I had been experiencing several incidents of lost steps in the movable gantry cnc machine and I had been going through all the root cause analyses to find out the cause(s). Apparently, there were a few causes for these and every time a lost step incident happened it was rather challenging to try to solve the problem.

Voltage surge protection capacitor and Hex Inverter IC connected in place

Voltage surge protection capacitor and Hex Inverter IC connected in place

The X axes were particularly troublesome because they were dual drives; the two stepper motors being located opposite each other, turning in different directions to make the same direction X linear movements in sync with the step and direction commands from the LinuxCNC software.

The motors which were salvaged from old machines were also suspected to be of different magnetic strength, although their labels were identical. During one of the troubleshooting sessions, because the rotation movement when turned by hand seemed to differ, I had replaced one of them although I made sure that both of them were the same NEMA size, ampere, volt, step angle. This meant that the motors were visibly different in body length.

The previous episode of motor drive timing belt teeth interfering with one another due to insufficient mechanical separation did not help at all. It cause the machine not to work properly.

X axes A4988 stepper drivers replacement

X axes A4988 stepper drivers replacement

In addition to this, there were the electronic faults or electronic adjustment faults. The latter also had their fair share of problems. With the A4988 stepper motor driver boards, the procedure was to measure the milli-voltage in order to set the maximum current. This was prone to error. If I adjusted the maximum current too high, the stepper motor tend to move by themselves without any signal. If adjusted too low, the stepper motor would lack the torque to drive the load. Because I was buying the A4988 boards from China, the instructions found on the internet for Polulu driver boards were slightly different, especially regarding the settings, due to the different resistor values on the manufactured product. The small adjustment trimmer on the board was also prone to drift.

During my initial hooking up of the A4988 driver boards, I was actually testing to see how to use them on my CNC Milling machine, because they were supposed to be designed for RepRap 3D printers. Because I had burnt my EasyDriver boards, I had wanted to substitute them by trying to use the A4988 boards. Well, they did work after some experimentation.

Installing TB6560 for all axes

Installing TB6560 for all axes

As problems like losing steps on my movable gantry cnc machine cropped up, I had some doubts that the A4988 boards were in tip-top condition. I sometimes had to decide after some troubleshooting whether it was a motor or a driver problem. Sometimes, I wondered whether the problem was because of too low motor torque, or too high mechanical load during machine cutting, or poor adjustment of maximum current for the motors, or faulty driver board, or electrical interference from the wires, mechanical fault in the drive train due to misalignment, lack of lubrication, dirt, faulty bearings, etc. So many possible causes!

TB6560 for all axes

TB6560 driver for all axes

Finally, I decided to invest in a higher current rated driver board. This was the TB6560 board. I reckoned that if the motors were not powerful enough to drive, I would need to replace them with motors with higher current ratings. In order to do that, I would need higher ampere stepper motor drivers. The TB6560 could be able to drive motors up to 3 amperes. In addition, the adjustment for the current was by dip switches. These would eliminate the adjustment problem inherent in the A4988 which used trimmers for this purpose. Also the selection of micro switching was by dip switches.

My first task was to make the X axes stable. I replaced these with two TB6560 drivers, one for each motor of the dual drive. After installing and testing, I could testify that the TB6560 drivers were worth it. The X axes were more stable than before.

After more testing with the new drivers, I decided to replace them also for the Y and Z axes.