varx/socialFound a neat site that walks you through disassembling your electric toothbrush and replacing the battery. Usually requires some soldering, but... very cool. (They're funded by selling replacement batteries!)
While disassembling my toothbrush, I came across an oddity. What are these little gray cylinders?
They're held loosely captive in a pocket of the plastic, not touching any other component. They're lightweight, rigid, non-magnetic, and maybe composed of something granular.
What the heck?
[EDIT: See rest of thread for possible answer!]
Under the microscope, they appear to be compressed pellets, with granules surrounded by a matrix of maybe finer granules, or a binder.
I scraped a bit off to check if it reacted with water ("are these you-voided-your-warranty tattletales for getting water inside the thing?") but the bits didn't noticeably react.
Lots of amazing speculation in the replies! But I think we can rule out everything related to balance, vibration (enhancement or reduction), electromagnetism, or lubrication. Remember, they're only touching plastic and aren't actually that close to any wires or moving parts.
I think we have an answer, or something very close to one! @futzle tracked down a teardown video on YouTube (https://old.mermaid.town/@futzle/113790355243281798) where similar pellets appeared in a completely different part of a different electric toothbrush.
And several of the commenters said that these are chemical pellets that neutralize gases that NiMH batteries can produce when charging, and which might otherwise reach explosive levels in a sealed space.
I can't find anything online to confirm, but it feels right.
Deborah Pickett (@[email protected])
@[email protected] Also take a look at 7m30 on this EEV Blog video: https://www.eevblog.com/2012/05/30/eevblog-284-braun-toothbrush-teardown/
Swift (will be at EMF)@varx compacted powder lubricant of some sort, designed to abrade down during use? Feels like a weird choice for a hygiene product, but it's my best guess.
@swift Interesting thought, but it's not against any kind of bearing surface—these recesses are between the motor and the battery compartment, well away from the moving parts.
In fact, when I scraped a bit off, it felt a bit like sand or something else abrasive.
@varx huh. And non-conductive?
Whatever they are surely has to be worthwhile because they've got to be adding to the manufacturing cost meaningfully both as extra materials and fiddly assembly. Otherwise, if they're lightweight, you'd just leave voids. And it can't just be spacing / gap filling because it'd surely be cheaper to just have the space they occupy filled with plastic.
@swift According to my shitty Radio Shack multimeter, the resistance is too high to measure.
Yeah, this is so weird. They're not there for heft or balance, shock absorption, desiccation, magnetic sensing, structural integrity, padding, or anything else I can figure.
I was wondering if they were there to tattle on the user for getting water into the case (like you see on some phone batteries, in the form of a water-reactive strip) but some bits I scraped off didn't react with water.
@swift Another thought was "what if they're spare parts?" In a larger appliance, you'll sometimes see spare fuses under clips in the casing. But there's nothing obvious that these would be spares *for*. And these aren't really intended to be serviced anyhow, as far as I can tell.
ducksauz 🦆At first I was going to say that they might be the carbon brushes for the motor, but the motor looks self contained. Perhaps they're graphite for the gears? Can you write with them?
@ducksauz Nope, they sit below the motor and gears and are abrasive, if anything. See this thread for more details: https://mindly.social/@cazabon/113790083859631922
C. (@[email protected])
@[email protected] Do their exposed ends touch something metal when the case is reassembled? Because they look like they could be motor brushes, which carry electricity down onto the contacts on the motor rotor. Those are made of graphite and a secret blend of herbs and spices, and definitely qualify as "kinda granular". Usually the electricity gets to the brushes via a little spring they're mounted on, which pushes them against the rotor, but it can be done other ways too. #BrushedMotor #MotorBrush
Yeah, after I responded, I clicked through to see the responses on your instance.
What a bizarre mystery. 🤷♂️
C.Do their exposed ends touch something metal when the case is reassembled?
Because they look like they could be motor brushes, which carry electricity down onto the contacts on the motor rotor. Those are made of graphite and a secret blend of herbs and spices, and definitely qualify as "kinda granular". Usually the electricity gets to the brushes via a little spring they're mounted on, which pushes them against the rotor, but it can be done other ways too.
