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Posts Tagged M2

3D Printing: Erratic Z Axis Motion

From a discussion on the Makergear 3D printer forums

A Makergear M2 user, while troubleshooting other problems, had the Z axis begin stalling and moving erratically.

the random up and down movement doesnt make any sense

It’s what happens when a stepper is mechanically overloaded: the rotor can’t turn at the commanded rate.

Start by cleaning & lubing the Z axis guide rods and leadscrew. If that solves the problem, just clean and lube a bit more often. Which none of us do until there’s a problem, of course. [sigh]

If it continues to stall, reduce the Z axis speed by a factor of four. If that solves the problem, then perhaps you tweaked the speed while you were fixing other problems and never noticed.

the technical reason why the motor would move in the opposite direction

The windings set up a rotating magnetic field which, in normal operation, drags the rotor around with it. When the rotor stalls, it vibrates back-and-forth and may wind up synchronizing with the field in the wrong direction.

Old Western movies had a similar problem with wagon wheels turning faster than the frame rate and looking like their spokes rotated backwards.

The stepper may emit horrible sounds, but stalling doesn’t do any damage to the motor or its driver.

I took the bottom of the motor apart

No sugarcoating: disassembling a stepper demagnetizes the rotor. You must buy a new Z-axis motor.

The motor is assembled with the rotor demagnetized, then it’s magnetized in place. When you take it apart, the rotor smacks into the stator, which creates a localized high-density magnetic path between the rotor poles. The rotor poles can’t support the high flux and demagnetizes.

You can put the motor together and it will “work”, in the sense that the rotor will go around, but the decreased magnetic field reduces the torque for a given winding current. You can’t increase the winding current, because the motor will overheat.

The PCB traces look mangled and warped

There’s a conformal coating over the whole PCB to prevent corrosion, so what you see is perfectly normal.

Any analysis of the data from my previous posts?

You’ve been doing a lot of fiddling with the machinery as part of finding the extruder problem, so: did you, at any time, even once, unplug / disconnect the Z axis motor when the power was turned on?

If so, that likely killed a driver transistor in that channel. Order a new RAMBo board along with the new motor.

New Rambo board came today and the z axis is working properly now.

Moral of the story: never fiddle with the electronics with the power turned on!

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Makergear M2: Z Endstop Crashes Firmware

From a discussion on the Makergear 3D printer forums

A Makergear M2 user reassembled his printer, only to encounter a problem:

As soon as my z endstop triggers, the firmware resets

The Z endstop cable is plugged backwards into the RAMBo socket.

The RAMBo socket has three pins: [+ – S].

The two-wire switch cable ends in a three pin connector shell (*) with one empty contact. Unfortunately, the cable connector is not symmetric, not keyed to fit the socket latch, and easily fits into the RAMBo socket either way.

Plugged correctly, the two switch wires go to the [- S] socket pins, putting the [+] socket pin in the empty contact.

If the cable is plugged backwards, the two switch wires go to the [+ -] pins, putting the [S] pin in the empty contact.

Plugged backwards, when the switch trips, it shorts the power supply to ground. Unpleasant consequences ensue.

(*) I’d be unsurprised to discover a machine with a two-wire switch cable ending in a two-pin connector shell. Those must plug into the [- S] pins, leaving the [+] pin waving in the breeze.

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Makergear M2: Bed Heating Failure

From a discussion on the Makergear 3D printer forums

A Makergear M2 user with an older printer (dating back to 2012) had a bed heater failure:

all of a sudden I noticed that my bed temps had started dropping

With a 12 V heater, the most likely problem is at the power input connector on the RAMBo board. The wires from the 12 V power brick generally work loose inside their screw terminals, whereupon the absurdly high current heats up the weak joint and destroys the connector. You can find some hideous pictures somewhere on the forum.

