for weighing things that move
For those not in the know ... all those expensive (really, really expensive) scales that scientists use? ... they don't really measure mass, they just measure a "difference" in gravitational force on a given test body. To obtain a true mass detector, you need to do your scale operations in a vacuum. Because of the buoyancy given to objects in air, a pound of feathers is not the same mass as a pound of iron. If you measured that same equality of supposed mass on the moon (with no atmosphere) ... the feathers would hold up the iron. Get it?
This is what I came up with ...
What's it four? ;o) This scale is balanced on a razor blade from a box cutter ... very strong steel. It rests on a steel channel that I got at Home Depot ... it's a shelving bracket that you screw to the wall and hang shelf mounts from ... very common stuff but just what I need. I wanted a piece about one foot long but Home Depot doesn't cut metal and I don't have a hack saw so I just left it at two feet long and screwed it onto the horizontal beam.
The vertical and horizontal beam is made from a single piece of wood (1/4" x 1&1/8" x 10') that I eyeballed to be as straight as possible (also from Home Depot).
I had another stick of wood to which I glued a plastic ruler. It has all the presidents on the other side. Isn't that wonderful. By the way, who's the oldest president who ever lived? ... Gerald Ford ... he's almost 94. His closest competitor was Ronald Reagan who died at 93 ... but ... then ... what is death? One could argue the case that Reagan was brain dead much earlier due to Alzhiemer's ... hmmm ... back to the proper balance.
I checked out the sensitivity of my device, before final assembly, by seeing if it would measure a postage stamp force on the far end. As set up, it registered a difference of about 2/3 to 3/4 of a sixteenth of an inch on my president's scale (I put a vertical line on the door in pencil). Later, I dedided to flip it over to use the centimeter/millimeter scale for more lines and greater accuracy. In the picture is a strip of paper. At first, I tried to cut a paper in the shape of a postage stamp ... but I couldn't put in on the beam. It kept falling off so I settled for a bent strip of similar area. This proves that I am really smart ... but also dumb ... as I tried about five times to put the other paper on before giving up. :o(
Here's my razor blade fulcrum. Because the machine is balanced at two points and both are steel to steel, it shouldn't slip with any moderate torque applied when I spin whatever I want on the balance. The torque will simply be transferred to our beautiful blue planet instead of making the whole thing fall down. See how I cleverly clamped it to an open door so that no holes needed to be bored in the ceiling?
You may have noticed that I put up a "mast" rather than just a plain " T " shape. I did this so that I could adjust the center of mass of the entire project. Thus, if I place a weight high on the mast I can raise the center of gravity of the whole and thereby increase the sensitivity of the apparatus. As a counter-weight I decided that a common vice wrench would suffice. I can grip it on anywhere and can use it to clamp on more weight if necessary, i.e. it's adjustable!
Of course, it wouldn't do to have a big thing taking up space when not in use so I designed it to fold up in the smallest space possible. Just remove the center screw, fold it up and put that screw in another hole that keeps it straight ... then use the C-clamp to hold everything else together.
I made a "pan" to set things in and act as a UFO hull in a soon-2-fail experiment. The pan is suspended from string and is an aluminum pie tin. I've kept it away from iron bearing materials to avoid any extraneous magnetic effects. I thought I might need to make an "air damper" to stop the scale from from swinging forever. However, I found that I could stop it quite well ... by hand ... down to about a few millimeters of swing ... then ... by using a 4" strip of paper touching the centimeter scale, it can be stopped down to a single millimeter (but don't breathe on it). Some expensive scales have magnetic dampers which amount to a magnet inducing currents in a metal which saps the energy of the "pendulating" scale. I don't know if "pendulating" is a bonified word but I'm making it one because it fits nicely.
Hear ye! Hear ye! Henceforth "pendulating" is an English verb meaning "swinging" especially in an experimental (or weird) apparatus.
I decree it to be so! - EBTX 11/21/38
This here is my anti-torque adjustable suspension for the pan. It is made from some extra screw in cup holders that I found in my tool box. I just hook two hooks over a long headless bolt and ... it swings ... er ... pendulates ... quite nicely. I mean it swings but won't rotate, OK? I put two cut-off plastic screw holders on the ends so that the thing won't fall off ... but they really aren't necessary.
Now, I just have to install a central hook to hang a string from and get some rotation to measure. Next stop ... an initial experiment for calibration. I have to account for ...
After which I'd be left with ...
Remember, if this works, it will be the crowning achievement of civilization ;o) ... so ... everyone reading this page should be holding their breath - starting now.
Experiment page is at UFO Experiment #1