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Thread: Inexpensive speedo sensor fix

  1. #1
    Baby Twin
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    Inexpensive speedo sensor fix

    A few days after buying my Mille, the speedo sensor showed it's Italian heritage by croaking. The price of a new sensor seemed excessive to me (~72) so I looked for an alternative solution, preferably one that would have a greater life expectancy and would be easier to source.

    The original sensor is a biased hall effect device, i.e. a hall effect sensor combined with a permanent magnet. The output is a an open collector, i.e. the signal wire is grounded when ferrous metal is in front of the sensor, and is floating when no metal is present. The instrument pack pulls this wire up to around 9-10 volts, giving a 0-10volt swing. My sensor was still working to some extent, but the voltage swing was from 0volt to less than 1 volt (too low for the instrument pack to register) which indicates a high leakage current (probably moisture ingress).

    I initially looked at cam sensors from car engines, some of these use the same kind of biased hall sensors. However, nothing I found fitted very well and they are still quite expensive if you buy a genuine part (and the after market parts can be quite short lived). So I started looking at industrial proximity sensors. These work on a different principal to the hall effect sensors; they create a high frequency magnetic field from a coil in the sensor. A conductive material brought near the coil will have eddy currents induced which oppose the generated field, effectively reducing the 'Q' of the coil. This is detected by the circuit within the sensor. The advantages of these sesnors are as follows:

    1) They are made by numerous companies to standard sizes. Cherry, Omron, Turck, Seimens, Honeywell, Autonics, Rockwell are just a tiny sample of the companies that manufacture these sensors. This means easy availability, and low cost.

    2) Robust. These sensors are designed for harsh industrial applications, normaly sealed to IP67 (fully waterproof) and resistant to harsh vibration and shock.

    3) They do not require ferrous materials to operate. This may be of interest to those that want to use Titanium disc bolts etc. The operating range is reduced with non-ferrous materials however, and I'm happy with steel bolts so I've not tried this.

    4) Most sensors have an LED built into the end of the body so you can quickly set up the sensing distance and confirm correct operation.

    I used eBay to source a suitable sensor, as buying direct usualy requires an account, and if you go through Farnell, RS, Digikey etc. you pay a premium, though it's still a lot cheaper than an Aprilia sensor. The key parameters are the output interface, which must be "NPN", and the switching frequency. Often these sensors are used for static applications like machine guard interlocks, so they are not expected to switch frequently, and some sensors will only operate at 100Hz or less. At 170mph, the Mille rear wheel is turning ~38 times every second, and there are 6 disc bolts so we need the sensor to have a switching speed of at least 38*6=228Hz to cover the speed range of the bike. Fortunately there are numerous sensors available that will switch up to 800Hz or more.

    The sensor I bought is made by Autonics, and distributed through Hong Kong. Cost is under 5 inc. postage and it took about 10 days to get here.

    The main issue is how to mount the sensor in the caliper bracket. Having a lathe I turned up a simple top hat bush to hold the sensor, and fabricated a small spring steel clip to retain it. This is probably overkill however, a simple alloy, stainless or even plastic bracket could be used with an M12 hole for the sensor and an M6 hole for the retaining bolt.

    The sensor:


    The sensor installed in the bush:


    The sensor installed in the caliper bracket:


    I reused the connector from the old sensor, the wires need to be connected as follows:

    Code:
    Signal     Aprilia Wire    Autonics Wire
    Ground     Blue/Orange     Blue
    Supply     Green/Violet    Brown
    Output     Grey/White      Black
    The Autonics cable is thinner than the original Aprilia, so you can cut the original sensor off, tape the Autonics cable to the original and then use the original cable to pull the new one through. This saves a lot of messing around. Cut the connector of the original cable with 10cm or so of wire left, then join this to the Autonics cable, preferably a soldered connection with heat shrink to insulate and protect it.

    I've not tested this absolutely flat out, but so far it works perfectly well into 3 figures. The sensor is rated to 800Hz which you'd have to be doing about 600 mph to achieve; even the mighty Mille would struggle with that

  2. #2
    Baby Twin
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    That sounds brilliant! Although I have to admit that I didn't actually understand a word lol! Good on you though for thinking outside the box.

  3. #3
    One Liter Duc Eater Deacs's Avatar
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    awesome info matey, much appreciated

    Deacs

  4. #4
    Baby Twin
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    No problem, hope it helps someone.

  5. #5
    Superbike Twin
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    nice one, that's what I loiks to see, problem solving with a background knowledge of what yer talking about. Spot on ol boy

  6. #6
    One Liter Duc Eater Deacs's Avatar
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    can we get this post made a sticky or get it moved to the "how to's" section please

  7. #7
    Superbike Twin
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    Superb info mate ! i change proximity sensors all the time at work on conveyors and equipment so this should be easy. I dont really understand everything technical you've said above but you obviously know what you're talking about !! i will be doing this as mine is totally knackered and doesnt even read. brilliant work, thanks

  8. #8
    Baby Twin
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    Quote Originally Posted by Smithy-R View Post
    I dont really understand everything technical you've said above but you obviously know what you're talking about !!
    Nice of you to say, but I'll put it down to my bullshit skills which have been finely honed by spending time with my manager at work

  9. #9
    Baby Twin
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    Just used this method to repair my speedo after going through 3 costly Aprilia items. Works a treat. Nice one !

  10. #10
    Baby Twin
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    Excellent, glad someone found this useful. I went to the IOM this year and I can confirm the new sensor still works ok at almost flat out RSV speeds

  11. #11
    Baby Twin
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    It ended up about half a mm from the disc bolt before I got it working 100%. When it was 1mm back it was picking up one side of bolt then the other side of bolt with the bolts having concave heads and counting each bolt twice. You can imagine the speeds it was reading, not to mention the amount of miles it was clocking up lol

  12. #12
    Baby Twin
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    Yes mine did exactly the same thing, careful adjustment works fine as you found. It would help to offset the sensor position towards the outer edge of the bolt.

  13. #13
    Evil Twin theruck's Avatar
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    great article. thanks

  14. #14
    One Liter Duc Eater
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    Going to repair my speedo using this method. Just ordered one of those sensors.
    I found mine had gone faulty today when i started the bike to come home from work
    Might have to resort to a mountain bike speedo in the short term

  15. #15
    One Liter Duc Eater 2TROKE's Avatar
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    Nice1 dude shall buy 1 as a back up spare incase mine decides to go on the blink for a fiver u can't moan if iget it in I won't be waiting for the post LOL................well done sir

  16. #16
    Baby Twin
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    Sorry about possible lack of pictures, had some problems with my webspace being hacked recently.

  17. #17
    One Liter Duc Eater
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    This is what i made to fit the sensor


  18. #18
    Superbike Twin CRAZY LEG5's Avatar
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    can a mod not move this to how to's as its a great bit of info

  19. #19
    Superbike Twin
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    Quote Originally Posted by CRAZY LEG5 View Post
    can a mod not move this to how to's as its a great bit of info
    Agree with this, great info and should be a sticky

  20. #20
    AMA Pit Boss supertedlover's Avatar
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    And someone should be producing and selling those nice little alu brackets.

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