The Flying Marbellos

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		Click!…Whirrr…Hummm…Bang! These are the sounds of “The Flying Marbellos”: a rolling ball sculpture with marbles and small metal “bugs” to run the show. The purpose of a rolling ball sculpture (RBS) is to transport balls to the top of a system of tracks, where they proceed to find different and amusing paths on the way down. Is this a silly thing to do? Yes! Do people love to watch these things for long periods of time? Yes! Put an RBS in a public place and you can attract a crowd surrounding it. I love watching mechanical things, but building this turned out to be even more fun. Since I have a fascination for mechanical things, and also enjoy working with Basic Stamp microcontrollers, this 6 1/2 foot tall RBS finds some different ways of going up with the balls as well as going down. It all starts with a motor that elevates the marbles to the top, and as they roll down they encounter switches that change paths with every marble. The insects and spiders add a circus flair to the whole thing. A helicopter carries one marble from a low platform to a higher one so that it can begin another journey down. An elevator carries another marble to the top, sends it to drop through the air to a pad where it bounces up and into a basket. One marble lands into the muzzle of a cannon, where a bug lights a torch, leans over and lights the cannon’s fuse, and then the cannon fires the marble into the basket. Two marbles at once go down into a tube, where 90 LED lights follow the marbles, cascading in sequence down the tube. Others follow turns, loops and spirals, jump from a ski jump and ring bells on their way down.
The Flying Marbellos (click to enlarge)

 Gravity makes the marbles come down the tracks, and 3 Basic Stamp microcontrollers help with the 21 switches, four stepper motors, one servo and 92+ LED’s. I chose Basic Stamps because they are so easy to use. Their online manuals and resources gave me plenty of information to learn to work with them, without my being an engineer. Coordinating the motors and moving parts required many changes of the program to get the right “look” and the right smoothness. With the Stamps it was easy to make changes and evaluate their effects.

Helicopter schematic diagram

The Helicopter One of the big stars of the show (and certainly the biggest challenge) is the helicopter. When a ball rolls into the cockpit of the helicopter, it flies by means of fishing line leading to a trolley above. One stepper motor, for the “X” (horizontal) direction of travel, pulls the trolley on a track across the top of the machine. Another stepper motor raises the copter (the “Y”, or vertical direction), so that when the two motors work together they lead it on an arc to the upper platform. As the trolley travels from one side to the other, it also rotates the copter, so that at the top it is facing 90° from where it started.

The trolley is made of pieces of brass soldered together, with 6 bearings to ride the rail: two on top and two each on front and back. I tried making this trolley with a brass sleeve to ride the rail (as I did the elevator and rescue device), but there was too much friction. The helicopter rotation arm puts the center of weight off center from the rail, and the ball bearings are needed to make it travel smoothly enough.

The “X” motor also connects to a potentiometer, so that I can measure the position of the trolley with a Stamp. This is only for cases where power is lost, so that when power is restored the copter can find its way back home. Otherwise, it is almost sure to crash when the power goes on. One way the power can go off is when someone thinks that the way to turn off electrical things is to unplug them (been there, done that). To ensure that this can’t happen during normal operation (turning it off with the switch), a relay holds the power on to the stamps and motors until the copter lands. The spot lights and ball-lift motor turn off, but the helicopter finishes its journey before all shuts off. This feature was disabled during most of the development of this project, when I wanted the copter to stop if I switched it off.

Limit switches tell me if the copter is at the ends of travel in the “X” direction, and if it is landed at its home landing pad. I did not use a limit switch at the upper landing, and instead used the precision of the stepper motors counting steps to determine the final position at the top landing. This works just fine, but if I had it to do again I would have a switch there, too, as it would make programming the flight path much easier. Another switch detects if a ball has loaded into the helicopter. Leverage is needed to convert the tiny movement of a microswitch into a larger movement that a marble can easily trigger.

The flight path of the helicopter can be calculated and worked out before ever flying it, but it turns out that doesn’t help much. One needs to see it working to evaluate the speed and smoothness of the movements. You can get an idea by turning the winches by hand and counting the turns. Make an educated guess, and watch it fly. It becomes immediately obvious how to tweak the numbers to get on the right path. Getting it close is not too tough. Getting it just right is an art. The easy reprogrammability of the Basic Stamp comes to the rescue.

The stamp controlling the “Y” direction also controls the rescue device. When it is involved in a rescue, it signals the “X” stamp that it is busy, so that both stamps will be able to start together when flying the copter. The “X” stamp tells the “Y” stamp to start, but will not tell it until the “Y” stamp no longer gives a busy signal. If one motor is trying to fly the copter while the other one is unavailable, all kinds of bad flying can happen.

