Replacing A4988 Drivers with DRV8825 on Arduino Mega 2560 + Ramps

[PyramidDave]

I have been having a problem with my printer stopping in the middle of a print. The message I am getting with pronterface is that it has lost its connection. The heatbed & Hotend still stay at the same temperature, the printer just stops moving. I thought it might be a heat related problem with the electronics, so I had a small fan blowing on the arduino & it got thru a 40 minute print, but then lost its connection soon after the print ended. Since I have a spare Arduino mega on my CNC machine, thought I would substitute the drivers on that board to see if that fixed it, but they are DRV8825 & ones on my i3v are A4988. This web page says they are interchangeable http://reprap.org/wiki/A4988_vs_DRV8...tepper_drivers but it seems like I will need to adjust something in the firmware for them. I only have 3 DRV8825 drivers, so I am planning to change the X, Y & Z, but leave the A4988 for the extruder. I had this same problem with octoprint. I also swapped a usb cable & reseated all the connections. Anyway, does anyone know the settings I should change Marlin in the Configuration.h file or have a different suggestion? Looks like it might be this value that needs to change:

#define DEFAULT_AXIS_STEPS_PER_UNIT {80,80,4000,841}

[Roxy]

If you have a flakey connection to the computer... The first thing to do is try printing from an SD-Memory card and see if the problem goes away. If it does, you very possibly have a bad connection or who knows, maybe the USB/Serial-Port driver has crashed on your computer??? But I would do that first to make sure it was a connection problem.

[Mjolinor]

You should not print over USB. This has been said a thousand times.

USB is not a real time protocol and that means that it does not deliver data when requested, it delivers it when it feels like it. All operating systems have other things to do and servicing the USB is way below telling Micro$haft and Google you personal details particularly on a Windo$e computer.

Some people are lucky and have never met this problem but someday it will bite them in the rear.

[PyramidDave]

I asked Colin this question also & he suggested printing from the SD card also, but thinks it might be the P/S as he has seen this similar problem before. Printing from the SD card 1st sounds like a good idea as it will rule out whether it is the USB connection on the arduino. I do not think it is a problem with the USB on my computer as I was having the same problem with octoprint, so I switched back to pronterface to see if that had the same problem. Also Colin said if I change to the DRV825 drivers, I just need to double the steps for each axis in the firmware that I change the driver on.

Thanks for the suggestions.

[PyramidDave]

Looks like it is the USB connection. I printed 2 prints with the SD card that were 45 minutes & 30 minutes long. I tried a 2 hour print from proterface again to see if taking all the parts off & back on again had fixed the problem. It failed after 5 minutes. I tried that same print from the SD card & still had the USB connected to my computer & pronterface was still connected. The print did fine, but proterface had lost its connection at some point, so that seems to point to the problem. I might take the boards apart to see if I can see some loose solder joints to fix before replacing the board. Does anyone have a suggestion for the best source for a replacement arduino mega 2560? Looks like makerfarm has good price of $20 for this & probably more reliable than some of the reviews I have seen on Amazon.

[Mjolinor]

Why do you think there is something wrong with it?

No amount of changing hardware is going to alter USB specifications. They are written by a standards committee and they are written in such a way that they are not suitable for real time communications.

[PyramidDave]

Using Octoprint from Raspberry Pi or connected directly to my computer using USB will give me a communication error after a short time & the printer stops. Printing directly from the SD card does not cause my printer to stop. Unless there is a problem on the USB connection on my computer & raspberry the problem looks like it points to somewhere in the USB circuitry of the arduino. Is that logic not correct? I have also tried 2 different USB ports on my computer with the same problem. Is there some Ethernet shield that I could attach to the arduino mega instead of using the USB connection?

[PyramidDave]

I found this ethernet shield http://www.banggood.com/Ethernet-Shi...-p-907969.html Is it possible to use this instead of USB?

[cperiod]

You'd have to find printer firmware which supports it... Marlin doesn't, but some others do. But, really, if it's the Arduino USB port that's busted (and it sure sounds like it) then you can find an Arduino Mega clone for around the same price.

[Mjolinor]

Using Octoprint from Raspberry Pi or connected directly to my computer using USB will give me a communication error after a short time & the printer stops. Printing directly from the SD card does not cause my printer to stop. Unless there is a problem on the USB connection on my computer & raspberry the problem looks like it points to somewhere in the USB circuitry of the arduino. Is that logic not correct? I have also tried 2 different USB ports on my computer with the same problem. Is there some Ethernet shield that I could attach to the arduino mega instead of using the USB connection?

No that is not correct. Read what I have written. USB specification does not support real time protocol.

USB SPECIFICATION DOES NOT SUPPORT REAL TIME PROTOCOL.

Any clearer?

Three times I said it now, this is the last time.