If you have more than one stepper driving Z-motion, you should have one limit switch per motor to detect “home”.
(Also, in my opinion, more than one stepper on any axis is a design bug.)
One of my printers went askew in Z, again. Why this happens is slightly irrelevant. As common troubleshooting advice covers this case, clearly this happens a lot.
I have two cheap-Chinese printers with this design fault. One an i3 clone (Wanhao/Monoprice), and the other CoreXY (TronXY X5S). Why this misfeature continues to be copied … I do not know.
As I was looking to build and update my printer with a current version of Marlin, was mucking about looking at configuration for Z_DUAL_STEPPER_DRIVERS and Z_DUAL_ENDSTOPS, before realizing the stock control board only had one Z-limit input.
Er, right. Maybe not.
(Wire up two Z-limit switches in series on the existing input, and grind one of the steppers? Sounds slightly dubious…)
Ha! Laziest solution (hack) might be to unplug one of the steppers, and run a belt to lock together the two lead-screws.
Not really a fan of designed-in adventures in mis-alignment.
Totally agree with you on this one. I vastly prefer belt-synchronized screws. Problem is, sync belts add a non-zero amount of parts-count and design complexity, which is a killer when you’re aiming for lowest-cost printer. Steppers are cheap at scale and wiring can route around corners… MUCH easier for the designer/manufacturer.
@Ryan_Carlyle I am a bit surprised that a stepper motor(!) + wiring (and controller board output) is cheaper than a belt + pulleys. Even accounting for assembly costs.
When you price out low-quality pre-wired steppers with integral lead screws at scale purchase quantities, they’re pretty cheap per unit. That integral-screw motor automatically includes a nice pair of preloaded support bearings and tapped bolt preps for mounting.
Belts and pulleys are also pretty cheap, but you still need two screws and one motor, plus a belt tensioner, plus more engineering to route the belt under the bed, plus more factory assembly/alignment time to sync the screws, plus non-threaded screw ends for attaching couplers/pulleys, plus a mount and bearings and bearing preload mechanism for the screw(s) not supported by a motor…
This is one area where it’s cheaper on net to buy a more complex and expensive part that can be manufactured at scale by a specialist, rather than assemble a lot of fidgety components yourself from parts that might or might not have a lower total BOM cost on paper. The Chinese are AWESOME at optimizing manufacturing costs like this.
I think the problem is cheap Chinese printers rather than dual steppers. I have dual steppers on my Mendel90 and they don’t get out of sync ever unless I have a major catastrophe. If your steppers are getting out of sync they must be skipping steps which is something you need to resolve whether you have dual steppers or not.
Duet boards allow independent homing of multiple axes. I use this on an i3 style machine to sync 2 motors. It’s even better in a setup with a bed that moves in Z with 3 motors.
I switched my hictop i3 clone to 2mm lead single-start Z leadscrews and it totally resolved the problem there because the 2mm lead eliminated problems with the gantry driving the steppers. I have purchased (but not yet cut and installed) 2mm lead single-start Z leadscrews for my Tronxy X5S for the same reason. (If I had found http://zyltech.combefore I placed my order I would have ordered the new leadscrews cut to length in the first place…)
@Keith_Seymour Guess my Hunger-Games lore is not deep. Do know the Italian woman who made all the food for the movie. Went to a few of her “secret dinners” in Hollywood. Dinner with a group of largely-Italian Hollywood folk was a misadventure…
I also have only one z-stop (geetech i3)…after 2 years no “sync” problems…Marlin have a “software z-move” limit to check for max. move in z…or you mean something different?
Digital Dentist Mark Rehorst agrees with you: https://drmrehorst.blogspot.com/2017/07/3-point-print-bed-leveling-vs-4-point.html “If the screws don’t stay synchronized (and there are many ways they can lose sync, including just powering the printer on), the X axis tilts, which means the XY plane tilts, and is no longer perpendicular to the Z axis. As long as that condition persists, prints will be skewed, even if your printer has autoleveling. Skewed prints won’t fit together properly, gears won’t mesh right, threaded parts may not work, etc. IMHO, using two motors to lift the X axis is just plain bad design.” [emphasis his]