@cazabon Nope, they only touch plastic. Here are two more photos, one of the entire core of the toothbrush (one cylinder removed and sitting on the desk) and one of a closeup of the recess where it was sitting. The wall of the recess that you can't see here is just solid plastic.
When assembled, the wall of the shell might be kind of close, but is also just white plastic in that area.
Hmm. So the rough edge on the mystery cylinder shown in your original post is where the plastic clip holds the cylinder in. Does the other end of the cylinder - or its side(s) - show signs of wear?
I'm wondering if they are actually just compressed graphite, as a dry lubricant for the motor/transmission shaft.
I've got what looks like the same brand of toothbrush. Now you make me want to take mine apart 🧰 🔧 🔨 ...
@cazabon One or both have been in and out of the recesses, so I don't know which end was out. Both have at least one end that looks very clean and crisp.
But they don't appear to be graphite, no. I can't write with them, and they're gritty and make a (small) harsh scraping noise against metal.
They're also below the motor, so anything that falls off of them would go into the battery compartment.
Okay, that's not it, then.
Well, I'm down to "CIA tracking device" and "alien abduction locator beacon" as my next-best guesses... 👽 👾 🕴️ 😎
I'd be interested in what you find out!
@cazabon Yet another mystery that could perhaps be solved more easily if only I had a portable X-ray fluorescence analyzer!
*checks prices on e-bay*
Yet another day I am reminded of why I do not own a portable XRF analyzer!
Deborah Pickett@varx Perhaps they are ballast? To alter the {mass, (second?) moment of inertia} of something that needs to vibrate with particular characteristics?
@futzle Yeah, I thought maybe they were chunks of metal for some purpose like that, but they're pretty light—the one I took out is only about 55 mg, which works out to 2 g/cc.
This toothbrush is also... how do I put this gently... not a precision machine. :-P It's one of the old rattly loud toothbrushes, not the newer "ultrasonic" ones.
@varx Also take a look at 7m30 on this EEV Blog video: https://www.eevblog.com/2012/05/30/eevblog-284-braun-toothbrush-teardown/
@futzle Nice find—and they're in a completely different placement and orientation there! But still a pair of them, and still the same size, clipped in in a similar way... WTF.
@varx Lots of conjecture in the comments to that video on YouTube.
@futzle Ohoho, I didn't think to go to the video's page on YouTube! This comment by Kayr Herkert sounds dead on:
« The 2 little black thingies are pellets that neutralize chemical gasses that can be produced when a nimh cell is overcharged. » and then has a dead link to a PDF about potassium hydroxide pellets.
My gut has been saying that these are used for their chemical nature, based on how they looked like a compressed powder. But I couldn't figure out what that would be!
Excellent find!
@futzle I don't *think* it's KOH, as NiMH batteries apparently release hydrogen has, and I can't find anything about KOH absorbing that. (It does react with CO2, but... that doesn't seem relevant. And I think that might only be in solution?)
But a catalyst or something to absorb H2 seems very plausible.
Maybe I can generate some H2 and expose one of the cylinders to an H2 atmosphere? :-)
@varx I am not responsible for the inevitable gas explosion. Godspeed!
AlgoCompSynth by znmeb 🇺🇦@varx Purina Tooth Fairy Chow Pellets.
@AlgoCompSynth Best answer so far. 😆
Jeff Turner ⛵@varx have you checked their radiation levels. Just seems like you checked everything else. My first guess was as balance weights but sounds like they are too light for that.
@jetsoft Not yet. 😅 If I had larger samples I'd be testing them against various solvents, with heat, etc.
And yeah, they're pretty light. Each is 55 mg, but the fully assembled toothbrush is 112 g, 1000x massier.
Picks the Evangelist@varx best guess is to rattle so you know for sure it's on.
they don't look dense enough to be ballast but that'd be my second guess.
they don't look dense enough to be ballast but that'd be my second guess.
@greycat This thing is *so loud* (with or without them) there can never be any doubt. :-D
Jim Lind@varx Maybe a placeholder for some other feature that your entry level toothbrush doesn’t have? So they shoved some thingamajigs in so the plastic doesn’t rattle.
𝐬𝐭𝐞𝐯𝐄 🌼@varx i think they are weights for handling the vibration.