Natural Science Forum / Physics / General Physics / March 2007

Well my latest test trial was another failure of design. Design is
hard work, because I have to jury rig a system and not make one
without cost consideration.  I tried some fishing line between the new
trolley and the scale. It all streched. And bounced.

So I took apart the scale and removed the strain guage inside it.  I
was going to make a special mount fo rit without any slack at all. I
proceeded to break a very fine wire on the strain guage ruining it.

So the twenty dollar fish scale was bought again!  ANd this time I
used the old scale as the mount and spliced 8 feet of telephone wire
in.  So now I have a remoted scale.

MY new vibration free trolly is a 3 inch tube inside a four inch
tube.  With little wheel to make the inside trolly.  IN static tests
it spun arround in a circle inside the other tube due to torque and
vibration. SO I put a trolly rim in to stop the spinning.  A rim of
aluminum channel.

SO now a static test indicates friction between the channel and the
wheel!

Bad news.

I will get so data this week end in the car.  I put greas on the
channel to try to reduce the friction. A 5 oz zero problem is the
current worry.

A 2 lbs.. 1 oz thrust static.

Experimenting is hard work.  Jury rigged and all. Statistics my save
me.  The last time I think I fudged the scale trying to average the
vibration reading. A procedure to simply take blind data is necessary.

1.turn on scale.
2. turn on power to propeller.
3.take the scale reading 10 second average.
4. accelerate to 10 or 20 mph
5. take scale reading.
6.Ignore zero offset reading apon stopping.

I think that statistics will get good readings without zero problems,
as long as zero's are dispensed with.

I hope statistics works.