[jacquesm]

If you can, please use servos and not steppers. Steppers are cheap and ridiculously easy to interface and get good positional control out of. As long as they don't skip steps. And they always do. So you end up running at 1/10th of the speed your tool could move at to avoid that, and even then you'll end up tossing workpieces because you lost synchronization somewhere along the line.

For 3D printers they work fine because there is no pushback ('loading') from the extruder. But for anything that cuts servos are the way to go if you want half decent speed and quality cuts, as well as long tool life.

[dbcurtis]

Steppers skip steps if you are asking for more torque than they can deliver. No other reason. It might be: 1) too small of a stepper motor, so it can not deliver sufficient torque for maximum load, 2) too small of a driver that can not deliver the current needed for the motor to reach its rated torque, 3) software bug that tries to accelerate the motor faster than it is capable of under the load at hand, 4) software bug that throttles the driver.

They all boil down to commanded torque greater that the system is capable of delivering. Fix your design. Be suspicious of software trying to accelerate too aggressively under load.

I have cut a lot of metal on a Tormach PCNC 1100 Series 3 machine, with steppers. NEVER had an issue. Correctly designed stepper systems DO NOT miss steps.

That said, servos systems typically are capable of greater accelerations for a motor of a give volume and current load, because of the closed-loop control. Use servos for speed, not because you are afraid of skipped steps from a stepper.

[jacquesm]

Correctly designed stepper based systems use encoders or other feedback mechanisms to detect missed steps and correct for them. Open loop systems will always miss steps, and most hobbyist aimed gear is open loop because it is super cheap.

FWIW I designed and built CNC equipment for a living.

As for the Tormach machines, they use 3 phase, not 2 phase steppers, and use current sensing on the stepper outputs to give them a feedback mechanism, and an encoder to close the loop completely these drivers and stepper motors are better than the ordinary two phase kind that you find in regular hobbyist aimed gear.

https://www.damencnc.com/en/nema-34-closed-loop-stepper-syst...

They are properly classed as a hybrid servo system rather than just a stepper on account of that feedback mechanism.

[Damogran6]

You're not wrong, and when the part being cut is worth 5 figures for the raw stock, it's probably a criticality, but it's important to not gatekeep this process, lest it become a no-true-scotsman kind of thing.

I built a couple of 3d printers from scratch BECAUSE the various components were cheap and approachable. Haven't done CNC because my interests haven't taken me there...but the thing about advancement is: While one fella is saying 'You can't do it that way!' someone comes around and does it that way, and the first person is left in the dust.

You can't really stop Laser printers from dropping to many thousands of dollars to $70...all you can do is ride the wave.

[jacquesm]

The probability of any given step being missed is proportional to the amount of value lost of the step is missed. Pretty weird how that works ;)

[Kirby64]

That's not necessarily true, it all depends on what your desired outcome is. Stepper systems can be open loop as long as you're aware of what the torque threshold is and make sure you don't exceed that. Obviously a crash would exceed that, but there's ways to detect that (e.g., stallguard on Trinamics stuff) without adding an encoder. The whole point of open-loop stepper systems is that you make sure you stay under the torque limit by a margin (say, 30% or so) and you are fine. A properly designed system should never lose steps ever, besides in a crash event. Or if you load it up with too much side force, but you can get that on any machine.

[PragmaticPulp]

Servos and closed loop systems are almost mandatory on large commercial mills due to the sheer scale and mass involved, but they’re not as mandatory on the hobby level.

In practice, hobby level machines don’t have near enough rigidity or spindle power to warrant high movement forces in the first place.

Nearly all of the hobby CNC machines on the market use open-loop steppers. They’re definitely not losing steps during normal operation.

The topic of steppers vs servos has been covered over and over on every hobby CNC forum for the past two decades. Closed loop systems are great if someone has extra budget to spare, but they’re unnecessary for machines using hobby-level spindle power.

[rmu09]

Stepper motors also have resonances that you can excite with typical step pulse trains, that can also lead to missed steps while technically not overstepping the torque budget.

