Here is another possible approach to reducing gear chatter [attached file]
which would be located forward of whatever flex plate we end up with?.
the red drive gear is coaxial with the eshaft, which drives the green
internal gear directly, and the power is transmitted to the outer purple
gear via the black-colored rubber bushings.  Of course this is only a
representation of a concept where rubber bushings are placed as close
as possible to the source of gear chatter, which is difficult to do with
planetary gears.  Also, the purple gear would not have to necessarily be
 outside the green gear, but it could be placed forward of the green gear,
and its 'fingers' could extend between the rubber bushings in an axial
direction instead of the radial direction shown in my crude drawing.  This
would be analogous to the products shown in the attached Centaflex file.
[So have we agreed that Rhino2 is as good as any?  Anything cheaper?]

This concept could be used to raise the prop thrust line, allowing more
room over the engine to consider using stock Mazda components such
as water pump etc.

Gene Kahn

Excellent idea Gene!!!! Good work. All we need is a new ring gear holder
and slots milled in the PSRU housing. I think chunks of round
silicone rubber rods will work.

What is shown is an internal spur gear but it will work fine with
a planetary. Much simpler than what we are trying to do now,
Will require a new PSRU housing but that is no real problem.

I think we can saw off Tracy's box and weld on a new aft section.
Will stiffen the motor plate in the bargain.

I will draw it up.

I like Rhino but it is up to 4.

Good work Gene. Why to think.

Raising the trust line is not the way to go. Not needed and less volume
for the cooling system. The RX8 water pump is no higher than the rotor
housing.  Been there done that.

Paul Lamar


I want to go back and reexamine what is causing the gear chatter to
start with...  Why doesn't my car suffer from this when I drive it at
low RPM?  Does the RX8 do this?  Can it be driven smoothly at an
engine RPM of 1000?  If not, I maintain that something in the
gear/prop system is flexing at a resonance similar to that of the
torque pules coming from the engine..  I suspect the resonance
frequency of the drive train may be very low because of driveline and
suspension flex - corresponding to an engine idle speed that's
extremely low - below its minimum unloaded idle RPM.

Side question:  The prop should be quite stiff in the lead-lag (to
borrow from helicopter main rotor terminology), but not as stiff in
the "flapping" axis.  Does the flapping flexibility translate into
lead-lag resonance?  If so, do props of different diameter/stiffness
have different chatter RPM peaks?

And another issue..  I believe somebody in the past made a PSRU around
the design concept that minimum gear lash would put any resonance out
of the operation RPM - Steve Beckham may have been involved?  I asked
a long time ago about wear causing gear lash to increase, and how that
impacted resonant/chatter behavior..  Any thoughts?  If this system
(spur gear?) doesn't suffer this problem, maybe it's because the
flexibility in the such a system is fundamentally different from the
planet gears that we're running..

Finally, is the chatter happening between the sun gear and the
planets?  Or between the planets and the ring?  Or are we hitting a
frequency where the carrier is involved in the resonance, causing
vibration between both gear interfaces (sun-planet, planet-ring)?

Maybe these questions have all been answered...  But if not, I think
we may chase this without much success.  However, if we can come to a
good understanding of the fundamentals, and robust system might be
fairly cheap and easily implemented..

If the automobile model is valid, maybe we just need something quite a
bit softer...  Making something more robust, as was done with Dave
Leonard's system, might make things worse by raising the resonance
interaction frequency..  It might need to be, at the same time, softer
and stronger.


Regards,

Matt-

The RX8 does not do it if you merely take your foot off the accelerator
in low gear (man TX). It will merely move away at low speed.

However if you rev it to say 4000 or 6000 RPM and you step off the
clutch you can get severe chatter in the drive line.  Higher revs
7000 to 8500 RPM results in no chatter just wheel spin while smartly
moving off.

Paul Lamar