Centrifugal force of a rotating object is MVVR. Where V is the
velocity, and R the radius and M is mass.
This means that unless C.G. is matched exactly, it is impossible to
ballance the engine at different speed.
Fortunately, I think the C.G. Of the rotor travels in a circle.
Therefore it is van be balanced by a weight at the C.G. path of the
rotor. The same goes for the imbalance of the eshaft.
Since counter weight is located only at the end of the engine, I
think you will get from limited twisting on the shaft.
That's IMHO. No guarantee on accuracy.
Henry Nee
Hi,
Can you please explain the problem and solution of balancing when
using a cut down e-shaft with single rotor 1/2 Mazda 13b engine.
Regards Zahid
Balance is controlled by these equations. The Wankel is not just
statically balanced but dynamically balanced as well.
In a single rotor engine the counterbalance weights must provide a
STATIC balance for the e-shaft eccentric and its rotor and must also
account for the DYNAMIC wobble caused because the static counter
weights are not located at the mechanical centres of the rotor and
the eccentric. It is impossible to do this.
They must be mathematically sized relative to their lateral position
from the rotor and eccentric centre line.
Paul Lamar
the Tracy ISO is physically attached to the flywheel. Does that need
to be brought in to balance equation as extra mass to mF (front
counter weight) or mR (mass Rear Counterweight)?
Regards Zahid
The rear counter weight is hiding behind the ISO.
Paul Lamar
Here is how I solved some of the balancing issues. There are a whole
lot of issues interacting when building a new engine configuration.
Weight control influences almost everything. A single rotor engine
certainly requires a considerable flywheel, if one wants the idle
speed somewhere below 3000 RPM. I integrated the rear balance weight
in the flywheel (picture). The front balance weight I modified with
tungsten inserts before dynamic balancing. I ended up with a clean
rotating setup. My engine is based on 12A rotor and housing, so I do
not have any direct comparison to 13B size parts. FWIW.
Richard Sohn N2071U
http://www.fairpoint.net/~res12/home.html
Hi Richard, I have read some postings where some have machined a
single rotor eccentric shaft from a 2 rotor unit. Paul mentions the
shaft needs to be hardened after machining. Could you give a
overview of the process you used to build your shaft ?
Thanks, Steve Carlisle
Here is what I did.
On the first e-shaft I concerted, I left the oil pump side of the
shaft with the front lobe unchanged. After machining the rear end of
the shaft to my mods, I only had one bearing surface to create. I
picked an inner ring of a INA needle bearing with an outer diameter
the same as the original MAZDA bearing, and pressed it on the shaft.
As it turned out, it was a solution, which never failed during all
the ground testing of the first engine I build, with a run time of
around 50hrs. I did not consider this a solution for a final,
flyable configuration. The solution I have in the engine now is a
case hardened bearing section. The biggest problem was finding
someone for the case hardening and grinding who was willing to do it
for and affordable cost. FWIW
Richard Sohn N2071U
http://www.fairpoint.net/~res12/home.html
I misunderstood the last email by Richard Sohn. He was referring to
case hardening process for e shaft . I thought he was referring to
case hardening for bearing. So please do not publish my last email.
Zahid Rahman
I am thinking, since the rotor rotates at one third the speed of the
esfaft. One needs a 3:1 reduction gear on the counter weight to
matched the rotor's rotation speed.
Corrections welcome!
Henry Nee
I'm not sure at all, but you have to compensate for the weight that
is centered in the shaft eccentric, and this rotates at shaft speed.
Or not? Thanks. Best regards. Salut † Jose Gros-Aymerich Madrid,
Spain
The rotation of the rotor is immaterial to the discussion. The rotor is
mounted on the E-shaft at the rotor's center of gravity. The E-shaft is
unaware of the shape or rotation of the rotor. The rotor could be
round, or any other shape. That does not matter. Whether the rotor is
spinning or sitting still has no effect on the location of the rotor's
GC. All the E-shaft knows is that there is a weight attached to it that
is pulling it off center. The weight is orbiting around the E-shaft at
the same rate as the E-shaft is turning.
No reduction drive is required because you are not trying to balance an
off center load generated by the rotation of the rotor. The rotation of
the rotor does not generate any radial force because it is spinning
around it's own CG. Only the E-shaft rotation generates a radial force
that needs to be balanced.
If the E-shaft was mounted on two bearings with the rotor attached,
outside of the engine so that the rotor was not spinning at any
predetermined ratio to the rotation of the E-shaft, the resulting
reactive forces generated would exactly match the forces generated when
the engine is totally assembled.
For a one rotor engine a counter weight would be required on each end of
the E-shaft 180 degrees opposite to the rotor. For a two rotor engine
the math gets a bit more interesting because the two rotors generate
radial forces that are not in alignment with each other. The distance
between the rotors is the moment arm of the force that is trying to
twist the engine around their combined CG.
Mark LaPierre
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