Odd Stepper Motor issue

[pjfossee]

So this all started because I had a broken thermistor in my hotend. I replaced it and figured while im at it Id replace the heater cartridge and hear block too since they were covered in plastic. But of course I took the cheap route and bought a Chinese heater cartridge which couldn't keep the temp of the hotend constant(I later read this was a common problem with Chinese heater cartridges). It also caused ATX PSU powering my printer to turn off because it triggered one of its protections. So I put my old heater cartridge back in. Temperature was back where I wanted it which was completely constant, but my printer turned off again! This time though, the ATX PSU and my LCD screen were still on, just all the stepper motors had stopped. They did not move at all, not even a buzz. So I went and looked at my RAMPS board figuring I fried something and after many voltage measurements later came to conclude that my Arduino board was fine so it must be the stepper drivers or RAMPS board. I didn't notice any melted soldering points and no smoke was released either. The stepper drivers still had voltage, but it could only be adjusted in uneven increments. Like it would jump from 1.2 v to 0.3v to 3.2v regardless of how small or large of a turn on the potentiometer I made. So I figured those were fried. Also, in my testing, I noticed that when I told the stepper motors to move in pronterface, they didn't move(I expected that) but the temperature read by my Thermistor would in increse about 1.5 degrees per stepper motor activated. So in total I could get the Thermistor reading to increase 6 degrees if I activated all axes. That made me think my RAMPS board might have an issue. I bought a new RAMPS board, new stepper drivers, and a new Arduino board just in case, and replaced all the old ones with all of the new ones but still the stepper motors would not move. At this point I had not plugged in the thermistors or any other electronic part. All that was installed was the Arduino board, RAMPS board, one stepper driver, one stepper motor, my PC and the PSU. I measured accurate voltage readings across the board. So that rules out a bad RAMPS board, steps driver, or Arduino board. All I can think of that could be broken are my actual stepper motors. But the thing is when I put an led into the connector from the stepper motor and manually turn the stepper motor, the led lights up. Also, a AA battery quickly inserted into each connector for each coil of the motor did make the motor move. I don't know if that rules out a bad motor, but from the tests I saw people do on YouTube with good stepper motors, mine behaved similarly. So basically I'm asking should i buy new stepper motors or is there another potential solutions?

[pjfossee]

Update: My stepper motors are fine. I temporarily got my printer working. Started working completely randomly. I discovered that the VMOT pin on my ramps board is extremely inconsistent when it comes to voltage. When it actually measures 12v, my printer works. However, it seems that anytime I plug something else into the board, the VMOT changes. And sometimes it just changes without me touching anything. When it does change it changes to less than 12v and usually stays there even after I unplug everything I just plugged in. And then it might be 10 minutes or 10 hours later before I get VMOT back at 12v. I don't know what's going on or even where to start replacing stuff. My PSU is an ATX EVGA 600B. Should easily be up to the job. Also brand new - only used in this printer, and worked flawlessly for 2 months.

[pjfossee]

Man I dream of the day I'll have had a printer that worked for more than a week. Basically right now there is an issue with the VMOT pin. I've determined the cause of all the other issues in the original post (most because I plugged in a stepper driver backwards). The VMOT pin on the RAMPS board does not stay 12v and tends to drop down to 100mv when I plug anything in. Occasionally it drops to 1.2v or 500mv, but it's always one of these low voltage values. When I unplug everything, the voltage stays low for a while, but when I plug the PSU back in, I can normally get 12v back after a few tries. And then I try plugging a stepper driver and stepper motor in and the 12v goes away again. I checked my PSU and it is outputting a constant 12.27v regardless of how much stuff is plugged in. But my PSU is the only constant between my old RAMPS + Arduino + Stepper Driver setup and my completely new one. And since I see the same issue in both setups, I can't help but think it's my PSU. When I just look at the isse though, it seems something is up with the 5amp rail on my RAMPS board as my PSU seems ok. So i don't know if Im just really unlucky and got two bad RAMPS board or if I broke my PSU.

[printbus]

What are you probing as VMOT on RAMPS? That doesn't jump out at me in a quick review of the wiki RAMPS schematic or on the RAMPS board that I have. EDIT: Oh, do you mean the vmot pin on one of the stepper motor driver boards? THe ONLY thing between that and the 12V input terminals on RAMPS is the polyfuse mentioned later...

How/where are you measuring the power supply output voltage? Hopefully at the input terminals on RAMPS rather than another set of 12V wires from the power supply?

When you were having motor issues but the LCD was still on, was the printer connected to anything via USB? USB will provide 5V to the Arduino and keep it (and the LCD) powered on even if the 12V power supply is off, for whatever reason.