Next most likely is a broken wire between the RAMBo and the heater, caused by repetitive stress injury from all that back-and-forth motion. You may be able to find this with a ohmmeter and some wiggle-jiggle action on the cable, but if even one strand remains intact, the resistance will remain very low at the meter’s trivial test current. Pulling the wires out of the braided sheath will be more definitive; the insulation will be wrecked at the break.

Least likely seems to be the connector where the cable from the heater terminates on the RAMBo.

Start by inspecting the connectors; you may find some seriously charred plastic.

Depending on what you find, you may have a zero-dollar repair.

It’s like you’re psychic.

Suffice it to say you’re not the first person to see charred plastic … [grin]

My solution was to move the high-current switching off the RAMBo board to a solid state relay, with the heater power from a separate 40 VDC supply:

M2 - SSR for Improved HBP
M2 – SSR for Improved HBP

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3D Printing: Native G-Code?

From a discussion on the Makergear 3D printer forums

From a new M2 user disillusioned by the learning curve:

Is there a 3D CAD software out there that natively creates .g or .gcode files It’s not just a 3D printing thing.

CAD (computer-aided design) software produces a solid model, which a CAM (computer-aided manufacturing) program then converts into the specific dialect(s) of G-Code required by whatever machine tool(s) will create the widget. You can create the solid model using many different CAD programs and convert it into G-Code with many different CAM programs, each with its own collection of features and warts.

3D printing calls the CAM program a “slicer”, but it’s a different name for the process of converting geometry into machine instructions.

Even in subtractive manufacturing using lathes and mills, you absolutely must understand how the G-Code interacts with the production hardware.

I unfortunately don’t want to learn all the nuances and parameters of the slic3r software

Then you must use a service like Shapeways: you create the model, send it to them, and get a neat widget a few days later. Their laser-sintered powder process provides much better built-in support than you’ll ever get from consumer-grade fused-filament printers, you can select from a wide variety of materials (including metals!), and, as long as you follow their straightforward design guidelines, you’ll never know how the magic happens.

If you intend to create more than a trivial number of widgets, though, the cost in both cycle time and money will begin gnawing at you. In round numbers, I’ve been designing and printing one widget a week for the last seven years, so adding a printer to my basement shop and learning how to use it has been a major win.

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Tour Easy: SRAM Grip Bushing

After installing the X.0 shifter, I sprang for new grips:

Tour Easy - SRAM X.0 grip shifter - new grip with bushing
Tour Easy – SRAM X.0 grip shifter – new grip with bushing

They’re 90 mm long, which turned out to be 4 mm shorter than the grips that came with the bike; a close look showed the original ones were cut down from SRAM’s 110 mm grips.

Well, I can fix that:

Tour Easy - SRAM grip bushings
Tour Easy – SRAM grip bushings

Ordinarily, you’d just move the brake levers by 4 mm and declare victory. In this case, moving the right lever would be easy, but the left one is firmly glued in place by the radio’s PTT button:

PTT Button - rounded cap
PTT Button – rounded cap

Believe me, solid modeling is easy compared to redoing that!

The OpenSCAD source code doesn’t amount to much:

// SRAM grip shifter bushings
// Ed Nisley KE4ZNU March 2019

Protrusion = 0.1;           // make holes end cleanly

//----------------------
// Dimensions

ID = 0;
OD = 1;
LENGTH = 2;

Bushing = [22.2 + 0.5,31.0,4.0];        // ID = E-Z slip fit

NumSides = 2*3*4;

//----------------------
// Build it!

difference() {
  cylinder(d=Bushing[OD],h=Bushing[LENGTH],$fn=NumSides);
  translate([0,0,-Protrusion])
    cylinder(d=Bushing[ID],h=Bushing[LENGTH] + 2*Protrusion,$fn=NumSides);
}

I loves me my 3D printer …

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3D Printing: Slow Hot End Temperature Oscillations

From a discussion on the Makergear 3D printer forums

A Makergear M2 user encountered a temperature control problem:

Problem: Temperature fluctuation on the hotend +/- 7 degrees C when set in the controls. A little more extreme when printing (~+/- 15).

