The modular marble machine
The marble pumpThis marble machine, like my marble machine 1, uses a marble pump to elevate the marbles. This marble pump is an optimized design to make it easier to build.
The pump takes marbles fed into one hole and pushes them up through the other. It's driven by a crankshaft made out of coat hanger wire.
The holes in this marble pump are 11/16" (17 mm would work too). This is an in-between size, not part of most drill bit sets, but you can buy this drill bit separately from places such as Lee Valley Tools, Rockler.com, Woodcraft.com, Amazon.com. I also have a YouTube video showing how to build the marble pump.
This shows the insides of the marble pump. You can see part of the crank on the left edge of the middle block, but it's mostly obscured. The crank moves a piston up and down and side-to-side. The piston is in the middle thicker piece of wood, which forms the slider. The piston is normally fully inside the slider, but I propped it up higher for illustration. The crank moves the piston in a circular motion. The side-to-side motion of the piston slides the slider back and forth, while the piston moves up and down inside the slider.
The crank is just made out of coat hanger wire, with a diameter of about 2.5 millimeters. Bending the right angle bends in the wire is relatively easy. The tricky part is when two bends are very close together. The crank has a "throw" or eccentricity of just over 10 millimeters. A sturdy stubby pair of needle nose pliers proved to be adequate for grabbing the short straight segment that is the crank throw. The photo shows the last bend of the crank being formed.
The crankshaft connects to a hand-crank on the outside of the box. It was tempting to just bend another crank onto the end of the coat hanger wire, but if the wire wasn't straight on the ends, it would become impossible to take the machine apart again.
And the wooden crank looks much nicer. The coat hanger / dowel coupling is achieved by inserting the coat hanger wire into a hole in the end of the dowel. The dowel is also slit at the end, and the bracket around the dowel clamps it firmly onto the wire.
This coupling isn't perfectly rigid, but that is actually a feature. It sort of serves as a slip clutch against overzealous torquing of the crank if the marbles jam. I haven't had this one jam on me yet, but it can happen if it runs out of input marbles, and a marble falls into the hole at the very same instant that the hole starts closing up because the slider is sliding away from the input hole.
Here's the pump in the machine. To the bottom right is the 'feeder ramp'. Any built-up track deposits the marbles into this ramp. The pump takes the marbles from this track and pumps them up the column in the center of the photo. It's a very elegant method of elevating the marbles, running efficiently and with a minimum of space used up. It really doesn't take much force on the crank to lift a stack of 25 marbles.
The marble run blocksOn my other marble machines, the descent paths are fixed. But this machine has no pre-built descent path. The descent path is something that is built when playing with the machine, making this one a highly interactive machine!
The building blocks are to some extent based on the marble run building block set that I built for a nephew. Though with the benefit of experience with the last set, I was able to refine my system.
Like Lego blocks, the entire system of blocks is built around discrete units of width and height. Basic side to side units are 3.2 cm (about 5/4"), and height units are 2 cm (about 25/32"). The elements can all feed into each other, but with a height difference of 2 cm from one ramp to the next. Some units use up a multiple of 2 cm of height. The zigzag ramp, for example, uses 4 cm.
I wanted the blocks to be able to interlock, but at the same time I wanted the blocks to be usable without interlocking. So that ruled out putting Lego-like studs on the tops or bottoms of the blocks. Instead, I opted for holes in both the tops and bottoms of the blocks. To interlock the blocks, a marble is placed in the space between the blocks. This won't lock together the same way as Lego would, but it prevents the blocks from sliding around.
I don't use the interlock all the time, just for certain track elements, especially where the marbles have to go around a corner - after twenty or so marbles, the tracks end up shifting a bit. And with each turn of the crank dropping one marble onto the top of the track, running twenty marbles down the track happens awfully fast. In fact, for elaborate runs, I end up pumping more than ten marbles to the top before the first marble even makes it all the way down.
I spent a bit of time trying to come up with reasonably safe and repeatable methods of making the parts. So I was less interested in trying adventurous table saw plunge cuts. It's OK for me to try stupid and dangerous methods in my workshop, but if I sell plans for a project, I have to make sure such crazy tactics aren't necessary!
Just sandwiching some of the parts together out of layers worked pretty well.
I had to do lots of testing along the way. The whole set is a bit of an engineer's toy. It's one thing to build a run that looks pretty, but making sure the track doesn't 'leak' marbles is a matter of trial and error.
Momentum of marbles is a fun thing, but it can lead to errant bounces out of the tracks.
I made quite a set of blocks - it's easy to get carried away! This image shows most of them, ready for varnishing.
I opted for the spray-gun to varnish the blocks. I find I can get a thicker, smoother coat of varnish with a brush, but with all these little pieces, I figured I'd save the time. The less smooth varnish is actually beneficial in this application because it prevents the blocks from sliding around too easily.
I don't have a spray-booth in my workshop, so spraying is really only an option when the weather is nice.
I took this photo by setting the camera on movie mode on a tripod, and taking a frame from the video afterwards. Looking at the video, I think next time I should turn down the pressure on my spray gun to get a coarser mist. There seems to be an awful lot of overspray! I have only used that spray gun a few times, so I'm still learning.
The building blocks fill up a milk crate nearly to the top if thrown in loosely.
The cool part is though, that all the blocks still fit inside the base. But getting them all to fit is a bit of a puzzle in itself, so that is more something to do when putting the blocks in the closet.
The blocks on the right side in the box are blocks for building up the structure. The block set is all about the ramps, but the ramps and other marble handling elements need to be supported at different heights and positions. So there are a lot of blocks whose sole purpose is to build up the "structure" to support the track segments.
And here's another shot of the configuration from the above video.
I have drawn up some very detailed plans for the machine, pump, and building blocks, along with many photos and explanation on how to construct it. It's a very detailed set of plans. Considering how much you get, I think it's a bargain, but I might be biased :). There's also a free video to help you with the tricky part. I figure, even if you don't want to build the whole machine, it's still worthwhile if you just want plans for the building blocks or the marble pump. But I suspect once you get going, you'll end up building the whole machine.
Some reader built modular marble machines
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