I was thinking to replace my steppers with these servo motors instead of the common closed loop steppers. Has anyone used these to his laser?
A lot of people have tried servos and I donāt know about these, but they have timing issues of the servos being sluggish. Better description might be the machine lases before/after where it should.
Good luckā¦ let us know if it works for youā¦
Open loop is the normal cnc steppers, closed loop is with servos .
Iām not sure if grbl can handle servos well but `a servo has a position feedback which allows it to remember where it was at any point .
Lasering does not really need servos which are more used in cnc applications where tools break and cause havoc.
I dont think lightburn is servo ready but the future is unknown .
Please report your progress
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Iāve not put them on a laser yet, but Iāve worked with them.
Theyāre ānewā in that itās a BLDC motor with a very high resolution magnetic resolver on back, and a board running SimpleFOC.
But, what is it compared to a similar sized stepper?
Initially, the stepper appears to have significantly more torque, but not in a function way- the torque rolls off quickly, itās down to about 20% by 1300 rpm. All laser motion controllers use ātrapezoidal accelerationā- basically, a fixed accel that doesnāt vary with speed. So when you put in your reduction ratio and set up the controller, you might set it up to go to only 800 rpm. At that point itās only got half its holding torque, that sets your acceleration limit and you canāt make any use of the other half of its torque.
Steppers are almost all 200 steps/rev. Microstepping doesnāt actually work that well to increase resolution.
These new servos, you can program any steps/rev- like up to 16,384. Yes, you need to program them with an RS485 dongle.
Now, about 5 years ago or so āclosed loopā steppers became the best. In addition to some performance improvements esp some better torque at higher rpms, they canāt ālose stepsā. Thereās an encoder the driver reads and if forcefully stalled, it will remember how far off it is and try to get back there, although there is a correction limit which, if exceeded, could make the driver just go into an error state and stop moving, and express an ALARM pin which you can use to shut down the machine by, like, pull an interlock back to the OPEN state so the Ruida will stop.
Yes, you DO want these. Yes you do. But you may want to use them differently to get best results. What Iād suggest:
- Direct-drive the axes! Do your calcs to match your axesā linear speeds to the motorās performance window by changing the pulley tooth count alone. In some setups, you may still want to couple it to another shaft so the pulley can sit between two fixed bearings so itās not torquing the motorās output shaft. In that case youād still need to use a shaft coupler, but avoid a pulley reduction.
- Tie ALARM pins into interlocks
- Power with 24V.
- Be aware that when braking (it was going fast and is told to stop), it will generate back EMF that a power supply canāt just adsorb, it can overvolt. If thereās other loads on the power supply, it might be consumed there. Otherwise you may need to add a simple circuit that will dump to a brake resistor. They do have onboard brakes built into the motors, but theyāre not very beefy- no room. The ihsv have stronger brakes than the xxAIMxx series, but still not a good idea to rely on.
Youāve probably found the ihsv57 series (100W-180W). But check out the AIM series:
http://shop.smc-powers.com/index.php?route=product/search&search=aim
Secret knowledge: the 42AIMxx motors are the SAME as the larger 57AIMxx. Compare the specs. They just put the 42AIM innards into a larger case to work with existing 57 (NEMA23) motor faces. The 57AIM might dissipate heat better but I canāt back that up with facts.
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Your info is very dated. Closed-loop steppers took over >5yrs ago.
No problem at all, GRBL/Ruida donāt know the difference. Both closed-loop steppers and these new FOC servos just take the same step/dir signals. Most (but not all) of the closed-loop steppers used a separate driver. The FOC servos put the whole driver IN THE MOTOR. The motor has a plug for 24VDC and step/dir. Also can take RS485 or CANbus commands to simplify wiring. Ruida canāt put that out, and I havenāt heard if GRBL can yet, but that would actually be pretty easy to implement.
