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Roger's Connection®

Magnetically Suspended Spinning Designs!

A Simple Hand-Held Example

In addition to being able to build static designs, Roger's Connection enables you to construct designs with freely moving parts. This is achieved by using a type of magnetic bearing to magnetically suspend smaller spinning structures inside larger ones! The friction of these bearings is so low, that it is mainly air resistance that finally brings the spinning designs to a stop, often after many minutes.

As mentioned earlier in the section called "An Important Roger's Connection secret - North and South", it was discussed how each magnetic tube has a north and a south end, and how this usually isn't something that you need to be concerned with when you are building. However when designing and building magnetically suspended designs, the consideration of north and south polarities becomes very important. Here is a simple example of a magnetically suspended tetrahedron that will start you on your way in the world of kinetic Roger's Connection designs. After building this simple hand-held design, the next section on this page will show you how to build a self-contained moving design that you don't have to hold.

To begin, build a tetrahedron as described earlier. But this time, make sure that the three tube-ends that are connected to the top ball are of the SAME polarity. It doesn't matter if they are all north poles, or all south poles, only that they are the same. It's simple to do. Begin by constructing the bottom triangle - the north/south polarities of the bottom triangle are not important. Next, take three magnetic rods, and connect them together as shown here. If two ends are repelling, then just turn one of the rods around and use the other end. The other end will attract, because each individual tube always has a north and a south end.

Hold the three connected rods vertically in one hand, and pull off one tube at a time, from the top, reconnecting the end that's pointing down, to one of the three balls of the triangle. Repeat this two more times with the remaining rods, pulling off the top tube and connecting the bottom of that tube to one of the connector balls. Finally, attach the top connector ball to complete the tetrahedron. In this way, you have ensured that all of the tube ends at the top have the same polarity. To complete your first magnetic bearing, take a new tube, and put a connector ball on each end. Now, find out which of the two ends attracts the top ball of the tetrahedron. You will find that one end will not attract well, or at all, and that the other end will attract strongly. You will then find that you can pick up the tetrahedron with the new tube you just attached. What you have just accomplished is to align the polarities of the rods in one of the two ways shown here. It doesn't really matter which of the two you have made - they both work as well.

Now hold the separate top tube vertically, and spin the suspended tetrahedron as shown here! Congratulations! You have just constructed your first magnetic bearing! And you can be sure that you are one of only a few people in the entire world who has ever done this!

As an experiment, try connecting the tube and ball that you were holding, to one of the other balls of the tetrahedron. You will find that the usually mixed combination of north and south poles on the other balls will result in a weak (if any) connection, or possibly even a repulsion. Finally, note that the tube that you were holding doesn't really need the second ball that is facing away from the tetrahedron, it was just easier to describe it that way so that you could try both ends to see which one would work.

There are many other kinds of magnetic bearings that are used in science and industry, which are usually much more complicated than this one. Often, they use electromagnets that are controlled by special electronic circuits, and sometimes they use superconducting electromagnets. Such magnetic bearing can often bear great mechanical loads, and sustain high speeds of rotation. Even though the magnetic bearing that you have just made here is very simple by comparison, it is still fairly strong, and demonstrates the principle of a very low friction moving connection.

When your spinning tetrahedron finally slows to a stop after many minutes (if you hold it that long!), it will mainly be due to air resistance against the rods and connector balls, and not because of the very tiny amount of friction between the two touching connector balls in the magnetic bearing. Other small influences that will tend to slow the tetrahedron down are the interaction of the magnets in the rods with the Earth's magnetic field, and tiny electrical currents that are induced in the top fixed ball by the moving magnets below. These tiny currents create their own magnetic field which partially opposes the fields of the moving magnets below. There are many subtle phenomena occurring in this simple little arrangement!

A Self-Supporting Spinning Design
That You Don't Have To Hold!

In the last design, you had to hold it up in the air for it to work. That's a nice beginning, but you can only hold it up for so long. Wouldn't it be nice if you could suspend the tetrahedron from inside a larger structure, so that you wouldn't have to hold it? Well you can, if you have the thirty tube set. There aren't enough rods in the Roger's Connection Junior set to accomplish this. Here is what the new design looks like.

You will be suspending your small spinning tetrahedron inside a much larger one! The long rods of the large tetrahedron are made from several individual rods as described in the section "Combining two or more rods for greater length". Using the principles described in the previous section for the hand-held design, you can attempt this new design on your own, or follow the steps below. If you try to go it alone, there are four secrets that you'll need to know:

  1. The three tube-ends of the larger outer tetrahedron that join at the top ball must all be the same polarity. That's a little tricky since you will also be using the longer joined rods.

  2. Not only must the three tube-ends described above have the same polarity, but they must have the opposite polarity of the three tube-ends that come together at the top of the small inner tetrahedron. (As before, the three tube-ends at the top of the small tetrahedron must be the same as well.)

  3. In the large outer tetrahedron, the base triangle uses four rods in each of the three sides. However in the long combined rods that connect from the base triangle up to the top ball of the large outer tetrahedron, only three rods are used in each one. The reason for this is so that the sides of the large outer tetrahedron are steeper, to allow the small inner tetrahedron to spin without hitting the rods of the large tetrahedron.

