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03/10/12 19:04
Modified:
  03/10/12 21:17
Read: 256 times


 		 #186573 - Some of your points are just wrong
Responding to: Per Westermark's previous message
Per Westermark said:
The amount of force applied to a pedal do not vary so much with number of sprockets. Why? Because when it goes uphill you select a lighter gear but you still push what you can. Because the other riders will. So you stay at almost same rpm on the pedals. And almost the same force. It's only the torque at the backwheel that will be different since it's on the other side of the gear system.


You cannot stay at the same RPM and same force applied to the pedals unless the power changes.

power = torque X angular speed

http://en.wikipedia.org/wiki/Torque

EDIT:
This should be the way that power is measured in this case. A simple solution to using a strain gauge would be to use strain gauges on the frame of the bike where the crank is located as the bearings holding the crank must be supported by the frame. The frame will flex to some degree. This removes your rotational strain gauge problem. Of course, some form of brain will be needed as the forces will be slightly split and would be a perfect job of an MCU to resolve.

I still believe that this is a very difficult way of producing a torque value and would be more dependent upon the bike itself.

List of 61 messages in thread
TopicAuthorDate
bikey design challenge      Jez Smith      03/09/12 12:14      
   Only 400W?      Per Westermark      03/09/12 12:23      
      Its a bit different on the road      Jez Smith      03/09/12 12:34      
         Brilliant idea in the bath      Jez Smith      03/09/12 13:35      
            Might work      Per Westermark      03/09/12 13:51      
               well...      Jez Smith      03/09/12 14:33      
                  So you are yourself saying 400W is a bit low max scale      Per Westermark      03/09/12 14:43      
                     O.K then 500 watts      Jez Smith      03/10/12 00:56      
                        Battery      Per Westermark      03/10/12 05:11      
            Fun with strain gauges      Oliver Sedlacek      03/12/12 05:57      
         You sure?      Per Westermark      03/09/12 13:48      
   nice ride      Andy Peters      03/09/12 14:31      
      fanks      Jez Smith      03/10/12 00:54      
   Sigma Rox 9.1...      Kai Klaas      03/10/12 09:59      
      Sigma fake      Per Westermark      03/10/12 11:07      
         What do you expect for that price?      Kai Klaas      03/10/12 12:09      
            Head or tail wind? Or riding in a group or alone?      Per Westermark      03/10/12 12:38      
               Way overcomplicating this      Joseph Hebert      03/10/12 14:02      
                  Sensors      Steve M. Taylor      03/10/12 14:22      
                     how indeed      Andy Peters      03/11/12 12:37      
                  Wrong - you are totally missing the drag factor      Per Westermark      03/10/12 14:22      
                     Not at all.      Joseph Hebert      03/10/12 16:03      
                        Real manufacturers haven't found your idea simple...      Per Westermark      03/10/12 17:09      
                           Point made      Joseph Hebert      03/10/12 18:46      
                           Some of your points are just wrong      Justin Fontes      03/10/12 19:04      
                              Sounds like you expect an infinite acceleration      Per Westermark      03/11/12 06:49      
                                 Repeat post Ignore      Justin Fontes      03/11/12 11:39      
                                 I try for a constant power      Justin Fontes      03/11/12 11:52      
                                    Crank rpm - not back wheel rpm      Per Westermark      03/12/12 00:31      
                                       I got the two confused      Justin Fontes      03/12/12 10:37      
                                          Bandwidth + return channel      Per Westermark      03/12/12 12:07      
                        Oh dear, so many variable constants      Oliver Sedlacek      03/12/12 06:48      
                  rocket science      Maarten Brock      03/11/12 03:58      
                     So don't ignore them      Joseph Hebert      03/11/12 07:39      
                        Of course, it is...      Kai Klaas      03/11/12 08:18      
                           wireless      Joseph Hebert      03/11/12 08:36      
                              Costs...      Kai Klaas      03/11/12 12:59      
                                 cost      Joseph Hebert      03/11/12 13:39      
                                    Another problem      Joseph Hebert      03/12/12 21:14      
                                       This was addressed earlier      Justin Fontes      03/12/12 22:02      
                                       Multiple strain gauges      Per Westermark      03/13/12 00:53      
                                          Competitive bicycling      Justin Fontes      03/13/12 10:24      
                                             Pulse      Per Westermark      03/13/12 10:55      
                                                If I had the power meter      Justin Fontes      03/13/12 11:14      
                                                   Normalizing with heart beats cancels some errors      Per Westermark      03/13/12 12:39      
                                                      Just to get some data to look at      Jez Smith      03/15/12 03:37      
                                                         Jez ?      Steve M. Taylor      04/14/12 04:35      
                                                            Oh Noes!!!!!!      Jez Smith      04/14/12 10:58      
                                                            The plan is      Jez Smith      04/15/12 01:55      
                                                               Brum doesn't HAVE mountains      Steve M. Taylor      04/15/12 14:51      
                                                                  Ah yes but no but      Jez Smith      04/15/12 23:23      
                                                                  Actualy...      Jez Smith      04/15/12 23:35      
                                                   If I had a power meter...      Oliver Sedlacek      04/16/12 04:20      
                                                      Ive been testing things      Jez Smith      04/16/12 04:41      
                                                         Well, no      Steve M. Taylor      04/16/12 07:41      
                                                            all very well thank you Steve      Jez Smith      04/16/12 08:45      
                                                               Getting nasty      Steve M. Taylor      04/17/12 10:54      
                                                                  nasty ?      Jez Smith      04/20/12 12:09      
                                 More time than money if access to machinery      Per Westermark      03/12/12 00:57      
                                 Strain gauge elastic fixtures      Oliver Sedlacek      03/12/12 06:55      
                           Sure      Per Westermark      03/11/12 09:42      

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