by matthiasm, published

Spider by matthiasm May 9, 2009

Featured Thing!


An eight-legged big spider robot.

The design goal was to create a legged robot that is large enough to walk regular stairs and strong enough to lift simple loads. It also had to be simple enough to use regular RC-srevos and could be cut with my minimal CNC machine.



The build process is documented here:


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3mm HD foamed ABS. But other sheet material would work just as well. The ABS was a bit too bendy and I had to add diagonals in the upper legs for reinforcements. It could probably be built in birch plywood or even HDF/MDF.

how thick is the material used?

This is not meant to be 3d printed. You can cut the pieces on a laser cutter.

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Spider by matthiasm is licensed under the GNU - LGPL license.

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CNC-machined from 3mm ABS foamboard, this thing is pretty impressive once all eight legs are moving. You will also need a lathe to create the axles and a few platic parts, a powerful servo controller for your 24 high-torque servos and a powerfull battery pack.

The dxf files all fit onto A4 (European standard size for paper, a whee longer than "Letter" format) simply because that is about the maximum size my Isel can handle (cute, huh?).

"boden" contains the floor part of the body. The holes in the middle are big enough to let you insert a racing pack style battery through the bottom. The parts that look like skates reinforce the lower axle hold and are inserted into the slot from below. The purple hexagons are only cut half depth and hold the head of the hex screw that makes the axle.

"cross" contains a bunch of cross sections that are glued in an X-shape into each upper leg. These cross section greatly reduce torsion and make walking much easier to calculate.

"joints" are all parts needed to create four hip joints. These are quite hard to build right, so be patient and do a few test builds before finally glueing everything. Again, the purple lines are half-depth and hold a standard ABS disk which serves as counterold to the joint bolt. The small purple circles are for sinking the heads of the screws that go into the servo disk. Remember that you have to build four clockwise and four counterclockwise joints!

"Legs" contains most parts for a single leg (add the cross section from "cross"). The skinny parts again are reinforcements an should be glued to the end of the upper leg (8 per leg).

"Middle" contains the middle section of the robot. The holes next to the servo cutouts are designed for a plastic rivet to hold the servo.

"Poles" contains all - um - stilts would have been a better name - that connect the bottom, middle, and upper section of the body. Careful! Therer are two kinds of pieces, one with a slightly set back cutout to allow full motion in the hip joint. Don't mix these up.

"Ribs" has more parts for the body for enclosing the battery bay and the controller cutot.

"Top" contains the top shell of the body.

All parts should fit tightly. If you find that cutouts and notches are wrong, you must verify your assembly. All these files have been tested and built. Please reference the photos.

You will need additional parts for the axes and servo mounts. And of course, the cutouts were designed for a specific servo, so you'll have to find a servo which is very similar in size. I will try to put more information here soon.

how thick is the material used?

3mm HD foamed ABS. But other sheet material would work just as well. The ABS was a bit too bendy and I had to add diagonals in the upper legs for reinforcements. It could probably be built in birch plywood or even HDF/MDF.

How big is this? the 3D printer I have access to is only 5X5X5

This is not meant to be 3d printed. You can cut the pieces on a laser cutter.

I woulld love to print this. How could I make these files into STL's?

Well, it's meant t be laser-cut from flat material. You can still print it if you take the 2D dxf files and extrude them by 3mm in a 3D program and print that out.

ok thanks!

This is really interesting. One of our 3rd yr student projects is very similar to this. http://www.eee.manchester.ac.uk/undergraduate/courses/projectwork/blogs/Martin/http://www.eee.manchester.ac.u...

Very cool! I am thinking about building something similar for a school project. Thanks for posting this! I bought the ABS yesterday and am making a few tweaks to the design so I can fit some of my servos in. I am also thinking of modifying two of the legs so that they can also be used as manipulators.

Making the thing is easy, making it walk less so. Making it walk and respond to tactile feedback is near impossible.

That's beautiful and very generous of you to share.

I am very seriously considering making this on my school's laser cutter. How much was spent on the motors and electronics?

Awesome. The servos I used were about 12EUR each (you need 8x3=24). The electronics I developed myself and cost about 30EUR. The battery was 20EUR. I had the pewter axles machines for about 0.75EUR each. Plastic disk and rivets, screws etc will probably cost another 20EUR.

There are a lot of places where I cut only 50% of the material. Something you cannot do with a laser cutter. The parts will still fit, but you shoudl verify that the axle sockets still work as planned and update the CNC files accordingly. You will also find a bunch of 2mm arcs in the cutouts. These would not be needed for a laser cutout, but they are not harmful either.

Good luck, hav fun, and feel free to contact me if there are any questions.

I'd love to make one of these! I was curious; Would you happen to have these files available in EPS format? The application I use for my router tends to change the physical size of the files, and I need something to reference by. If not, its all good. Ill make it work :D

-- Sorry, it changes the size of DXF formatted files

How strong of servos do you need for this design to work well? I imagine it would not work well with low-torque servos.

12 kg cm is recommended. My servos have 10 kg cm and just do it.

This is so awesome! A must-build!

Impressive! I'd really like to build something based on this design. And by the way: what is "foamed pcb" and where do you buy it?

Um, I meant ABS. Tsk, tsk.

Ah, thanks. The cuts are neat with impressive laser-cutter-like sharp corners. What kind of bit did you use, and did you cut the whole design with the same size bit??

I used a 2mm bit for the whole thing with two cutting edges at a 6000 rpm and slow advance (lame router...).