Eggbot Quality Troubleshooting

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Revision as of 13:40, 14 July 2014 by Steven Herzberg (talk | contribs) (Loose Eggs & Screws)
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If you are having quality issues with your prints that might be due to a misalignment of some sort, we hope that this guide will help you to find the source of the problem. This guide contains some helpful pictures that show how configuring the EggBot in different ways can produce different outcomes.

"Hardware" issues

Our test file


This is the test file that we'll be using for our examples. Note that the print quality is fine and consistent. The "O's" have closed shapes, the vertical parts are vertical, the horizontal parts are horizontal, the slants of the "W's" have consistent width, and so forth. (Some of the examples that we'll show later do not have these properties!)

You can download the example file here. (TODO: ADD LINK)

This was printed with the Deluxe EggBot on a chicken egg with an Ultra Fine Point Sharpie. The egg was oriented with its "fat" side pointing towards the egg motor (headstock).

The print settings were as follows:

  • Timing tab:
    • Speed when pen is down: 300 steps/s
    • Speed when pen is up: 400 steps/s
    • Pen raising speed: 50 %/s
    • Delay after raising pen: 200 ms
    • Pen lowering speed: 20 %/s
    • Delay after lowering pen: 400 ms
  • Options tab:
    • Reverse motion of Motor 1 (pen): checked
    • Reverse motion of Motor 2 (egg): checked
    • Egg (x) axis wraps around: checked
    • Start with pen centered: checked
    • Return home when done: checked
    • Enable engraver, if attached: unchecked
    • Curve smoothing (lower for more): 0.2

Dry pen


A common problem that can happen when using old pens, or pens that have been left uncapped is that the pen does not start drawing immediately when you expect it to. It is usually easy to fix this problem by taking a scratch piece of paper and, right before you start your EggBot, "bleeding" your pen a little on the paper to get the ink flowing again, as shown below. Sharpie pens last approximately forever if treated well; if it doesn't start drawing immediately, you might consider leaving it capped for a few days and trying again, rather than throwing it out.


Alignment of the egg in the egg cups


This skewed image is the result of misaligning the egg within the couplers, like so (exaggerated for clarity):


In order to avoid this you should place the egg between the couplers with the egg as flush as you can get it against each coupler. To align the egg in place, turn the egg (or the egg coupler) and watch the egg as you turn it. (You may want to use the "Raise pen, turn off motors" option in EggBot Control to make this easy.) Adjust its position until there is as little wobbling as possible; that is, until it doesn't seem to "change shape" as you rotate it.


This egg is properly aligned.

Loose Eggs & Screws


If your plots look like this, with circles that don't close and differing widths of your letter parts, it likely means that something is loose. It can be either the egg itself-- slipping in the coupler -- or a loose screw somewhere on the EggBot. Make sure that the egg has a secure connection to the motor through its coupler, and can't wiggle independently of the motor. And, make sure that the screws on the EggBot are tight and secure.


If the hex screw below the pen arm's hinge is loose, the pen arm will move left and right as the pen is dragged across the egg. Try to gently wiggle the pen arm left to right, it should not move at all.


In this case, the screw that mounts the distal pen arm assembly to the proximal pen arm (shown below) was loose, with the kind of poor results that you might expect.



The plot above-- where the pen is wandering "all over the place" was caused by trying to draw when the screw that holds the pen was loose (about to drop the pen).


To check if the pen is securely fastened, gently try to pull it out.

Vertical position of the pen motor


The pen motor can be moved vertically to adjust the pen arm for drawing on spherical or ellipsoidal surfaces. For drawing on chicken eggs, we normally position the pen motor about in the middle of the slots as shown here. For a sphere, position the motor at the very top of its slots. For a more elongated egg (maybe a turkey egg?) you may need to go lower yet in the slots.


If the pen motor is positioned too high in the vertical slots (here, at the top of its slots while printing on a chicken egg), the pen will not make contact over the full surface. To correct this, lower the motor in the slots.

