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Deleted member 4366
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I recently stripped one down so i can describe how it works.
To disassemble it, you take the crank/chainwheel off, then remove the 4 screws in the back. There's 4 shim washers in there, so be careful not to lose any. The sensor is held on with three small screws.
The sensor is partly mechanical and partly electronic. There are two adjacent castellated ridges. One is fixed to the crank and the other to the chainwheel, and there are springs between them. They line up together when there's no load, but when there's load on the crank, one moves out of phase from the other against the springs, so the gap between the castellations decreases. The sensor is optical. It measures the frequency and size of the gaps, and sends that info to the controller so that it knows how dast and how hard you're pedalling.
To me, the whole arrangement is a bit rough. It's too easy to get dirt in there, which will mess up the optics. Mine was full of dirt. I don't think it's a good idea to use one of these in salty winter conditions or anything that involves mud. I can see the need to regularly disassemble and clean all the parts, especially the slots in the sensor.
The main mechanical part:
The cover plate to which the sensor attaches over the little window (right of photo). Note the shims:
The sensor:
The middle part of the cover-plate is free to rotate relative to the outer part, but the sensor screwed to it has two anti-rotation lugs to hold it still while the outer rotates with the chainwheel. Mine has a lug broken off:
To disassemble it, you take the crank/chainwheel off, then remove the 4 screws in the back. There's 4 shim washers in there, so be careful not to lose any. The sensor is held on with three small screws.
The sensor is partly mechanical and partly electronic. There are two adjacent castellated ridges. One is fixed to the crank and the other to the chainwheel, and there are springs between them. They line up together when there's no load, but when there's load on the crank, one moves out of phase from the other against the springs, so the gap between the castellations decreases. The sensor is optical. It measures the frequency and size of the gaps, and sends that info to the controller so that it knows how dast and how hard you're pedalling.
To me, the whole arrangement is a bit rough. It's too easy to get dirt in there, which will mess up the optics. Mine was full of dirt. I don't think it's a good idea to use one of these in salty winter conditions or anything that involves mud. I can see the need to regularly disassemble and clean all the parts, especially the slots in the sensor.
The main mechanical part:
The cover plate to which the sensor attaches over the little window (right of photo). Note the shims:
The sensor:
The middle part of the cover-plate is free to rotate relative to the outer part, but the sensor screwed to it has two anti-rotation lugs to hold it still while the outer rotates with the chainwheel. Mine has a lug broken off:
