Pedalling technique thread
Comments
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C and D should be the same. Is the difference explained?
It would be interesting to know whether splitting a crank measurement into two halves is representative of the actual individual leg efforts, personally I'm sceptical.
Paul0 -
Downstream measurement (e.g. crank spider or chain tension based measurement) of the net torque values will always be different than with independent pedal force measurement. For a start it's measuring the *net* torque contribution from *both* legs, and cannot distinguish individual leg torque measurement in the way independent crank/pedal measurement can.paul2718 wrote:C and D should be the same. Is the difference explained?
e.g. from an SRM or Wattbike's POV, 20Nm of net torque at some point in the pedal stroke could come either from (say) one leg applying +15N and the other +5N, or from one leg applying +25N and the other -5N. With downstream measurement devices all you know is the net torque value of 20Nm, but not what makes up that net torque. That's the point.
IOW these devices are not actually measuring the same thing, so it's no surprise we see a different torque profile in the charts.
That's the point, it isn't, and is why one needs to be very careful when considering such crank (or chain based) net torque measurement devices when assessing pedalling dynamics, let alone considering taking corrective action based on them.paul2718 wrote:It would be interesting to know whether splitting a crank measurement into two halves is representative of the actual individual leg efforts, personally I'm sceptical.0 -
The paper's author is open to questions at google groups wattage forum.frisbee wrote:The raw strain readings or through whatever filtering and processing the devices have?
I don't see where it's normalised to zero at zero degrees?frisbee wrote:From years of working with force sensors on similar applications it all looks a bit weird. Like, Why is the pedal system normalised to 0 at 0 degrees.
e.g. in chart A the dominant-leg torque measurement at zero degrees ranges from about zero to very slightly positive, which is pretty reasonable expectation for the torque being applied at top dead centre. For the non dominant leg the torque at zero degrees ranges from slightly negative to slightly positive, again not an unreasonable expectation when the cranks are vertical.0 -
Can someone explain exactly what good pedalling technique is please, and explain why this technique delivers more sustainable power.0
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Stalin wrote:Can someone explain exactly what good pedalling technique is please, and explain why this technique delivers more sustainable power.
Based on previous threads, I think the answer to both questions is "No, they can't" (explain it, that is)...0 -
But chart C is apparently the sum of the two legs measured independently, so should be the same as the sum of the two legs...Alex_Simmons/RST wrote:e.g. from an SRM or Wattbike's POV, 20Nm of net torque at some point in the pedal stroke could come either from (say) one leg applying +15N and the other +5N, or from one leg applying +25N and the other -5N. With downstream measurement devices all you know is the net torque value of 20Nm, but not what makes up that net torque. That's the point.
I shall go have a look.The paper's author is open to questions at google groups wattage forum.
Paul0 -
Stalin wrote:Can someone explain exactly what good pedalling technique is please, and explain why this technique delivers more sustainable power.
First you have to look at the advantages and disadvantages associated with natural pedalling techniques. Each leg has a possible 180 degrees of the pedalling circle over which effective maximal force can be applied to the pedal, best pedalling technique is the one that makes the most of these 180 deg. Maximal power application can be made more sustainable by extending the peak torque application sector from 30 deg. to over 90 deg. as this reduces stress on the muscles.0 -
The total integral should be (less perhaps any minor mechanical losses), but that doesn't mean the shape of the curves has to be the same to end up with the same area under the curve. Note how the pedal measurement has higher peaks but also lower troughs than the net torque measurement.paul2718 wrote:But chart C is apparently the sum of the two legs measured independently, so should be the same as the sum of the two legs...0 -
I've read the paper. I can find no explanation for the difference between figures C and D. For the paper not to be trivial this difference has to exist, but unless it is a consequence specific to their particular SRM, or the way in which they've tapped into its raw torque readings, I don't see why A+B shouldn't add up to C whether A and B or C are measured. It's like a basic sanity check.
I'll read it again.
Paul0 -
D is a chart of the direct measurement of C, and C doesn't equal D. The question is why, which, AFAICS, isn't answered.
If I measure the torque at each end of the crank and add them up I should get the same as if I directly measure the total torque in the crank.
Paul0
