BergHugi wrote:
mhepp wrote:
Could you use a weight hung on a pedal?
Something along the lines of: set cranks horizontal, hang weight from pedal, release and record power measurement. Repeat but with the wheel off and bike on the trainer. Theoretically, the same force is being applied with measurement in the same(-ish) location.
Might not be a long enough duration or a large enough weight to be meaningful but could be a starting point of comparison.
With this method you only know
the applied force but not power. In addition, what bike computer / app to use to get a static force or torque measurement?
When one knows force, one knows power as long as one also knows velocity.
Power = dot product of (linear) force and velocity,
Power = dot product of torque and angular velocity.
Torque is just force applied at a distance to a fulcrum; and angular velocity in unit of radian/s is easily converted from rpm.
SRM report slope as Hz/Nm and offset in units of Hz. In effect, the offset is indirectly reporting torque. And from a set of offsets generated from respective torque inputs, one obtains a linear regression yielding the slope and offset when zero torque is applied. This is the entire underpinning behind static calibration.
What complicates static calibration for the H3 (or indeed any smart trainer giving power reading at the hub) is that it's quite difficult to apply static force to the hub without the hub rotating. For crank-based PMs and powertap, one simply applies the rear brake when hanging an object with a known mass (usually from a pedal), and one can obtain the static force applied.
Without further contraption, do this on a smart trainer, and the chain will rotate. The hub on the smart trainer has to be held still somehow in order for the static calibration to work.
Graph x-coordinate is torque (in Nm); y-coordinate is reported offset (in Hz)