  4. There is a final important secret! Instead of connecting the small tetrahedron directly to the top ball of the large tetrahedron, insert a single additional ball between them - so that you have: the top ball of the large tetrahedron, connected directly to another ball below it, connected directly to the top ball of the small tetrahedron. The extra ball allows extra clearance so that the small tetrahedron has as much free space to spin as possible. To be clear, the middle of these three connector balls is only connected to a ball below, and to a ball above, but not directly to any rods.

Since the combined rods are not as strong as single rods, you will have to be a little extra careful when constructing and spinning this design, so that it doesn't come tumbling down - although everyone who builds these, including the inventor of Roger's Connection, has had many tumbling experiences! So be patient and careful, and you will be successful!

Here are the exact steps to use to make the tetrahedron-within-a-tetrahedron spinner, keeping in mind the information above. Note that the rods shown in the following illustration all have a dot on one of their ends. This dot is intended to show the polarity of the rods. It doesn't matter whether the dot end is north or south, only that they are all the same.

  1. Build the small tetrahedron described in the previous section, "A Simple Hand-Held Example", and set it aside. Be sure that the polarities are correct.

  2. Create the triangular base, using three connector balls, and long combined rods of four rods per side. The north/south polarity in this base triangle is not important, although it will be stronger if the polarities shown below are used.

  3. Create one long combined tube using nine separate rods. It's easiest to lay it out flat, instead of holding it up in the air. You won't actually be using a nine section tube, this is just a way of getting all of the polarities lined up properly for the remaining steps. These rods will be used for the three upper lengths of the large tetrahedron.

  4. Lay out the combined nine-section tube in front of you, left to right. Next, you will need to determine which end (the end to your left, or the end to your right) will be pointing upwards in the large tetrahedron. The end which will be pointing upwards, will be the one that attracts the upward pointing ends of the rods of the small tetrahedron that you built in step (1) above. Move your small tetrahedron to either end of the long nine-section tube, and see which end is attracted to the top end of the rods of the small tetrahedron. Before you do this test, temporarily remove the top ball from the small tetrahedron. If this isn't done, you will find that either end of the nine foot section will be attracted to the ball, and that isn't what we are trying to determine here.

  5. Once you have determined which side attracts (is magnetically opposite) to the top of the small tetrahedron, adjust the nine-segment tube, if necessary, so that the attracting side is now on your right. That will make the following descriptions easier.

  6. Now remove a three-tube section from the right side of the nine-tube section, and attach it to one of the connector balls in the large base triangle, so that the end that was on your left (in the nine-tube section), is now the end that is attached to the ball. Repeat this step in exactly the same way for the two remaining connector balls in the large base triangle. Although the illustration below shows the new sections pointing upwards, you may leave them lying flat on your work surface until you are ready to connect their other ends in the next step.

  7. Connect the free ends of the three, three-section rods with a connector ball as shown below. It's a little tricky holding this all together without the sides collapsing as you assemble them, but it gets easier with practice.

  8. Do not attach the small tetrahedron yet! First, connect an additional separate connector ball to the bottom of the ball at the top of the large tetrahedron. This will provide some additional clearance for the small tetrahedron. The small tetrahedron will be able to magnetically attach to this extra ball, even though it isn't directly connected to a magnet..

  9. And finally, attach the small tetrahedron to the extra ball you just connected in step (8) above. This step is extra-delicate, as the extra weight will tend to cause the sides to buckle. (Before connecting the small tetrahedron, you may wish to check that the rods in the three-section sides of the large tetrahedron are well aligned, with none of the rods off-center with respect to the next tube.) Now give the small tetrahedron a gentle push from the bottom, and watch it go! In this step, extra care is required to keep the whole structure from collapsing, so be gentle. Congratulations! You are one of only a few people in the entire world who has ever constructed this amazing design! At this point, many people want to see how fast they can get the small tetrahedron to spin. The trick is to apply enough force to achieve a good speed, but not so much that the entire structure collapses from the initial push. Good luck!

Are you having difficulties? Here are some common reasons:

  1. The number of rods in the sides, and in the base of the large tetrahedron should be different. The long base rods should be made of four single rods each, while the long side rods (the ones that connect at the top) should be made of three single rods each.

  2. The extra ball described in step (8) above, is almost essential. Is it missing?

  3. Are the polarities mixed up? Here's a review. The three tube-ends at the top of the small tetrahedron should be the same. The three tube-ends at the top of the large tetrahedron should also be the same. But, each of these two sets should be different from one another.

Much fancier "spinner" designs are possible using additional parts beyond the basic set. Here is one such design. It features a spinning tetrahedral dipyramid (simply two tetrahedra with a shared face) inside of an icosahedron. The octahedron is connected by a magnetic bearing both at the top and at the bottom. The outer icosahedron sits on five tetrahedral legs attached to the bottom of the octahedron. This design is a little reminiscent of an old-style rotating pendulum clock. This design uses 54 magnetic rods, and therefore requires two regular-sized Roger's Connection sets for its construction.

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