20 replies to this topic

[Michael393]

Ok I bought the Hunter 67H transducer sold by sailes marketing for about £30 (There is some universal ones out there the Alpine one is the most common but they costs £80-£140 and i was quoted about £100 to fit them). The guy that fit it said it was tight as he had to move some things as there was very little space behind the speedo but it is possible and now it works in case anyone has the same problem in the future. (He charged me £60 to fit it). Now I have the amazing Retro looking Sat nav/stereo/ipod dock/phone BEcker Mexico 7948  Smiths_Time_Clock.jpg   138.95K   7 downloads

[Guess-Works.com]

silly question, but isn't the magnetic pickup from a bike ( pushbike ) speedo, a pulse generator ?

[dklawson]

silly question, but isn't the magnetic pickup from a bike ( pushbike ) speedo, a pulse generator ?

Yes and no.

The bike speedo pickups are reed switches looking for a magnet on the spokes/rim. If your aftermarket electronics are only looking for contact closure, if the speed is not too high, and if you can bond a magnet onto a rotating drive component... then you can use the reed switch. Reed switches can also be temperamental when subject to vibration so they need to be rigidly mounted on a bracket that damps out vibration. I have a Sigma bike computer on my Mini as secondary speedo (calibrated in MPH to supplement the KPH stock Smiths unit). It is dead nuts accurate but it had problems until I found a good way of mounting the switch.

[Guess-Works.com]

When I was looking at building cruise control units (may actually get to do this sometime), I intended on mounting the sensor in the rear wheel hub with the magnet attached to the rotating hub ( using one of the 1/4" unf holes as a fixing ) and then the sensor to the back plate... that way it keeps eveything neat and tidy and out of the way of driveshafts and the elements aswell..

Edited by GuessWorks.co.uk, 09 November 2009 - 05:55 PM.

[GraemeC]

When I was looking at building cruise control units (may actually get to do this sometime), I intended on mounting the sensor in the rear wheel hub with the magnet attached to the rotating hub ( using one of the 1/4" unf holes as a fixing ) and then the sensor to the back plate... that way it keeps eveything neat and tidy and out of the way of driveshafts and the elements aswell..

That's essentially how my rally trip is set up, only using a Hall effect sensor looking at the head of the wheel studs.
Very neat and away from the oily bits.

[dklawson]

That sounds like a good plan John. The only caveat I would suggest with a pickup and magnet mounted on the rear flange is to use some high-flex rated wire. Since the radius arm will be moving up and down a lot with suspension travel you should choose a wire accordingly. Our firm uses a lot of 3-wire proximity sensors from Turck. They have sensor cables that have been rated to over 20 million cycles of flexing and twisting.

Also keep in mind my earlier comment about mounting the reed switch if you use that for your sensor. The rear hub will have a lot of shock loading that will create false triggers on a reed switch. If you reach a resonant frequency for the reed switch you may find your car going slower and slower as the cruise control tries to compensate for the huge number of pulses it receives while the switch is freaking out.

You may have better luck using a 3-wire proximity switch as I mentioned above. You would only need to use a "longer" 1/4 UNF flat head screw for the drum which would appear as a target for the sensor to look for. 3-wire devices are not vibration sensitive and they are typically IP rated for moisture and dust sealing. Were you in the U.S. I'd send you one from my salvage collection at work. In the U.K., my advice would be to troll eBay and look for surplus items there. The most common ones have an 8mmX1mm threaded barrel body. However, there are also "flat packs" that are small rectangular packages. The flat packs may be easier to fit behind the drum than the 8mm barrels.