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TIC 36V4 motor configuration (loss of torque)

Hi, everyone, I bought 2 tic36v4 and I’m trying to configure it so it works properly with my stepper motors.
I used this nema 23 and this other nema 23 both of 4.2 Amps, so I set the TIC current limit to 4297mA and use refrigeration. I powered the motors with a 48V 32A power supply that I happen to have.
The first one (SCA5618M4204-A) has 1.8mH, and 0.5 Ohms per wiring, and 140 Ncm of holding torque.
The second one (SCA5618L4204-B) has 2.1mH, and 0.55 Ohms per wiring, and 230 Ncm of holding torque.
I perform several tests of the holding torque of each motor to be sure that the driver drives them properly but neither reaches the values specified by the datasheet.

Then I tried a different configuration, and finally, find that the motor respects their specified holding torque when I configure the driver with a “Slow Decay Mode” and 15us for the “Fixed off time”.
The problem is that when I use the Slow decay mode and micro-stepping (like 1/8 or 1/16) then the steps behave weird, like shorter or weak steps and then one stronger. If I use a decay mode different from Slow the motor will lose its torque.

So, my question is how I have to configure the driver so my motors respect their datasheet?.
I upload my settings.

tic_settings.txt (1.3 KB)

Hello.

It sounds like you are expecting to get the full holding torque while microstepping. Please note that the higher microstepping ratio you use, the lower the incremental torque of each microstep is. You can find a more detailed explanation of this in section 2.2.3 of this app note from TI. The impact is quite significant, with 1/8th steps only giving an incremental torque that is around 20% of the holding torque and 1/16th steps dropping down to approximately 10%. If you need higher torque while keeping good rotational accuracy, you might look into other solutions like adding a gearbox or some other way to mechanically reduce the motor output.

The decay mode and off time affect the regulation of the current in the motor coils, so it’s probable that only certain settings allow the current in your motors reach the rated level on average. Using an oscilloscope with a current probe would be an ideal way to investigate that to see how the coil current is behaving, but we realize that is not a practical solution for everyone. Unfortunately, the optimal settings will depend on many details like the specific motors and power supply, so it is not really feasible for us to help you tune your settings; it will likely take some trial and error in the process.

By the way, it sounds like you are using some additional cooling, but since the Tic 36v4 does not have any meaningful over-temperature protection (the gate driver IC has over-temperature protection, but the external MOSFETs will overheat first), you should be very careful that the MOSFET temperature stays under 140°C since you are setting the current limit higher than 4A.

Brandon