Engineering Projects/StrandBeest/Howard Community College/spring2012/p3550cf/crankandframetutorial

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Building the StrandBeest: The Tutorial

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This is the third tutorial in a series of 3 that will allow you to build a strandBeest. 
Please take a look at the previous tutorials to familiarize yourself with the process.
The first is a lesson in cutting the parts on a CNC router.
CNC Tutorial
The second tutorial covers building the leg assemblies.
Leg Assembly Tutorial
Now that you have learned the first steps you can continue with this tutorial to complete the build.

Gathering the Parts and Tools

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The first step is to assemble the tools and all the parts in one place. You will need:

All the tools for the build


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  1. A drill
  2. a 1/2 inch drill bit
  3. a 3/4 inch drill bit
  4. Wood Glue
  5. some clamps to hold parts while glue dries


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  1. 3 3-foot 1/2 inch wooden dowels
  2. 1 3/4 inch wooden dowel
  3. the 6 complete leg sets from your previous build
  4. 2 3 foot by 4 foot pieces of .25 inch masonite

Preparing the Parts

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  • Use the masonite to cut out 16 (4 extra) circles on the CNC machine as in the first tutorial. The drawing this time will be simply a 9.36 in diameter circle, with a center hole and 3 holes at 4.31 inch radius 120 degrees apart.
CAD drawing of circles for CNC machine
circles getting cut on the CNC
one circle cleaned up and ready for build
  • In the center of each of the 12 circles, drill a 3/4 inch hole.
  • with a file, cut a notch in one side of the hole.
drilled and keyed
  • Drill a 1/2 inch hole in one of the 3 outer holes on each of the circles.
  • Cut the 3/4 inch dowel into 12 1.5 inch sections.
  • With the file carve a notch in each end of the dowels that matches the ones in the holes on the circles.
  • Cut 6 - 1.5 inch sections of the 1/2 inch dowel.
  • take each of the 6 leg sets assembled in the previous tutorial and detach each leg from the frame at the inner corners of the upper triangles, also disconnect the center arms from the temporary crank.
  • drill a 1/2 inch hole in each of the loose ends of the legs and frame, except the center hole on the frame. The center hole will be drilled to 3/4 inch. See the holes drilled in the picture below(image is upside down).
full leg set with holes drilled
  • Now you will use the wood glue to set a 3/4 inch dowel segment in each of 6 of the circle's' center holes.
  • I did not do this and it resulted in failure of the crank shaft, so... you should pack the notches on the dowels, lined up with the notches on the holes with wood filler.
  • in the other 6 circles glue into the small hole of the circle a segment of the 1/2 inch dowel.
2 parts drying
Now all the parts are prepared and you can begin the final construction.

Building the Beest

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Take one of the mounting brackets and the 2 1/2 inch dowels, and insert a dowel in each of the end holes (but not the 3/4 inch middle hole) and glue in place with wood glue.
NOTE: the glue must set for at least 30 minutes before you can handle it, and 24 hours before it is fully set and can handle a full workload. If you must continue working with the frame before the 30 minutes is up, be sure that you have any unset parts clamped securely.

Mount glued to frame(2nd mount actually, but same principal)
Wood Glue for the crank shaft and frame
  • Next, place the special circle with both crank and center shaft on the frame. Place it center shaft down, into the 3/4 inch hole in the middle of the mount.
closeup of inlaid crank
  • Attach one leg by the 2 loose drilled 1/2 inch holes on the knee arm and upper triangle by sliding onto the 1/2 inch dowel on each side of the mount. One leg per side. Do not glue.
  • Slide the 4 loose connector arms from the 2 legs onto the crank post in the middle in the following order; left leg-lower arm, right leg upper arm, left leg upper arm, right leg lower arm. See image above with one arm in position. Again, do not glue.
  • Now you will take a circle with a center post but no crank post and glue it in place on the crank post of the existing circle, where you just put the arms. be careful to get no glue on the arms, as they need to move freely. Clamp in place.
Any means necessary to hold it while it dries
Arms attached to crank
  • Now take the next mounting bracket and slide it onto the 2 1/2 inch frame dowels and slide the protruding crank from the previous circle into the middle hole. Glue the side dowels, but not the middle.
mount in place on frame
  • Attach the next 2 legs as before.
  • Take a circle with no center post, but with a crank post and glue in place on the protruding center post. Make sure to position it with the post facing up.
  • Place the 4 loose connector arms on the post.
  • You will repeat the last 5 steps until all 6 leg sets are on the strandBeest.
Here is an image of 2 complete leg sets together.
2 leg sets assembled with crank
front view