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 HELP.. Pen arm will not drop to plot on some designs
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By: Anonymous: C Krueger () on Saturday, April 16 2011 @ 07:42 PM PDT (Read 11230 times)  
Anonymous: C Krueger

I have the egg bot together and it generally works. I am having a problem with some designs where the egg bot appears to be going through the correct motions to plot a design, but the pen does not drop to the egg.

An example is the globe sample from the egg bot wiki site. It draws some of the design but not all. I am also having trouble with text where it will draw a portion of the text character but not all.

Any thoughts?

Thanks in advance for your help.






       
   
By: dnewman (offline) on Saturday, April 16 2011 @ 08:25 PM PDT  
dnewman

When you first start plotting or change to another object with a different geometry or larger/smaller dimensions, you need to make adjustments to the pen travel.

0. As a one time adjustment you will want to adjust the placement of the proximal pen arm along the pen motor shaft so that pen tips fall on the axial line between the egg cups.
1. You will want to adjust the head and tailstocks to get the "egg" centered relative to the pen motor.
2. You will want to adjust the distal pen arm height. You want to aim for having the pen nice and vertical with the distal pen arm horizontal when the pen tip contacts the egg.
3. You then set the pen servo's up and down positions via the Setup tab of the Eggbot Control extensions.

It is step 3 which it sounds like you need to check. You will need to make sure that when the pen arm is in the down position, the pen tip contacts the egg at the extremes of travel. Sacrifice an egg to check this or put a piece of paper under the pen tip when you check. Also note that some very fine tip pens can be touchy and not like to draw when held at angles far from vertical -- at least that's my experience with Copic Multiliner SP 0.03 and 0.05 pen tips.

There is a nice setup video which EMSL put together in which they demonstrate most/all of these steps. You can view it at,

http://www.youtube.com/watch?v=3zsbW9qmZk4

And there's a fair amount of helpful information at the Eggbot wiki. If you have not already, see especially

http://wiki.evilmadscience.com/Making_your_first_plot#Prepare_your_EggBot_for_drawing_on_eggs

Cheers,
Dan


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By: dnewman (offline) on Saturday, April 16 2011 @ 08:32 PM PDT  
dnewman

OTOH, if the issue is simply that some times the pen arm doesn't drop at all, then here's some questions for you:

1. Can you see if the servo horn turns down but the distal pen arm doesn't lower?

2. Is the servo horn not turning down when you would expect a pen down operation?

3. Is there any consistency to this?

Dan


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By: Anonymous: C Krueger () on Saturday, April 16 2011 @ 08:39 PM PDT  
Anonymous: C Krueger

The pen arm actuator does not drop as it is supposed to. It is strange because it works fine on some designs.





       
   
By: dnewman (offline) on Saturday, April 16 2011 @ 09:07 PM PDT  
dnewman

Just to be certain, you don't by any chance have a clear, acrylic eggbot do you? One of the beta test units sold back in 2009? I ask because of your use of the term "actuator". Those units did not use a servo to raise and lower the pen arm. Instead they used a solenoid.

If, however, you have a white framed Eggbot made by EMSL, then I understand you to be saying that on some drawings the servo horn doesn't turn and thus leaves the pen arm raised in its up position?

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By: Windell (offline) on Saturday, April 16 2011 @ 11:45 PM PDT  
Windell

Dan's questions here are excellent diagnostic questions. If you can answer them a bit more fully, we stand a pretty good chance of helping you to get your Eggbot working, one way or another.


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By: Anonymous: C Krueger () on Sunday, April 17 2011 @ 07:38 AM PDT  
Anonymous: C Krueger

No I just got the Egg Bot last week.

I asked the EBB for its version info, and it replied:

EBBv13_and_above EB Firmware Version 2.0.2

It does have a servo motor that lifts the pen.





       
   
By: linuxwrangler (offline) on Sunday, April 17 2011 @ 08:36 AM PDT  
linuxwrangler

Some things to check.

If the servo does not rotate up and down at the appropriate times, consider an electrical or programming problem. I suspect this is unlikely.

If the servo is rotated down but the pen does not contact the object at certain positions, double-check some of dnewman's suggestions. In particular:

1. If it contacts on one side of the "equator" but not the other, then the object is probably not centered well.

2. if it contacts toward the equator but not toward the poles, your vertical adjustment of the pen servo may be off. Release the servos or power the unit off and rotate the pen back and forth checking to see if the pen is at a fairly constant distance from the object. If it is, watch to see if the pen is held down against the object throughout its travel. The weight of the pen holds it down better when the pen is toward the equator and the pen weight has less of an influence toward the poles. Sometimes this is enough to prevent the pen from drawing well at the poles. This depends on the type of pen, its weight, etc.


