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No limit switches - 2130 - Will that really work?

Posted by tbeaulieu 
No limit switches - 2130 - Will that really work?
February 16, 2018 11:23AM
Hello, I'm brand new to reprap. Just starting the wiring on my steel frame arduino/ramps 1.4 build loosely built on Tom's cheap prussa I3 video series.

I just got the X axis moving manually (hello world) using the standard controller chip. The printed limit switch mounts that I got are just not compatible with my build and I'd like to eliminate the switches entirely. Tom's video on the 2130 states that the chip makes this possible. I yanked the controller chip and replaced it with a 2130 and did the pin mods needed to reroute the 5 pins to the AUX, limit switch port and new (selector?) port. After work I'll try to tie in the 2130 library and test.

Has anyone successfully done this? Am I ok thinking that I can use the wonderfully solid hard stops on all axes to home this, BUT to then be able to specify offsets for a "logic home" that would position the extruder in the first usable location? The hard stops would be off the bed.

Thank you.
Re: No limit switches - 2130 - Will that really work?
February 16, 2018 11:36AM
Stall detection works very well with the big brother TMC2660 on a Duet Board . IDK if the weaker TMC2130 will be as easy to tweak. Some experienced users gave up on using the common TMC2100, because they were so hard to tune.

Make sure, the nozzle is off the bed when you home Z.
Manual homing position is the parameter to change the coordinates. But I prefer G92 X... Y... Z... as a command line in the slicer start code, because it is easier to change.
Re: No limit switches - 2130 - Will that really work?
February 16, 2018 11:50AM
I can't give you details on using sensorless homing with Arduino/ramps/TMC2130 because I haven't tried it. But we've been supporting sensorless homing for a few months on Duet electronics, which use the TMC2660 - the big brother of the TMC2130 with double the current capacity. So you may find our wiki page at [duet3d.dozuki.com] helpful. The configuration details for Marlin will be totally different, but the general principles and limitations won't change.

The main takeaways are:

* Sensorless homing is much less accurate than traditional homing using a microswitch. On a Cartesian printer, this doesn't really matter on the X and Y axes, unless you want to support resuming prints after power failure. On delta printers, it's OK to have imprecise homing if you have a good Z probe and your firmware can do fast auto calibration after homing (again, unless you want to support resume-after-power-failure).

* It helps to reduce the motor current during homing, so that you can get a motor stall without the belt jumping on the pulley, without having to reduce the motor torque during normal printing.

* Stall detection works over a limited range of speeds. The actual speed range depends on your motors and your supply voltage. The traditional approach of homing quickly, then reducing speed and homing again to get greater precision may not work, because stall detection doesn't work at low speeds.

* High-inductance motors may be better for low-speed stall detection, but they reduce the maximum movement speed you can achieve using a given supply voltage, so from that point of view they are undesirable.

Bear in mind that Joseph Prusa's I3 Mk3 has a controller that supports software-settable motor current, it uses 24V power, and he was able to choose stepper motors that work well with the TMC2130 stall detection.

HTH David

Edited 1 time(s). Last edit at 02/17/2018 02:56AM by dc42.

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: No limit switches - 2130 - Will that really work?
February 16, 2018 06:06PM
Thank you for your tips. I'm digesting it all.

I had the X axis working manually with the LCD controller knob. Replaced the 2100 with the 2130 that was modified, installed the library and made the changes to the .h files to enable 2130, enable it for the X axis, enable sensorless homing and finally, I moved the CS pin to pin 40 and changed that in the pins_RAMPS.h. Oddly, changing it to to nearby pin 57 did nothing, but pin 40 TRIES to move in both directions, but it does not.

M119 says X is not triggered, but it acts (I think) as if it were. If I put a physical limit switch in, I can trigger/clear the stop, but nothing changes as far as the stepper's movement goes. It whines, but doesn't move. I saw this last night as I was tweaking the settings with the 2100 and it was solved with the jumpers under the controller chip and (heck I changed a bunch of other things, but not since it was working, so I had hoped the 2130 would just "work").

Any suggestions would be appreciated, as I've spent a couple hours leaking curses ..

PS this is a german chip with the website "www.fysetc.com" printed on the board.

Thank you.

EDIT: Progress? Apparently this mfgr shipped the board with a crappy combination of default jumpers that is part of, or the entire, problem. I have the motor moving now. I had to remove a surface mount resistor and then span two jumper blocks with solder. These are ridiculously tiny and I had to use a loupe. Even then, it was incredibly sloppy and iffy work. This would be better done with a microscope. While researching this, I see that this mfgr has a new version of this board (V1.1), which has corrected these mistakes, and even added the riser pins. Had I known I would have bought those. Onto modifying the other axes boards ...

I got the information from the following page.


Edited 2 time(s). Last edit at 02/17/2018 01:26PM by tbeaulieu.
Re: No limit switches - 2130 - Will that really work?
March 15, 2018 07:08PM
Update ... I've been using sensorless homing in X and Y for a couple of weeks now. It seems to be just fine. I may be missing something but I don't see how sensorless homing's accuracy could possibly be an issue. Once you home, the print is off and running. It doesn't home again, right? Again, I'm green enough that maybe I'm missing something. I will say that I see Y steps missed on taller prints that I'm trying to work out, but I didn't think it would be related to homing.

Also, if I set my speed too low, the homing trips immediately, so I think that is proving the statements above. It's enjoyable learning and trying out different approaches, so who knows where I'll end up down the road with this thought process.
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