Reading between the lines, what seems to be happening is the polyfuse on the RAMPS 5A input is tripping and going into protective mode while the printer is connected to a computer via USB. How extensively have you scrutinized the wiring from RAMPS to the cartridge heater? Do you have anything like a print cooling fan connected to the RAMPS D9 output? Remember that on RAMPS, the + outputs for those are always hot. Even when the hot end heater or fan output is switched off, those + outputs still have 12V on them... Could be there's an intermittent short between, for example, the cartridge heater D10 + output and a ground wire for an endstop, the hot end thermistor, or some other point that is at ground potential.

Other than the bed heater and motors, do you have anything else that runs off 12v like other fans or LED lighting connected to RAMPs in any way? Where are they connected, and have you scrutinized the wiring for them?

One thing I'd look at is whether there's continuity between the cartridge heater case and wires going to the heater. There shouldn't be. If there is, that could be putting a voltage onto the aluminum block. Then you'd have to worry about whether either of the wires to the hot end thermistor are exposed at the block as well.

Then I'd go into divide & conquer. Remove all the outputs from RAMPS but one, play with that one, and when convinced that one is OK, add another. Even with the motors, you could connect one at a time and do some manual single-axis movements through either gcode commands or via the LCD.

[pjfossee]

I figured it out Printbus! Thanks for the reply, you are such a nice guy. I wouldn't have read through that angry wall of text i wrote. Anyways like you said I checked the Polyfuses and they were still working as in they were allowing the voltage to flow through. The voltage drop was coming before the Polyfuses. Turns out it was something wrong with the connector for the PSU power cables to the RAMPS board. Since I bought a new RAMPS board I used the connector that came with it. That explains why my old and new stuff both had the same problem. And per the VMOT pin, I was referring to the connector on the RAMPS board that corresponds to the VMOT pin on the A4988 stepper driver. Sorry I'm still learning the lingo. I appreciate your help. I must say though I understand how the RAMPS board works much better after this experience. Even though the solution was so simple, I learned quite a bit.

[printbus]

Glad to hear you got it figured out. At least now you have a pile of parts for spares, or, um, for planning a new printer build. Yeah, that connector should have occurred to both of us earlier. I remember someone commenting during my build that they had went through issues with their pluggable connector and were recommending I ditch mine. I replied that while I'd never use a connector like that in my own designs, I wasn't going to hassle trying to remove it until I had troubles.

[pjfossee]

One more quick question. So I got that whole issue sorted out, but my z axis is still finicky. With one z motor plugged in it works fine, with two the buzz and barely move or not at all. I tested both motors on othr axes and they work fine. I also tried a different stepper driver to no avail. Also true different ramps and Arduino. Not sure again, probably something silly.

[printbus]

There are two things that make the z-axis application unique, compared to X, Y and the extruder. First, there are two motors in parallel on the same motor driver. Second, due to the effective gear reduction from the threaded rods on the z-axis, it takes a lot of steps to get much linear movement in the z-axis.

Are you still running default settings on Z-axis as far as feed rate and acceleration? What is the z-axis feed rate? 2mm/sec? Jumpers installed under the stepper driver so you get 1/16 microstepping? If so, I'd try raising the current limit setting on the stepper motor driver. I've always felt that since the z axis driver has two motors on it, it should/could be set as high as twice the current as the others. As a worst case solution, unless you eventually hope to have a 2nd extruder, you could install another stepper motor driver for the z-axis into the spare driver location on RAMPS and reconfigure Marlin to have two z-axis motor drivers instead.

If you've tried to increase the z-movement rate by increasing the z-motor feed rate setting, that likely won't work. My testing concluded that there's not much headroom above 2mm/sec as far going any faster.

Are these issues with freestanding motors or with a mechanical load on them? If unloaded, maybe it's worth trying with the mechanical load hooked up. Steppers don't like resonations, and maybe there's something funky going on without the dampening effect of the load. It's a stretch, but it's all I have to offer.

[beerdart]

Increase the voltage at the driver.

[pjfossee]

Thanks for the replies. I might try putting one z motor on the second extruder. I got the z motors to work by reflashing the firmware with lower accelerations and a lower feedrate, but it's still not peefect. Whenever I start a print, the motors squeal but don't move. I don't know why this would only happen with print g code. I would like to try to reconfigure the marlin firmware to have the second z motor on the second extruder, but I fried my only other stepper driver so that isn't an option for the next few days. I'll order new stepper drivers, but maybe while im at it getting another RAMPS board might be worth a try. Also they don't work under load if that helps. I was rubbing the stock setting before i lowered the acceleration and feedrate. Maybe the stepper can't support both motors.