[jacquesm]

You can work around those resonance points quite well if you know what you are doing, the trick is to realize that the back-EMF around those resonance points can be so high that your stepper is momentarily generating power rather than consuming it. If you try to force it through that point by adding more current then the stepper will stall completely. A properly designed driver that is matched to the load of the stepper will use a complex voltage/current model that will drive the stepper just right to avoid this problem.

This technology originated with the Berger-Lahr company in concert with an Italian driver manufacturer for five phase stepper motors, which were the first to be driven past this resonance point, the tech was then perfected and adapted to other, cheaper steppers as well.

[nielsole]

My guess is that the tormach detects skipped steps in the controller ("sensorless stall detection")

So it probably does skip steps, but corrects for it

[jacquesm]

That is exactly what it does. This is also a setup that will work fine, but it is actually much closer to how a servo would operate and negates quite a bit of the cost difference due to the far more expensive drivers, with encoders and current sensing on the stepper wires.

The encoders will tell you when to increase power because you're about to miss a step, the expected movement is lagging compared to the amount of input current. The current sensing will help you to detect tool strike situations before damage is done to the motors due to overcurrent.

[aidenn0]

If you detect missed steps, and apply feedback, isn't that now a servo mechanism?

[throwaway9d0291]

I disagree.

I've been running a small CNC for a while now and though I've had skipped steps, they've never been the cause of a failure. When they've failed, it's been because:

- I stalled the spindle and I'm trying to plow the no-longer-rotating endmill straight through my stock (and if steps weren't skipped, the tool would break)

- I forgot to turn on the spindle and I'm trying to plow the endmill straight through my stock (and if steps weren't skipped, the tool would break)

- I've somehow forced the machine to try to push through its limits and crashed an axis into the chassis (and if steps weren't skipped, the machine would be seriously damaged)

Basically, the only time the steppers have failed is when not doing so would lead to much greater damage, so I'd go so far as to say that skipping steps are a feature, not a bug.

If your steppers are failing in the middle of a job where nothing has gone wrong, either your steppers or your drivers are messed up but it's not because steppers are inherently bad.

I'd recommend servos for applications that are demanding on torque, power, speed and/or accuracy. I wouldn't recommend them for your first DIY machine because of the additional risk, expense and complexity they add.

[yudlejoza]

General question regarding robotics/motors:

Is there a classification of a system in terms of 'highly precise pre-defined/pre-programmed' movement vs 'feedback based movement'?

As an outsider, mainly watching youtube demos/videos, I've noticed the old kind of robotics, from ABB, Fanuc, and what not, with massive robotic arms planted to a firm-foundation, is based on precision pre-programmed movement. (I believe) there is no feedback though sensors or cameras or anything.

But the new trend is based on feedback, whether traditional control-theory feedback, or neural network based reinforcement-learning feedback, which I guess eases the rigors of pre-program design and makes the system more flexible in new situations. But of course it's an open research topic, and involves every-increasing sophistication of sensors, high-def cameras, lidars, and what not.

Wondering how the choice of stepper/servo, or some other mechanisms like hydraulics/pneumatics relates to the above categorization.

Thanks in advance.

[LeifCarrotson]

Classic industrial robotics and CNCs have and have always had sensors - encoders for position, plus the servo amplifiers give feedback for the amount of current the motor is using, which is proportional to torque. You can definitely use feedback from those control systems. This has been true since the earliest systems in the 70s, and is only starting to become optional with recent hobbyist 3D printers and stepper-based robotic arms and such.

They can also use machine vision in a limited sense. For example, I worked with one last week that drove screws. There are known numbers and locations where screw pilot holes are expected to be, but they have a variability greater than the radius of the screw. So, the arm moves the camera into position so the field of view is a bit larger than the tolerance on the pilot hole, takes a photo, locates the circular feature of appropriate size, then moves the screw to that location.

