Head-crash at power down?

  • I'm at the point of wiring and configuring the electronics of a delta build, my first-born DIY printer, and have just installed OSM 7HM19-2004S 0.9-degree steppers to replace the 92oz.in 17HS24-2104S 1.8-degree motors originally purchased for the project. While the holding torque of the new motors is some 30% less than the first units, due to the shift from 1.8 to 0.9 (my best guess at least) the change in the ability of the steppers to keep the effector assembly elevated when powering down seems significantly greater than this and the whole thing now crashes into the bed at a disconcerting velocity. While the weight of my effector plus the Hiwin MGN15H carriages is somewhat higher than is typical I doubt that it weighs as much as more conventional designs with the addition of a flying extruder for instance. I'm a bit surprised that I've not encountered mention of the problem on forums, but am quite curious as to how this is typically remedied. I would be grateful to receive any suggestions.

    Thanks a lot!

    • Michael

  • Hi, when I was using a flying extruder on my delta I also found that the steppers did not provide enough support when the power was off to stop the nozzle descending into the build plate so I fitted a counterbalance weight and a couple of pulleys and it was no longer a problem.

  • Thank you burtoogle. That was my first thought too, but at this point I'm still hoping that a somewhat more elegant solution exists.

    Were I to go with the counterweight approach I'm inclined to believe that the counterweight cables would be best attached to the Hiwin blocks with a simple wiffletree arrangement in order to minimize possible negative effects of the counterweight's inertia. This limits the range of motion of the counterweight to essentially that of the Z-axis rather than that of each carriage block (three separate counterweights in that case). Pretty much the same as securing the cables directly to the center of a flying extruder.

    Any photos of your own solution by chance?

  • Pretty much the same as securing the cables directly to the center of a flying extruder.

    Yes, that's what I did. Sorry, no photos. I had a thin cord (bowstring yarn, very strong and comes waxed!). The cord ran from the flying extruder vertically upwards to a pulley mounted in the middle of the top triangle, then to one side where there was another pulley and thence downwards to the weight which just dangled down the back of the frame. Elegant? well, it worked very well and that's all I cared about.

    I stopped using the flying extruder because I found that its mass was still enough to cause artifacts on the print. I am now using a flex3drive extruder and so I don't need the counterweight anymore.

  • administrators

    I use a heavy-duty keychain retractor to help support the weight of the Bowden tube, and that is sufficient to prevent the effector from falling when I power off.

  • Thanks again burtoogle and David for your responses. Looks like counterweight it is. (Or your retracting chain David, nice idea!)

    burtoogle, I've been eying the flex3drives for a while. Sounds like you're happy with yours? I had what I consider very good results in my experiments with the flying extruder on my small delta, a clear improvement in surface quality over the full Bowden. But your comments reinforce my feeling that a flex3drive will likely be the best option for my application, as long as one of Jason's dual extrusion options proves workable.

  • Hi papilio, the flex3drive extruder has generally worked well so far. My only problem has been that it doesn't have any means of adjusting for filaments whose diameter varies greatly from 1.75mm. I have some TPU filament that is around 1.55mm dia which it prints very nicely but only after I found a means to take up the slack in the over-centre lever that holds the filament idler wheel in place. It would be much better if it had some adjustment like most other extruders do.

  • Thank you burtoogle, always most pleased to hear of others' experiences with these!

    My current thinking is that I'll stick with my 1.8-degree steppers for the time being and consider the 0.9-degree units as a later upgrade. This being my first home build it probably doesn't make sense to add any unnecessary complications at this point which will likely just delay completion of the project. Once I get up and running, I'll investigate the 0.9-degree solution along with making a switch to those 16-tooth pulleys.

    I'd be grateful for any opinions on the 1.8-degree motors which I have on hand, 17HS24-2104S from Stepperonline. Are these considered a good match to Duet Ethernet? I'm getting quite a bit of noise from them, certainly more than I'm used to on my smaller printer to be sure (running TMC2100 drivers), including significant whining when idle. But I'll be picking this up in another post.

    Thanks to all for your help!

    • Michael

  • administrators

    Yes that motor is a good match, although probably more powerful than you need for a delta printer.

  • Good to know, thanks David. My brain still spins in the context of anything electronics-related, but hopefully I'll get there.

    Likely due to previous experience designing astronomical telescopes, I'm thinking that this thing is rather over-designed. Somewhat more mass than is typical so I wanted to be sure to have the torque for it. Experience will tell.

  • What a brilliant idea David! I picked up a T-REIGN large retractable gear tether yesterday, problem solved beautifully. I'm pleased that I can go ahead with the 0.9-deg steppers now, thank you.

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