The Gravitic Motor

In this section, I'll be developing better the idea of the Gravitic Motor, Idea #147.

The Gravitic Motor is all about getting small displacements (perhaps under a mm range), in a cheap fashion. I cannot promise you that it actually works, or that it provides such a displacement because to my knowledge no one has ever built such a machine. It is not necessarily superior in any way to other conventional means of getting small displacements, except perhaps that you could build it with things you will find in your local hardware shop. People have been know to use threaded rods or even piezoeletric drives for small range displacement, with great success. 

The history of the Gravity Motor goes about this. I've always been crazy about the notion about manipulating small things, things in the nanoscale, even though I don't actually hold the necessary knowledge (in terms of Quantum Theory) to do so. Building things with the very foundation blocks of nature, the atoms or molecules, that must be Godlike. It has always been one of my top Research goals. Of course, Star Trek played a real part in this fantasy of mine, with Borg nanoprobes and all that.

But at the same time, Quantum applications are really distant from me and the next common man. It all seems to require really fancy lab equipment that, to tell the truth, don't even exist here in Brazil. So it is presumptuous to at least consider you will be manipulating nanostructures in your garage. But the will persisted to investigate this, and I started to actively seek means to get small displacements. That is about it. Lets jump to the idea.

On the left image, we see what would this machine be like. Don't bother if you can't make out the text, I'll be guiding you here. It is a tall H structure made with PVC pipes. You should use pipes that can be screwed, because then it would be possible to dissassemble it easily. 

There are straight pipe sections and and T type connectors. On the bases there are also those pipe enlarging adapters. I've upgraded this design so pipes get thicker in the base. This augments the autonomy of the Gravitic Motor, as we will discuss later. On the two pipes at base there are caps (caps are end sections that seal a pipe, without letting water leak). The top section pipes all have same diameter, and the pipe with the faucet can be made a little thinner, optionally. The collumn pipes are opened on the top, you can enlarge it a little too, or put a funnel, as shown in the image. 

The bottom horizontal pipe is just really a pipe with a plastic faucet, nothing more.

On the top horizontal pipe there is something inside the pipe, that you placed there. It is the float. The float is a piece of a low-density material that can move forward and backward a little inside the horizontal pipe. There is a hole in this tube, on the top side of the float. This hole is necessary so we can attach a table into the float, with a pin. The hole has just the width you would like you table to move.

On top of this moving table you place whatever you are going to work with using the Gravitic Motor. The float is oiled or greased too, to reduce friction as much as possible. It moves very tightly inside the horizontal pipe. Ideally there would be no water leaking from one side of the horizontal pipe to the other. It is presently unknown if this would actually hold true in an actual construction.  

On top of each one of the columns, there are pebble droppers. These drop, on wireless command, a single pebble of standard size. Some effort needs to be devised to design them, and this is not included here. Alternatively, it could also drop fine sand too.  

The columns are filled with water up to a level. You don't want to fill them too high. Actually you want them a little above the top horizontal pipe.

During operation, you would place your working samples on the table, and a tool or efector would act on them. Say this is a microscope, a pick and place tool, or a drill, just for the sake of an example. Whenever you want the table to move right, you drop a pebble on the left collumn. This raises the water level a bit, and seeking to balance the pressure, the floater moves to the right to even things out. The table displaces a bit to the right. If you want to move left, drop a pebble on the right.

A day of operation may involve many individual left-or-right motions. In the end, the pebbles will accummulate in the bottom of the machine, up to a point where you will be forced to get the water out, sort of dissassemble the pipes and get the pebbles out. Refil the water, and you are free to start the fun all over again.

In reality, a few calculations involving some very naive physics indicate that this machine has a smallest displacement possible, and that has to do with the floater's friction. Since its friction depend on the weight of the things you place on the table, you end up only being able to work with light things. This is a real inconvenience of the Gravitic Motor. But it makes sense in the end, because usually when your are working in small displacements, you are working with light feathers. 

I've added a glass dome and vibrationless devices to the apparatus. You might get real pro here and actual vaccuum the whole chamber too.  

At first, it seemed to make sense to use tiny water dropplets instead of sand. But I quickly realized you can't really make tiny water dropplets. You are limited to those tiny dropplets people use in intravenous applications. So small solid particles should work best. 

Detail of the horizontal top pipe, showing the floater inside and the hole on the surface of the PVC pipe.

Now, on the left image, you can see what could be a 2-axis version of the Gravitic Motor. You are seeing them from the top, each circle is one of the base PVC pipes. The idea is to keep each pair of motor syncronized, for every drop on a column on a motor, you drop on column on front too. The right detail (an exploded view) shows the piece that is under the table, how the two axis cross with each other allowing independent motion. It could be possible, albeit very cumbersome, to come with a Gantry setup for the motor too. 

Possible applications (end-effectors):

Variation #1: Attach two independent springs on each side of the floater, inside the tube, that are fixed on the collumn sides, so that it dampens oscillations.

Variation #2: I've considered once that you could use a magnet instead of the floater, and get the motion out on the table via magnetic interation. This would have the added advantage of not having to drill the hole on the PVC pipe. It is a very elegant idea, might I add. The magnet would be kept in place by springs.

Variation #3: Use silica aerogel on the floater (very pro).

Tips Section

If you are feeling brave enough, join me in the Math Section of the Gravitic Motor, were we discuss how far we got into the math of things there.

BANNER IMAGE CREDITS: ESA/Hubble & NASA, A. Filippenko, R. Jansen 

Want to know more about this image? Follow this external link.