Dynamo lighting switch for quill stems? It's possible.

[somervillebikes]

Velo Lumino's TMAT stem switch, the collaboration between Tom Matchak and myself (hence the name, TMAT), only works on threaded stem systems because it is designed as a cartridge that fits inside the steerer below the top of the stem, and integrates its own preloading bolt and stem cap.

A bigger challenge is how to design a similar functionality for quill stems on threaded systems. These don't offer a roomy internal space for a cartridge-style unit. So I decided to leverage the power of the magnet to explore the concept. The TMAT switch operates on the principle of the reed switch, which is a tiny mechanical switch encased in glass, which contains two ferrous reeds that become attracted to each other in the presence of a magnetic field, so waving a magnet over the reed switch closes the contacts. It's also one of the features of the TMAT switch that make it completely waterproof and corrosion-proof.

I took the same two components of the TMAT switch (reed switch and magnet) and reimagined them for a quill stem. Since most quill stems are made from aluminum alloy, they are invisible to magnetic fields (the concept won't work with steel quill stems). So, I stuffed a reed switch inside the hollow quill of a stem, fitting in the narrow space between the stem wall and the stem bolt, facing the rear of the stem, and I drilled a small hole in the bottom of the tightening wedge to allow the wires to pass through:

Next, I designed a 3D printed spacer-like ring to sit on top of the headset locknut, and which also contains an embedded magnet. The idea being, as you rotate the ring, the magnet moves closer to the reed switch inside the stem, and closes the contacts.

I rigged up my modified battery flashlight (my TMAT switch test light) to the experimental quill stem switch,  and gave it a go. Enter, TMAT/Q!  (Video link).

The next step is to devise a more refined "spacer ring" that contains travel limits and a quality tactile feel and appropriate visual aesthetic, consistent with the threadless stem TMAT switch. This is Tom's expertise, having developed the sophisticated ball-bearing mechanism of the TMAT stem switch and the DockIt decaleur system.

With any luck, The TMAT/Q will debut later this year, expanding the Velo Lumino portfolio of performance lighting integration solutions. 

Anton

velolumino.com

[Evan Estern]

This is so cool!  Would it be a big project to add this switch to an existing unswitched system?  In my case: Internal wiring/Son hub/Velo Lumino tail light/Edelux headlight.

[somervillebikes]

Thanks Evan. Not a problem at all to reconfigure an unswitched system. It's literally just splicing one wire in the system.

[Evan Estern]

I'll keep an eye out for this.  Very interesting.

[Ryan Witt]

This is pretty exciting and I’m definitely hoping to be a customer. I’m interested in having a switch to interrupt my USB charger circuit so the light gets all the power. Yes, I could just unplug the cable, but it’s much nicer to have a switch and hide the charger in a bag.

How does one orient the reed switch inside the stem? Is it on the end of a plastic tube or something? Do some aluminum stems lack clearance?

Any plans to have more than two positions on the switch? It might be tough to fit another reed and set of wires inside but would be an awesome thing to have.

Cheers,
Ryan

[A. T.]

Hi Ryan,

The switch can absolutely be used to control a USB device instead of the lighting, but not both. Unfortunately it's only a 2-way switch. A 4-way switch is something I really wanted to make back in the beginning (Off, On1, On2, On1+2), but I'd have to have jammed two reed switches in there and either one or two magnets, and then the trickiest part of all would be orienting them in space such that the order of activation corresponded with rotation of the knob. Not possible in such a small space.

For the TMAT/Q, the reed switch is fitted inside of a nugget (in this case a plastic cylinder like you mention) that slips over the stem bolt like . There's only a few mm of space around the stem bolt!