Jumpy Guy
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| posted on 28/5/04 at 04:20 PM |
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wheel rotation and Speedo calibration
Guys, since my feeble brain had forgotten whatever it knew about mechie engineering-
I'm looking to build my own speedo-
how do speedos usually work? measure speed of what? wheel rotation?
in which case, how fast will a 15" wheel rotate at e.g. 60 mph?
Basically, Im trying to determine what scan rate I'll need when i design the program for the speedo...
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ady8077
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| posted on 28/5/04 at 04:45 PM |
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Hi
It will depend on how your sensing the revolutions, i've fitted 4 magnets onto the propshaft and a reed switch. Prop shaft revolutions = Number
of magnets x differential ratio x tyre revs per mile. You'll need to no the rolling circumferance of your wheel and tyres to work your tyre revs
per mile
Hope this helps
Adrian
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britishtrident
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| posted on 30/5/04 at 05:27 PM |
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First what you need to work out is the wheel dia to the tyre tread and from that get the circumrenece
tyre size =195/50x15"
To find wheel dia
((195*0.50*2)/25.4) +15 =22.68"
Circimfrence = dia*22/7 = 71.82 or 1.98 yards
giving
889 wheel turns per mile or 889 wheel rpm at 60 mph
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