Good morning, Trying to home my machine out for the first time using the openbuilds control software. When i manually press the Z axis homing switch i get this error: [ ] ALARM: 1 - Hard limit triggered. Machine position is likely lost due to sudden and immediate halt. Re-homing is highly recommended. [ undefined ] When i try to home the machine out though the Z axis blows right thru the limit switch. I cannot tell if this is happening with the X/Y axis because i cannot get that far. Is this just a GRBL setting or something deeper?
Also, check the Troubleshooting tab and make sure the CORRECT AXIS for each lights up, accidentally crossing X and Z wiring for example will also result in failure
I did end up crossing Y and Z somehow... thank you!! this leads me to another question... I can home my machine at a much faster feedrate then I can jog it. When I try to raise the jogging feedrate over 1400 mm/min the drives seem to "grind" a bit and over 2000 mm/min the motors won't even move, just hum. Is there something in the GRBL I might have wrong? i'm running 425oz steppers on a 1605 lead screw.
That is a big heavy piece of metal to spin up, so yes, will slow you down - you'd need lower acceleration just to overcome the weight of the screws themselves and spin them up to speed. . 1605s only have a 5mm pitch too (so 5/8ths the speed of our leadscrews with an 8mm pitch) which will further limit your top speed. You'll have to play around with the Acceleration and Max rate values to find a good middle ground where it doesn't stall but still gets decent acceleration and top speeds. The Grbl wiki explains it a little deeper.
It's tricky, size itself isn't the issue. So, basically our entire ecosystem is painfully engineered to all work really well together. Our motors have specific inductance/resistance/torque curves etc to suit our controller and leadscrews. Our leadscrews are chosen for certain specs in turn, and so forth and so forth. Replacing a component - untested in the bigger picture - with another - without weighing the effect that would have, is the problem here. A 1610 would be almost twice as fast as a 1605, with the same acceleration profile (same diameter, same weight - twice the pitch) (16mm diameter, 5mm pitch vs 16mm diameter, 10mm pitch) But our 8mm diameter 8mm pitch leadscrews (0808? not really what ours is, ours is TR8*2, but using the same numbering scheme to explain it better) would be faster - because its lighter and can accelerate to that top speed in less space - thus over the total length of the move, it gets "faster". There is a good reason we use those Even if you were to fit larger motors, you'll have more torque - which allows you to increase the acceleration rate, but the stall point would still be the same max RPM (or possibly LOWER - as larger motors, have more self-braking Back-EMF - another chapter of the same discussion - bigger isn't always better). The choice of the 5mm pitch is still the limitation to speed here - as the acceleration is only first and last sections of the run - not much 16mm Ballscrews are great, but they are just not an appropriate part for this ecosystem, without major changes, to everything else in the ecosystem. Depending on your expectations of course The real question is, why are YOU using 1605s: Did you pick the 5mm pitch to get better resolution or more torque (good reasons to pick a low pitch screw, but you'd know it would have a tradeoff in speed) or are you trying to build a massively fast machine - happy to trade off torque or precision instead (might as well go for high helix screws, rack or belts - way faster). Or was it just a case of hearing Ballscrews are better? (to which the answer is "depends") Boils down to your needs - and what is the BEST way to achieve them - making only the neccesary trade-offs along the way. An upgrade is only an upgrade if it actually improves the situation after all. Otherwise, its just an experiment
This whole thing has been an experiment for sure. Taking ideas you see online and wanting to build your own.. I picked 1605's because that's all I could find in a 2000mm length. I really overlooked how pitch effects speed but I was somewhat looking for the best of both worlds with precision of a lead screw instead of belts. Looking back I never really had an issue with my "store bought" cnc and those belts. I like the idea of better reliability with the lead screws. I wanted a large footprint table to be able to do larger projects but at 1350mm / min it will take some of my large projects a very long time to complete. So now I think i've identified my design flaw with the 1605 lead screws. I guess I need to figure out if I want belts or rack and how I can incorporate it into my current design without completely overhauling the machine. I do have some resistance in the X axis when I get to each end of the lead screw. Almost like there could be a little deflection in the screw and as you get closer to the edge something isn't quite in line causing the gantry to bind up ever so slightly. I would like to speed up the machine at the cost of precision though. Any thoughts on what you'd do if it was "your machine"? few pictures and my 3D design .stp file attached for reference.