However, you're right, these robotic systems are doing fundamentally different things than Boston Dynamics and self-driving cars. They're solving a different problem. The difference is less about stepper/servomotor/hydraulics or other control systems, and more about the degree of control that the users can and want to exert over the robot work environment. If it's easy to mandate that there will never be an obstruction in front of the screw you're trying to install, and the machine must power down the servos if a human is inside the fence, and you can demand of the drill machine a certain tolerance on the hole location, you can have a more reliable, simpler to debug, quicker to build robotic cell. If keeping humans out of the equation and the environment obstacle-free is impossible (as on a battlefield or parking lot), then you have to reach for less reliable, more complex control algorithms.

[fest]

From what I have seen, what some of the research gets wrong is focusing too much on actuators and less on the frame rigidity/dynamics. Even if it's possible to arrive at somewhat okay-ish position performance using vision based feedback, the control system can't really cope with dynamic issues (imagine an end effector on a thin, long piece of wood: even if you can move it around to a certain position based on vision feedback, once you change the load on it, the piece of wood bends, once you decrease the load it snaps back etc).

[bluGill]

In theory you can compensate for this by detecting the movement/vibration and moving the cutter to compensate. You "only" need 100khz sensors, fast processing and super quick actuators. You can lower this a bit with lower depth of cut and slower feed rates.

Like I said in theory. In practice we don't really have the ability to sense that well. While drivers that are that quick exist, they are exotic, or have limited range of motion.

[yudlejoza]

Oh yes, this is one of my pet peeves.

I do think taking into account the feedback from the load as well as the weight of each section of the arm itself, needs to be done. In addition, some aspects of vibration control also need to be incorporated. (I guess the right word is proprioception, as mentioned in another commentor).

[fest]

Yeah, it definitely needs to be done- if not for other reasons then just to find out exact machine limits and have more data for the next design iteration.

[tlarkworthy]

open loop/closed loop. (though industrial arms will have proprioception too). Note a good fast moving robot arm needs position feedback in the 100kHz range, which a lot of sensors are nowhere near.

[jacquesm]

The feedback is done with optical sensors called 'encoders' on the servo axle.

[YZF]

You just need enough margin with steppers so you don't lose steps. Particularly during accelerations. That margin shouldn't need to be x10. It also depends on what screws you're using and whether there's any other reduction. You can get huge linear forces from a relatively tiny stepper. You're also going to need margins with a closed loop DC brushless/servo system otherwise while you won't lose your position you will get a position error.

There's also systems with steppers and encoders.

A common issue though is that the steppers are driven at too low of a voltage. You also want the right kind of driver that PWMs a high enough voltage to maintain the current at speed. That's because as the speed goes up the motor has higher back-EMF voltage that the driver needs to overcome. Constant voltage drive really suffers as the motor speeds up.

But sure, DC brushless + servos are nice, more expensive, and require more expensive controllers.

[PragmaticPulp]

Agreed. High powered servos and associated controllers are great with an infinite budget, but properly sized steppers are perfectly fine for hobby CNC machines.

The forces involved can be estimated ahead of time with simple math. It's easy to verify stepper motor holding torque with a common kitchen scale. Cutting forces can be estimated with readily-available calculators online.

[imtringued]

What's wrong with a kit like this? https://www.omc-stepperonline.com/closed-loop-stepper-kit/ye...

[PragmaticPulp]

Those are great if they’re in your overall budget. Depending on machine layout you could need 4 of those. Spending $400 on motors alone puts this firmly in the very expensive end of the hobby CNC spectrum.

The closed loop functionality will never come into play with properly sized motors, though.

If the machine gets to the point where the closed loop function is trying to make up for lost steps, it’s almost certainly because something has gone wrong (crashed machine into workpiece, for example). At that point, it’s actually better to halt the machine and alert the operator, which is what a lot of people end up using closed loop stepper feedback for.

New Trinamic stepper drivers have some built in functionality to detect stalled steppers, which can be used for the same effect.

Closed loop steppers definitely aren’t bad, but they’re not a must-have for hobby machines.

[jacquesm]

Nothing, technically that's a servo system using a stepper motor as the actuator, which is fine.

