Yoda Bust(s)

Posted on September 3, 2013 by Jay

I have been printing Yoda busts on my Rostock Mini.

The first (small) sized one printed very well, but I had some problems when I tried scaling up to 160% size.

If you look closely, it has a small discontinuity just above the eyes. (It looks like the top of his head was sliced off and put back on slightly “off”.)

It looks like one of my axis lost a step, so I ran through various diagnostics (more airflow over the stepper drivers, higher current to the steppers, upgrading my slicing software, etc) and eventually the problem got worse:

Then I heard some squeaking from my 3D printer and started to move things around manually to isolate it and I realized that my straight rods and linear bearings were dry. The final solution was to oil my straight rod and liner bearings, although I can’t confirm that the upgrade to Slic3r didn’t also help things out. All in all, it only took four tries to get things right:

So now I have a large yoda head to float on my desktop levitation box:

Bubble Display Source Code & Bill of Materials

Posted on September 1, 2013 by Jay

This open office / libre office / open document spreadsheet lists (most of) the parts I purchased for the bubble display, as well as the supplier part number. As some of the parts were surplus, or purchased from China via ebay, the suppliers may or may not still have them available. I didn’t keep the BOM document entirely up to date after I started to put things together, especially for several last minute runs to the hardware store, but it generally shows all of the major components.
Bubble Display BOM

This is a source code dump that includes the arduino code that I wrote for the bubble display. It’s not very nice looking, but it may help others to learn what I did on the software side of things. You’ll also need a Shifter library for the 74HC595 shift registers and a WS2801 library for the RGB serial LED string.

bubbleDisplay.ino

The “images” are encoded as individual pixels, hard coded as an array, generated by python code from simple .GIF images. Edit the image in an image editor, and then run the code to generate the C code array data.

BDPictureMaker.py

Building another Toroid

Posted on August 3, 2013 by Jay

Since my first toroid was out of tune, I decided to actually follow directions this time and use an 8″ inner tube (2″ diameter) for my Toroid. I bought an 8″ inner tube and 50 yards of Aluminum Duct tape so I wouldn’t run out.

Then I went off-label and added a 4″ Big Daddio anodized aluminum personal pie pan which I’m going to try as a mounting system.

After drilling a hole in the base of the personal pie pan, I wrapped it and the inner tube with aluminum tape.

After this picture was taken I had to extend the aluminum tape down to cover the hole in the pie pan, as the anodized aluminum pie pan was apparently not conducting. After I did that I got less than 300 ohms resistance measurement from the outside of the toroid to ground.

The size of this toroid is much closer to spec, although the Big Daddio pie pan holds it about 1″ higher than a straight piece of cardboard. Unfortunately, when I measured it’s resonance, I found a big signal at 340 kHz, (2.93 micro-seconds) which is even higher than my first toroid! Obviously I’m doing something wrong.

Electric Truck Battery Pack Status Report

Posted on July 26, 2013 by Jay

I’ve been driving my electric pickup truck since February of 2011, and have almost 2.5 years on my first lead acid battery pack (twenty six-volt GC-8 golf cart batteries by Energizer/Johnson Controls/Costco). I’ve put just under 2000 miles a year on the truck (4449 miles since I got it, 16011 miles total as an electric truck) but have charged the batteries around six hundred times. My average trip is relatively short (7.43 miles) and I’m averaging around 800 watt/hours per mile driven (measured from the wall, including charger and battery inefficiencies.)

When I first got the truck I could drive 20 miles with ease, and if I pushed things and drove carefully I could get up to a 30 mile trip out of the battery pack without pushing it below 80% discharged. Over the last 2.5 years / 600 cycles the pack has degraded, and one battery basically failed. I replaced the failed battery (it had about 1/2 the capacity of the rest of the pack and was limiting my maximum range to 5-7 miles per charge) with a replacement for $100 and now the pack is performing at a reasonable rate for a 2.5 year old set of batteries.

My current max range is around 15+ miles (I’ve driven several 13-14 mile trips carefully without getting any low battery alerts), which is enough to make it to the hardware store and back with a long piece of lumber. My typical commute is a 4 mile round trip to the MARTA station, so it can very easily make this trip. I expect that in the next year I won’t be able to make it to the hardware stores, but will probably still be able to use it to get to the MARTA station for a one or two more years.

I plan on replacing the entire pack in one or two years, depending upon how things shake out. It appears that my battery costs per mile will be in the 0.30 – 0.40 range, which is under the federal mileage rate, but does not count the cost of electricity (around 0.09 a mile) or maintenance. I have actually been very happy with the cost of maintenance on the truck. I replaced the two front shocks myself, had a shop service the brakes when I purchased it, and replaced a few pieces of interior trim and a parking break lever with parts I got at a junk yard, but all told the maintenance costs have been under $300 for the last few years. Compared to the maintenance needed on our internal combustion engine (ICE) vehicle this is a pittance…I could have bought two new battery packs for the truck with all the money we have spent on the family car in the shop over the last two years.

Building a temporary toroid

Posted on July 25, 2013 by Jay

I decided that I couldn’t wait for the official oneTesla stamped metal toroid to arrive, so I built one myself out of stuff I bought at the hardware store.

(Specifically 3″ flexible aluminum ducting, and aluminum Duct/Plumbers tape. I couldn’t find any 2″ flexible ducting…more about this later) I ran out of tape, so I couldn’t make it quite as nice as I would have liked, but a lack of tape isn’t my only problems from an aesthetic standpoint. I’m really looking forward to having the professionally stamped toroid, as it should maintain the great aesthetics of the kit.