I also made a hidden test button, which could be used to start partial flights. A quick push gives one flight path, and a longer push gives a different path. This was really useful when programming the flight path. In the final version, I use it to fly the copter only one way: to land on the top and stay there, which is useful for transporting the RBS.

When the helicopter lands at its temporary upper landing or at its home landing pad, there is some sway to it. Since it is important that it land predictably in the right place, there are guide rails to assist it. At the base of the copter is a “V” shaped guide rail on each side, and the bottom skids of the copter also assist in guiding. On the landing pads are vertical rails that guide it into position, one at the top pad and three at the bottom. They are made of 1/16” brass rod, and painted black to make them inconspicuous.

The elevator is attached to a slide that rides on the same kind of rail (rectangular brass rod) as the helicopter. The slide is soldered together out of pieces of brass. On one side some pieces of .003” brass shim are soldered in to give clearance. The whole thing is clamped together with it around the rail and another piece of shim. Then the rail and one shim are slid out, and it is soldered. It is important that the solder is flowed in from the outside, and in sparing quantities so that it doesn’t get inside of the slide. This gives a slide that is .003” bigger than the rail. When the motor lifts from the center of gravity of the elevator, and two coats of car paste wax are on the rail, it slides up and down easily.

The Rescue Device The rescue device uses the same type of rail and slide, only this time the slide holds still, and the rail moves (Figure 10). A slower speed allows a smaller winch diameter, and the stepper motor is strong enough to operate it all without a counterweight. Limit switches detect when the device is at the bottom, and when it is loaded with a marble. I didn’t feel a switch was needed at the top of travel, since the number of steps that the motor makes can govern this quite well. It just needs to start from the lowered position. It is then possible to finely tune the height when it is raised by changing the program on the stamp.     Movie 3.8Mb

Cannon Mechanism.

The cannon is “lit” by a circus clown bug. He holds an LED “match” in his hand. The match lights, and he leans over to light the LED “fuse”. As he leans over, he extends his match arm to light the fuse, kicks a back leg into the air, and turns his head 90° toward the cannon. A servomotor moves it all. The bug’s body movements are managed by the front of the bug rotating on a different axis than the back half of the bug. When he leans over, the relative motions of the two halves can make the arm, leg and head move. This part of the project made me feel like a watchmaker. Do you think Mr. Rolex ever played with servos, LED’s and bugs? Maybe not, but then he probably had all of his marbles.

Clown mechanism

Servos need to be on a separate power supply than the Basic Stamps. The servos draw a bit of power, and cause the voltage to drop enough to “brown out” the supply, which would cause a stamp on the same supply to reset.

The LED Cascade

Ten circular rows of 9 (5mm) LED’s surround a tube through which two marbles travel. The lights follow the path of the marbles as the go down the inside of the tube. Actually, the first marble hits a microswitch before it gets to the tube, and the lights follow a predetermined sequence that appears to follow the balls. The mechanical marble switch that precedes this lets go of two marbles at once (Figure 13). A marble separating mechanism is needed so that the two marbles are not right next to each other, to get the effect that I wanted. A tight spiral inside the tube makes the marbles go down the tube more slowly as they spin their way down.     Movie 1.7Mb

Track can be bent by hand, pliers and vise. A wonderful bending jig can be purchased at Micro-Mark. Flower pots make good round forms in varying diameters for bending the rod. A great idea I learned a little too late for this RBS: fill a big traffic cone with cement. When it hardens you have a heavy, stable place to bend many different diameter curves. All methods are useful, as each situation may require a different bending technique.

The tracks need to be banked so that a marble going around a curve does not fall (or fly) off. This is directly affected by the weight of the marble and the speed it is going when it hits the curve. The weight should be controlled by marble selection. The consistency of weight is more critical if the marbles bounce, leap, or get shot from a cannon. Buy 100 marbles, weigh them, and sort them into piles. See what weight range has the most marbles, and with luck there will be 20 marbles that are within 0.2 grams of each other. Use these “official” marbles to operate the RBS. Now save a slightly heavier and a slightly lighter marble for testing. An official marble may negotiate a curve almost every time, but the lighter and heavier ones find the curves that are banked almost right, and help you figure out whether they need more or less bank. Test each foot or two of track as you make it, as it is a lot easier to change the angle of bank before too much track comes after it. The track spacing affects the speed: wider makes the marble roll slower, and makes banking less critical. Narrower spacing makes the marble roll faster, but the angle of bank on the curves is more critical, and it is easier for the marble to leave the track. I used 15/16” diameter marbles (they are listed as 1”), and the inside distance between tracks is 3/4”. It is a good idea to have selected the marbles before making the tracks.

