Servo & stepper combined, question, and the newest RD6445 controllers.

[Ian Stewart-Koster]

I've been thinking again, because I was not satisfied with the unknowns and cautions given 5 years ago, about putting a servo in our biggest laser, just for the X axis - for faster turnaround in engravng.

I'd originally been told that both X & Y have to have the same type of motor - either steoppers, or servos, but not one of each.

I was reading somewhere that the newer Ruida controllers with the bigger display, (6445G) can also handle BOTH types of drives, at the same time - because the signals sent to the drives are PWM.
I'm just not sure how the controller figures different acceleration factors etc - but you sent the X & Y parameters in the old 6442, so the 6445 should be the same.

A friend was looking at buying a laser, and the actual SERVOS the maker is putting in, are proper servos with encoders, not the Easyservo, which is a closed-loop stepper. And the same servos for X and for Y.
The servo is a Leadshine BLM57130 (nema 23) , with matched drive Leadshine ACS606.

(I was reading the specs on the ACS606 drive and was fascinated it says they can drive both AC and DC servos equally well.)

Our big laser has a much smaller stepper for X as it only has to move the 2 heads and the chain, whereas Y has to move the gantry, and both tubes, and water etc.

And I realise there's a speed limit at which if exceeded, the dots will fail to land, but I still like the idea of tinkering and learning - and was wonidering if anyone had an opinion here on the 6445 controller, how well they are with servos, and the practicality of using a servo for X and the existing stepper for Y ??

Thanks for any thoughts. (and apparently the RD6442S can't do what I'm wanting)

[John Lifer]

Saw an offering for a used Boss laser, and pulled up their website. The new models have Servo drive motors. Supposedly up to 1300mm/s speed. Which is three times what I drive my 1300x900 machine. Unless the controller is WAY better and The glass tube technology improved, I HIGHLY doubt that you can really engrave anything well at nearly that speed. I see missed items at 400 which is my max. Now my controller is 6 years old, but I don't think that Ruida's technology has increased that much. I know folks drive the lasers way faster than 400mm/s, but 1300? I'd have to see it.... The used laser is prior to the servo motors, which I would also like to see....

[Kev Williams]

I may have read your previous threads about this before, but regardless, take this for what it's worth:

IF you're planning on putting servo X-Y drive motors on ANY laser running a glass/DC/Chinese laser tube in order to speed up engraving times-- save your time and money...

My 80 watt RECI equipped Chinese Triumph 1390, that still runs like new after 9 years (knock on my head), thanks to the controller Triumph uses, is capable of 1000mm/second raster speeds. Right now the machine will run up to 600mm/sec speeds with near equal precision and quality of detail as any of my 3 metal/RF tubed lasers. HOWEVER- once past the 600mm/sec speed, the problem of how DC lasers fire comes into play, which is, they simply can't/don't fire fast enough to keep up. What happens is long X runs engrave just fine while short "intermittent" runs simply do not. Engraving "TTTTT" is a great example; at a given power level at high speed the top of the T's will engrave nicely but the vertical shafts will barely show up. Adjust the power so the vertical shafts DO show up correctly and you'll likely find you've burnt the tops of the T's half-way thru the material. Additionally, basic engraving quality itself begins to suffer above 600mm/sec. I've tried to adjust backlash settings to compensate but that doesn't help much.

Faster engraving speeds require a laser tube capable of firing fast enough

[Ian Stewart-Koster]

Thanks John, and Kev.
Kev, yes, I'm totally aware of firing speeds, and with our biggest laser, I find 450mm/sec is the best practical speed I can get for accuracy and efficiency. I can ask it to go at 800mm/s, but the job takes longer because of deceleration & acceleration turnaround time at each end of the X pass.
(Our old ULS M300 has no mass in the head, relatively speaking, but I can run big engraving jobs and cutting jobs on both at the same time, and over 30 mins, one or the other might win by a maximum of 2 minutes- which is nothing, relatively speaking._))

The reason I am asking is to speed up the X axis acceleration TIME, and shorten the acc & deceleration landing and turnaround space on each side of a job. Not to run faster over the substrate itself- I'm content with the engrave results at 450mm/s.

Servos can accelerate really fast and not get a headache and lose steps like steppers can - I've spent 15 years tweaking the PID settings on our cnc router servos for figures that suit me most reliably for efficiency, as opposed to direct speed, which is different in a router, because it depends on the depth into the substrate, and substrate hardness, and number of teeth of the cutter, and spindle RPM etc.



I'd been led to believe the RD6445S controller can happily control say an X servo and a Y stepper with the right drives, (or X & Y servo & Z stepper- but Z never runs at the same time as X & Y anyhow, so that's a no-brainer)
I'm still interested in thoughts- thanks again!