sensor placement.

billy.
billy. Posts: 29
edited August 2010 in Workshop
wanna pick peoples brains on this..........


when i fitted my strada to my bike i had too enter the circumfrence(1 complete rev) measurement into the computer, now after doing this i fitted my senser as close to the top of my fork and the magnet as close to the outer edge of the wheel as i could.

now i have seen riders and pictures with there sensor half way up the fork..........


surely this is "tricking" the sensor and therefore the computer in to thinking that the magnet has made a bigger revolution when infact its only done half what it has been told.

does this sound about right or have i missed something?

Comments

  • bigbelly
    bigbelly Posts: 83
    The magnet and pick up only records the revolutions per minute of your wheel. You have mentioned that you have already entered the circumference of the tyre into the computer. Hence, 1 revolution of the wheel equates to the circumference of the wheel.

    If the measurement you entered into the computer was the circumference of the magnet placement (distance magnet traveled per revolution) - then your original train of thought would be correct.
    shame the rider doesn't match the bike...
  • Speed isn't calculated by how far the sensor has travelled but by the number of wheel revolutions. As long as you enter the correct circumference the computer will be accurate and you can position the sensor where you like.
  • rake
    rake Posts: 3,204
    bigbelly wrote:
    The magnet and pick up only records the revolutions per minute of your wheel. You have mentioned that you have already entered the circumference of the tyre into the computer. Hence, 1 revolution of the wheel equates to the circumference of the wheel.

    If the measurement you entered into the computer was the circumference of the magnet placement (distance magnet traveled per revolution) - then your original train of thought would be correct.
    it still wouldnt tell you how fast the bike was going though.
  • billy.
    billy. Posts: 29
    Hairyside wrote:
    Speed isn't calculated by how far the sensor has travelled but by the number of wheel revolutions. As long as you enter the correct circumference the computer will be accurate and you can position the sensor where you like.


    no, but......


    how it works in my minds eye is this........


    the computer has been told by us that a full reveloution is X amount of MM's, thats from the extreme edge, so surely it uses this to gauge distance/revs/in a time period from this number.......a magnet placed at the centre of the spoke would be revolving a shorter distance than a magnet placed on teh end/towards the nipple of the spoke.

    i just cant get my head round the fact that i told my computer that the circumfrence was 2069(if i remember like), but if i placed it half way down the measurement would be greatly reduced.

    might sound like i'm being 4nal, but its just niggling away at me. lol.....
  • sungod
    sungod Posts: 17,538
    all the sensor does is count revs

    you told the computer the circumference of the wheel, not the circumferene of the path traced by the magnet

    doesn't matter where you fit the sensor, it'll still count one rev per rev, and the distance travelled in one rev will still be the circumference of the wheel
    my bike - faster than god's and twice as shiny
  • Weejie54
    Weejie54 Posts: 750
    edited August 2010
    the computer has been told by us that a full reveloution is X amount of MM's, thats from the extreme edge, so surely it uses this to gauge distance/revs/in a time period from this number.......a magnet placed at the centre of the spoke would be revolving a shorter distance than a magnet placed on teh end/towards the nipple of the spoke.

    i just cant get my head round the fact that i told my computer that the circumfrence was 2069(if i remember like), but if i placed it half way down the measurement would be greatly reduced.

    might sound like i'm being 4nal, but its just niggling away at me. lol.....

    The revolutions per minute are the same wherever the sensor is placed. Only if the sensor is placed very close to the axis would the pulse likely be affected (owing to the size of sensor).
  • billy.
    billy. Posts: 29
    sungod wrote:
    all the sensor does is count revs

    you told the computer the circumference of the wheel, not the circumferene of the path traced by the magnet

    doesn't matter where you fit the sensor, it'll still count one rev per rev, and the distance travelled in one rev will still be the circumference of the wheel
    Weejie54 wrote:

    The revolutions per minute are the same wherever the sensor is placed. Only if the sensor is placed very close to the axis would the pulse likely be affected (owing to the size of sensor).


    arrrrrr......fully understand now.

    sometimes as humans we cant see the wood for the trees. :lol:
  • topdude
    topdude Posts: 1,557
    Have you considered the fact that the wheel is travelling at three different speeds :?
    The bottom in contact with the road is stationary,
    The axle is travelling forward at the same speed as the bike,
    The top of the wheel is travelling at twice the speed of the bike,
    How fast does the magnet travel :shock: :shock: :shock:
    He is not the messiah, he is a very naughty boy !!
  • Weejie54
    Weejie54 Posts: 750
    Have you considered the fact that the wheel is travelling at three different speeds Confused
    The bottom in contact with the road is stationary,
    The axle is travelling forward at the same speed as the bike,
    The top of the wheel is travelling at twice the speed of the bike,
    How fast does the magnet travel Shocked Shocked Shocked

    As far as the computer is concerned, the magnet is stuck to the tyre!
  • zanes
    zanes Posts: 563
    topdude wrote:
    Have you considered the fact that the wheel is travelling at three different speeds :?
    The bottom in contact with the road is stationary,
    The axle is travelling forward at the same speed as the bike,
    The top of the wheel is travelling at twice the speed of the bike,
    How fast does the magnet travel :shock: :shock: :shock:

    Relativity thou art a cruel master :wink:
  • Bikerbaboon
    Bikerbaboon Posts: 1,017
    topdude wrote:
    Have you considered the fact that the wheel is travelling at three different speeds :?
    The bottom in contact with the road is stationary,
    The axle is travelling forward at the same speed as the bike,
    The top of the wheel is travelling at twice the speed of the bike,
    How fast does the magnet travel :shock: :shock: :shock:

    Depends on your frame of referance. You are taking the referance of the road as stationary, If you are looking at the sensor useing the roads referance would be incorect.

    looking at the wheel again from the correct referance frame you will see that it has a constant speed.

    linear velocity of a section of the wheel would come from
    4 pi^2*r/360*R

    R is how long it take to compleat one reverlation. and r the radius of the wheel. The direction of the velocity would be perpendiular to the radius.
    Nothing in life can not be improved with either monkeys, pirates or ninjas
    456
  • Dales1
    Dales1 Posts: 46
    Sensors should be half way down the fork. That way, it reduces the effective rotating mass - you don't have to push that heavy magnet round such a big circumference.

    Dales.
  • anto164
    anto164 Posts: 3,500
    topdude wrote:
    Have you considered the fact that the wheel is travelling at three different speeds :?
    The bottom in contact with the road is stationary,
    The axle is travelling forward at the same speed as the bike,
    The top of the wheel is travelling at twice the speed of the bike,
    How fast does the magnet travel :shock: :shock: :shock:

    time to add this in to confuse people..

    2008551448_sine_wave.png
  • morstar
    morstar Posts: 6,190
    anto164 wrote:
    topdude wrote:
    Have you considered the fact that the wheel is travelling at three different speeds :?
    The bottom in contact with the road is stationary,
    The axle is travelling forward at the same speed as the bike,
    The top of the wheel is travelling at twice the speed of the bike,
    How fast does the magnet travel :shock: :shock: :shock:

    time to add this in to confuse people..

    2008551448_sine_wave.png

    Waves back!