Hi Chris,
I am using strips of steel from a steel measuring =
tape for
the pivot. I cut strips about 1/8” wide across the tape and =
I use 2
pieces spaced about an inch to give side to side stiffness in boom
motion. A regular scissor will cut the tape and may also work to =
trim a
double edge blade. You are correct the boom is a bit high in the
picture. Before mounting the boom it can be hung from a thread in =
the
pivot clamp and the line of the thread will point to the cg. I =
think in
most AS-1 types the cg is actually below the boom and the boom should be =
up and
not level. On my boom the coil below the arm and the extended =
damping
plate below the arm tend to put the cg well below a horizontal arm at =
about the
edge of the mass and the hinge side of the mass. The boom can also =
be
balanced horizontally before mounting to get a cg for the lift test type =
of
calibration or for a calibration coil computation. =
With my adjustable spring mounts I played with angles =
down
to 30 degrees while I had the optical sensor. Without temperature =
control
it is to much of a struggle to maintain stability at lower angles and =
longer
periods. The spring I have is negative length -0.191 =
inch. I
measured 6 weights between 7000 and 14500 grains and used linear =
regression on the
measurements. An easy way to do this is to hang a small plastic or =
paper cup
from the spring and add lead bullets to the cup. In the =
US =
many of us
have reloading scales which can measure to 1/10 grain up to 500 at 7000 =
grains
per pound. A vernier caliper can then measure extension from a =
fixed
point to the cup rim allowing k to be determined fairly =
accurately. After
assembly, period measurement can then confirm the total boom mass since =
it is
harder to weigh beyond the scale capacity. =
There is a hidden advantage to brazing the =
frame. When
the garage is 10 degrees F the torch is warmer than a drill =
press!!!
Randy