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ramps connects, motors don't move

Posted by ambiguousphoton 
ramps connects, motors don't move
December 07, 2011 12:14AM
Hi everyone,
I was using Ramps 1.4 and Sprinter + Pronterface and I was able to get the motors to work. For some reason the end stops seemed to work at one point (plugged into X-, Y-, Z-) but I was double checking the Y and it didn't seem to stop but was grinding it at the end. I got scared and disconnected it from the computer and then unplugged the power+usb. There was no smoke and the stepper drivers didn't seem really hot. Now when I plug it in to the computer, the ramps says it connects with the computer but I don't get any movement when I press X,Y,or Z. Do you think I blew out the electronics or is there something that needs to be reset? I was systematically trying to go through 1 stepper driver at a time with 1 motor (the Y actually so the one that grinded for a few secs) and I couldn't get that to move. What is the next thing to try?
Re: ramps connects, motors don't move
December 07, 2011 05:33PM
Disconnecting the USB cable from the computer or turning the power off should not break anything. But disconnecting the motor while the 12V power is on can damage your stepper controller.

Verify that you have 12V power going into RAMPS. The Arduino gets power from the host computer so it will still work even if the 12v supply is off, but the motors won't obviously turn or the nozzle won't get hot in this case.
Re: ramps connects, motors don't move
December 09, 2011 02:39PM
Thanks for the reply. I think that it was trying to connect to a different USB port number so that was the issue. I also discovered a few bad solder connections so that helped with another issue where 1 motor wasn't turning.

I have one final question now that I am calibrating the axis. When I tell the extruder to extrude 100 mm, the first time it does it continuously but as it gets to the end of the first 100 mm it starts doing it in steps. After that point if I retract or extrude, it does it in steps. The only way to make it go continuously is to reset the software. This wouldn't be such a problem except that the calibration is totally different for the length that it extrudes whether it is continuous or in steps. After about 8 iterations of calibration where I was setting the steps/mm setting anywhere between 580-1300, I picked up on this. I thought it might be a power or slipping thing, but it doesn't seem to have a problem feeding it.

Has anyone else noticed this and should I be calibrating to the distance it travels during the continuous feed or the one where it takes steps? Also, I notice that the heatsink for the extruder gets pretty hot during all of this. It is too hot to touch for more than a second or two. I have the pot at the 12 o'clock mark because I was worried about slipping as the initial cause for the different feed rates. Do I risk burning it out?

Also, as a final thing, I notice the x axis stepper gets pretty hot and after I move it, I can hear it pulsing back and forth but there is no significant belt movement. The stepper also has a habit of doing that once activated for the first time.

Thanks a lot for your help!
Re: ramps connects, motors don't move
December 09, 2011 03:56PM
If you have the pot set too high on a stepper motor driver, the driver will overheat. Then it starts to shut down repeatedly to try to protect itself from burnout. Sounds to me like your initial intermittent drive problem may have been due to having the pot set too high. In thinking it was skipping you may have made the overheating problem worse by turning it even higher. Sounds like a similar problem with the x motor.

I'm told the difference between and is less than a quarter turn of the pot. Try lowering both E and X pots a bit.

Andrew Roberts
Re: ramps connects, motors don't move
December 10, 2011 11:05AM
Hi Andrew,
Thanks for responding. Just to clarify, if you are extruding and it does it in steps that is due to overheating and not something in the program? I sort of assumed that the pololu drivers got scorching hot over the 30 minutes or so that I was playing around with it, but I guess it is possible that it got that hot within the first few minutes of extruding.

Will lowering the pots in general mess up any steps/mm calibration that I had before?
Re: ramps connects, motors don't move
December 11, 2011 08:02AM
If your pots are set too high, your stepper drivers will overheat and give you the symptoms you have now.

If you have a pot set too low, the motor will skip steps (or just sit still and buzz faintly, in extreme cases).

If an X or Y motor skips steps, you see an offset in the position of the current layer of the print, relative to the levels below. It's pretty obvious - you'll recognize it when it happens.

If the z motors skip, I guess that your layer heights will be irregular, because the nozzle won't be lifting up the same amount each layer. If you are really unlucky, and one z motor skips and the other doesn't, you'll eventually end up with your x-rods no longer parallel to the bed, and the z motors will skip even more.

I don't know what the symptoms would be if the extruder motor was occasionally skipping steps. I can guess that you will under-extrude, but I don't know what that would look like. Thinner strands?

The short answer is no, your calibrations won't be affected. Well, unless they were wrong, and somehow relied upon your motors running irregularly winking smiley

Either way, you really don't want to run your drivers scorching hot. I'm half an hour into a print, and my z heatsink is at room temperature, my x and y heatsinks are slightly warm, and my extruder heatsink is touchable, but uncomfortably warm (I might have to do something about that, I hadn't checked it before.)

I'll repeat the mangled line in my last post:-
I'm told the difference between too much drive and too little drive is less than a quarter turn of the pot.

Andrew Roberts
Re: ramps connects, motors don't move
December 11, 2011 05:17PM
sorry to hi jack but rather then make a new thread.

when adjusting the pots does anti-clockwise increase the current or decrease?

Re: ramps connects, motors don't move
December 11, 2011 11:57PM
Anti-clockwise decreases current, clockwise increases current. Just like a car speedometer. Turn it up to 120mph and it'll catch fire. Well, maybe smiling smiley
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