Archive for April 21st, 2017

3D Printer Design Conversation: Part 5

The final installment of musings about building a large-format 3D printer …

(Continued from yesterday)

Perhaps they saw your blog post?

The old-old (original) high-resistance Kysan motor costs something like $45 and, apart from minor cosmetic differences, looks /exactly/ the same as the old-new low-resistance motor. If you were picking motors and didn’t quite understand why you needed a low-resistance winding, which would you pick? Hence, my insistence on knowing the requirements before plunking down your money.

To be fair, I didn’t understand that problem until the Thing-O-Matic rubbed my nose in it. With all four motors. Vigorously.

So, yeah, I think I had a part in that.

comes back to the same numbers over and over

The new-new leadscrews have something like half the pitch of the old-new and old-old threads; I don’t recall the number offhand. In any event, that gives you twice the number of motor steps per millimeter of motion and roughly twice the lifting force. This is pretty much all good, even though it may reduce the maximum Z axis speed (depends on your settings & suchlike).

When it moves upward by, say, 5 mm and downward by 5 mm, you’re measuring position repeatability. That level of repeatability is pretty much a given (for the M2, anyhow), but it doesn’t involve stiction & suchlike.

Can you move the platform up by 0.01 mm, then down by 0.01 mm, and measure 0.01 mm change after each motion?

Do larger increments track equally well in both directions?

Move upward a few millimeters, then step downward by 0.01 mm per step. Does the measurement increase by 0.01 mm after each step?

Repeat that by moving downward, then upward in 0.01 mm increments.

If the platform moves without backlash & stiction in both directions with those increments, it’s a definite improvement.

I wish I knew more
everything you learned is burned into your head forever

The way to learn more is exactly what you’re doing.

Two things I learned a long time ago:

1. Whenever you have two numbers, divide them and ask whether the ratio makes sense.

2. Whenever you don’t understand a problem, do any part of it you do understand, then look at it again.

Also, write everything down. When you come back later, you won’t remember quite how you got those results.

Which is precisely why I have a blog. I search with Google (site:softsolder.com microstepping) and /wham/ I get a quick refresher on what I was thinking. That’s why I keep link-whoring URLs: that’s my memory out there!

You’ll sometimes find scans of my scrawled notes & doodles. They won’t mean anything to you, but they remind me what I do to get the answers in that blog post.

modern controllers utilize much higher voltage and current bursts

More or less. Microstepping drivers apply a relatively high voltage, far in excess of what the winding can tolerate as a DC voltage, then regulate the current to a value that produces the appropriate waveform.

This may be helpful:

https://softsolder.com/2011/05/05/thing-o-matic-mbi-stepper-motor-analysis/

The mass of the bed APPEARS to be cancelling out any magnetic or mechanical stiction.

That can’t be true in both directions: the gravity vector points downward and the results aren’t symmetric. I think you’re reading noise. If the sequences of motions I described don’t produce the results I described, then you’re /definitely/ measuring noise.

From back in the Thing-O-Matic days:

https://softsolder.com/2011/05/22/thing-o-matic-z-axis-resolution-repeatability-backlash/

E3D hot end setups vs MakerGear’s?

No opinion.

I’d want that groovemount post in an all-metal socket, though, rather than the traditional plastic, to get solid positioning and tolerance control. Makergear has the right idea with the aluminum V4 heater block mount.

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