Technical Journal of the Ihpva Number 53, Spring 2002
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HUMAN POWER TECHNICAL JOURNAL OF THE IHPVA NUMBER 53, SPRING 2002 From the editor . 2 A brief introduction, Theo Schmidt . 2 Contributions to Human Power . 2 Articles Comparison of measurements of bicycle spoke tension using a mechanical tensiometer and musical pitch John S. Allen . 3 Adding arm power to a recumbent Daniel Kirshner . 7 Bicycle design, safety, and product-liability litigation David Gordon Wilson . 10 Letters Human-powered trackway systems John Barber . 6 Demise of rickshaws . 19 Independent feelings of water molecules George Tatum . 19 Arm-powered tricycle, Mike Eliason . 20 Theo’s mini ice-scooter, Theo Schmidt . 21 Future of the HPVA?, John Snyder . 23 The future of Human Power, Jean E. Anderson. 23 Book reviews Von Null auf 140 mit 93 Zähnen: Aerodynamik von Pedalfahrzeuge by Andreas Pooch reviewed by Theo Schmidt . 22 The Recumbent Bicycle by Gunnar Fehlau; translated Number 53 by Jasmin Fischer; reviewed by Dave Wilson . 22 Spring 2002 $5.50 Comparison of measurements of bicycle spoke tension HUMAN POWER using a mechanical tensiometer and musical pitch Number 53 Spring 2002 $5.50/IHPVA members, $4.50 by John S. Allen Abstract double-crossed, not laced, 215 mm. root of tension. Therefore, every A brief introduction FROM THE EDITOR he tension of 140 spokes in four This wheel had a steel rim and a very doubling of frequency — one musical I am 48 and live with my wife in an This issue of Human Power is a bit bicycle wheels was measured wide range of spoke tensions. octave — raises the tension by a fac- HUMAN POWER old house in the foothills of the Bernese different. David Gordon Wilson has using a tensiometer — a • A 406 mm 36-spoke wheel with 14/15 tor of 4. A spoke whose fundamental is the technical journal of the Alps near Lake Thun. It’s full of parts T asked me to take over as editor at least mechanical device designed to measure gauge (~1.8 mm diameter) spokes, frequency is only 1.2 times as high as International Human Powered from human- and solar-powered vehicle for a while, as he is involved in starting spoke tension —and by plucking triple-crossed, 183 mm. the value given in the table — a musical Vehicle Association and boat projects. I grew up near a company building small gas turbines the spokes like harp strings and Using wheels with different spoke minor third higher — is already under Number 53, Spring 2002 Mount Tamalpais in California, where and in completing the third edition of determining their tension using the lengths, patterns and tensions made it more than 1.4 times as much tension, Editor mountain biking started, and studied in Bicycling Science. Dave Wilson has standard formula for the fundamental possible to determine how these fac- and is likely to fail quickly. Theodor Schmidt Basel and in hilly Wales and England, made Human Power into the world’s frequency of vibration of stretched tors affected the relationship between Bicycle spokes rarely break due to Ortbühlweg 44 where I was introduced to HPVs. premier technical journal wires. The measurements by the two the tensiometer measurements and excessive tension; but the rim may not CH-3612 Steffisburg, Switzerland on HPVs, (including HPBs, methods were compared. When spokes musical measurements. withstand it, and when the rim relaxes [email protected] around the spoke holes, the wheel fails. HPAs) and also some sta- were laced such that they touched each The musical method Associate editors other, the musical measurement was Weight loading on a wheel decreases tionary applications of The fundamental frequency of vibra- David Gordon Wilson of the average tension of a laced pair, tension of the few spokes at the bottom human power. If there were tion of a stretched string or wire varies 21 Winthrop Street and so there were 93 rather than 140 of the wheel greatly, and raises ten- a knighthood for human according to the following equation, Winchester, MA 01890-2851 USA musical measurements. Tensiometer sion of the remaining spokes only very power, he would deserve it! assuming small amplitudes [1]: [email protected] measurements of laced spokes were slightly, but lateral loading while pedal- I would like to broaden where averaged for comparison with the ing out of the saddle causes significant Toshio Kataoka, Japan our scope to include 1 1-7-2-818 Hiranomiya-Machi articles to do with the phi- musical measurements. F = the fundamental frequency [Hz] increases in spoke tension and can lead Hirano-ku, Osaka-shi, Japan 547-0046 losophy of human power. Both types of measurements proved 1 T to rapid failure of an over-tensioned F1 = wheel. On the other