Now, force feedback is an interesting complication I haven't considered! That would certainly make the project extra complex if it is needed. I think sideways forces on a bicycle wheel are usually minimal, except when you are going down a track full of ruts. This is no off-road bike, so I won't worry about that possibility just yet. I am imagining the rider is more involved with feedback from the vestibular system than the hands. I'm tempted to hack this up just to see if it would work. Now I have worried a little about what kind of sensor to sense the position of my underseat handlebars with. The handlebars themselves will be a conventional carbon fiber straight handlebar in a conventional gooseneck bearing welded onto the frame. You need lots of strength in a handlebar because the rider pulls on the bars to oppose the legs. The sensor has to accept getting wet, and either has to accept 360 rotation or be arranged with a heavy duty end-stop since you have a 40 cm lever to haul on it with. I can't imagine the end-stop torque on a conventional pot being good enough. Rotation at least 180 degrees is essential. Is there a waterproof pot that would fill the bill? OTOH, servomotors are quite waterproof all by themselves and contain a nice high quality pot and a beefy end-stop. Maybe I could hack apart a small servo and couple it's pot to my PIC. I could even stick the whole thing in the servo case! ANd thus we also have the makings of a force feedback system. Big servo drives the steering wheel, and a signal off the big servo feeds back to the PIC processor. PIC drives the little servo which is coupled to the steering bar. Signal off the little servo POT drives the PIC which runs the big servo. Now, can any one spell O S C I L L A T O R ? I can imagine this thing going down the road flapping, or getting unstable at certain speeds. -- Lawrence Lile Bob Ammerman Sent by: pic microcontroller discussion list 11/25/02 07:22 PM Please respond to pic microcontroller discussion list To: PICLIST@MITVMA.MIT.EDU cc: Subject: Re: [OT]: Bike gear ratios I would think a bicyclist is depending on force feedback from the steering gear. This would complicate a steer-by-wire system. Bob Ammerman RAm Systems ----- Original Message ----- From: To: Sent: Monday, November 25, 2002 10:47 AM Subject: Re: [OT]: Bike gear ratios > 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. > > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body