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Skipping g-code?

Posted by sheck626 
Skipping g-code?
March 05, 2013 08:43PM
I just printed for the first time on my new build and, all things considered, it went much better than I expected. The issue seems to be skipped (or bad) g-code. I'm printing a calibration angle thingy and it starts off very well and works fine until it gets about 1/4 through and then is messes up. Sorry I don't have pics (I was excited my printer actually printed something recognizable), but it actually started printing 1 "cube" below the bottom as if it missed the code telling it to move back up (or it erroneously received code to move it there in the first place). According to my calipers, it failed at the same layer. It's not a simple case of a stepper missing a step since it's off by an entire "cube" which is 10mm and it seems to fail at the same place each print. I'm using slic3r and pronterface with marlin firmware and I'm using RAMPS for my hardware. I'm going to try another object and see if I get the same issue. All in all, I can't believe it printed as well as it did despite the error.
Re: Skipping g-code?
March 28, 2013 12:59AM
Ok, the problem wasn't skipping g-code at all, it was the stepper drivers overheating causing them to miss entire moves. You need a fan+heatsink if you're using the pololu stepper drivers, period. No question about it. I had to ghetto mount a fan before I could even print anything for longer than about 15 minutes. The fan is not optional. Once I had a fan blowing on the critical drivers (X,Y,E axis), the "skipping" issue went away completely. Those chips get REALLY hot otherwise.
Re: Skipping g-code?
March 28, 2013 09:39AM
Actually I have never used a fan on my RAMPS, and earlier I had to replace a pololu because of a wiring issue. The new one did not have adhesive for me to attach the heat sink so I ran for well over a month before I finally got some adhesive.

I would not recommend this, and I think a heatsink should always be used. Certainly a fan is beneficial too, but not necessary. If your driver chips are overheating, perhaps you have the current dialed up too high?
Re: Skipping g-code?
March 28, 2013 11:04AM
Maybe that's the case since I never adjusted it after the build. I just turned them all the way CCW and then back about 1/4 turn.
Re: Skipping g-code?
March 28, 2013 11:03PM
Reading the wiki, I noticed this:

"The voltage divider and pot are poorly selected for the currents used. The board uses a 10k pot and 20k resistor to set the vref, so the effective range is 0-1.7 volts, or 0-4.2 amps! The IC is only rated for a maximum of two amps if you have perfect heat dissipation. This makes it much more difficult to set the ref voltage since at 1/4 turn you have maxed out your driver."

So it would seem that at 1/4 turn from "no current", I'm already maxing out my driver. I don't feel like replacing 4 SMT resistors though. Not that I can't, but ugh. I think I'll just treat it like it's my shower where a 1mm turn goes from slightly too cold to let's extrude some of my skin temperatures.
Re: Skipping g-code?
March 30, 2013 05:42AM
if you know the parameters of your steppers, u could prolly change some things on the drivers to improve certain performance issues (maybe something like this mods ...)

looking at what you described ... MOD that Rsense!!! i even tried 0.68 ohms lol (very low current steppers)

__my mixed bag blog || aka --> [http] || ___ so 3D printing is everywhere ... dont worry, hospitals can now 3Dprint body parts, they will charge you $1million excluding surgical fees ... you will die paying your debts. thats their aim ___ if every patent expires tomorrow, everybody will surely get a 3dprinter and make EVERYTHING ! ____ there is a "DIY-DTG" t shirt printing forum, you can mod an EPSON printer to PRINT like a pro. ___ CNCzone? overly commercialized it seems ___ my country? they will be taxing you for every cm of road you use and track you to your grave using GPS and its government authorized, now they will fire all the traffic wardens instead.___ EEVBLOG? there is only 1 way to do things --> take it apart like a pro
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