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Doesn't know where "home" is
06-05-2017, 10:52 PM (This post was last modified: 06-05-2017 10:55 PM by roachslayer.)
Post: #1
Doesn't know where "home" is
Got my iboardbot assembled and drawing, very slick! However, it is completely unusable after EACH print, requiring power-down and moving the X-axis back home Every. Single. Time. ad nauseum!

Procedure:
  1. Move the print head to the bottom left ("Home")
  2. Power on
  3. Enter a text print ("Hello", or whatever)
  4. Bot successfully prints "Hello"
  5. Upon completion of the above, the print head does NOT return home, rather, near center X and bottom on Y.
  6. Try print "Hello" again (without even erasing)
  7. The print begins "H" way to the right and fails to complete because it tries to move off the glass to the right!

I have to turn it off, move x to the left, then power on after EVERY print because it does not return home upon completion. WHY?

Erase (clear board) doesn't work at all, it just pegs to the right of the board, can't scan across the whole glass properly (tries to go way off the the right, then left an inch, then right again pegging the edge). Up and down on Y seems to work ok, but even then it moves too far to erase (leaves lines that do not get erased)

What I expect:
  1. iboardbot should remember where "Home" starting point is (steppers here, not DC motors for crying out loud)
  2. Repeatability (same as above, should be able to repeat things in the exact same manner without powering off and moving the head first)
  3. Steppers should be OFF when idle! Not engaged and holding (sucking power!)
  4. Y axis should not move so far when erasing, leaving unerase streaks
  5. The ability to calibrate this thing so all the above aren't so wacky


Not that the stepper motors being powered at all times is related to my print issues, but it sure is annoying that is sucks power, and is not movable (hence my having to power down every time I need to adjust it).

Anyone else seeing any of these issues? Suggestions?

Thanks!

Note: I noticed Y makes two passes to erase (up, and then back down). One way to address the erase issue leaving streaks is to OFFSET a little on the way back down. The darn thing swipes in the exact same Y position on it's way up as it does down, and all it needed to do is make a half-step offset on the way down and it would cover every "pixel". Either this, or it just needs to not move so far (it moves in a longer stride than the actual eraser vertical surface, and yes, my felt covers the full surface).
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06-06-2017, 10:26 AM
Post: #2
RE: Doesn't know where "home" is
The iboardbot should go back to "home" after a short pause. It looks like there is a little bit of friction not allowing to move the drawing header smoothly. If you remove the belts, can you move the pen holder with your fingers easily?
Once the drawing header is "at home" the stepper motors should go idle...
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06-06-2017, 07:52 PM (This post was last modified: 06-06-2017 07:54 PM by roachslayer.)
Post: #3
RE: Doesn't know where "home" is
(06-06-2017 10:26 AM)JohnQ Wrote:  The iboardbot should go back to "home" after a short pause. It looks like there is a little bit of friction not allowing to move the drawing header smoothly. If you remove the belts, can you move the pen holder with your fingers easily?

Yes, I have eliminated friction as an issue. It seems to be a problem related to initial startup movement of the stepper, even with no belt at all!

What I am seeing is that the steppers will make noise like they are supposed to be moving, but are oscillating, frozen, not spinning. This results in iboardbot THINKING it has moved to the expected position (such as home) but never getting there, thus it's point of references is off.

A light nudge actually causes it to suddenly move again when in this frozen state. It's not a friction issue, but rather, an initial kickoff issue, as if a stepper phase conflict of some kind. This appears to happen mainly when a big move is executed (sweep to erase, or return home) but seems NOT to be a problem for little moves (it will consistently draw letters, lines, etc just fine!).

Given the above, and given than I had eliminated excessive friction as a factor, I immediately suspected a problem with current. I adjusted the ref voltage on my stepper drivers (up to .770v, from .500v default), giving it considerably more current. NO CHANGE in behavior. Sad

I noticed this same strange "freezing" behavior when I use my brain shield with b-robot. Sometimes it just freezes, making lots of noise like it should be spinning, but instead is oscillating. Again with no friction, this happens with wheels off the ground!

jjrobots, I am using a complete brainshield kit I bought from you, but my steppers are my own. They are 7HS16-2004S1, which is a 2A 1.8deg 64oz stepper, almost identical to what you sell in your kits, even the same wire colors (and pinout from what I can tell). I've tried running them at 6v and 12v, and adjusting the current as mentioned. I'm kinda at a loss as to what to try next. Have you seen oscillating freeze at any point in your tests?

(06-06-2017 10:26 AM)JohnQ Wrote:  Once the drawing header is "at home" the stepper motors should go idle...

They are energized and holding firm (no buzzing/oscillation though) immediately after turning on and no commands given. If by idle you mean not moving, this is true. But if by idle you mean powered down, I'm not seeing that.
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06-06-2017, 09:02 PM
Post: #4
RE: Doesn't know where "home" is
IF the iboardbot can draw we have achieved something here. But the lack of power... this is strange.
The main reasons could be:
- Stepper motor drivers: but you have already checked the current delivered and adjusted it to the max
- Stepper motors: based on the featured you have sent they should be strong enough to move the robots but maybe the internal wiring is not the same as the "officials"? Can you try to swap the cables and give it a try?
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06-08-2017, 10:35 PM (This post was last modified: 06-08-2017 10:37 PM by roachslayer.)
Post: #5
RE: Doesn't know where "home" is
Further experimenting so far:
If I swap one of the two coils around (polarity on one set of coils), it seems to work consistently without the oscillation I described above. Erasing works, returning to home works... but MIRRORED (because it's all backwards, of course). Letters still draw fine, but mirrored too.

If I swap cables for BOTH coils, then I get everything mirrored AND get the oscillation problem back. Hmmmmm.
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06-14-2017, 07:57 AM
Post: #6
RE: Doesn't know where "home" is
hmmm.... Is there a chance you can use another stepper motors?
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