Bug: Luban allows faster speeds than the rotary module can accept

Hey everyone,

I’ve been using a marking spray that works best at 80% 10w laser and 3000mm/min. I decided to do some cups for a project and noticed that I was having some lost steps when the rotary module was rotating. Mounting of the object was solid… When I lowered the steps to a lower value (1500mm/min), the rotary module was able to keep up with the task.

Luban needs to have limits set for values based on the least capable device. Or, at least a flag that tells you that’s a bad idea.

Thanks,
Chris

In general this speed limits are set in the controller firmware.
You could check your settings with M503 in the console.

If there are lost steps there seems a defect or a inproper gcode.

Just for the information on this thread, I’ve done some in depth testing of this and found the max speed the rotary can do is 2700deg/min. Neither Luban or the Snapmaker controller actually do the math to convert deg/min to mm/min surface speed calculation with the diameter.

However, Lightburn does since version 1.14. :wink: It’s better to turn the scan direction 90 degrees so the Y axis moves at the actual set speed, the rotary simply can’t match any real surface speed.

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Thanks for sharing this - it is surprisingly consistent with what Snapmaker claims on the shop page - 45°/sec = 2700°/min:

For the non-math inclined, how would I back calculate the 2700 degrees per minute into a mm/min?

That’s the real problem.

Should not be too complicated… Circumference of a round object is 2πr, where r is the radius. The circumference is 360°. So rotary speed ω [°/s] to linear speed v [mm/s] would be (r in mm):

v = ω 2πr / 360° = ωπr/180°

So 45°/s for an object with 50 mm radius translates to 45°/s x π x 50mm / 180° = 39.3 mm/s

mm/s to mm/min is trivial, just *60s → 39.3 mm/s x 60 s/min = 2356 mm/min.

Or you enter ω in °/min directly, same.

EDIT: for practical use the V_max for different radii, assuming 2700 °/min:

r [mm] d [mm] Vmax [mm/min]
5 10 236
10 20 471
15 30 707
20 40 942
25 50 1178
30 60 1414
35 70 1649
40 80 1885
45 90 2121
50 100 2356
55 110 2592
60 120 2827
65 130 3063
70 140 3299
75 150 3534
80 160 3770
85 170 4006
90 180 4241
95 190 4477
100 200 4712
105 210 4948
110 220 5184
115 230 5419
120 240 5655
125 250 5890
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@Hauke Has a very good, in depth explanation, however it can be simplified a bit. Surface speed boils down to Circumference x RPM. So going at our max speed of 2700deg/min, we divide by 360 to convert to RPM, since 1 rotation = 360 degrees.

deg/min ÷ 360 = RPM
2700 ÷ 360 = 7.5 RPM.

To find your maximum surface speed for your object, take the diameter you measure with calipers and multiply buy pi, or 3.14 for simplification to get the circumference . For say a 100mm object (mug maybe?)

d x π = Circumference
100 x 3.14 = 314.

Then multiply together get mm/min surface speed.

RPM x Circumference = mm/min
7.5 x 314 = 2355

Which matches what @Hauke got (minus the rounding error using truncated 3.14). This will be the max speed you can engrave across the surface. :slight_smile:

TL;DR Version;

d x 3.14 x 7.5 = Max Speed in mm/min.
Measure the diameter of your object and swap for d

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