[archi42]

Does this also hold when using drivers like the ones built by Trinamic? A servo is essentially a feedback control loop, ensuring your motor will slow down if is reaching its torque limit. As I understood the data sheet for the Trinamic controllers, they can measure various parameters (e.g. back EMF, applied current,...). Cooperating with the motion controller, a similar feedback loop can be implemented. (Thinking about this, a servo would need to "talk" to the motion controller as well anyway - if the motion is lagging behind due to a torque limit, the motion controller needs to compensate for that instead of just scheduling motion on an independent axis).

[jacquesm]

Those should work fine.

[PragmaticPulp]

> Steppers are cheap and ridiculously easy to interface and get good positional control out of.

This is exactly why 99% of beginners should start with stepper motors.

Building a CNC is an exercise in tradeoffs. It's tempting to want to choose the best option at every juncture, but that's a recipe for blowing your budget. I strongly recommend that beginners start with sufficiently-large stepper motors to get things done, then consider more expensive motors as a later upgrade.

> As long as they don't skip steps. And they always do. So you end up running at 1/10th of the speed your tool could move at to avoid that

They definitely don't always skip steps. I've never skipped steps on my hobby CNC during normal operation. Only crashing the machine causes skipped steps, at which point I have bigger problems to worry about.

It's very easy to measure the maximum force your stepper-based CNC can apply before skipping steps. You can use a common kitchen scale and manually force the CNC axis to compress the scale until it skips.

In my case, the maximum stepper force is about an order of magnitude higher than the calculated cutting forces in aluminum. If someone was trying to push the cutter so hard that it was overwhelming common NEMA 23 steppers, they're going to need an extremely rigid machine. Most hobby-level machines aren't rigid enough to use high cutting forces, and unless you have a 2.2KW water-cooled spindle, you won't have enough power to cut at those speeds anyway.

As long as your steppers are sized appropriately, it's really not a big deal.

> So you end up running at 1/10th of the speed your tool could move at to avoid that

Again, not really an issue in practice. Use sufficiently-sized stepper motors and the movement speed is just fine.

I strongly suggest that anyone building a CNC focus first and foremost on keeping it simple and cheap. Get it built, learn from the process, and improve on your next iteration. Closed-loop stepper motors are a reasonable upgrade path, but the idea that you're going to be skipping steps with regular steppers just isn't true.

EDIT: Here's a video of a common Shapeoko with significant added weight moving at 1000ipm on the tiny stock steppers without issues: https://www.instagram.com/p/B1wSmXfnm6C/ The stock settings are 200ipm, which leaves ample safety margin for normal operation. 200ipm is plenty fast for rapids unless you're trying to reduce cycle times on large-scale manufacturing, in which case you wouldn't be using a hobby CNC machine.

[taneq]

All of this is spot on.

[justinclift]

> So you end up running at 1/10th of the speed your tool could move at to avoid that ...

Doesn't that only happen when the controller either doesn't know (or can't decently handle) the limits for a given machine?

eg if a machine could (say) only accurately (without losing steps) push the spindle at 1000mm/min, with maximum jerk of (say) 0.5

If your controller doesn't know to keep in those limits... it makes sense steps will be lost when going past those limits.

So, seems more like a tuning problem?

That being said, closed loop stepper systems exist, though I haven't (yet) personally tried them.

[PragmaticPulp]

I think he's exaggerating for effect. Properly sized steppers have more than enough margin for rapid movement on hobby machines without losing steps ( Video example at 1000ipm: https://www.instagram.com/p/B1wSmXfnm6C/ ).

Skipped steps are only a problem if the machine is tuned wrong, like you said, or the steppers are too undersized to keep up.

People tend to underestimate the strength of common NEMA23 steppers while overestimating the cutting forces they need. Most hobby machines don't have enough rigidity or spindle power to require more than a few pounds of lateral cutting force.

[YZF]

To be precise, it's not the strength of the stepper, it's the gearing through the screw that converts the torque of the stepper into the force on the tool.

