My Clearpath Review

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Abraham Saenz
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Joined: Wed Jul 13, 2016 3:48 pm
Location: Panama
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My Clearpath Review

Post by Abraham Saenz » Sun Jan 08, 2017 1:42 pm

After 2 months playing with this beauties I'm finally able to say I've conquered them!

First of, generic laser cutter controllers like Ruida's are made to work with stepper motors. Stepper motors are inherently more precise than servo motors. Yes, you can beat stepper motors with a properly tuned servo any day, but in my case, my combination of a digital stepper motor driver and high torque NEMA 23 steppers are still the preferred drive system for this types of machines.

The first few weeks after using the Clearpaths I was extremely frustrated. The motors did not meet my expectations on the slightest. Cutting paper, which require fast acceleration and quick settling times was just rubbish. for acceptable results I had to use ridiculously low acceleration values and my cuts took twice as long as the steppers because of that.

The reason for the poor performance was just poor tuning. Don't blame me, blame Teknic's auto tuning software. Teknic advertises these motors as requiring "Not tuning at all" because their auto tuning software is so great it will take them to their peak performance with no intervention other than adjusting the "Fine tuning" slider bar.

I've made a video comparing the auto vs manual tuning settling times for a typical move on my applications

https://www.youtube.com/watch?v=jxRLM_igEGA

Now, even when I've reduced settling times to 4X less as compared to the auto tuning, 50 ms is barely good performance for a servo motor, a high performance servo would be settling in 10 ms or less, the problem seems to be now the inertia ratio, specially on the Y axis. Even thus the Y axis motor is around 3.5 Nm of peak torque (about 2.5X what my steppers where capable of), they still have a relatively low rotor inertia of 0.163 kg-cm^2. Rotor inertia is far more important than torque when choosing a servo motor, my advise to you is to go with the biggest motor (physically) that you can fit on your machine and budget, or use some kind of gearing if possible, the ideal inertia ratio for a laser cutter would be in the 3:1 or less, if you can't calculate the total inertia of your system, bigger would always be better, except for your wallet.

All in all, my machine now engraves as fast as 1200 mm/s with 20000 mm/s acceleration and cuts paper at 100 mm/s with 1200 mm/s min acceleration. This is about 2.5 times as fast as I was able to achieve with the stepper motors for speed, and about 4 times for acceleration. Overall, my system is at least twice as fast with no loss in cutting quality compared to the slower stepper motors.

So is the investment worth it? in my case it was, we can now cut much more in much less time. I spent about 1000 dollars in two motors with accessories, according to my calculation I my investment should have been returned in about 3 months, so YES.

Do I recommend them for a laser cutter? probably not, unless you are someone with the knowledge and time to tune them properly.
Acctek AKJ6040+Clearpath Servos+90W EFR laser tube, 1.5 inch lens, polyurethane belts, Boeshield T-9 Lub :)

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