Mailing List flyrotary@lancaironline.net Message #2635
From: Russell Duffy <13brv3@bellsouth.net>
Subject: RE: [FlyRotary] tachs
Date: Wed, 20 Aug 2003 07:52:57 -0500
To: 'Rotary motors in aircraft' <flyrotary@lancaironline.net>
Message
Yes, Please, Todd. I have the Tiny Tach, but it is true to it's name. I'd rather install a 3 inch circular one.
Rusty said I'd need to divide by 12 to use the EC2 output. Right?
How much? 
 
3 inch tach!!! John, I think what you really need is some glasses :-) 
 
For the record, since the tiny tach expects one pulses per revolution, you'd have to divide by 12 to get the proper reading if you hooked it up to the tach output.  I don't think that would be the best way to hook a tiny tach up though.  
 
Most normal tachs come with a switch, or some other method of setting the number of cylinders, and the choice is usually 4,6, or 8.  Since 4 cycle engines fire half of their cylinders on every rotation, the tach expects to see half the number of cylinders pre rev.  If you use the tach output of the EC-2 for a normal, off the shelf tach, you'll have to divide as follows:
 
4 cylinder setting, 2 pulses per rev, divide by 6
6 cylinder setting, 3 pulses per rev, divide by 4
8 cylinder setting, 4 pulses per rev, divide by 3
 
Now that I think about it, what the heck does that Geo 3 cylinder engine do :-)
 
Rusty (it's too early)
 
 
 
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