[jacquesm]

And that will give you slop which will translate into imprecise workpieces and surfaces that aren't flat.

[PragmaticPulp]

At the hobby CNC level (what’s being discussed in this article), the rigidity of the machine is far more of an issue.

I think your advice is spot-on if someone was designing a 5000lb vertical mill out of steel, but hobbyists building DIY bench top machines face a different set of problems.

Hobby level machines are almost always limited by rigidity, not movement motor torque.

[jacquesm]

I've built a whole pile of CNC machinery, both lightweight and heavyweight. If you don't actually care about what you produce, fine, go with open loop steppers. If you want to control a device that produces accurate work products that do not need extensive rework (or to be tossed) then use something with a feedback mechanism.

I'm fine with you advocating for steppers for non-contact or drawing work (laser cutters, engraving and so on). But if you care about your tools, you don't want to wait for hours for what should be a small job then add the bit of money for a servo or a hybrid solution, on the total cost of the machine it won't make a lot of difference and the machine will be so much more reliable and faster that you'll end up using it much more frequently.

Right tool for the job and all that, bench top CNC with small servos is a very powerful tool in the hobbyists arsenal, and if you scrounge ebay you'll find they can be quite affordable. Note that anything that cuts has a stand-time, and if you move slower or make many passes because you can't really cut then you will end up spending a fortune in tooling which at some point will easily outweigh the price of the feedback mechanism, which automatically compensates for increased load and toolbit wear.

[jacquesm]

> I think he's exaggerating for effect.

I wasn't. You'll never make it through your first resonance point without current feedback, and a good stepper driver can easily go into very large multiples of that frequency.

Then there is microstepping.

> Most hobby machines don't have enough rigidity or spindle power to require more than a few pounds of lateral cutting force.

This is true, but a different problem.

[PragmaticPulp]

I think you’re approaching this discussion from a commercial/industrial scale.

Hobbyist CNC machines simply don’t have the same issues as large commercial-grade CNC mills. None of the popular hobby CNCs use closed loop motor control. Skipped steps are simply not an issue at this scale.

[numpad0]

I long had dimensional accuracy issue that the whole axes seemed to stretch and contract like 5%, on a cartesian 3D printer, and it just went away after I switched to Servo42B setup.

I think it’s microstepping. Steppers with microstepping enabled and controlled by an 8-but micro must be assumed to produce zero holding torque and assumed they always miss a step or two.

[craftinator]

Upgrade the controller. For a hobbyist machine, the ESP32 CNC controller sold on Tindie is well suited to deal with that, and costs ~$35.

[StavrosK]

I made a PCB for an ESP32 CNC controller, if anyone finds it useful:

https://gitlab.com/stavros/esp32-cnc

[craftinator]

Nice! I'll check it out! Here's a link to the one I'm using:

https://www.tindie.com/products/33366583/grbl_esp32-cnc-deve...

The developer is really responsive, might be worth collaborating since you have put in similar work.

[taneq]

I'm running one of these on my Lowrider 2 and it's pretty great. The only real issue I've had was with limit switches (I got cocky and didn't use shielded cables, then ran the sensor cables with the stepper ones, so I had to add pull-ups and filtering caps to smooth out the noise... lesson learned!) The web interface does seem to crash semi-regularly if you step off the straight and narrow but once you know the pitfalls it's great to be able to drive your router around with a laptop or phone, and to be able to upload files over wifi.

[dekhn]

There are several newer boards from Bart (including the 6-pack which has some add on modules).

Grbl ESP32 is great. Easily the best of the firmwares I've used so far.

[jbay808]

Microstepping does not reduce torque in any respect.

[dekhn]

I've been curious about this for a while- I've got a modest CNC (X-carve) with steppers. If I wanted to upgrade my machine to feedback servos, how simple could it be?

I already have a CNC controller with stepper drivers. Do servos have a stepper interface, and internalize all the servo logic and feedback? IE, can I just buy "servos" that have internal feedback, and send them the same step and dir signals, or SPI signals, needed to drive steppers?

