How to determine the rpm of my stepper motor?

Other Hardware Motors, Mechanics, Power and CNC
1

Hi there,

I set-up a NEMA 23 stepper motor with Arduino UNO and grblShield. I'm using UGS Platform to control the motor. My relevant settings are:

$0 = 10 (step pulse, usec)
$1 = 25 (step idle delay, msec)
$2 = 0 (step port invert mask:00000000)
$3 = 0 (dir port invert mask:00000000)
$4 = 0 (step enable invert, bool)
$5 = 0 (limit pins invert, bool)
$6 = 0 (probe pin invert, bool)
$10 = 3 (status report mask:00000011)
$11 = 0.010 (junction deviation, mm)
$12 = 0.002 (arc tolerance, mm)
$13 = 0 (report inches, bool)
$20 = 0 (soft limits, bool)
$21 = 0 (hard limits, bool)
$22 = 0 (homing cycle, bool)
$23 = 0 (homing dir invert mask:00000000)
$24 = 25.000 (homing feed, mm/min)
$25 = 500.000 (homing seek, mm/min)
$26 = 250 (homing debounce, msec)
$27 = 1.000 (homing pull-off, mm)
$100 = 250.000 (x, step/mm)
$101 = 250.000 (y, step/mm)
$102 = 250.000 (z, step/mm)
$110 = 1000.000 (x max rate, mm/min)
$111 = 500.000 (y max rate, mm/min)
$112 = 500.000 (z max rate, mm/min)
$120 = 1.000 (x accel, mm/sec^2)
$121 = 10.000 (y accel, mm/sec^2)
$122 = 10.000 (z accel, mm/sec^2)
$130 = 200.000 (x max travel, mm)
$131 = 200.000 (y max travel, mm)
$132 = 200.000 (z max travel, mm)

As I understand it, the x max rate controls the speed of rotation. I thought that $110 = 1000.00 meant 1000mm (or 1m)/min but the shaft is spinning WAY faster. What am I misunderstanding? Thanks in advance.

Best,

Jason

2

What did you expect? And how did you measure the actual speed?

3

Hi,

I'm basing this purely on visuals. 1 meter per minute is fairly slow. My set-up is spinning quite rapidly. I was wondering what I was misunderstanding. Thanks.

Jason

4

The item $110 = 1000.000 (x max rate, mm/min) refers to the linear movement of the tool caused by the motor and the gearing attached to it. It is not intended to represent the RPM of the motor.

Have you correctly set the $100 = 250.000 (x, step/mm) for the number of steps per linear mm?

...R

5

Right. I thought I could calculate the RPM by taking that value for $110 and using it in conjunction with the circumference of the shaft. My thinking being that the rotation of the shaft is related to the linear movement of the tool (getting from point A to point B). Am I wrong?

I didn't make any changes to $100 (currently set at 250.00)

6

soul170:
Right. I thought I could calculate the RPM by taking that value for $110 and using it in conjunction with the circumference of the shaft. My thinking being that the rotation of the shaft is related to the linear movement of the tool (getting from point A to point B). Am I wrong?

I didn't make any changes to $100 (currently set at 250.00)

Use the thread pitch instead of the diameter.

Paul

7

For a leadscrew:

linear velocity = revolutions-per-second * thread-pitch
linear force = 2π * motor torque / thread-pitch (ignoring friction losses)

8

MarkT:
For a leadscrew:

linear velocity = revolutions-per-second * thread-pitch
= steps-per-second * thread-pitch / steps-per-revolution
linear force = 2π * motor torque / thread-pitch (ignoring friction losses, and in SI units)

9

Thanks Mark. Thanks Paul. I will do that calculation. I really want to understand what I'm doing so that I can have more creative freedom. I appreciate your help.