Period vs frequency

In my previous post, I was struggling a bit with accuracy on the acceleration component of the power tracking.

I’d originally been calculating instantaneous roller speed from the period between the last two sensor pulses, but I think this was suffering with a bit of jitter in the measurements. For the next attempt, I started to calculate the speed from the pulse count over a set period.

These frequency based results (based on pulses per second) were somewhat smoother, but in order to remain responsive to speed changes, I needed to make the period shorter. The data in the graph below was generated at 4hz, but still smoothed over 4 samples.

freq_power_data_4hz

To maintain accuracy, with a reasonable number of pulses per period, I’ve also needed to increase the pulse rate. For the above test, I just stuck another three magnets onto the roller, but have since ordered an optical sensor. This should allow very easy adjustments of the pulse rate, just by printing up new encoder disks.

 encoder_disks

Until now, I’ve been sending the raw speed data over a serial link to a PC, where it’s saved and then post-processed in a spreadsheet. Next post I’ll cover a new development platform, where I’m able to do the curve fitting and power calculations in real time.

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