Oh… I am not actually sure. that could be a fix. Basically, have it always reset the tmc’s after 30 seconds or something on boot.
The same could be said if they home without enabling the bltouch starting gcode. I provide the starting and ending code. They need to cut and paste it. Currently you even need to edit and compile the firmware to adjust for mesh leveling if you build any other size, so a single line of ending gcode should not be a huge ask.
We provide the hardware and code snippets, if they do not use them we can be faulted for that. I do not think I can be held responsible for everything that can go wrong if we provide a clear solution.
Zipt tie
The thing I am 90% worried about is power outages. This klipper thing is new and I can’t test it yet so I am unsure about it.
The current build as designed it is not an issue, the bed is so light it barely falls, not fast enough to pop anything so now this new design with a larger standard bed they will drop…I am not sure if it will be fast enough to pop anything. JJ’s is 3-4(?) extra pounds, heavier than the current new as-designed machine will be, so that is sort of a new case. I am not sure that there have been another boards killed this way but knowing he popped 2 boards make me feel like I need to prevent it.
trust me that crossed my mind. I got something I’m going to try. will post pics when I’m done. Its a pain because everything is in the way. xy rails, belts in the back. motors lol
I think from my perspective, this seems pretty straightforward, providing the requirements are clear and it doesn’t feature-creep into the stratosphere.
Having the brake only ever be triggered by the steppers changing from enabled to disabled is super easy to do and, aside from the cost/complexity of needing to have the brake able to see the enable line, pretty damn cheap.
If the challenges all lie in the corner cases then that’s great, maybe we just need a list of them brainstormed up and we can go through and start ticking them off. Having the TMC2209s fault if the enable line is only de-asserted briefly is a great example. Perhaps that’s something that gets determined as rare and can be handled with a note that a power cycle of the controller will be needed if this happens. Perhaps resetting the TMC2209s before starting the homing process would solve it. Perhaps making sure that the brake doesn’t fault the TMC2209s would be possible.
I dunno, it really doesn’t seem particularly complex at all. There’s a good chance that means I"m missing a lot of the nuance.
Well after several cuss words and putting the matches down twice I got the springs installed-ish. No way I can print with them installed like they are. This was all I could come up with quick to just get a test. And those damn nuts under the Z motor mount… I forgot all about them and the first one dropped out. Trying to get it back in and dropped it again… now cant find that thing with a search warrant. luckily I had a few more. fought and fought with that to find out in the end the tip of the screw was messed up. New screw and got that one back in. the other 2 I knew damn well to make sure that nut didn’t fall out LOL.
Here is a short video of the test. It didn’t do right. the one on the right side bound up on the motor. After the video I figured that out and bumped it and it lowered down nicely. Only issue I see is how the hell to mount these things where they aren’t in the way. They are not small at all.
That’s possible but will need some kind of 3d printed part to hang it from. Nothing I have around here that I can think of anyways will work. And a zip tie wouldn’t last long. these things are SHARP.
Another question is whether one could just put some large zeners on the power supply rails so that you can’t ever take them over the damage threshold. On the SKR Pro, it’s U2 that’s getting killed:
The fuses aren’t blowing, so we’re either reverse biasing something or we’re overvolting the 5v rail. My bet is we’re overvolting it.
Ryan- can you do a characterization test?
Disconnect the steppers from one of your printers’ control electronics so you don’t blow up a board.
Do this first with a DMM in voltage mode across one coil. use 100v range.
Move the bed up to Z max. Place a 3-4 lb object on the bed, and make sure you protect from the drop messing up your frame.
Let it drop.
How high is the max voltage (It will probably be worse than your DMM shows, and what polarity?)
I’m betting that if we look carefully at what happens it will explain why the SKRs regulators are blowing and probably be a bit of a forehead slap.