It actually looked a lot nicer back when I only had one round of tape holding the two ends together. I also had some extra “Great Stuff” expanding foam that I had just used to plug some holes in the house, so I filled the inside of my toroid with some foam to give it a bit of extra rigidity before I taped it closed.

I used a piece of thin plywood to hold the toroid, and wrapped it in aluminum tape (until I ran out).

I used the last of my tape to completely cover the top and bottom of the wood circle and bridge to the toroid. I also taped the breakout point coming off of my toroid.

Now, for the big annoyance. Because I couldn’t find any 2″ tubing, I substituted 3″ tubing instead. The toroid has a major dimension of close to 11 inches and the diameter is 3″. The oneTesla recommended toroid has an 8″ major dimension and a 2″ minor dimension. I don’t know how much this will affect the Tesla coil, but I’m hoping that as long as I run it at 1/4 or 1/3 of the max power things won’t break.

Update:
Unfortunately, this toroid was measured about 70kHz out of tune (233kHz for the primary, vs 303khz for the toroid that I made). I only turned the power up to 40% and the primary oscillated, (you can hear the buzzing) but I never got a spark. I have a smaller 2″ diameter inner tube and more aluminum tape on order now…

oneTesla build

Posted on July 21, 2013 by Jay

Who has a 99% complete tesla coil? Yes, that’s right, due to my extensive blogroll of the technorati (i.e. MIT students) I found out about the oneTesla kickstarter before it got super popular and got in on the ground floor (first 100 backers). Over the next month they got more and more interest, and I kept watching the features of the kit I had pledged/ordered go up. [Better interrupter, stamped toroid, etc…] Of course, like most kickstarters, it took them about three times longer than they had anticipated to actually ship the rewards, but I got my kit and (after a few customer service emails) put it all together!

The only thing missing is the stamped toroid for the top, so I can’t quite spit out long sparks to the tune of the imperial march, but since I was expecting to have to make my own toroid out of an inner-tube and aluminum tape when I made the pledge, I can’t complain about a few delays in such a custom component.

So until the toroid’s ship, you (and I) will just have to watch other people’s oneTeslas making music:

Suction Cup Cell Phone Mount

Posted on May 6, 2013 by Jay

This is a windshield mount for a (landscape mounted) cell phone that I designed and built. It has a ball & socket mount for easy adjustment.

The rectangular holder on the end can be customized to any cell phone.

And the whole thing takes about eight hours to print.

If you want to print your own, I posted the design files on thingiverse.

Top speed 275 mm / sec

Posted on April 20, 2013 by Jay

Although my print head can move at 300 mm/sec, my extruder can not reliably keep the plastic flowing at that speed. (Perhaps if I turned up my extruder temperature above 195 C…)

I have decided that 275 mm / sec is a reliable top speed for my extruder after printing a relatively large part at that speed with the temperature turned up to 200 C.

This video shows layers being printed in about 15 seconds with 3 exterior perimeters and 25% infill.

Here is another video of the twisted koch snowflake vase (scaled up to 150%) being printed at 275 mm/sec top speed. Due to the fractal nature of the sides of the vase the platform rarely got up to the top speed, as it never had a long enough path to accelerate up to full speed.

Printing at 300mm/sec

Posted on April 19, 2013 by Jay

I decided that I needed to switch to a different (larger) 3D object so that my printer could accelerate up to full speed on some long straightaways. Here is what 300 mm/sec printing looks like on a larger square object:

However, my extruder just couldn’t keep the plastic flowing (at least, not at 185 C), and it jammed. So I have decided to try 275 mm/sec with the temp set to 200 C (lading to an actual extruder temp that is closer to 195 C).

Stepping up the speed on my Rostock-Mini

Posted on April 18, 2013 by Jay

Now that my Rostock-Mini is basically finished, I have been adjusting the parameters of Slic3r to increase the print speed. Why? Because this is my sports car 3D printer….It’s small, looks cool, and is fast! In contrast, my Prussa Mendel is the family mini-van: Nothing to look at, reliable, with a large print volume.

Because the Rostock-Mini has the cold end of my extruder mounted on top of the frame (not on the motion platform) it doesn’t have to move the weight of the extruder stepper, gears and associated hardware. The filament is pushed down to the platform via a bowden tube (think bicycle brake cable) and the only part that needs to accelerate and decelerate is the hot-end and associated fan / air duct. The lighter the platform is, the faster it can move and change direction while maintaining positional accuracy.

The Twisted Kochflake vase that I’ve been using for my test print has 7 layers at the bottom with “infill” but above that, it’s just made up of four perimeters of plastic traced around the volume of the interior of the vase. This means that some layers require a relatively short amount of motion/time, especially near the lower part of the vase. I have my Slic3r software set up to not allow any layer to take less than 15 seconds to give the plastic a bit of time to solidify before we put the next layer on top of it, so in some parts of the videos below the platform is not moving at it’s true top speed because of this software limitation. Also, due to acceleration constraints, the platform can’t get up to full speed on small bumpy surfaces. When the printer is printing the bottom seven layers (you’ll see it going back and forth to fill in the circle with plastic) or the wider part of the fractal pattern as the vase grows up you’ll see where layers take longer than 15 seconds (4 times around the vase is a single layer) and the platform will be moving at top speed.

Here is my printer set to 225 mm/sec, which is faster than most printers that have a moving single extruder will be able to do:

Here is the twisted Koch Vase at 150 mm/sec, which is approaching the top speed of most gantry style homebrew 3D printers that move the cold end of the extruder.

This is a relatively slow 75 mm/second video:

Jay's Technical Talk

My external memory

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