John,
Yip, I tried this on a 912 and it didn't work. The main reason was presence
of other cyclic and non-cyclic noise. This swamped the signal and made it
impossible to trigger to scope.
The proprietary balancing machines use a similar principle, but incorporate
an integrator for the accelerometer signal. Didn't have the time or energy
to investigate this though - sorry.
Dave
-----Original Message-----
From: JohnJMoran@aol.com <JohnJMoran@aol.com>
Date: 28 September 2000 18:16
Subject: Spinner Balance Measurement
>The cost of dynamic prop balancing has caused me to begin investigating a
>homebuilt method using available technology:
>
>Analog Devices make an accelerometer evaluation kit (ADXL05EM, $100)which
>measures acceleration to 5 G in one axis. This unit is about 2" X 2" X 1"
>plus mounting tabs and a 3 foot long cable. Seems like this could be bolted
>temporarily to the Rotax gearbox to measure vibration. Painting a white
>stripe on the back of the spinner backplate and mounting a photo pickup
>adjacent would provide a sync signal for an oscilloscope, allowing a view
of
>engine vibration vs prop angle. This should provide guidance on where to
>place washers and, with a bit of experience, how many are needed.
>
>My understanding of the equipment used to dynamically balance props is that
>it is similar to the arrangement described above. One possible problem
with
>this homemade version is interference from the ignition, although careful
>sheilding should handle this.
>
>Has anyone tried anything along these lines, and what were the results?
>
>John A044
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