Hacking the ShopBot (3 Hacks)

People wonder what it is exactly that I do for ShopBot, and it’s actually kind of hard to explain. Officially I work part-time doing “special projects”, but it really boils down to about 50% “real work” and 50% play (some would say 5% real work and 95% play!). One of the things I enjoy most of all is building all kinds of machines and mechanisms that are powered by stepper motors and controlled by the ShopBot software, and I figured that y’all might be interested in seeing some of these toys and prototypes.

First, let me make one thing clear right up front. None of these projects are original to me…they were inspired by things I’ve seen or read about. I just thought they were neat and, usually after a lot of head-scratching and false starts, got them to do MOSTLY what I wanted them to do. The reason they worked as well as they do is because they rely on exactly what a ShopBot and the ShopBot software does well… move “something” around very precisely and let you interact with that “something” in a lot of ways. It’s just a matter of figuring out WHAT you want to move, and HOW you need to interact with it. Here’s a sampling of some of the projects that I’ve been playing with. If you get interested in playing around with this sort of thing or just want to see what some REALLY creative people do with robots, check out the ArtBots show in New York.bchack1

A ShopBot “Drawing Board”bchack3So on to the neat stuff. The first mechanism was inspired by a chain-driven graffiti machine named Hektor. If you read about Hektor one of the first things you’ll notice is that creating Hektor was a pretty complicated procedure that involved creating circuit boards and a lot of programming to basically just make 2 stepper motor go back and forth and turn an output switch on and off. Hey, wait a minute, the ShopBot software does that already!

I sent the link to Hektor to Ted at ShopBot and he dug through the ShopBot parts bin and came up with some old stepper motors, aluminum plates from belt-drive gearboxes, some hardware and beaded chain from the old cable drive days, and some small solenoids to build into a prototype. The geometry for creating the toolpath was a little funky because of the way that the position of the pen is defined by the length of the 2 chains instead of the standard x/y coordinate system, but a little bit of high school math made it pretty easy to create a “shopbot-to-chain drive” convertor. A couple of different versions were built, including a 4’x8’ version and a smaller one that writes on 12”x18” paper.

The reason I like the “ShopBot drawing board” so much is that, because there’s always a little bit of vibration in the chains, it’s drawings look much more like they’re “hand drawn” than anything that’s done on a printer or plotter. It’s great for doing signs and illustrations and generally just playing around with designs.

[See a video of the drawing board in action.]


A ShopBot “Egg Plotter”bchack5

The next thing that caught my eye was a small “indexer” type machine that was used in Bruce Shapiro’s “Bits to Bytes to Bots” classes. Bruce has some VERY neat things on his The art of motion control web site, but the thing that caught my attention was his “egg plotter” that lets you draw or write on an egg or other round-ish object. Like the chain drive drawing machine it uses just 2 stepper motors and a solenoid that’s triggered by one of the output switches, but in the egg plotter the movements are rotational rather than linear. One stepper motor rotates the egg and is driven by the Y-axis channel while the second motor moves the pen from side to side and is driven by the X-axis channel. It’s very similar to the way that you can “wrap” a ShopBot file around a cylinder when you’re using an indexer. The unit values for the 2 axis’ depend on the circumference of the egg, so each egg has to be measured pretty accurately for the file to work out correctly. A solenoid at the top of the pen holder (the PVC tube sticking up in the picture above) lifts the pen and is triggered by one of the output switches.bchack6Now I know you’re asking “What good is it to be ale to write on an egg? What can you do with it?”. To be honest with you I wasn’t sure what the answer to this question was myself (other than it was just fun to play with!), until the Physics teacher at our local high school contacted me about doing some trophies for his annual “egg challenge” project. The egg plotter turned out to be just the thing, and here’s a picture of the trophies that I came up with. They’re drawn on real eggs with the “insides” blown out, and painted with gold, silver, and bronze spray paint. [See a video of the egg plotter in action.]


5-axis motion

bchack8One of the potentially neatest features of the new ShopBot software is that you can now move 5 axis’ at the same time. It seemed like a fun thing to play with so I decided to put together a 5-axis movement system for the Benchtop in the shop. I wasn’t confident enough in my programming to actually make it cut anything, and 5-axis software is AWFULLY expensive, so the next best thing was to move a camera around…one of those USB eyeball cameras turned out to be the perfect size for the job.

All the parts for the mechanism were cut on the benchtop except for a couple of aluminum couplings that had to be machined (just the excuse I needed to buy a little metal-working lathe!) to connect the 2 extra motors to the plywood parts. Three ball-bearing material handling rollers act as bearings for the A axis, but the rest of the parts are simple hardware-store bolts and bushings. A piece of PVC pipe fits nicely into the router mount on the benchtop, so even though it’s z-axis travel is limited a bit, it’s easy to remove the router and pop this unit in.

Software to control it has been the biggest problem. So far I’ve only been able to program it’s motion by drawing the camera path in 3d in CAD and creating a toolpath, drawing lines along that path that point to the object that I want it to look at, and then using the properties of these lines to manually add the 4th and 5th axis coordinates to the 3d file. Very time consuming and doesn’t give the smoothest motion.

youTube Video:

5-axis camera motion

Sorry about the quality of the video…those cameras have manual focus so I couldn’t keep it in focus all the time.

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