While on the subject of bikes, I have a project I have been kicking around. I've built a number of recumbent bikes, some with underseat steering and some with a conventional handlebar on a really long gooseneck. The long gooseneck models are easy to build, but suffer from excessive weight. The rider can pull very hard on the handlebars, and so I end up beefing up these components so they weigh quite a lot. Also, brake cables become excessively long, and the back brakes hardly operate at all because they stretch. This is also sometimes a problem on tandem bikes with long cables. Underseat steering solves both problems nicely. The handlebars are under the rider's seat, brake cables are shorter than a regular bike and thus stiffer. Another advantage is the arms hang at a natural angle. Folks like me with carpal tunnel appreciate it when our hands are used in relaxed, natural positions, as opposed to bearing weight on a regular bike, or up in the air. Underseat steering has one complication that is a showstopper, though. You must have some linkage from the handlebars to the front wheel. I have used cables, rods, and various other things. Any play in this system can result in wierd oscillations in your front wheel. These oscillations usually kick in at high speeds going downhill. They can get really scary. The forces involved in steering a bicycle are really quite small. though. I usually steer my recumbent with one finger. One hangs on to the steering bar more for support, or to oppose pedaling, than to steer. I keep imagining an underseat steering mechanism with a servomotor connection to the front wheel, a steer-by-wire system. It is not hard to find standard servos which will handle 300 oz-in of torque, seems like plenty. Most steering is actually very fine adjustments, not gross movements. I can imagine a system which would monitor it's own battery, and alert the user if the battery was low. Seems like a really interesting project. -- Lawrence Lile "Peter L. Peres" Sent by: pic microcontroller discussion list 11/23/02 04:10 AM Please respond to pic microcontroller discussion list To: PICLIST@MITVMA.MIT.EDU cc: Subject: Re: [OT]: Bike gear ratios On Sat, 23 Nov 2002, Jinx wrote: *>> Apparently there is a french company called Mavic Mektronic that *>> makes an electronic gear change system for bikes with Derailleur *>> type gears. Uses a push button on each handle bar, one for up, one *>> for down shift - F1 paddle change style *> *>I'd heard about something on the market but hadn't looked into *>it too seriously, thanks for the link. I reckoned a couple of steppers *>with worm gears could do it, kind of like machine heads on a guitar, *>there's not that much tension in the wires Last time I used a bicycle and tinkered with the derailleur gear mechanism I found out the hard way that the wire tension is 3-4kgf-ish. The force required for the torpedo-style (in-hub) gear changers is much lower, but with 2kgf peaks and some continuous tension. Peter -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.