Stepper Motor Behaves erratic - Not a duplicate question

Hi there,

I have a Prusa I3 serving me good the past few months, not without problems but was quickly sorted out. I use the Arduino Mega with Ramps 1.4 and have A4988 stepstick drivers with R100 sense resistors.

At first, my printer started shifting layers and I found that one of my lead screw nuts had quite a bit of play on it and I have read I must check my A4988 to be sure the Vref is OK. It did print two short prints with no problem, but when I read further I also realized that the sense resistors may be different than that of the pololu A4988 driver. I therefore had Chinese cheapies because my sense resistors was 0.1 Ohm. I quickly set the Vref so that I get 70% of 1.7A and started a 24 Hour print. One of the best prints that I had in quite a long time. I checked the stepper temperatures every now and then and the axis steppers was between 40 and 50 degrees Celsius, and the extruder between 50 and 60. To my knowledge that is actually low temperatures for the steppers. I then did a 5 hour print thereafter but did not check the temperatures again. Also good. And then with the print thereafter I went to check the printer after a while and came across a very load noise and an Y-axis stepper that behaves very erratic. Firstly I checked the wiring and made sure all the wires are connected and checked the resistance in the coils and there seems to be no problem there with 2.5 Ohms on each coil and are correct compared to the other stepper motors.

But when I checked the wires going into the Ramps 1.4 I found a molten connector going into the Ramps 1.4. The rest of the wires looks ok and did not look like they melted also. Well then I thought it must be the stepstick that is fried and swopped it out The stepper still behaved erattically. I then put the X-axis stepper on there and it ran smoothly. WTH??????

I am now at my wits end. Can anyone shed some lite please. Oh, the steppers are 42byghw609. 1.7A and I set the stepstick vref to 0.952 to get 1.19A.

You will probably get much better advice on the RepRap Forum where they specialize in 3D printing.

You can get an overheated connector just because the connection was not made correctly. If the connection between a motor and an A4988 comes loose it can easily and instantly destroy the A4988.

You seem to be saying you are using el-cheapo A4988s without proper documentation. If so, just dump them and get good quality devices from a known supplier such as Pololu.

...R

Picture of the damage? What kind of connection was this? Could it have been affected by vibration?
Have you checked the motor windings aren't shorting to the motor case? Is the winding resistance
stable if you tap the motor (perhaps there is winding damage - sometimes a wire can sneak out and
get rubbed by the rotor - till the insulation is removed and then shorts.

the ramps uses dupont connectors which to me are not solid connections on the board try using a8825 drivers and adjust the pots while motors are moving via dry run and not by some measured voltage as that only gets you close the motors are low price but work well if you did all prints back to back the drivers thermal protection may have triggered