objects.


Each pair of lights are held to the 3D printed part with a rubber O-ring.


The 3D printed part has a hole in the middle which allows the small protrusion in the back of the light to be inserted.


The lights come with a band that is screwed in from the back, which is easily removed.


The lights are really bright. The description says they're COB chip-on-board LED lights. I don't know if it's unique or if most LED lights do this. But it causes glare and is bothersome to look into directly. So I experimented with attaching a layer of translucent PVC privacy film that normally is applied to glass windows. I tested 3 types: naked, film directly against the light, film offset from the light.


Naked had too much glare. The film offset from the light had too much loss of light transmission. The film directly against the light was ok, but the white lights still had too much glare so I eventually applied a double layer of film for the white lights, while the red lights had a single layer of film. In the comparison image below in the top row, the red light is naked, while the white light has a single film. Having a large film wrapped around the entire light was too bulky and made it difficult to attach the O-rings. So instead I cut a small strip that only covers the center area of the light.

The light is very bright, although a little heavy. I run it on low mode instead of high mode. But low mode seems to be pulse modulated, which means that it is flashing on and off at very high frequency to make it appear darker even though the intensity of the light output is the same. When your eyes are looking at it, your brain feels a little bit confused. If you hold the light in your hands and shake them very fast from side to side, it seems to strobe. If you hold the light still, it appears to be a steady output. I don't know how many Hertz is the pulsing, but probably slower than 150 Hz, which is why it feels strange to look at.

Last edited by tomtomtom123; 11-13-19 at 02:23 PM.
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