Discussion on question by Amirmkr: How to obtain torque constant for stepper motor?

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2:22 AM

@tlfong01 I didn't scope but measured the voltage using a voltmeter. It shows that the voltage is 0-3.3VDC as the PWM is 0-255. Similar to Arduino digital pins except for the Arduino it is 0-5VDC.

pjrc.com/teensy/td_pulse.html

@tlfong01 As I mentioned, I got to change the holding torque using the digital pin of Teensy connected to "standby" on the driver. PWM = [0,255] equals Holding Torque = [0,6] Nm

@tlfong01 I assumed that we have a linear relationship between Torque and Current (Torque matters, if the relationship is not linear then let's not talk about the torque constant). As it is also in the video that you referred to.

@tlfong01 This video is what I want.

tlfong01

2:58 AM

@Amirmkr You made 4 comments. This is a quick reply to your first comment, about using PWM to create an analogue signal. You might like to read the following tutorial first.

Teeny 4 PWM (Pulse Width Modulation)
https://www.pjrc.com/teensy/td_pulse.html

Teensy can output pulses digital signals that are useful for many projects. PWM creates an output with ***analog-like properties***, where you can control the intensity in fine steps, even though the signal is really a digital pin rapidly pulsing.

The problem is that what Teensy 4 creates is NOT a true analog voltage. This 'fake' analogue voltage can control the brightness of an LED, but no guarantee your motor driver accepts it.

3 hours later…

tlfong01

5:54 AM

Arduino PWM and Analog Output (True Analog Output using Low Pass Filer and DAC) - Pro HP Halvorsen - South-Eastern Norway Uni
https://www.halvorsen.blog/documents/technology/resources/resources/Arduino/Arduino%20PWM.pdf

* Arduino UNO has no true built-in Analog Output Channels (only PWM)
* ***What if we need a real Analog Out Signal (0-5V)?***
* We will use a 2 different options:
(1) Create a RC Lowpass Filter that converts PWM to Voltage
(2) Use a DAC chip/IC (Digital to Analog Converter)
* Such a chip uses either the SPI bus or the I2C bus

tlfong01

6:38 AM

More videos on Stall Torque, etc.

(11) DC Motor Problems: Examples 1-4 (Motors #5) - Prof Aaron Danner, EE and CE Dept, NUS
https://www.youtube.com/watch?v=iQpDBn9rIeM

(12) DC Motor Problems: Examples 7-10 (Motors #9) - Prof Aaron Danner, EE and CE Dept, NUS
https://www.youtube.com/watch?v=fRDLt-Lpkuw

(13) DC Motor Problems: Examples 5-6 (Motors #6) - Prof Aaron Danner, EE and CE Dept, NUS
https://www.youtube.com/watch?v=QMEumXn0uTk

(14) Torque constant and back-EMF constant - Prof Aaron Danner, EE and CE Dept, NUS
https://www.youtube.com/watch?v=9eUxWdtOrik

Ref 13, Example 5 is good for you! :)

tlfong01

7:01 AM

You have not told me how did you measure the torque in you tests. As mentions in the chats, I used a bag of screws as the torque load, similar to what Prof Danner is doing.

(15) Let's build a DC motor from a coffee can (Motors #1) - Aaron Danner
https://www.youtube.com/watch?v=RdalvgGQQlo

(16) Let's build a 3-pole DC motor that's self-starting (Motors #2) - Aaron Danner
https://www.youtube.com/watch?v=-s7MCBjHv4k

(17) ***Let's measure the torque of a DC motor*** (Motors #3) - Aaron Danner
https://www.youtube.com/watch?v=2Fnh7tJzchc

2 hours later…

tlfong01

8:40 AM

@Amirmkr Well, actually I never bothered about the Torque constant, either for DC motor or Stepper motor. For stepper motor, I only know that the "step" pulse tells the step motor to move one step. In other words, if you send 2000 step pulses, then the motor moves 2000 steps, or 10 revolutions. About the current, YOU might like to tell me how the current is related to what.

5 hours later…

tlfong01

1:31 PM

Another Question.

Now read 1.4 of driver user guide, with extraction below.