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By: Anonymous: C Krueger () on Sunday, April 17 2011 @ 08:47 AM PDT  
Anonymous: C Krueger

The pen setup makes contact as it should.

The pen does not drop to contact the egg on some design elements. Say I write a name in inkscape then convert the image to strokes etc.. The egg bot will plot a potion of each letter and raise go to the next letter and do the same.

It does this with egg bot sample images as well. On the globe sample it will draw some of the details but not all. Pen contact is not the issue it is that the servo does not let the pen down to plot the design. And like I have said, Some of the designs work fine.

Thanks for your thoughts.





       
   
By: dnewman (offline) on Sunday, April 17 2011 @ 08:55 AM PDT  
dnewman

Are you perhaps saying that the Eggbot begins drawing before the pen has finished lowering? In such cases, if the segment to be drawn is sufficiently short, the pen tip may never make it to the egg surface before it is again raised. If this is what you are seeing, then you need to adjust the delay which occurs between the "lower pen" operation and the "begin drawing" operation. Adjust this with the "Timing" tab of the Eggbot Control. Increase the "Delay after lowering pen" and then click the "Apply" button. In general, you want the delay to be long enough to allow for the travel time of the pen down. That travel time in seconds is the difference between the pen up and pen down positions dvided by the pen lowering speed. Multiply that value by 1000 milliseconds / second to convert to milliseconds. Milliseconds is the unit used for the delay.

Not that you are seeing it, but there's a similar issue where the pen is raised but moved too soon resulting in unwanted lines tracing a part of the path between the last line and the start of the new one. This too is adjusted on the "Timing" tab. It's the "Delay after raising pen".

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By: dnewman (offline) on Sunday, April 17 2011 @ 09:04 AM PDT  
dnewman

P.S. The pen up and pen down positions are set/shown on the "Setup" tab. If, for example, you have

pen up = 57%
pen down = 49%

on the "Setup" tab, and

Pen lowering speed (%/s) = 10 % / s

Then it will take the pen 8% / ( 10% / s) or 0.8 seconds (800 ms) to finish lowering.

Note, in practice the pen tip will make contact with the egg surface sooner. That's because the pen down position is typically a bit further down than it needs to be. So, for example, by the time the pen is lowered to 52% it may already be making contact with the egg surface -- that would only be 0.5 seconds. For example, the pen will usually come to contact sooner the closer it is to the egg's equator. Of course, that will depend upon the geometry of your egg.

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By: Anonymous: C Krueger () on Sunday, April 17 2011 @ 09:22 AM PDT  
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No that is not exactly what is happening. I am uploading a flash video showing what is happening. The video is about 2Mb I hope I can upload it.





       
   
By: Anonymous: C Krueger () on Sunday, April 17 2011 @ 09:28 AM PDT  
Anonymous: C Krueger

It doesn't seem to have uploaded. The file can be downloaded here.


http://www.keisf.com/images/video/eggbottext.flv

Thanks,





       
   
By: dnewman (offline) on Sunday, April 17 2011 @ 09:48 AM PDT  
dnewman

So, the servo horn is turning down but the distal pen arm itself is not lowering itself? High anti-gravity field flux in your local vicinity :-) Well, if the servo horn is really lowering but the distal pen arm is not following it by lowering the pen, then that would suggest some sort of intermittent hinge stiffness or mechanical impingement. Or, something else entirely which doesn't occur to me.

Intermittent hinge stiffness would be quite odd. Yes, materials can have memory but it wouldn't be coming and going this way. (Leave the pen arm up high overnight and maybe, just maybe you might have a problem with it not lowering completely the next day -- but I think EMSL was careful in not selecting hinge materials with much memory that way.)

An intermittent impingement I can make more plausible but it still seems unlikely. For example if the two wooden pieces forming the upper pen arm are a little too close AND the screws attaching the hinge are too loose AND the meeting wooden edges of the upper pen arm are not parallel, then occasionally those two edges may impinge against each other somehow. But this too is a BIG stretch. On my Eggbot, I do occasionally find the one screw holding the metal L bracket a little loose and the distal pen arm rotated a little. However, I've never had any impingement caused by that. If a piece of gunk was in that hinge interface, it should fall clear and stop causing problems.... Some sort wood spur left on one edge of either of those mating edges on the upper pen arm?

Windell will likely have some good thoughts to offer.

Dan


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By: Anonymous: C Krueger () on Sunday, April 17 2011 @ 09:56 AM PDT  
Anonymous: C Krueger

Sorry, The video does not show that the servo is not turning down either some of the time. The Pen doe work just fine when the servo motor rotates down to allow the design to be plotted.

The servo is not lowering the pen when it should. It seems like a software or EBB issue.





       
   



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