12B.jpg 12A.1.jpg

Conversely, if the pen motor is too low in its slots, the pen may not make contact at the edges of the plot region.


Headstock / Tailstock position


When the headstock is correction positioned, the shaft of the pen motor points directly toward the thickest part of the egg (or sphere), as shown above.



When the headstock and tailstock are misplaced such that the pen motor is positioned too far to one side, you will find that (1) the pen cannot reach the surface everywhere that you would expect it to and (2) there will be some distortion of the print due to the misalignment.



A similar condition, in the opposite direction.

Horizontal pen arm


This photo shows the correct orientation for the distal pen arm and pen. Note that when the tip of the pen contacts the egg, the distal pen arm extends out straight and flat, down towards the center of the egg.



If, on the other hand, the pen arm is not horizontal when in the down position, it will cause the drawing to be skewed. (You will see similar types of issues when the pen arm backer is in the wrong position.)

Pen arm backer position


When the distal pen arm is correctly positioned-- dead flat when it the pen tip is contacting the egg -- then the tip of the pen should point directly down and towards the thickest part of the egg. If it does not, that may indicate that the pen arm backer is in the wrong position and that you need to move the whole pen arm closer to, or further from, the pen motor.

This pen arm backer shown above is in the correct position, since the pen tip points directly down and towards the thickest part of the egg, when the distal pen arm extends straight out and flat.



If the pen arm backer is too close to the pen motor, then you may see this kind of distortion-- curvature of the letters with respect to the pen motor position.



And similarly, when the pen arm backer is too far from the pen motor.

Bumping the pen arm


Here is the "diamond" test pattern, shown without any major quality issues (for reference).



Here is the same pattern, but drawn with the EggBot misaligned such that the starting position of the pen arm was poor and the pen arm bumped into the tailstock of the EggBot while drawing. When the pen arm reaches the end of its range, it may bend and try to continue plotting there, or the motor may skip a step ("cog") and lose alignment.

If you are having trouble with hitting the sides, check before plotting -- using the manual ("walk motor") commands if necessary -- to make sure that the pen arm has free travel over the entire range that you intend to use.

Map Projection



These two plots show an example file -- a circle inside of a square -- that are plotted on a (roughly) spherical ornament and on an egg. And yet, they don't really look like that-- and this isn't really an "error." While some of the distortion that you see is due to minor misalignments within the EggBot, a more major factor to consider is the change in geometry that comes from projecting our rectangular drawing file onto a non-flat surface. In geometry, this is called a map projection, and the EggBot uses equirectangular projection, where distances are mapped directly to angles.

On the sphere, the circle appears (more or less) spherical. The square's top and bottom are straight (when photographed from this particular angle), but the other two sides (longitude lines) do not appear straight (when photographed form this angle). On the egg, the distortions are more severe because the curvature is so different in the two axes. We usually compensate for this (when drawing on eggs) by stretching the design horizontally by about 150%. (See also this note from our troubleshooting guide.)

"Software" issues

Motor reversal issues


Doh! This occurred when the "Reverse motion of Motor 1 (pen)" was left unchecked when the egg was positioned so that its "fat" end was on the headstock. This can also happen when the "Reverse motion of Motor 1 (pen)" is checked, but the eggs "fat" end is in the tailstock.


This mirrored image of "Hello World" is the result of "Reverse motion of Motor 2 (egg)" being left unchecked while the "fat" end of the egg is in the headstock, and vice versa.

Timing issues


This is the result of moving too fast. The "Speed when pen is down" setting was set to 700 steps/s, which is usually too fast to create a neat drawing. The speed of the motor caused the pen to shake when drawing.


With the "Speed when the pen is down" setting set to 500 steps/s, while it is an improvement, is still too fast. There are still jagged lines.


This can happen when the "Delay after lowering pen" setting is set too low. The EggBot will start to commence the drawing before the pen has actually made contact with the egg, leaving gaps in your drawings.


This is when the "Delay after raising pen" setting is set too low. The EggBot will start to move to the next destination before the pen is lifted off of the egg, leaving stray marks.