It’s a prototype, not a production device. You’d completely enclose the gear teeth in a production device to keep debris out.
No, it’s freewheeling ceramic ball bearings against aluminum (possibly an exotic aluminum alloy). The way they get to 99% mechanical efficiency is by eliminating friction, which by definition reduces wear.
The balls are ceramic, but I’m pretty sure the bearing surfaces that roll against the cassette are still steel?
What cassette? I don’t know what that is, sorry! Not a pedal power guy, really.
EDIT: I looked it up. A bike cassette is a sprocket stack, which is exactly what this eliminates. There is no cassette, but now I know what you meant, the extremely complex drive plate that sits in the same place a conventional cassette sits.
The contact points of the shaft against the ornately channeled drive plate are free rolling ceramic balls, as I understand it, which is how they got the friction losses down to 1%.
EDIT: @Beanolini corrects me below, I spent too much time listening to the sales pitch and not enough time zooming in on the pictures! Mea culpa.
That gear looks very thin, I don’t know if that would handle the torque without bending or deflecting. But I am not an engineer, and this is just a prototype.
I think a USB LE (low energy) solution would work. It’s performant enough for the task of switching gears, so long as you maintain a direct connection between Peripheral and Host. Unfortunately this also increases power consumption by a bit.
Also there are enough ready to go, low cost BLE solutions in the market so it’s a pretty cheap wireless solution.
I’d imagine the tolerance between the bearings and the rear gear ring must have very little give in order to work. I’m also terrified of a pant leg or finger (you’ve got to lubricate that thing from time to time) getting pulled into the gearing at either end of the drive shaft.
Argh. Bluetooth is fine for things like cadence and speed sensors, but keep it out of my drivetrain, TYVM. Good old cables work fine for me, and require no batteries.
It looks like they’re ball bearing units mounted around the shaft:
so the contact points would indeed be steel against aluminium, whether or not the balls inside are ceramic.
Given that bicycle chain drive can achieve 98% efficiency just using off-the-shelf parts, this seems like a lot of work for not much improvement…
Our local bike-share bikes are mostly shaft drive- I think the main advantage there is its resistance to vandalism.
IME, 2 times out of 3, “bluetooth” is a flag for “this is a crappy thing that won’t work as advertised”. YMMV.
BMW Motorbikes have used shaft drives in their range for years.
This looks like a fantastic ankle cheese-grater. Should never happen, but ultimately, always does!
Thank you for the correction, I have edited my post to point to it!
Now I’m even more convinced that the shaft design is weak. The ankle-biter drive plate is a really great idea (and can trivially be enclosed to protect the ankles) if the high-strength materials needed can be economically worked. But a bluetooth controlled variable length shaft with more than a dozen separate tiny bearing rings? Too complicated for me, I’d prefer a mechanically or magnetically controlled sliding shaft with spherical contact points.
They’re likely coming at this from the point of view of them sweet sweet patent dollars, so they have no incentive to simplify and make things more robust and easier to repair.
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