Author Topic: Magnets, Speedometers and Ignitions  (Read 305 times)

Offline John Croucher

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Magnets, Speedometers and Ignitions
« on: January 17, 2022, 01:15:01 PM »
I have been working on two projects.  The Buell Blast ignition and the Moto Guzzi ITI speedometer replacement.

Both involve magnets and sensors.  The Buell Blast was changed from the stock ICM to a mechanical advance with a rotor disc magnetic pulse generator on the cam.  The two magnets mounted on the rotor disc have the polarity reversed to send the a signal to ground with the coil and then opposite pole ungrounds the coil to fire the plug.  It works great, have an advance curve rather than on and off signal from the TPS. The springs can be changed with the mechanical advance to change the advance points and the Compu-Fire controller can be rotated to change the initial timing.  Only problem was, the Compu-Fire has mounting holes do not line up with the Buell engine mounting holes.  To correct this, I removed the magnets from the rotor disc and placed them in a new location to fire when required. 

The speedometer replacement is a VDO speedometer electronic unit that uses a choice of 3 types of signal generation.  3 wire Hall Effect, 2 wire Inductive and OEM control box.  I initially used a bicycle reed type sender and a magnet to operate the VDO unit. It worked great and was not listed as a method to send a signal.  Then the reed sensor started failing.  Research found that the Reed Sender wear out after Billions of cycles.  Sounds like a lot of cycles, but I had 4 magnets generating a signal every 1 wheel rotation and 22,000 miles.  This added up to be billions of cycles. 

In the replacement process of the reed sender I bought a two wire Inductive sender, mounted, calibrated and went for a ride.  The speedometer did not work right.  I removed the Sender, made a test rotor with two magnets and mounted in the hand held electric drill, held it close to the sender.  The speedometer worked great.  Based on the label rpm's on the drill motor and the number of pulses from the magnets, the speedometer was very close.  Moving up and down smoothly. 

Where I found the problem to be is the magnets were mounted on the rear brake rotor that is made of high carbon stainless steel that picks up the magnetic energy from the 4 magnets I mounted.  This cause many erratic pulses to the inductive sender as the magnets and the slots in the rotor passed the inductive sender and the confusion in the speedometer.  I tried mounting the magnets so the same pole was toward the sender, but that did not help. Moving the sender further away did not help either.

Now I am down to two choices, mount the signal generator magnets on the aluminum rim or hub or go back to the reed sensor.  I think I will go back to a reed sensor.  They are cheap and the mounting the magnets on the rotor makes for a better set up.

I found this interesting that the magnets in the two application had such an impact on how electrical signals are sent, the polarity of the magnets can be on different sides of a magnet and control other functions.  I tried to find data on mounting the inductive sender and interference, but found nothing that addressed this issue. 


Online Tom H

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Re: Magnets, Speedometers and Ignitions
« Reply #1 on: January 17, 2022, 02:28:44 PM »
Don't know if this will help. There is a GM speedo electric sender that mounts to the GM trans cable opening. I don't think it's the same thread as a Guzzi. I was thinking of going with this and a 6" speedo cable extension so that I could mount the sender in the battery area. Then make some adapter for the extension to get it to attach to the Guzzi trans.

When my speedo craps out and I go electric, this is what I may do, or just get the GPS version?

Tom
2004 Cali EV Touring
1972 Eldo
1970 Ambo V1000
1973 R75/5 SWB with Toaster
2007 HD Street Bob
1953 Triumph 6T (one day it will be on the road!)

 

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