$111.00 experiment. Two 1610 2000mm long ball screws. https://www.vxb.com/16mm-Ball-Screw...1t_7gZDBGZB5fusMz7NahI7r4As3cxMAaArsFEALw_wcB
Do you have a datasheet on your motors? Doesn't look like ours (right?) Lets just check that their electrical specs are suitable if they are from a 3rd party
Thanks Giarc, I click on that link though and all I see are 1605's... Yea Peter, I got them from amazon. 425oz running the Y axis and 340oz running the X and Z. I believe this was so i didn't exceed the max voltage or amps the black box could handle...? its been a long drawn out project...
Inexpensive ball screws generally have a relatively large-but fairly fixed- lash- between 0.1 and 0.5mm, typically, depending on how well they're rolled, the size of the balls, and whether it's a 3 or 4 channel nut- so with an advanced controller you can dial it out about 80% in software. Double nut screws are the best way to fix this, at a price- it's not as easy as "two nuts and a spring" like on leadscrews, though you can DIY a double-nut with screws and shims if you get a second nut. Long, thin, screws will also have windup- and whip, if you don't have a method of tensioning them or keep the speed well below critical. I'm not sure if I'd use a 16mm screw above 1500mm in length. I'd probably transition up another 5mm for every 500mm after that- 2010s on 2m, 2515s on 2500mm, 3020s on 3m, etc. Basically a 100:1 aspect ratio... Something along those lines anyway. But to tension them you need a frame that can actually take the stress- without bending, because this isn't just about strength, it's about precision as well- of pulling on each end of what's basically a 3/4" diameter steel bar. Then you need motors that can accelerate and decelerate them at high speeds- which steppers generally just aren't great at, so you're typically over-powering. There's a reason machine tools are massive, even for quite light work. And why high quality woodworking power tools are big lumps of cast iron too. Selecting a screw is not a light undertaking! I love ballscrews, but they have their pros and cons depending on the situation. Often on longer axes, rack and pinion is the way to go- if you have a good anti-backlash method to use. I'm personally against putting 8mm leadscrews on 1500mm axes, but in general the OB system works well together. Once you step outside of it, it's a big world.
Yes, the 425s technically needs bigger drivers for optimal running (you are driving them a little under current which takes away some torque, and they are a little high inductance which limits top speed too, but overall not too bad). But the 340oz ones are even worse! 17mH inductance and 4.5v coils , yikes! May need to use 48v or even highter at the driver to drive them properly, they will be very slow on 24v. Ideal motors for BlackBox has 3v coils, and around 1-2mH inductance - then it performs around 6000-8000mm/min on our leadscrews and stock frame kits
So a motor swap out "should" improve the speed? While 6000-8000mm/min sounds fun I don't even think I need that much. Would the OB steppers handle the 1605 leadscrew to say 4000mm/min max?
I honestly can't confirm it, as its not something we tested. Maybe just try one of our motors, on X-axis as a test. Should make for an affordable experiment
Our high torques still perform well with BlackBox yes, still optimised. Look, theres so much different on your machine, as much I want to, I just can't gaurantee anything, it's too different from our stock setups - just note that.
I completely understand and appreciate the advice... it's worth a shot before I go and start re-designing the whole motion system. Thank you!
For speed, increasing body length is a poor idea- as Peter shows, while it does increase torque, it mainly just increases inductance and resistance. Increasing body *width* is the way to go. That's translates to higher-power NEMA34s. Wider diameter, shorter body. You're basically increasing the length of the lever that the electromagnets are pushing on, instead of adding a bunch more levers. Can keep the smaller, shorter coils- which means lower resistance and inductance. You're not running NEMA 34s above 2.5Nm with a BlackBox though.
Ooops. They were on the bottom of that page. Here are 1610s. https://www.vxb.com/16mm-Ball-Screw-2000mm-long-p/sfu1610-2000.htm
I have the 1605 on my X and Y axes. They are 1500mm, not 2000. I run them at 2450mm/s. If I go any higher I start to get whip. I didn't put the under tension, yet, even though I have the thrust bearings already. Just to lazy, I guess! I had to decide what stepper I'll use and in the end I went with 2 NEMA 34 on the Y axis. The price was almost the same as the 450oz NEMA 23 but way more torque. Something like 4nm or so.
