Rostock-Mini Tweaks

Posted on September 22, 2013 by Jay

I brought my rostock-mini 3D printer home so that I could take it to a class, and while I had it here, I decided to update a few minor things.

First, I swapped out the stepper motor brackets (which also serve as the legs) with three I had designed and printed that were 20mm taller. I have a full RAMPS board under the base plate of the rostock-mini, and although it fits, the fit was “very close”. I didn’t like the fact that my stepper motor wires would touch the surface the printer was sitting on, and the limited airflow paths. This extra 20mm really helps things out, and also opens up the possibility of installing an LCD control panel under the base plate in the front. (If I can figure out how to avoid my bed leveling knobs.)

Second, I upgraded the springs on my adjustable print bed to some that were a bit taller and a bit stiffer. My overall build volume was shortened from 187mm to 185mm, but now I have a lot more range for adjustments and the bed is more rigid (while still allowing the print head to push the spring loaded bed down if it crashes horribly).

Third, I wrapped some plastic spiral wire harness wrap around the wires leading down to the print head, to give them a better visual appearance.

Finally, I changed out my bowden tube from using M4 nuts to hold the tube to using screw in Push To Connect adapters. The goal was to allow me to remove the tube from either end without having to unscrew the plastic part holding the nut in place. However, the cheap PTC adapters I bought appear to be single use, in that they don’t release the tube reliably without breaking, so basically it just makes the bowden tube look slightly more professional.

Using OpenSCAD to teach Computational Thinking

Posted on September 20, 2013 by Jay

I am using the OpenSCAD parametric 3D design tool to teach students about programming concepts such as conditional execution, encapsulation of code, and iteration. Students are motivated by building visual objects, and if you have access to a 3D printer the students are very motivated to get their part printed.

Here are some documents I share with educators to be used to learn/teach about OpenSCAD and 3D printing:
Outline of the class

3D printing vocabulary

Using OpenSCAD
OpenSCAD-Examples

Student Assignment

Fixing the problem where gparted (parted) won’t see a partition due to a mac partition table

Posted on September 18, 2013 by Jay

I purchased an external HD that was “mac compatable” but I used it with a linux system and used fdisk to put two partitions on it.

Later on, I wanted to use gparted to easily resize one of the partitions, but it refused to see any partitions at all on the disk.

fdisk could still see them just fine, but reported “Partition type: mac”

It turns out that the problem was that the disk originally came with a mac partition table in addition to (right after) the regular MBR Master Boot Record.

I noticed that the first partition didn’t actually start until 63 sectors into the disk (at the beginning of the 2nd cylinder).
Device Boot Start End Blocks Id System /dev/sdb1 63 1171893554 585946746 83 Linux

So I used DD to copy the first cylinder to a file:
sudo dd bs=512 count=62 if=/dev/sdb of=firstCyl.bin 62+0 records in 62+0 records out 31744 bytes (32 kB) copied, 0.000715733 s, 44.4 MB/s

Looking at that bin file in an editor, I saw the string “Apple_partition_map” which is a dead givaway of what the problem was.

So, I wrote out all zeros to the first cylinder:
sudo dd bs=512 count=62 if=/dev/zero of=/dev/sdb 62+0 records in 62+0 records out 31744 bytes (32 kB) copied, 0.00165608 s, 19.2 MB/s

And then I copied the first sector (512 bytes) back from the firstCyl.bin file I had made:
summetj@constantine:~$ sudo dd bs=512 count=1 if=firstCyl.bin of=/dev/sdb 1+0 records in 1+0 records out 512 bytes (512 B) copied, 0.00183878 s, 278 kB/s

And it worked! Now gparted is no longer confused by the apple (mac) partition table that I zeroed out, and sees my partition.

MakerGear Hot End Molex Connectors

Posted on September 9, 2013 by Jay

I recently replaced a MakerGear hot end with a different model (MG Plus) but wanted to maintain the same connectors (used for the resistive heater and the thermocouple). The MakerGear connectors had a positive locking clip, while the JST connector that came with the MG Plus thermocouple was only friction fit.

FYI – The MakerGear hot end and Prussa Mendel kit I have use the following Molex Micro Fit 3.0 Family parts:

The female connector (with the bump) is a Molex 0436450200 (DigiKey part number WM1845-ND).
The male connector (with the hook that catches the bump) is a Molex 0436400201 Digi-Key part number WM1855-ND
You will also need the associated female and male crimp connectors for the internal contacts: Molex 43030-001 tin 20-24 guage wire (DigiKey part: WM1837CT-ND CONN TERM FEMALE 20-24AWG TIN) and Molex 43031-007 tin 20-24 gauge wire male terminal (DigiKey Part: WM1841-ND WM1841-ND CONN TERM MALE 20-24AWG TIN)
( You might want to get the crimp connectors for smaller wire (higher gauge numbers) depending upon what wires your thermocouple uses, but I got 20-24 gauge for use on power connections and just soldered my thermocouple wires into them.)

The cartridge heater on the MG Plus nozzle came with enough wire to reach all the way down to my RAMPS board so I ended up only using the molex connectors for the thermocouple, and running the resistive heater wire all the way down. This left me with a set of wires going to my hot end terminating with a molex, and I eventually plan on using this for an “always on” fan for cooling the top of the hot end (as opposed to the “under RAMPS control” fan for layer cooling).

Bubble Display Jr – Designs

Posted on September 6, 2013 by Jay

As part of building the bubbleDisplay I made a lot of prototype tubes, nozzles, and even a small prototype display before actually committing to building the final product. This left a lot of random bubble display type parts laying around my garage. I hate throwing things out, and I wanted to have a bubble display of my own, so I’ve started to design a BubbleDisplay Jr that I can make out of leftover parts. Because I’m limited to stock on hand, I couldn’t make all of the tubes the same length (unless I wanted them all to be 9″ tall….) so I went with a Superman Memory Crystal style sculpture:

Of course, since I have a 3D printer now, I decided that printing the bracket to hold the air hoses and LED’s would be the way to go:

There….now you can’t say I don’t plan out my projects before starting them.

Bubble Display Overview Video

Posted on September 4, 2013 by Jay

I spent a lot of time last summer and fall building this 62″ wide bubble display. So much time that I didn’t get a chance to edit together and post an “overview” video showing the whole thing in action. Well, here is that video. If you are looking for more build details just read all my posts tagged with “Bubbledisplay”. If you just want to sit back and watch the whole thing come together via videos, start watching my “BubbleDisplay” channel on YouTube At the beginning.

Building a Signal Generator – Paper Prototyping instrument panels

Posted on September 3, 2013 by Jay

To test the resonant frequency of a Tesla coil or other resonant circuit you need an oscilloscope (which I have) and a signal generator (which I didn’t have). I was able to follow these instructions from RM Cybernetics to build one from a 555 timer and use it to test my primary and secondary.

The only modifications I made to the circuit was the addition of a toggle switch so that I could use two different capacitors, giving a “low” and “high” frequency range (plus a “air gap” capacitance that basically runs the 555 as a 2Mhz sine wave generator). I built the circuit on a protoboard that came with a box, and decided to use a laster cutter to make the instrument panel. To do this, I opened up Inkscape to design a control panel using vector graphics. I would print each design out and tweak it until it fit my box and circuit perfectly. I then tested various dial positions on my 10K audio scale (logarithmic) pot using my oscilloscope to mark the approximate frequency on the dial. After a few trials, I was able to laser cut the design onto a piece of 1/8″ craft plywood to get the finished product.

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.

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