Wednesday, May 26, 2010

Gulliver's Traversals II

After getting the electronics soldered, assembled and tested, the mechanical parts provided their own set of challenges. Here's Gulliver's assembled traverse arm, upside down.

One of the interesting challenges was to create a system where the traverse arm would move along the threaded rod. I decided to go with a design concept I've seen online (but can't currently locate the link) that included melting the "teeth" into plastic blocks to create a backlash-free plastic "nut" that's then mounted on a carriage made with bearings. Here's the final "nut" being formed, with a number of the test pieces I did to get to the final. I'm using 1/2 inch diameter - 10 thread per inch ACME thread rod. After experimenting, I realized the maximum effective width of the "nut" is limited to around 1/2 inch before it simply grabs the thread rod, causing too much friction. To make the "nut," I drilled a 15/32 inch hole between two pieces of HDPE plastic plate stock, squeezed the thread rod between them in the vice, then heated the upper tip of the rod with a braising torch until the plastic started melting. I then sqeezed the vice harder and let the whole thing cool, forming the teeth exactly around the rod.

Here's the assembled carriage. the "nut" piece can bee seen peeking out from between the bearings.

I ended up going with simple tubing to connect the motor to the thread rod because the end of the rod is just enough out of round to cause the motor to rattle back and forth when I tried connecting them with a rigid brass fitting. The jury is out on whether this is a workable long term solution. We'll see.

Here's Gulliver's arm assembled and ready for testing (resting upside down).

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