I donāt know your actual age, but if this is your first ānobody needs this new fangled stuff!ā compliantā¦ congrats on becoming old. I think my first moment like that was complaining about fuel injection and ECUs vs carbs and distributor sparks.
Lasers can get a lot of benefit from running these servos. They can run notably faster when cutting small curves or small vectors, like following text fonts. They can raster at higer speeds with better accel.
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You seem to be a guru in this field!!!
Thanks for the great info. So they are not so simple as it seems, connect the step dir, the power and make some configurations. They need programming knowledge to make them work from the serial port?
There are some good & valid points here.
Our cnc router has servos - I love them.
All our lasers have steppers.
I watched some videos of how fast certain servos (or maybe closed loop steppers/easy servos) could accelerate a device, and I figured thatās be great in engraving huge jobs.
Haha.
After much testing on two mahcines we had at the time, sure I could have the head running at 700 mm/sec, but only at the expense of some loss of fine detail as it moves faster than the PSU could fire single dots.
I eventually established that about 350 mm/sec was most efficient for speed plus accuracy for our needs. Going faster also led to more space being needed to speed up and slow down at each end of a scan. If I set the acceleration higher, you risked lost steps and gained other inaccuracies.
For cutting, youāre only moving relatively slowly - and there is not the resistance on a head as there is on a CNC routerā¦ BUT I found I needed to go more slowly than ideal in order to not have corners overshoot, and circles develop wobbles, and some straights begin with dampened sine waves.
So although the machine can move faster, accuracy with slowness became my ideal - accuracy was more important than speedy slop.
When we had a big flat-bed, 2-tube laser custom made in China 6 or so years ago, I asked them to fit those easyservos instead of steppers.
They did, then they tested the machine, and set a complex path, and had it running for 48 hours. They do a pulse at the beginning, and one at the end, and then restart it after 48 hours and expect the same starting point and end point.
They did not achieve that, so they pulled those out and put standard Leadshine steppers in, and tested it and all was fine after two 48 hour stints.
They could not explain the easyservo failure - They blamed translation, but I feel inexperience was part of it - maybe it had not been tuned properly?
I paid for them and the 2 easyservos were shipped out with the machine - and the drives came with them too.
I begain to wonder if I could use a speedy one for X, and a stepper for Y.
They told me no, both had to have the same specifications or natureā¦
I am not totally convinced. I was going to build a smaller one using those āspareā parts - as an experiment - but Iāve been too busy. I have all the parts needed - tube, laser PSU, spare controller and 24v PSU, and everything else.
Accuracy in small letters and curves is important - maybe the servos can do that better than the steppers canā¦?
So after all these information, i think the most affordable, easy to install and reliable solution for now is closed loop steppers like leadshineās, that are used on Thunderlaser machines.
The FOC servo will outperform closed loop steppers in every category. As always, you want to match the configurations with the motorās performance curve.
When the torque of a closed loop is 2nm, but the torque of same size DC servo is 0.6nm, is it comparable or need to be same nm so bigger and heavier motor?
Good luckā¦ Love you hear how you end up with this implementation ā¦
You are aware that @Dannym has an RF machine and you have a co2 from what I can tellā¦?
These are ready to work servos with integrated driver and encoder? Connecting them to ruida directly?
Didnāt know he has RF but I think also with CO2 i have benefits using servo. For accuracy for example, not loosing steps etc
I was thinking of speedsā¦ most of these machines will outrun the response time of the tube/lps anywayā¦ Thatās why many find a slower scan speed results in better detail, at least with glass tube.
Generally, rf lasers have a larger diameter output beam, which results in a smaller dot size and the beam has a higher quality or M2 value.
RF tubes are digital devices, a glass tube is an analog deviceā¦
I checked out servos. Although I had training on them 3 plus decades ago there was a bit to learnā¦ same basic idea, a few decades of technology differences.
