Eggbot; filling in some missing information

I guess it is that time of year, people are building Eggbots. I built one, and needed to learn a bunch. Some of the information was vague, or not connected to the original design, or anyone elses design.

I started with a Russian frame that I liked on Thingiverse. This was mostly lacking any real documentation. Elliot from Hackaday has a page with lots of information, including how to make a CNC shield move a servo, and how to get G code out of inkscape.

The Russian frame had a bunch of options for the pen holder. I chose the simple one, and am having success using that with a sharpie fine point. Being an American, it was easier to get 1/4-20 5/16-18 threaded rod than 6mm, so that is what I used. I cut 3 1ft pieces. For the rest of the bolts and screws, I used metric (m4 and m3 mostly), since the motors assume metric.

One tool that I will call essential is the taper cutter. Cutting threaded rod is easy, but the threads are suddenly all mucked up. Either the taper goes away, and threading on a nut has to be aligned perfectly, or the threads are bunged up so badly nothing will thread on anymore. This tool will make the trouble disappear, in about 2 seconds!. Sure you could file a taper in using a file, or grinder, but for less than $5, why?

The Russian  frame also assumed some 16mm bearings, that I didn't order. Another similar frame used skateboard bearings in a holder with the same bolt pattern as the stepper motors. I just reprinted the left frame from the Russian frame and two of these bearing holders for the end.

I couldn't find O rings that would hang onto the egg good. One end or the other would slip, and the drawing wasn't real good. I found some #17 bath diverter washers that seemed to be a better shape, and fit the end caps well. They still slipped.

I've started playing with some table foot rubber pieces, like on the bottom of a crutch. They are more grippy. I'll update when I know more.

Some page, maybe another one on Thingiverse suggested I use a CNC V4 Shield. A great design, with the Arduino Nano right on the board with the stepper drivers. The trouble is, the common Chinese clone makers messed up the board. A couple others have figured out the changes needed, and published the wiring changes to make this board work.

What I have seen though, the inkscape G code output doesn't quite make the pen up/down command that the GRBL expects. The delays are about 100 times longer than they say (seconds instead of milliseconds) as well  (Update, in the save dialog, it lets you set delay to 0, that seems to work). Long delays with the pen over at an angle almost always messes up the continuation of the lines. I end up hand editing the G code output. I should probably build a python or perl script to fix the output, or just figure out what unicorn changes are needed.

Changing the GRBL source code, it is important to remember you moved the code to the Arduino directory, so change it there, not where you expanded the code. If the motors are going backwards, reverse the plugs on the CNC V4 board.

For test eggs, I have been using the 18 for a dollar plastic eggs that I can get at the Dollar Tree. I like hard boiled eggs, but I didn't think I'd eat 24-36 in the next couple of weeks. I should look into dry erase markers to see if I can erase the test eggs.