Eggbot drawing problems

[bthinkerton]

Eggbot is having some trouble drawing circles. I have included the image link below. The circle on the left is what I am trying to draw and the circles on the right are being drawn on the egg. Just to clarify, the examples were drawn by hand. It draws better when I plot the drawing closer to either egg cup. I have tried adjusting the potentiometer for the stepper motors and it has not solved the problem. What seems to be the problem?

[Windell Oskay]

It sounds like possibly something is loose– maybe a screw not tightened somewhere? Does everything feel solid to your hands?

[bthinkerton]

Everything did feel solid to my knowledge. Unfortunately I do not have the eggbot right next to me at the moment. I will double check that everything is tight tomorrow. Do you have any other ideas?

[Windell Oskay]

If the machine itself is solid, it could be the pen wobbling in its holder, or the egg not firmly “coupled” into the couplers. Try to wiggle the egg by hand– if it is not firmly locked in place, then you may see this kind of behavior.

[bthinkerton]

I will try that tomorrow and give an update. Thanks!

[bthinkerton]

I just tightened everything and the egg is secure between the couplers. It looks to me like the pen is deliberately drawing the wrong shape. The movement of the pen arm is not a perfect circle.

[dnewman]

In addition to Windell’s comment,

Try to wiggle the egg by hand– if it is not firmly locked in place, then you may see this kind of behavior

it helps to also rotate the egg around several times as you are trying to wiggle it.  You may have it placed firmly between the couplers, but if the egg’s axis is not coincident with the eggbots rotational axis, then the egg will very quickly precess as it is turned.  That precession causes it to begin to slip or otherwise not rotate as expected and you then can get distorted circles which are even incomplete.

In my work flow, I do my best to get the egg’s axis well aligned when I initially load it, but then I hand spin it several full revolutions while trying to wiggle it about.  That usually causes some slight shifting but the end result is a well seated and well aligned egg.

[bthinkerton]

Is any part of the pen arm supposed to move at all?

[bthinkerton]

Not counting the movement from the stepper motor of course.

[Windell Oskay]

Only the hinge should move freely.

If it looks loke the stepper is not moving how you expect, you may need to re-adjust the motor current; we have sometimes seen steps skipped or jumped if it’s too high or low.

[bthinkerton]

We figured it out! Thanks for the help. Some wood screws on the pen arm were not tightened enough.

[Windell Oskay]

Great– thanks for the update!

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