Brazing is very easy to do, using an oxy-acetylene torch and brass brazing rod. It is similar to soldering, but is very strong and not as watery when melted. It is easy to make joints that are smooth and nice-looking. Use plenty of flux, made into a paste and applied with a little brush. . I use Harris Stay-Silv White Brazing Flux. After the joint is made, the flux will be very difficult to remove. Just scrape off the part that the marble touches, and leave the rest there. After a week or two this flux will have picked up moisture from the air and softened, and a wire brush in an electric drill will remove it fairly easily. The wire brush will seem to barely affect it if it is used too soon after the joint is made.

Many times only a few places need to be brazed, so that those joints can hold things in place while the next joints are made. A handy timesaver is a “gas saver”. It gives you a hook to hang your torch, where the weight of the torch causes some valves to turn off the torch. A tiny pilot light stays lit. When you need the torch you pick it up, pass it across the pilot flame, and go. The settings that control the flame are just the way you left them, and you save a lot of time in turning on valves, lighting the torch, and adjusting the flame.

The main frame around the whole thing is made from welded 3/4 “square steel tube, with ½” square struts. Welding is not as easy as brazing, but with a grinder and some Bondo and some paint, even my amateur welds look fine. After everything is made, remove the flux, and lightly sand it. A sandblaster would be perfect if you have access to one. Then spray paint the whole thing with a darker background color, and then brush paint just the tracks with a lighter, brighter color. The paint on the tracks holds up pretty well. It will wear off of some very small and narrow areas, but the overall “look” is still there. After it is painted, the tracks are waxed with automotive paste wax.

The bounce pad is made from a slice out of the center of a Superball®. (How to slice a superball here) The ball is made of some of the bounciest stuff invented by man, and they call it Zectron. Dr. Seuss couldn’t have picked a better name. I embedded the ball in plaster inside a small wooden box. Brass nails stick out of the ball in areas that will avoid the path of the saw. The plaster grips the nails, which hold on to the ball as it is cut. The box, plaster and ball are all cut together into slices with a table saw. When the pieces are disassembled, a nice 7/16” thick pad of Zectron is what remains.

The pad is mounted on a 1/2” thick disk of steel plate. Thinner steel does not work so well, as the heavy mass of the steel is needed under the Superball for a good bounce. The steel disk rests on machine screws that fit loosely into holes in the underside of the disk. These screws can be adjusted to “aim” the plate and direct the bounced ball into the basket. Another machine screw is threaded into the bottom of the disk to hold it down. A plastic rim circling the pad is screwed to the steel disk and holds the pad in place, assisted by epoxy glue.

Metalworking

One of the useful tools for the mechanical parts is a lathe. I used a small and relatively inexpensive Sherline lathe, which did the job well. One thing the lathe can do is drill a hole into the center of a turning piece. If the work turns and the drill holds still, the drill automatically wants to go into the center. The lathe can accurately enlarge holes in gears or sprockets to accommodate a shaft. Bushings can be made to make a large hole fit on a small shaft. Freehand turning of insect parts, pulleys or the important plumb bob is enjoyable.

Almost everywhere there is a rotating part I used ball bearings. A pulley is made so that the inside diameter of the pulley is .001” smaller than the outside diameter of the bearing. The two are pressed together, and they stay together. A lathe will also cut brass tubing precisely, so that spacers and bushings can be made. Several sizes of telescoping brass tubing came in handy for making everything fit together. A center drill is perfect for starting holes. It is a tiny, short drill on the end of a much thicker shaft. This keeps the point from bending to the side, and allows for accurate hole positioning. With a center drill, a drill press and decent eyesight it is possible to get holes within .006” of where you want them.

The bugs were made of copper and brass. Sheet copper can be worked by annealing: heating it red hot, and then quenching it in water. It is worked by pounding it with a rubber mallet over a metal or wood form, or a metal hammer against a plastic or rubber form. As the copper is worked, it gets work hardened. Anneal it again, and then work it some more. It sometimes takes 8-10 times of annealing and working it to get to the shape you want. Brass is annealed by heating it red hot, and then allowing it to cool slowly on the bench. When the shaping is done, the piece can be pickled for 5 minutes in a 10% solution of sulfuric acid to remove the oxidation. Fine steel wool gives a nice appearance after that. Pumice on a wet rag wheel gives another nice finish, and Tripoli metal polish on a dry rag wheel will make it very shiny. Gold rouge will make it into a mirror finish.

