Klann LEGO Spider v1.0
by MkMan, published
The Klann Lego Spider is a LEGO compatible prototype of the Klann linkage (see http://www.mechanicalspider.com).
Update to v1.1 at: http://tinyurl.com/y8lhcr3
The legs for the vehicle were milled from 3/8" plastic sheet stock. All the rest of the components are from LEGO Mindstorms (see http://tinyurl.com/6nj6w), which we use to introduce first year students to robotic concepts.
The project evolved somewhat during the build, as can be seen in the videos and pictures. The turning video shows a simple timed turn where the vehicle moves forward for five seconds, reverses the direction of the left legs for five seconds, then moves both sides forward again for five seconds. The forward motion video shows a skinny version of the vehicle that had to be widened when turning was added, since the skinny version simply fell over on its side instead of making a turn.
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The following are notes on methodology rather than an instruction set:
In order to derive the precise locations for each of the axles, I used Klann's U.S. Patent application US 6,478,314 (see http://tinyurl.com/klannpat), particularly Figure 1 and Table 1. I converted the published figures to provide approximately a 3 inch stride, which would make for a large, but not unmanageable LEGO vehicle.
In this prototype, 3/8" HDPE sheet stock (see http://tinyurl.com/yzrqdct) was the preferred material, although I experimented with several plastics. You can distinguish the three ABS legs by their yellowish hue and by the distinctive burning plastic smell when milled. I attempted to use LDPE as well, but it ate an endmill immediately and was abandoned.
I experimented with face milling the material to the thickness of LEGO pieces (0.308 in.) but realized that for this prototype, keeping the stock 3/8" (0.375 in.) was acceptable. LEGO axle holes are 0.180" diameter, 0.314" between horizontal centers and 0.376" between vertical centers.
The material was held atop a 1" block of HDPE for milling. It was important to drill first, then mill, as at times the plastic flexed enough that the smaller parts were milled out entirely rather than being held by the 0.010" that was left in the depth cut. I learned that the hard way and the resulting foot had to be drilled on a press, which produced enough error in the linkage distances that it causes significantly more friction, which caused the foot on the back left of the vehicle to bind at the end of the turning video.
I've included the Mastercam files used to mill out the legs. File ks100.mcx includes the attachment plate and ks101.mcx does not, since you only need one plate per set of feet. The corresponding .stl files are output from Mastercam, so your mileage may vary. The ks100.dxf file is a conversion of ks100.mcx and ks102.dxf displays each of the parts with its corresponding dimensions to facilitate manual scaling.
In the initial stages, shown by the leg assembly pictures, I was able to use LEGO snap in pieces in each of the linkage points, but once the vehicle was assembled, due to the weight and strain on the joints, I had to replace them with LEGO axles.