We just did a feedrate test engraving a Dithered image with just S0 (white) S255 (Black) commands to pulse the laser on/off. The Feedrate was set at 200IPM in the gcode file and it took 47:29 (2849 sec) in time to engrave. The engraving is 10" X 8.34", but we used Skip White in PicEngrave Pro 5 to cut down on the overall engraving time.
We reversed engineered the gcode and it has a 9417.644408 inch perimeter (travel distance). To confirm the actual feedrate it engraved at, we did a simple calculation.
9417.644408 / 2849 = 3.305596492804493 * 60 = 198.3357895682696 Inches Per Minute.
This test confirms that the S commands for laser control are executed close enough in real time when using the J-Tech PWM grbl. To achieve these kind of accurate feedrates, some settings need to be changed in grbl to increase the overall performance.
$0=30 (step pulse, usec)
$1=255 (step idle delay, msec)
$10=18 (status report mask:00010010)
$11=0.005 (junction deviation, mm)
$14=1 (auto start, bool)
$110=5250.000 (x max rate, mm/min)
$111=5250.000 (y max rate, mm/min)
$120=12000.000 (x accel, mm/sec^2)
$121=12000.000 (y accel, mm/sec^2)
Here is the laser's travel path. There was a total of 587639 lines of gcode that we ran with our PicSender streamer.
Here is the TTL engraving on Birch Ply.