Or, do I have to replace my controller/drivers with a servo-specific driver? The reason I ask is that I have an extremely inexpensive stepper system (grblesp32 6-pack controller with external drivers) and cheap steppers, and definitely am hitting the point where I have to dial back all my parameters to finish cuts without dropping steps.

[craftinator]

Or just use a gear reduction? You really need to be dealing with high force systems to justify the cost and added complexity of using servos. I've built a mill from scratch that can handle decent sized steel milling using NEMA23 sized steppers and some decent 10:1 gear reducers and a nice spindle. IMO a better spindle and structure is where you should be spending your money, and if you really are afraid of losing steps, you should use encoders that are DECOUPLED from the motors, not integrated into them...

Servos are great if you're working with huge forces, need a lot of speed, need ridiculously high accuracy, and have a team of engineers to actually build and tune the thing. Ridiculously expensive and complex unless you're looking to go into busines manufacturing CNC systems.

[jacquesm]

Gear reduction gives you slop, if you need to reduce the better way is probably using a kevlar toothed belt and two pulleys. Still not perfect but better than gears. Finally, the best way (and most expensive way) is by using a properly pre-tensioned ball bearing driven spindle ('ball screw').

[craftinator]

I work in the non-destructive testing industry, testing aerospace parts. We build CNC testing rigs fairly regularly, with x and y axes longer than 30 feet, and carry loads of >1000 lbs. These need to be able to center on holes with diameters of <1 mm, because that's what we calibrate our equipment on.

The most reliable build setups we have are kevlar belts coupled with 16:1 reduced stepper motors, and decoupled encoders that index using constant pressure rack and pinions. Even pre-tensioned ball screws give us enough slop to be a problem without encoders, and kevlar belts are an order of magnitude cheaper; going with a reduced stepper vs a servo takes the cost down by half.

[jacquesm]

Ah good point, yes, at those lengths you really don't want ballscrews, they are impossible to support and will warp. But for short distance (up to 8' or so) with a support on either end they are fine.

[craftinator]

Yeah, my brain is kinda tuned to those long distances. I also kind of harp on people who say they need really high precision systems, so use servos and spend bookoo bucks on slop-reductive hardware.

Even a cheap encoder, when decoupled from the motor, and directly coupled to the axis it measures, will give better axial positioning than a servo. It boggles my mind why people seem to ignore this in favor of a motor that knows where it is in space, but doesn't know where the axis it is driving is in space.

[taneq]

> As long as they don't skip steps. And they always do. So you end up running at 1/10th of the speed your tool could move at to avoid that, and even then you'll end up tossing workpieces because you lost synchronization somewhere along the line.

My experience has been roughly opposite of this. If you overload your motors, you're going to lose positional accuracy and probably wreck your workpiece regardless of whether you use steppers or servos. If you don't overload your motors then the difference is moot, and with steppers there's less to go wrong.

[PragmaticPulp]

In practice, hobby CNC machines use the closed-loop feedback systems to halt the machine and alert the operator that something has gone wrong.

Hobby-scale machines shouldn’t need closed-loop systems for positioning during cutting operations. Especially if they’re using a 300-400W (sustained) consumer router as their spindle as this article suggests.

Cutting forces at this scale are in the single-digit pounds. Nothing a common NEMA23 can’t handle with plenty of margin. Trying to push a low-powered spindle through the workpiece on a low-rigidity hobby machine causes more problems.

[IgorPartola]

You could always run smart steppers like Mechaduinos or the similar option from Big Tree Tech. Your firmware might not even need to be modified, though there is work being done on Klipper to run firmware directly on the steppers so each one is treated as an six board responsible for a specific function.

Nothing against your advice just providing another option that uses steppers that don’t skip an occasional step (that is to say that if you ask for more torque from a stepper than it can handle, smart or not, it will not produce more torque out of thin air).

[jacquesm]

Yes, that's an option. Technically that is a servo system from a classification point of view. Anything that contains a motor, a controller and a feedback mechanism is a servo system.