I found them to be pretty expensive, when used instead of plain olā steppers. It is nice they can possibly recover. Iāve run all of my time with the supplied stepper motors, even doing my share of abusing themā¦
Mine has run at 1650mm/s, but itās purely academic, what it does do it make for quicker jobs and faster response to changes. Acceleration is currently around 50,000mm/s^2ā¦ itās on the edge here, but rarely have any issues.
I also found that the ones I were eyeballing would not fit in the confines of where the X motor was, even though they were the same NEMA motor size ā¦ The encoding cover made the case too long.
@Dannym advised they loose torque as they speed up, which as he advises would limit acceleration values to their lowest pointā¦ slowing down a job even further.
You can wire it to your Ruida door or water protect circuit and the machine will stop ā for me too much effort and cost for what seems little gain.
Few people with hobby machines have themā¦ less people that have opinions about them results in less input with issues.
Glad to hear from you when your project is completed and how it works out for youā¦
Best of luck with this
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was thinking of speedsā¦ most of these machines will outrun the response time of the tube/lps anywayā¦ Thatās why many find a slower scan speed results in better detail, at least with glass tube.
In rastering, yes, an HVDC excited tube is limited by its response time. Some of the drivers cite 1ms response time, so giving it 1ms to ramp on, 1 ms to get an even burn, and 1ms to ramp off would be limited to 300hz and would still have 2/3rds of the dash being blurry edges. However, if you are just carving out block fills with a powerful laser, a higher raster speed is a very good thing even on HVDC excited. The sloping of the fillās edges may not be noticeable.
Generally, rf lasers have a larger diameter output beam, which results in a smaller dot size and the beam has a higher quality or M2 value.
RF lasers do not have an inherently larger beam size. For a given wattage, itās usually much smaller actually.
RF tubes are digital devices, a glass tube is an analog deviceā¦
No. The time from when the Ruida PWM goes high and actual power output of the tube peaks is in the tens of microseconds range. In HVDC excited, itās about 1ms. The RF should effectively produce at any duty, even <1%. The HVDC excited laser has no ālow endā, somewhere about 15%-20% duty the laserās output just stops. Thereās a window of like 1%-2% where the beam will just randomly turn on and off and wonāt functionally produce fractional power in this region.
I found them to be pretty expensive, when used instead of plain olā steppers.
No. Check again. Note you donāt need to buy a separate motor driver. Donāt compare them by holding torque. Also note you may be able to direct-drive it which eliminates the pulley-and-belt redction
Mine has run at 1650mm/s, but itās purely academic, what it does do it make for quicker jobs and faster response to changes. Acceleration is currently around 50,000mm/s^2ā¦ itās on the edge here, but rarely have any issues.
If youāre just cutting large rectanges, very little gain.
But vectoring out small details and text outlines are typically slowed WAY down below the commanded speed. And also note than the ādead zoneā at the lower end of the HVDC excited tube means if you slow down too much and hit the tubeās min power point, you will be forced to burn at higher watt-sec per mm because the tube output will die if you reduce power any further, and you canāt get the motors to drive the axis any faster. Higher accel can make jobs run faster and that can be almost like running on a higher wattage machine. Better than a larger machine, actually
I also found that the ones I were eyeballing would not fit in the confines of where the X motor was, even though they were the same NEMA motor size ā¦ The encoding cover made the case too long.
That can be true. The motor has to put a magnetic encoder on the other end of the shaft, that takes up space. The FOC controller is usually located inside the motor and that adds a lot to the size. However, the comparison is a bit complicated apples vs oranges to decide what stepper is āequivalentā to comare the lengths.
@Dannym advised they loose torque as they speed up, which as he advises would limit acceleration values to their lowest pointā¦ slowing down a job even further.
STEPPERS lose torque rapidly as they speed up. You can enter a high max axis speed but low accel, OR high accel but low max speed. A servo generally allows you to use higher speeds AND accels.
You can wire it to your Ruida door or water protect circuit and the machine will stop ā for me too much effort and cost for what seems little gain.
