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David Butcher: PPPM and the Science of Pedal Power

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How much power can a Human Being create? The best way to find out is to measure it!

On Sunday, October 18, 2009, I had the pleasure of working with Eric Fuller and Randyn, two students at UMass Boston (the University of Massachusetts), to conduct an experiment with the PPPM. The experiment resulted from Eric's request for data regarding pedaling rates and corresponding power outputs. I did not have any data to share, so the experiment was organized to generate and record the data in real time. This page shows the results.

The experiment was structured as follows:

I was the test subject. At the time of the experiment, I was 55 years old, and I weighed 150 pounds. I ride the pedal generator used in the experiment daily, so I would estimate that I am in better-than-average physical condition.

Before the experiment, the team agreed on a test protocol. Eric served as the test director and also recorded data. Randy recorded respiration data during the first half of the experiment, and pedaling cadence data for the second half. David (me) maintained specific Watt outputs requested by Eric, and provided pulse, Watt-hour and Voltage data.

The test protocol specified power output and timing, and the resulting data was collected for specific intervals. Power outputs started at one Watt, incremented by 10 watts per interval to 110, and then decremented by the same amount back to one Watt. Timing was one minute of testing followed by one minute of data recording. Rider power outputs were changed 15 seconds before the next measurement interval began, to allow cadence, pulse and respiration to stabilize at the new power levels. Pedaling continued at previous power levels during the data recording interval, until the power level change 15 seconds before the next measurement interval.

The rider fully warmed up before the measurements began by generating approximately 45 Watt-hours at a moderate page (75 Watts). The rider's power output was reduced to 1 Watt approximately 10 minutes before the experiment began.

The Stickam widget you see to the left was used to share a live video feed and chat room during the experiment. Test direction was given using the chat feature. Pedaling cadence was monitored visually. Respiration was monitored aurally. Pulse was measured using a pulse-monitoring fitness wristwatch with an infrared sensor. Watts, Watt-hours and Voltage were measured using a WattsUp meter.

Important: The power output metric (Watts) was not synthesized or estimated. It was an accurate, real-time measurement of the actual amount of energy flowing from the Human "power source" through the PPPM (pedal generator) into a large battery bank. "Power Output" metrics from exercise equipment displays are not comparable to this metric.

If you are researching Human Power and you would like information on a wide range of equipment and applications, plus a detailed history of the use of Human Power, I highly recommend the book "The Human Powered Home."

PPPM Pedal Generator Output Metrics - Human Power Output Data

Mins Watts RPM Resp Pulse Volts Watt-hours Comments
000161#72##The experiment begins
0630622376##Connection issues caused Video lag (missed cycles)
105076268212.8#Weren't we supposed to be tallying Volts? :-)
126076368613#Some breaths were double-counted (David's fault)
22110943011214#Pre-planned maximum Watts. Not David's limit.
2610090321081478Weren't we supposed to be tallying Watt-hours?
Green Science: All of the equipment used in the experiment (at the PPPM end) was powered by the energy being generated during the experiment!

Chart of PPPM Pedal Generator Human Power Output Experiment Results

Chart of PPPM Pedal Generator Human Power Output Experiment Results

The chart shows the results of the experiment. All values are plotted to show how they vary in relation to each other. The bottom scale represents two-minute measurement intervals - one minute of measurements and one minute of data recording and preparation for the next power level. The left scale represents the values of each measurement. The easiest metric to follow is Watts, beginning at one Watt, climbing to 110 Watts, and then descending to 1 Watt again over the time frame of the experiment. All other measurements are relative to Watts of output.

Notes: We forgot to tally Watt-hours until we were are the second 100 Watt level. This metric can be safely interpolated, however, as it is the result of a specific power output for a specific time, and both of those numbers are known.

Our technique for counting breaths changed at the first 100 Watt level. We had been relying on David to make a "clicking" sound on each breath, but it turned out his breathing could be directly counted simply by listening to the sound of his exhale. The breaths/minute numbers are probably more accurate after the first 100 Watt level.

After the experiment was over, David demonstrated two 30-second sprints at 130 Watts, with 2-3 minutes of a 75 Watt pace between the sprints. The only metrics collected for the two sprints were cadence and heart rate:

  • Sprint 1: 130 Watts, 96 RPM, 113 Heart rate
  • Sprint 2: 130 Watts, 100 RPM, 110 Heart rate

All metrics shown were collected using the PPPM I with a single generator. A future experiment may be conducted (if several more motivated individuals will participate!) using the PPPM I with double generators. That experiment will enable David's top level of sustained power output to be measured.

Other technical information:

  • A diagram of the pedal power generation circuit used during the experiment
  • Equipment powered during the experiment: Laptop computer, 9 Watt CFL, 400 Watt Inverter, 1 Watt LED, eGo Electric Scooter charger
  • Total power generated prior to and during the experiment: 120 Watt-hours - pedaling was continuous
  • A typical daily workout for David: 110 Watt-hours

Do you have questions, or comments on this experiment? Enter your thoughts or questions in the field below and then press the button labeled: "Experiment Comments"

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