In a message dated 04/13/2005 2:36:58 AM Central Daylight Time,
lendich@optusnet.com.au writes:

<< George (down under)
 
 >          This is going to be a silly question to the experts, but I can't
 > help but ask it:
 >
 >          I haven't been able to understand why the balance weight is even
 > needed. I don't doubt that it is needed, but I don't understand why. I
 look
 > at the eccentric shaft, and it is symmetric. The rotors are 180 degrees
 out
 > in relation to each other. The rotors spin 1/3 as fast as the eccentric
 > shaft, to which the balance weight is attached. How would the
 > quickly-turning balance weight do anything in opposition to the rotors?
 > What, exactly, does the balance weight counter balance?
 >
 > >>

If the rotors were directly opposed across the shaft there would be no need
for counter weights. The weights don't weigh enough on their own to counter the
rotor weight.

The counter weights only remove the longitudinal couple caused by the
displacement of the rotors along the shaft. The distance between the rotors
determines the weight of the counter weight required to remove the couple.

Lynn E. Hanover