The pieces are soldered using 96/4 tin/silver “silver bearing solder”. It comes from the hardware store in thick wire form. I pound it flat with a clean hammer against clean steel, and then cut it in half lengthwise with tin snips. Cut it and split it again until there are pieces 1/4, 1/8, and 1/16 the size of the original wire. The pieces to be soldered are cleaned with fine steel wool and painted liberally with “LA-CO Regular Soldering Flux Paste”, the stuff plumbers use. After the pieces are clamped or held into place, the solder is cut into tiny pieces and set right next to the joint to be soldered.

The trick is to heat the pieces to be soldered with a propane torch, without allowing the torch to directly heat the solder or the flux. The flux burns at only a slightly higher temperature than the solder melts. If the piece is heated too long or too hot, or the flame spends too much time on the flux then the flux will burn. Heat the work slowly, moving the flame so that everything heats evenly. Sometimes you touch just the very edge of the side of the flame to the work. When everything is hot enough, the solder melts and flows right into the joint. If the flux burns and turns brown or black, the solder will never flow.  The only solution is to take it all apart, clean it again and start over. If the flame is too big to heat the pieces without getting the flame on the joint, then a smaller flame is needed. There are some refillable butane torches that have a very tiny flame.

Heat shielding compound is reusable clay that can hold a soldered part in place while you solder another part right next to it. It can also be used to hold parts in position for soldering. As it heats up it gets hard, and also keeps too much heat from getting to the parts that it protects. When done, spray it with some distilled water and put it in a jar, and it can later be used over and over.

Why RBS?

This was a truly fun project to build. Getting each stage working was a challenge, and was satisfying to see it work the way I wanted it to. In a public place, people love to watch these kinetic art machines, and sometimes there are crowds that can accumulate. I heard complaints that sometimes a person could not get close enough to see what was happening. “The Flying Marbellos” won “Overall Best of Show” at the Solano County Fair, and "Award of Excellence" at the California State Fair. It is on display in my office waiting room, along with my musical water fountain “H-2-Opus” (Nuts and Volts, June 2003).

Biography

Victor Chaney is a dentist in Vallejo, CA. His college bachelor’s degree is in Physics, and his electronics education is mostly self-taught. He has learned it from books, magazines and the Internet.

Parts:

1. Stepper motor, 12V, 200 steps, Jameco Reliapro mfg. #42BYG228, Jameco #155432

2. Triac 10A, 200V mfg. #SC146B, Jameco #31819

3. Triac Driver NTE3048, Jameco #273471

4. Solenoid, 120VAC, Dormeyer #7014, Grainger #2X661

5. Ball bearings for helicopter, .125” ID, .25” OD, McMaster # 57155K63

6. Roller Chain #41, ½” pitch, McMaster # 6280K492

7. Gearmotor 120VAC, 10 rpm, McMaster #6142K54

8. Gas-Saver, McMaster #7948A11

9. Universal Bender, Micro-Mark #82819

Sources:

1. McMaster-Carr is a great source for brass, steel balls, tools, gears, chain, bearings.

2. Jameco Electronics has electronic parts, steppers.

3. Parallax, Inc. is the originator of  Basic Stamps and tons of free information on how to use them.

4. ServoCity: servomotors, linkages.

5. Sherline lathes

6. Little Works of Art Marbles:  incredible selection of marbles.

7. Rolling Ball Sculpture Forum: a discussion group where you can get help and search for information.

8. Small Parts, Inc. is where you find heat shielding compound, and other useful things.

9. Micro-Mark: telescoping brass tubing, Universal Bender.

This is taken from an article I wrote for Nuts and Volts Magazine, and it appeared as the cover story in the December, 2005 issue. It is reprinted by permission of T & L Publications, Inc. Note that there is updated information.

RBS Construction goes to pages of more construction details

Programming: zip file that includes Basic Stamp programs for operating everything, and how the pins of the Basic Stamp are hooked up. The .bs2 and .bsp files are programs written in Pbasic, and are readable as text files with any program that can read text, like Notepad or Word. The comments in these files also contain information as to how it all works. Parallax has a free editor that makes reading these files easy, in color, with a wonderful help system.

Movies:

Helicopter (5.4mb) The flight of the helicopter from bottom to top.

Bounce (1.9mb) A marble leaves the elevator and bounces off the superball pad into the basket.

Cannon (5.4mb) Watch the marble travel down the spiral , load into the cannon, where a bug lights the cannon which shoots the marble.

Short Cannon (2.7mb) shorter version of above, less challenging to the bandwidth.

Elevator (4.6mb)  The journey down to the elevator.

Cascade (1.7mb) Into the cascade of LED lights.

Rescue (3.8mb) A wayward ball, which has left the track, gets placed back on track by the rescue device.

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