hand a common [email protected] There are two reasons for accurate enough to use in establishing 2L m this. Firstly, we are getting the correct tension of spokes when error in wheel building is to leave the Philip Thiel, Watercraft L = the length of the string spoke tension too low, resulting in a 4720 - 7th Avenue, NE less material than before building bicycle wheels. The function T = tension of the string weak wheel, since spokes go slack Seattle, WA 98105 USA as HPV physics become relating the measurements conducted more and more specialised; using the two methods is linear and m = mass per unit of length under smaller loads, and fail to hold Production the rim steady. The excess motion in a and secondly, the status of consistent, though there was some This resolves to T = 4 F12 L2 m JS Design & JW Stephens human power in society is a discrepancy between the results. Each which is used to calculate the tension slack wheel is what breaks the spokes IHPVA precarious one and we need method proved to have strengths and from the measured frequency. and allows the nipples to unscrew. Paul MacCready, Honorary president to give it all the support weaknesses related to convenience, The cross-sectional area of the spoke As the Paul Gracey, USA, Chair, we can in order to improve which will be discussed. and the mass per unit length m are thickness Table 1. Open, Secretary/treasurer the quality of life in present Patient Jason exactly proportional to each other. of a wire Length Length My own projects have mostly been The wheels used increases, our Publisher and future societies. Please send your in the investigation Therefore, for two different strings or (mm), (mm), Musical articles and letters. human-solar hybrid vehicles and boats wires of equal length, one thick and equation for plain butted pitch IHPVA The tension of the 140 spokes of Human Power continues to be and formerly racing these in the Tour another thin, the frequency is the same musical pitch PO Box 1307 four bicycle wheels was measured. The 308 F# San Luis Obispo, CA 93406-1307 USA produced by Jean Anderson and John de Sol. These have always been either if the tension per unit of cross-sectional becomes wheels were: 292 G [email protected] (Elrey) Stephens of the HPVA. It is sent easily transportable or semi-amphibi- area is the same. One way to think of slightly • A 622 mm, 40-spoke dished rear wheel to HPVA members together with HPV ous in order to tour without being car- this is to imagine two identical spokes inaccurate 276 308 G# Human Power (ISSN 0898-6908) is with 14 gauge (~2.0 mm diameter) because the News (now edited and produced by dependent. I’m vice president of Future side by side, both of the same gauge A, published irregularly for the Inter- plain gauge spokes on the right side 262 292 Peter Eland of VeloVision) and is avail- Bike Switzerland, where one of our and at the same tension. They vibrate greater bend- 440 Hz national Human Powered Vehicle and 14/16 gauge butted spokes on able for subscription to all other IHPVA specialties is organising races for HP at the same frequency. Now imagine ing stiffness Association, a non-profit organization the left side (~1.6 mm diameter over 248 276 A# members at reduced rates. rail vehicles. lightly connecting them together all adds its con- dedicated to promoting improvement, most of the length, ~2.0 mm near — Theo Schmidt along their length. They still vibrate at tribution to 236 262 B innovation and creativity in the use of both ends); both sides quadruple- Steffisburg, Switzerland the same frequency. Finally, imagine the stiffness 224 248 C human power generally, and especially crossed, spoke length 296 mm. merging them into one, thicker spoke. generated in the design and development of • A 630 mm, 36-spoke wheel with 14/15 212 236 C# It still vibrates at the same frequency. by the wire’s human-powered vehicles. gauge (~1.8 mm diameter) butted Contributions to Human Power These facts greatly simplify the tension. The 201 224 D spokes on both sides. One side is Material in Human Power is copyrighted measuring of spoke tension for wheel discrepancy 191 212 D# The editor and associate editors (you may choose with whom to correspond) welcome laced triple-crossed and the other by the IHPVA. Unless copyrighted also by builders. To determine whether a spoke is not large the author(s), complete articles or repre- contributions to Human Power. They should be of long-term technical interest. News is laced radially. Spokes on both 181 201 E is optimally tensioned, we don’t have to and only sentative excerpts may be published else- and similar items should go to HPV News or to your local equivalent. Contributions sides are 296 mm long.