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).

Gulliver's Traversals I

Finally, and at long last, progress on a project related to personal manufacturing! Meet Gulliver, well, Gulliver's traverse arm, anyway. He has a long way to go, but at least there's something to show for all the work! Once he's somewhat further along, Gulliver will be assisting with Mechanisms, Thermofluids and Kinematics classes and eventually, I hope to fit him with an extruder to make him into a 3D plotter.

Here's Gulliver's traverse arm upside down, being tested, with the controller box and the Mach3 software I'm using to run it. Artsoft's Mach3 software is a state of the art machine control application, extremely configurable and has a free downloadable version that you can use indefinitely. Highly recommended!

Not too long ago, Gulliver started out as merely a printed circuit board, entirely bare. I forgot to take that picture, so here's Gulliver's "central nervous system" with just the first resistors and capacitors soldered in. This kit is the HobbyCNC Pro Driver Board package, and I can wholeheartedly recommend it to anyone willing to do the soldering and assembly. It's very low cost, high quality and comes with clear directions.

After quite a bit of squinting and soldering later, his main motor controller board is ready.

His "central nervous system" is finished up and all four axis motors hooked up and tested.

All hooked up, but nowhere to go. Here's the finished motor controller.

Repairs and Remakes

All week it's been fixing and shoehorning, shaving down or shimming up. I came up with a novel (for me) way of making small grooves with a hacksaw blade. The students were celebrating that I was going to become rich from my invention until I reminded them that a hacksaw blade costs a buck.

A number of hydraulic motors had to be re-bracketed and re-pulleyed and a hydraulic friction testing piston needed reinforced. So it has gone.

PCB Opus 1

In all these years, although I've done minor repair soldering here and there, I'll have to admit to never having populated a PCB with components. I'm beginning work on a pendulum traverse system for one of the professors and decided it was a good opportunity to save several thousand dollars by doing the microcontroller and motor control board from open source hardware. In addition, its a great opportunity to begin creating my first microcontrolled system. I have a backlog of 5 or 6 projects already, this being the simplest!

I'm using an Arduino Deumilanove and purchased Adafruit's Motor Shield, which I highly, highly recommend! The shield comes as a PCB and components and you have to solder them in yourself. The instructions are clear and very complete. I'm fortunate to have been able to simply head over to Radio Shack and buy the tools for a basic soldering setup, and by following the picture by picture instructions, the soldering took less than an hour and the board is running the sample code for DC and stepper motors like a champ.

Busy Busy

It's been the busy time. Many projects all come together for the end of the year. The seniors are all working on (i.e. frantically trying to finish) their Senior Design Group Projects.

These are parts for a motorcycle "landing gear" project that is designed to assist riders who have difficulty with balancing. "Why should someone with balance problems be riding a motorcycle?" you ask. Perhaps those who have fallen off of one previously, but who still love to ride.

Another team is working on a torsion testing machine that will twist samples to destruction, measuring the torque required and the angles at which the samples pass from one state to another.

Not to be outdone, the faculty have been asking for things as well. Here's one of the more exotic, a set of clear cast acrylic flanges with brass inserts that will be used to study fluid dynamics. The prof. couldn't find what he wanted, so he asked me to design and fabricate them.

J'adoube

I'm rather pleased with the way the chess pieces have come out!


The Mastercam/G&M code files for each of the pieces have been finished and tested. I'll have students testing out my lab procedure and finishing up the rest of the aluminum set next week, then I'll probably teach one of my assistants to make them and have him cut the brass set. They are cut from 0.875" round rod stock in either 6061 Aluminum or C360 Brass.


They take more hand finishing than I'd like, since the aluminum likes to chatter around 3.5" from the chuck, but a couple fine grits of sandpaper and some fine and very fine scotch cleaning pads put a nice shine on them.

Fits and Starts

Nothing spectacular to video today, but plenty of uneven progress on various projects over the last week or so. Charlotte continues to interest folks, having taken up a place of honor atop my small drawer cabinet. The rook is done and the knight is close to completion. Aluminum and brass rod stock has arrived for the full set. A lab to introduce diode functionality was written and done by the electric circuits class. And so on!

One noteable happening: last night was the inaugural meeting of the MSU Robotics Group where students are getting together to research and fabricate robotics related projects. For starters, they're going to be making a stationary arm that sets up dominos in patterns for domino toppling. The plan is to fabricate the mechanics and control it with an Arduino. The design options are being weighed and suddenly (as with so many things) a relatively simple concept turns out to require a surprising (for the students) amount of complexity. I'm happy with what has been accomplished already and looking forward to going over the designs with them, next.