If nothing ever goes wrong, then there is no gain. But itās good to have a plan if a motor stalls or jams. This is esp true if you are tuning for speed and push for the edge of motor performance- which does diminish at higher temps, so a max tune at room temp may stall after 30 min or so of running.
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Yes, connect directly to the Ruida. As always, make sure you have configured both Ruida and motor for the same active edge.
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The RF laser is also CO2. Theyāre in aluminum or ceramic resonator bodies. I call the common glass tubes āHVDC excitedā as thatās most accurate, vs. āRF excitedā.
The higher accel and speed can yield major benefits on the HVDC excited machine too. High detail jobs can run faster
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What do you mean having the same active edge?
Also have you tried them? DO they have big advantage to knows steppers?
A motor drive can be set to move on posedge or negedge of STEP signal.
At first, it wouldnāt seem to matter. There must be an equal number of posedge and negedge in the long run. If the controller thinks itās posedge but the drive moves on negedge, it seems like it would just step very slightly later.
But thereās actual probs. The controller can only change the DIR signal far from the active STEP edge, otherwise the drive could be confused as to whether that is a forward or reverse STEP. So it often changes DIR on the inactive negedge of STEP. If the controller is set to posedge and drive is negedge, you can get weird behavior where the stepper seems to drift because every time it changes dir it can be confused about which direction the STEP is supposed to go.
Itās a bit more confusing in getting the terminology right- we often use the motorās opto input by tying STEP+ to a fixed +5VDC and let the controller pull down STEP-. The optoās LED inside the drive will turn on, so you might want to call that the posedge, but the STEP- wire is doing a negedge on the oscilliscope vs ground but positive if itās vs +5VDC.
Also have you tried them? DO they have big advantage to knows steppers?
Iāve been using closed-loop steppers for years. The new FOC servos look great, I need to make a direct drive motor mount, add a 24V power supply and maybe braking resistance, and try it out.
Also, BIG FYI- these are part of the SimpleFOC revolution, and ANY BLDC can be a precision stepper! Add a small magnet on the unused side of the shaft, add a magnetic hall encoder board just past it, and a controller like the
That has a STEP/DIR input.
BLDCs can be pretty torque-y, but they donāt advertise that number. If I have this right, I believe the equation is : max power*9.55 /max rpm.
max power is in watts
max power should have been reported at the max rpm, which should be the motorās recommended max voltage * kv number. And a ā6sā motor is intended for the voltage of 6x 3.7V lipo. This part can be a bit unclear, Iāve seen a motor listed as ā24V/36Vā and also ā8sā (29.6V) and also āmax voltage 41.5vā. To calc torque correctly, I need the correct rpm the reported 1800W power was taken at, which would be voltage * kv. These voltages arenāt all that different but Iād like to be more certain of the voltage thus the torque.
So, the N5065 140kv 8s motor- used in skateboards- is 1800W and should have a holding torque of 4.2nm(!!!) And would go to >4100rpm if it was asked to do it.
Thatās massive overkill, but you donāt have to give it that much power. That motor is under 1/2 kg whereas a big nema 23 can be 2x that. You can potentially use the rotating back half as the output and saw the shaft short and put the magnet on that shortened shaft, mount the hall encoder PCB just past that, locate the driver apart from the motor, now the motor and encoder are ~70mm long 50mm dia.
And thereās plenty of other motors around, Iāve been looking for low KV ones for their better torque while avoiding any need for gearboxes or reduction belts. Theyāre less common, physical construction limitations mean a smaller motor is usually less torque, and theyāre used on small quadcopters which have small dia, high rpm props that donāt have a large torque load
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Picked this up from a number of people that use and sell themā¦ I donāt have one, but one of the engineers stated itās the main reason for itās exceptional ability for detailā¦ same lens ā smaller spotā¦ However Iāll suppress this.
Must have misunderstood you hereā¦ My limited training with these never really addressed the torque
Iām standing there I can shut it offā¦ if itās lost is place ā is the Ruida smart enough to continue the job with servos?
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