Post by tzsteve on Sept 17, 2015 14:44:04 GMT
jsut a little bit of stuff, How I see it
centrifugal force = 4 x 3.142 x 3.142 x M x N x N x r (in Newtons)
so doing the maths for an imbalanced crank or flywheel and totaly ignoring the
the weight of the conrod and piston.
consider a crank to have an imbalance of .01Kg at 25mm from the center
at 2000 rpm.
M=0.01kg
r=0.025m
N=2000rpm
__
¦¦=3.142
we get a force of;
4 x 3.142 x 3.142 x 0.01 x 2000 x 2000 x 0.025
or
4 x 9.9 x 0.01 x 4000 x 0.025 = 39.5 newtons aprox,
thats like having a weight of 4KG pulling on the crank.
......................................
if we consider a flywheel with the same weight imbalance acting near the
edge of the flywheel say 80mm (0.08M) from the center.
we get something this;
4 x 3.142 x 3.142 x 0.01 x 2000 x 2000 x 0.08
or
4 x 9.9 x 0.01 x 4000 x 0.08 = 126 Newtons,
thats like having a 13kg weight pulling on the flywheel.
not bad for a 10 gramm imbalance (a fin or two)
.........................................
this is why i consider a well balanced flywheel
to be more importent than a (theoreticaly) well balanced crank.
these out of balance forces increase rapidly with rpm and distance from
the center.
if you double the distance you double the force.
if you double the rpm the force goes up by 4 times.
i have tried to keep it all as simple as posible `cos after this it can
get a bit complex (it gave me a headache when i had to learn it).
...........................
this is the crank that is in my current engine only one small hole is visible there are another two deeper holes on the inside of the web near to the bottom of the crank web.
centrifugal force = 4 x 3.142 x 3.142 x M x N x N x r (in Newtons)
so doing the maths for an imbalanced crank or flywheel and totaly ignoring the
the weight of the conrod and piston.
consider a crank to have an imbalance of .01Kg at 25mm from the center
at 2000 rpm.
M=0.01kg
r=0.025m
N=2000rpm
__
¦¦=3.142
we get a force of;
4 x 3.142 x 3.142 x 0.01 x 2000 x 2000 x 0.025
or
4 x 9.9 x 0.01 x 4000 x 0.025 = 39.5 newtons aprox,
thats like having a weight of 4KG pulling on the crank.
......................................
if we consider a flywheel with the same weight imbalance acting near the
edge of the flywheel say 80mm (0.08M) from the center.
we get something this;
4 x 3.142 x 3.142 x 0.01 x 2000 x 2000 x 0.08
or
4 x 9.9 x 0.01 x 4000 x 0.08 = 126 Newtons,
thats like having a 13kg weight pulling on the flywheel.
not bad for a 10 gramm imbalance (a fin or two)
.........................................
this is why i consider a well balanced flywheel
to be more importent than a (theoreticaly) well balanced crank.
these out of balance forces increase rapidly with rpm and distance from
the center.
if you double the distance you double the force.
if you double the rpm the force goes up by 4 times.
i have tried to keep it all as simple as posible `cos after this it can
get a bit complex (it gave me a headache when i had to learn it).
...........................
this is the crank that is in my current engine only one small hole is visible there are another two deeper holes on the inside of the web near to the bottom of the crank web.