Slow cycling like that indicates the hot end’s PID loop coefficients don’t match reality.

Preheat the extruder to maybe 200 °C, run a PID calibration (M303), store the results in EEPROM (M500), and that should do the trick.

PID coefficients depend on the hot end’s physical condition, so you should re-do the calibration whenever anything changes on the hot end. Even removing & reinstalling the same hardware will change the contact points between, say, the thermistor and its hole in the hot end.

A dab of good heatsink compound on the thermistor should stabilize its contact with the hot end, although that will change the reported temperature and PID coefficients. Probably doesn’t make any real difference, but I felt better:

M2 - Thermistor with heatsink compound
M2 – Thermistor with heatsink compound

Which prompted a question from a user who regularly swaps entire hot ends to change nozzle diameters:

run a pid cal when I set my starting height each time I switch?

Assuming you swap entire hot ends, including their thermistor & heater, then you can calibrate each one, write down its PID values, manually set ’em with M301 when you install it, then use M500 to store ’em in EEPROM.

Because you bend those fragile thermistor wires every time you swap hot ends, keep a couple thermistors on hand. You’ll need ’em.

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3D Printing: Peculiar Octopi Problem

From a discussion on the Makergear 3D printer forums

A Makergear M2 user had a strange problem:

Octopi claims the serial connection went down.

LED2 was blinking red, rapidly, and LED3 was shining with a steadfast red light.

LED2 shows the extruder heater PID loop is running and LED3 shows the extruder fan is on:
https://reprap.org/wiki/Rambo_v1.1

You just never noticed the blinkiness before … [grin]

Because the extruder heater is still running, the firmware hasn’t detected a (possibly bogus) thermal runaway or any other fatal problem. It’s just waiting for the next line of G-Code, but Octopi isn’t sending it.

Casually searching the GitHub issues, there’s a report of intermittent serial problems from last year:
https://github.com/foosel/OctoPrint/issues/2647

Which points to the FAQ:
https://community.octoprint.org/t/octop … eption/228

Look at the Octopi Terminal log to see if the conversation just before the failure matches those descriptions.

Assuming you haven’t updated the printer firmware or anything on the Octopi, then something physical has gone wrong.

First and least obviously, the Pi’s MicroSD card has probably started to fail: they’re not particularly durable when used as a mass storage device and “the last couple of years” is more than you should expect. Download a fresh Octopi image, put it on a shiny-new, good-quality card (*), and see if the situation improves.

Then I’d suspect the Pi’s power supply, even though you’re using the “official rpi power supply”. All of those things contain the cheapest possible electrolytic capacitors, running right on the edge of madness, and produce bizarre errors when they begin to go bad. Get a good-quality wall wart (**), ideally with a UL rating, and see if the situation improves.

While you’re buying stuff, get a good-quality USB cable (***) to replace the one that (assuming you’re like me) you’ve been saving for the last decade Just In Case™. Use the shortest cable possible, because longer does not equal better.

After that, the problems get truly weird. Apply some tweakage and report back.

(*) This is harder to do than you might think. You may safely assume all cards available on eBay and all “Sold by X, Fulfilled by Amazon” cards will be counterfeit crap. I’ve been using Samsung EVO / EVO+ cards (direct from Samsung) with reasonable success:

https://softsolder.com/2018/10/16/raspb … sk-memory/
https://softsolder.com/2017/11/22/samsu … ification/
https://www.samsung.com/us/computing/me … 22y+zq29p/

The card in question eventually failed, so having a backup card ready to go was a Good Idea™.

(**) Top-dollar may not bring top quality, but Canakit has a good rep and costs ten bucks through Prime.

(***) Amazon Basics cables seems well-regarded and work well for what I’ve needed.

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