If you have an already dead SKR (but one that didn’t blow the regulator) with otherwise bad 2209s, do a smoke release test with the instrumentation hooked up- maybe even with the scope (Probes and scope set to the highest voltage setting if it is safe to do so given the peak voltage above)
NOTE: Yes, all over everywhere are warnings to machine users not to move the machine by hand or at high rates when drivers are connected but not powered/enabled. This is a well known problem. I’m being lazy as I bet there are good papers written about this in the literature. I first blew up a controller this way in about 2014 when I first encountered a LulzBot AO100. That wasn’t a Z drop, dumb butt me just moved the print bed backwards by hand at a reasonably fast clip because I wasn’t thinking. (Bed slinger printer) The first of many RAMPS boards I killed.
@vicious1 or anyone else, is there anything further you would like me to check with these springs before I take them off so I can start printing again? Going to have to come up with a better way to mount them permanently but that’s tomorrows problem lol.
Have been hoping springs are cheap and good enough. But…
Whether or not tension springs or counter balance end up being recommended… Am also hoping this topic ends up with a “Stepper extension board” being created with 6 pairs of connectors. That minimally has over-voltage protection for the controller on at least 3 of the connector pairs for the Z steppers.
Given bang for buck priority… Out of the following two requirements, 2) seems to be the priority? Especially if people avoid Alu for Bed Support plate. Just use Alu for Bed.
“stop the bed hitting hard stops at speed”
“avoid an over-voltage on the stepper driver boards”
Controller protection seems more important than physical braking/slowing/halting hard drop? Physical damage from hard drop can be mitigated using cheap TPU/rubber bumper, or TPU whoopee cushion maybe?
Came close to making a dumb connector board for my enclosure (without voltage spike protection). Currently just have a simple 3D printed DuPont shell holder thing (red circle) has been good enough to extend stepper wires to controller using premade 12" 22AWG DuPont extension cables (blue squiggly)…
I don’t disagree. Its just figuring out the right way to mount them out of the way of everything else. A good way is not jumping out at me right now. I was looking at it all when I was putting them on. But I am NOT a designer that’s for sure.
That will probably be doing what the TMC2209 is already doing in this case. It’s just re-directing the induced current into the rails, which is what the issue seems like here if the main board is dying while the stepper drivers are fine.
I think the thing is that 1) will also prevent 2) in most of the cases. 2) will not necessarily prevent 1).
Doing both would be ideal, but may need to cover too many corner cases to be worth doing, at least in one design.
Adding over-voltage protection of some kind to the input of the SKR boards may be a better approach to solving that if it’s just those specific boards that are brittle due to regulator choice.
I wasn’t saying clearly what this simple board opens up…
Imagine a variant of this that places the required protection for whatever rails need it - on the intermediate board. It could also provide a connectorized place to break out the enables and maybe diode OR them together. So that then could be the way to get the enables over easily over to a “brake module” without otherwise having to modify the boards with brittle regulator designs.
Edit: Changed to say “protection” and “whatever rails” based on the good feedback below.
Ah, I follow now. It’s a great option for adding an active brake module and that would easily work with the size constraints of that board.
For adding zeners, I don’t think it’s the 5V rail that will be the issue, it’ll be the Vmot as that’s likely where the output drivers will be bypassing to.
It would be one way to add the zeners, although they could be added anywhere that connects to Vmot, if what I’m thinking is right. I’d also be a little leery of just doing it with zeners as they tend to be pretty variable in their specs. Set the Vr too low and they leak/overheat under high line conditions. Set them too high and their dynamic impedance doesn’t let them sink enough current to protect things. It’d be interesting to know what the actual threshold on the SKR boards is before damage occurs. Doing some form of SCR based crowbar isn’t too hard, if that is the case.
I forgot all about them and the first one dropped out. Trying to get it back in and dropped it again… now cant find that thing with a search warrant. luckily I had a few more. fought and fought with that to find out in the end the tip of the screw was messed up. New screw and got that one back in. the other 2 I knew damn well to make sure that nut didn’t fall out LOL.
