The ones in the photos above will only fit a square taper bottom bracket, which are outdated these days. Well, at least on decent bikesadrian_sm wrote:Now you would think that these very common off the shelf PAS sensors would be fairly universal in being able to mount to most bikes cranks. Wrong.
adrian_sm wrote:I was looking for an off the shelf PAS that actually fits modern bikes without needing to modify them, as my design goal is to not have to swap out or modify any of the standard bike parts when installing my friction drive. So
1) A different bottom bracket won't work.
2) It doesn't fit on the non-chainwheel side either, typically their is even less space there.
3) I am designing my own controller, so Speedict is nice but would double up on most features of my controller. Plus I believe they don't have a different PAS sensor than the one I showed. Page 7 of their user guide shows the same type of unit, and I can find no further details with my limitted search.
So still no solution.
Lebowski wrote:These simple PAS 's don't detect torque, right ? It's just a simple magnets / reed switch combo ?
As I said previously/ I am looking for an off-the-shelf solution that does not require modifications or replacement of existing components.
The PAS sensor above only suits old outdated square taper bottom brackets.
I don't want to glue on magents.
I don't want to have to replace the BB with a Thun BB.
Is there any other off-the-shelf PAS sensors that suit modern cranks? Anyone?
justin_le wrote:What we need is a magnet PAS ring that attaches inside the inner chainring, and is split in 2 semi-circular pieces so that you can insert it in place without even removing the crank arm.
justin_le wrote: The pickup should attach to the downtube
justin_le wrote:If somebody makes it, it will sell.
adrian_sm wrote:Looks like it would make the chain ring floppy (side to side), hall sensor accuracy in that setup doesn't look great. I think a strain gauge based setup would be easier.
Plus the whole sensor on the spinning thing issue if getting the wires/signal back.
Lebowski wrote:They don't sell strain gauges in the shop here so they're hard to get
adrian_sm wrote:justin_le wrote:What we need is a magnet PAS ring that attaches inside the inner chainring, and is split in 2 semi-circular pieces so that you can insert it in place without even removing the crank arm.
But what does it mount to? Modern cranks don't have any exposed axle, so it would have to be the chainring.
Hang on why make it two pieces, just make it one piece with a cutout.
Obvious would be to use the chain ring mounts, as they are standardised. But that would still probably require using longer chainring nut/bolt things.
Hang-on, most of those nuts/bolts are magnetic (at least the ones I have). How about just get some 6mm diameter rare earth magnet, stick them on the inside of the chain ring bolts, then mount the sensor. That could work. Wonder if the magnets would stay on?
Down tube size and shape vary drastically, I was thinking the seat tube would be better, ie. standardised in size and round most of the time. But some front derailuers brackets sit really low (like on my Gaint MTB dura ace) and would get in the way, so it may not be a universal solution. The sensor mount would need some degree of adjustment if an existing bracket is in the way. Maybe back to mounting it off the bottom bracket nut, not sure.
Lebowski wrote:I once thought about a homemade torque sensor, one which detects the actual torque you're providing.
What I came up with is a thick steel plate (or other material) which attached between the crank and the chainrings.
Normally the crank and chainrings are connected together using 4 or 5 bolts (let's assume 4 for the sake
The cranks attach to the red holes, the chain rings to the green holes. The plate has slots in it
such that pressure on the cranks will bend the plate (in the planar direction) and change the
angle between the red and green holes. The plate has magnets (little blue squares) glued to it
such that the torque can be measured with hall sensors (torque changes the angle between the
magnets, a sensitive microprocessors can measure this based on speed and timing etc)
what do you guys think, should be simple, no ?
MattyCiii wrote:I wonder how hard it would be to put wireless strain gage into pedals? No modification to crank arm or Bb required. Some room in the pedal platform. Bolt on. Nice.
justin_le wrote:MattyCiii wrote:I wonder how hard it would be to put wireless strain gage into pedals? No modification to crank arm or Bb required. Some room in the pedal platform. Bolt on. Nice.
I was going to do this as my senior design project at university a few years ago and it's good to this approach finally show up in the market. It make the most sense for modular fit with with any bicycle, and the relative motion between the pedal and crank can easily spin a micro generator that keeps the sensor circuit powered up and transmits the load data wirelessly to a computer on the bike.
Not quite so easy as a DIY project though.
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