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Pen jumps between letters while printing

edited April 2015 in Egg-Bot
Hello All.  I've been enjoying assembling and getting to know my new Ostrich Egg-bot.  Everything seems to be working fine, however the pen bounces up and down when it's raised between individual letters.  That is, while the egg is rotating to the next letter position, the pen bounces--thus leaving a 'trail' of little dots on the egg.

I've also noticed the same thing when it finishes printing and raises the pen to reposition to 'home'--it will leave a trail of dots across the egg while it bounces.

I've slowed down the pen speeds and egg speeds, but to no avail.

I've adjusted the power going to the motors so that they hold their position well and seem to be working like they're supposed to.  

Any suggestions?

Many thanks.



  • It's likely that you have a bad servo. One thing you can try is different servo positions, as some servos seem to be happier in different "up" positions than others. In any case, please contact us so we can send you a replacement. 
  • Thank you, Lenore.  I did reposition the servo arm, but it didn't help much (maybe a little).  As you suggested, I contacted customer service requesting a new SG90 servo.  Many thanks and all the best.
  • I've seen lots of post on the forum about the servo jumping. Mine jumps
    too, and I wonder if it's not a software issue. I doubt that so many
    servos would be "bad."

    Mine bounces sometimes (not every time) when the servo is lifting the pen during use. I haven't
    paid attention if it does this when the pen is lifted while the stepper
    motors move the egg or only when lifting the pen when complete, but like
    I said, it seems random.

    I have pasted a link to a video to show what happens when I gently drop the pen arm onto the servo horn.
  • Unfortunately, I think it is just a batch of servos that had bad quality control from our manufacturer. We've been doing more testing here since we discovered the problem, and this batch has a higher than usual failure rate. We're working with our supplier on the issue, and we'd be happy to send you a new one, if you want to contact us
  • Thank you Lenore! I have requested a new one :)
  • edited May 2015
    Just another question. I wondered if I could have "messed up" the motor by not following the instructions that well from the manual starting on page 32 (step 30)? Honestly, I was confused about the installation of the servo horn. In particular, I didn't understand the reason for placing the horn in the "center" (step 31) and then removing it and placing it elsewhere for the "final position" (step 32), all without moving the motor shaft, which is difficult because that horn is difficult to remove. I was worried that I could have done any of the following:
    • Pushed the horn too far to find the center (I thought perhaps this was causing the servo to bounce)
    • Placed the horn in the wrong place (center)
    • Potentially placed the horn in the incorrect final position (also potentially causing the servo to bounce)

    Is there any reason why Step 31 installs the horn at the "center" and then in step 32 we are asked to remove it (which is difficult) and then place it elsewhere? I don't honestly see the point in installing the horn at Step 31 without doing anything but just removing it again, but that's my opinion...

    Just some thoughts I had...

  • First: there is essentially no chance that you messed up the servo motor on your own. Historically, these servos have been extremely reliable; I've never heard of one being ruined by following our normal setup routine. However, it is very plausible that you just got one of the "bad eggs" from that batch-- The servo factory has admitted fault here.

    Second: As a servo motor comes from the factory, its output shaft can be facing in any direction (within the 2/3 of a turn that it can face). Because we don't know its initial orientation, we move the shaft through its range, to point it in the center of its range. We *also* need to have the servo horn pointing in the correct direction. These are separate requirements, so there are two steps. IF you are certain of the initial orientation of the servo motor shaft, you can skip the first step. Since you've already got the software working, you can do this with your replacement: Use the EggBot software to "raise" and "lower" the new servo, before the horn is in place. Once it's in the "down" position, press the horn on, in the correct orientation for the "pen down" position.
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