Agenda:OLPC -ML Summit - Monday, March 5th

Location: One Cambridge Center

• 9:00 - 10:00 a.m.   Breakfast•

10:00 -11:00 a.m.  Presentations from OLPC on Current Status

• 11:00-12:00 p.m.    Presentations from ML on XO projects                            Cynthia Brazeal (Center for Virtual Life)                            Henry Holtzman (MAS.964 - One Laptop Per Child)                            Benj "Mako" Hill                              Polychronis Ypodimatopoulos (Networked XO apps + Viral Comm on XO)                             Matt Adcock (Distributed wikis/wikipedia on XO)                            Sanjoy Mahajan                            Alex Wigner-Gross - Wikiosity                            Barry Vercoe                            Mihir Sarkar (TablaNet)                            Ned Twigg                             Noon-1 p.m.          Lunch (Topic: OLPC Summer of Code / Planning for May Event/ Opportunities for ML/MIT                             student involvement in laptop deployment)

1 p.m. - 2p.m.      Peripherals For Laptop ($10 Mindstorm.Scratch, Medical Peripherals, Sensors etc.).                            Mitch Resnick ($10 Mindstorm.Scratch)                            Scott Manalis (USB HIV Test)                            Ed Boyden                            Joe Paradiso                            Marko Popovic (H2.0)

2 p.m. - 3p.m.      Laptop Entrepreneurship - Joost Bonsen3 p.m. - 4p.m.      Gen 3.0 and beyond ($50 Laptops)

Experimental study on the energetics of the crank generator and the pull-cord device

Marko Popovic*,

Colin Bulthaup**

Hugh Herr*

* MIT ML Biomechatronics Group, ** Potenco

Overview

• 10 test subjects (age 8-12 years)• Generator devices attached to solid base.• Mechanical properties linked to the circuit parameters.• Three experimental conditions:

– Crank generator, max power 1 minute

– Pull-cord device, max power 1 minute

– Pull-cord device & oxygen mask, comfortable pace 3 minutes

5.1 W12.8 W

3.9 W

(Steady metabolic consumption 4.4 W )

Average Electric Power

LabView view on power generation

Crank 1 minuteMax power

LabView view on power generation

Yo-Yo 1 minuteMax power

LabView view on power generation

Yo-Yo 3 minutesModerate pace

Power Generated over 60secsCrank Yo-Yo

Metabolic Study

• The energy cost estimated from O2 consumption and CO2 production

(with respiratory exchange ratio, V(CO2)/V(O2) less than one)

• K4 telemetric system consists of silicon mask with flow-rate turbine and O2, CO2 analyzer

• Resting values of O2, CO2 were subtracted from values obtained during the trials with pull-cord device

Rate of Net Metabolic ConsumptionR

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Efficiency• Efficiency defined as ratio of generated electric

power and rate of metabolic energy cost

SEX AGE MASS (kg) HEIGHT(m) P1*(W) P3**(W) RMC***(W) Efficiency (%)

F 8 29 1.32 13.4 8.5 189 4.5

F 11 43 1.55 15.0 3.4 84 4.1

F 12 39 1.57 16.0 4.5 79 5.7

F 8 20 1.22 9.6 3.0 33 9.1

M 10 39 1.40 16.3 5.8 82 7.1

F 12 43 1.50 14.0 4.5 80 5.6

M 11 45 1.67 9.5 2.7 46 5.9

M 8 27 1.32 8.5 3.4 109 3.1

F 10 29 1.42 12.5 3.5 78 4.5

N/A 10±2 35 ± 9 1.44 ± 0.14 12.8±2.9 4.4±1.8 87 ± 44 5.5 ± 1.7

* P1=average generated electric power during 1 minute pull cord trial** P3=average generated electric power during steady metabolic consumption period during 3 minute pull-cord trial*** RMC=rate of metabolic cost during steady metabolic consumption during 3 minute pull-cord trial

Questionnaire• How did you like the hand-crank generator?

• How did you like the pull-string generator?

• Were you comfortable wearing the face mask?

- The hand-crank was uncomfortable but it could possibly work better if the handle was a little bigger.

- It was OK. Hands and arms became a little tired.- I don’t like it. It hurts my knuckles.

- I felt this was much more comfortable than the hand-crank generator and I produced more power with it.

- I preferred the pull-string generator over the hand crank. It was easier to gain speed to generate power.

- I loved this. It didn’t hurt like the hand-crank and felt like it didn’t take as much energy as the hand crank.

- It was perfectly comfortable wearing the face mask.- Yes – no problems- The face mask feels weird.

Discussion & Summary

• Max power generation during 1 minute trials strongly in favor of the pull-cord device with average output ~ 13 W; for the crank

generator average output is ~ 5 W

• Comfortable pace power generation with the pull-cord device during 3 minutes trials resulted in a moderate average generated power , ~ 4.5 W, and moderate efficiency, ~ 5.5 %.

• Net efficiency equals product of bio, transmission & motor efficiencies (back of the envelope estimate ~0.25, ~0.7, ~0.6)

Discussion & Summary

• Results strongly dependant on the experimental setup.

• Results dependant on posture and specific movement strategy.

• Realistically, presented numbers should be thought as a lower bounds on both generated power and efficiency.

• According to filled questionnaires kids were typically more satisfied with the pull-cord device.

References

• C. Hausswirth, A.X. Bigard and J.M. Lechevelier, The Cosmed K4 telemetry system as an accurate device for oxygen uptake measurement during exercise, Int. J. of Sports Medicine 18 (1997) 449-453.

• J.M. Brockway, Derivation of formulae used to calculate energy expenditure in man, Human Nutrition: Clinical Nutrition 41 (1987) 463-471.