Microstepping with Pololu stepper boards on a Gen 3 motherboard

Microstepping is fanastic.

Check out this video I made of a Wade's print. The sound isn't the best but the printer is actually very quiet. I added in some time lapses to shorten the length of the video.




Mike

Nice! That's very fast, isn't it? It is compared to mine at least.

I noticed that you, like me, don't have any thick sheet mounted (across the bars in the x direction). I get a rather bad wobble (noticeable due to jagged edges) when the x carriage change directions - which I though was due to the lack of said thick sheet - but I see you don't. So do you use some other way to stiffen the frame, or could it be my cheap threaded rod that can't take the stress?

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-Nudel
Blog with RepRap Comic

My Mendel uses 304 Stainless Steel for all the threaded rod and I don't see any real wobble so far in my testing. Another Mendel I saw that was built with standard bright Mild Steel has more wobble. If you decide to replace the threaded rod, it should only be the top sides of the triangle (the ones that run from the bottom of the Mendel to the top) that need replacing. The base of the Mendel should be fairly sturdy, given the amount of rods in it. It'd also be a real pain to replace them all, as opposed to just the top sides.

That said, while I don't have boards on mine (and preferably don't want boards on mine), I want it to be stiffer. I'm considering lengthening the top rods slightly, and then adding two rods per side on the OUTSIDE of the frame, leaving the rods just outside the Z axis rods (hence why they need to be lengthened, to intersect with the top side of the triangles just above the bed height (to avoid the bed hitting them, but low enough to make a difference). Fortunately I have some threaded rod left over to try this, but I will still most likely reuse the top rod as the bracing pieces, at least for one side.

Another option instead of lengthening the top rods is to make the top Z axis end pieces longer and include the part in them, and possibly doing the same to the bottom vertex parts as well. I'd like to see the idea work before I try doing that though.

Once my Mendel is fully running (waiting on parts to get my extruder working again) I've just got to figure out the angle and print pieces a bit like the blocks for the Y axis smooth rod, but at the correct angle rather than 90 degrees.

That does sound nice - and it's pretty quick too. Nice to see ever more copies of my extruder out there! Wish I'd included a "send me beer" clause in the license. But then I'd have to send half of each beer to Adrian, then Nophead, etc down the line...

As for the wobbling of the Mendel, I don't think switching steels will get you much. Stronger steels are stronger - they can take higher loads before they bend and stay bent (aka "plastic" deformation), but the Young's modulus (aka Elasticity) is about the same - they're just as stiff as the weaker alloys. Some numbers here:

[www.efunda.com]

A quick cross brace, like the Darwin threaded rod cross braces, or something like Cefiar mentioned, or even just tightening up the joints will probably help more than switching to stiffer steel. I like the thick sheet myself though - it's easy, and it's handy for mounting electronics, and light.

Wade

Hi Nudel
You can't tell from the video and it's not really obvious in the picture below, but the frame is a trapezoid...... or trapezium, depending on where you live . Just to avoid confusion, there are three of us working on this. We canted the frame sides in at the top, !/2” on both and away went the wobble. That's all, nothing more.
Just to note: ABS is forgiving, not sure how PLA would react to the stress, and ….. should you decide to try it yourself you may have to realign your machine.

frame.jpg

Hi Wade
Send me a beer? I think we probably owe you about a half a case by now. If you ever make it to Niagara Falls “Beers on me”.

Somebody wrote in a “we need list” in another thread “We need a more reliable extruder than Wades” …......???? !@#$%????.......... I thought: How can you get more reliable than...... Always works? The extruder in the video has pushed 23 Lbs. of filament and counting. Hopefully we can contribute to the cause in a similar manor in the near future.

Bruce

Cefiar: Yes, I too appreciate the good access you get when not using that thick sheet. I have my tech zone electronics mounted on the side of the machine, which makes it really simple to work on the extruder.

Wade: Thanks for the explanation. Unfortunately I've made a few smart (at the time) solutions where adding a cross brace or thick sheet would either interfere badly with the cabling, or limit the z height to 4-5 cm. It's no big deal to rebuild or change some of it though.
And you should have a buy-me-a-beer paypal donation button somewhere. I'd buy you one. Good thing you didn't include it in the license though, as it probably wouldn't be very healthy to drink that much beer anyway.

Bruce: That is brilliant, thanks! My Mendel is PLA though, and while it's more brittle than ABS I don't think it'll be a problem. But I'll tighten a small amount first to test it.
Your bed looks cool btw, and sorry for hijacking your thread.

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-Nudel
Blog with RepRap Comic

Can you post your software? also what host you use? thanks!

Nudel: no worries, we love to help when we can. We plan on creating more videos of neat stuff in the future but love the micro stepping so much we decided to start there.

DanielG: We use java 5 update 22 on windows xp. Skeinforge from June 29, 2010 and the nightly build from October 18, 2010 for RepRap host. Hope this helps.


Mike

Bruce, that's a great idea - the trapezoid (the two horizontal bars are still parallel, right?) uses the smooth Z rods for cross bracing; a very elegant solution. Will try it myself.

Wade

nice idea bruce! did you just screw them in more, or did you ream out the holes on an angle (or did you adjust the holes in cad and print them out)?

I've been thinking about wire bracing and turn buckles. no plans yet, though.

Nudel, let me know how you make out. We're just finishing up a set of PLA parts to try it out ourselves.
You can play Guinea pig instead.
I should probably post it as a tweak in the Mendel forum....... If it works OK with PLA.

OK.... Wade: I assembled the black one completely according to spec, then to minimize the wobble I loosened all the inside nuts on the top threaded rods a turn and then tightened the outside nuts, and repeated until it stiffened up. I noticed the top bars beginning to bend from the stress and so I stopped, which turned out to be 1/2” on either side, or 1” shorter overall. So no Buback: I didn't ream the holes or alter the plastic parts in any way. Reaming is not a good option as it removes border layers, which provide structural integrity around the holes.
With the blue one I knew I what size I wanted so I measured up some heat shrink to the proper length and centered it on the rods and torched them. Heat shrink, by the way makes an excellent surface for the filament to slide back an forth on.

Bruce: Just tightened it up with a total of 2.2cm, and it's holding up without problems. The PLA made a little squeaky noise, but nothing serious, and I can easily tighten more. It feels better, but I have yet to power it up and test it properly. I think I want to print a few spare vertexes before I tighten much more though, just in case.

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-Nudel
Blog with RepRap Comic

Does anyone have an example of using pololu driver boards with opto endstops? Also what size decoupling caps and how many did you use?

Thanks!

Jeremy made up several of these boards and that's what we are using. We only micro step X and Y. You don't really need to for Z or the extruder.

Pololu.jpg

Decoupling caps. We don't use them.

Edited 1 time(s). Last edit at 02/05/2012 11:51AM by Bruce.