mark chandler
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| posted on 21/1/07 at 04:02 PM |
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Hall effect and blade clocks
Hi all,
Been struggling to get my blade clocks to work in the lowest cost possible way, my findings so far are:
Taking the sensor wire only (ignore the batt and earth) by using either a reed relay or hall (ABS) sensor I can get the thing to work.
I kept fooling myself into believing I had an issue with the clocks as I could not get them to work, the problem was insuffcient pulses. By leaving my
setup running for a while I started to clock up tenth of miles very slowly.
What I have now is the hall sensor pointing at a toothed wheel in my lathe, this has 12 lumps and at 1500 rpm is reading 20mph.
With school boy maths 6000 rpm on the prop will equate to around 120mph, so by increasing the number of lumps to around 18 on the prop/adaptor and
pointing the sensor at this I am hoping to get away without any kind of speed healer and save £70.
So my question is:
How fast will a hall sensor run to ?
How fast will a reed sensor run to ?
Th estimated number of hits will be 450 per sec.
Cheers Mark
 
Rescued attachment clocks_hall.JPG
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Bob C
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| posted on 21/1/07 at 04:10 PM |
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I'd expect a hall sensor to do 450Hz - I'd expect it to do3 or 4K!
I'd expect a reed switch to do up to about 50 & not to last very long at that rate.
Good luck
Bob
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David Jenkins
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| posted on 21/1/07 at 04:20 PM |
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A typical decent quality reed switch is usually rated for 1 million operations - and it wouldn't take long to rack up that number is such an
application!
A hall-effect sensor is probably the best option, or possibly an optical one (e.g. a chopper blade between a LED and a photo-transistor - often
available as a single unit.)
I made a speedo sensor using a steel chopper blade with 7 blades, between a hall effect sensor and a small magnet... it's coped well so far.
David
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mark chandler
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| posted on 21/1/07 at 06:39 PM |
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Great, looks like the ABS sensor is going to come up trumps on this one then as I already can hit 20mph @ 1500 rpm (thats as fast as the lathe will
spin).
Next thing is to develop the stator, I tried a few odd gears that I had lying around but got good results with offcuts and tape.
Regards Mark
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mark chandler
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| posted on 28/1/07 at 07:47 PM |
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Done a lot more work on this and the answer is 9 magnets on the prop, use the sierra hall sensor from the ABS as a pickup.
This is correct for a 3.62 diff with 185/60/13 tyres.
No need for £70 on speedo correctors etc.
For a different wheel ratio add or remove magnets.
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