Re: Question on Torque, Currents, steppers, voltages, CONFIG settings


Robert Benward
 

Guy,
If you double the voltage, the current will rise to twice the value in a given time.  If you terminate the pulse at a certain current, you will reach that time twice as fast (which means more RPM).  The higher the voltage, the better the performance at high RPMs & torques.  The voltage does makes a significant difference. Use 24V.  In your case, you might even go higher.  You most likely do not need that regulator near the motor connectors.  Unless you are using drivers that can't handle the voltage, just jump out the regulator pin1 to pin3.

While playing with slewing, a few things can happen, you are going too fast for the motor, you are not allowing the current to rise high enough before you terminate the cycle. 

You can also stall the motor (which you did with your fingers), the motor loses step, and you are finished. 

The motor needs a ramp up time, it can't go from zero to 500RPM in an instant, you need to ramp it up slowly.  Once you skip a step, the motor will most likely stall and you need to go to zero again and start over.  So, for starters, keep you slew rate in check, start slow.  In config.h, this is listed as acceleration time.

Missing the target current can cause a fault, a possible cause while ramping up and then stalling (I think you are using TMC5160).  Setting a target current too high will cause this.  Start low in both current and slew rate, and go back and forth between the current and the slew speed increasing each a little at a time.  Eventually you will reach the maximum RPM you are going to get out of the combination of motor and voltage. 

Look at the curves at the bottom, the faster you go, the less torque you can deliver.  At speed, you may only have 10-20% of the holding torque.  The bottom graph shows the starting RPM for a given torque and no load torque, and the then the maximum torque at speed.

Bob



Once you are through the time constant, the current is simply V/R (note, you may never get there at high RPMs).


Speed Torque Characteristics PKE Series
Stepper Motors Speed Torque Curve

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