[IgorPartola]

I actually see that as an option (ODrive) in the featured article :). I am really curious to play with them myself as I’m about to start building the MPCNC.

[traverseda]

Stepper motor drivers that support stallgaurd (trinamic's stepper drivers) seem like the best of both worlds, and even in-theory can give you some force feedback.

[beervirus]

I’ve always wondered why more home CNC machines don’t just use closed-loop control.

[analog31]

At one time, it was harder and more expensive. You could do open loop stepper control with four big transistors, some logic, and a whopping heat sink. Closed loop meant learning how to tune the loop, and also involved the cost of the encoders.

If you're using surplus parts, then getting enough documentation to make a servo system work can be touch and go. Steppers are pretty much brain dead simple.

Even with servos, the entire machine has to be pretty stout in order to ride through a bump that would cause a large stepping motor to miss a step. At that point, if it's a homemade machine, something else will end up out of kilter too, such as your clamping or the workpiece itself.

[sschueller]

Closed loop stepper controllers have become "dirt" cheap: https://www.aliexpress.com/item/4000684515100.html

[SV_BubbleTime]

As someone with a CNC router with steppers I can not agree more.

[gorkish]

You might be able to interface Mechaduino or MKS controllers between your steppers and drivers to make them pesudo-closed loop. They still get driven by step+dir however the position is continuously integrated by the controller and stepper is driven directly to the correct position based on a fitted magnetic encoder and calibration profile.

[CamperBob2]

What do you think of these? https://www.crowdsupply.com/iq-motion-control/iq-motor-modul...

[jacquesm]

For their size those are very impressive, I'd be quite concerned about cooling them but there must be applications where their form factor would be a game changer.

[justinclift]

Looks like the wrong kind of thing? Those seem to be high speed drone motors.

Am thinking they'd not have enough torque, unless you gear them pretty high.

[CamperBob2]

Further down the page, they explicitly call out CNC applications. ("IQ motors are smoother, quieter, and more efficient than stepper motors, and they will never skip a step or get lost.")

They are basically a stepper motor from the application's point of view, but with some of the advantages of a servo, as far as I can tell.

(No affiliation, just curious if these guys are onto something useful.)

[gji]

Just judging by the torque specs and comparing to a nema23 stepper, seems like it needs an order of magnitude more torque to compare. Note that in the comparison chart they compare to a nema11, which is tiny compared to the steppers used in most hobby cncs.

[devwastaken]

Have any recommendations on servos for this purpose?

[mferraro89]

OP here: Teknic Clearpath servos are considered good value and come in lots of different sizes/price points. Wiring them up could not be simpler, but know that you need a windows computer to tune them.

If you are comfortable with soldering, motor sizing, and python, you can pick up an ODrive control board and some sort of position sensor and turn almost any motor into a servo motor.

[craftinator]

I've purchased a couple of these for UT CNC systems; definitely good bang for your buck, but that's if you need to drive a 1200 lb bridge at 6 in/s, and have $600 per motor to spend.

I ended up not using them because I found it was simpler, cheaper, and fit the mounts better to buy a pack of NEMA34 steppers and a few $15 dollar encoders. Seriously, spent maybe $800 on decent quality steppers/encoders/amps for 3 axes, where the ClearPath servos would have been $1600 for the same 3 axes, but wouldn't have provided position feedback nor allowed position localisation to be decoupled from the motors (which is the best way to do things in most cases).

I think it's hard to justify the costs of these types of motors unless you have some very specific torque/speed/spacial requirements that require them. If you're building a machine that is worth >$4000 per axis, then maybe, but if not, simple steppers are the way to go.

[jacquesm]

Ebay. That's by far the best place to spot really good gear for a small fraction of the sticker price.

The usual suspects for brands, personal favorite: Panasonic Minas series drivers + associated servos. Cheap, super reliable and available in just about every size that you could possibly want.

[formerly_proven]

I've looked into this a few times and it always seemed like there is a huge abundance of servo motors, but the market for servo amplifiers seems to be tiny in comparison. I always suspected this is because the electronics of decommissioned machines are just scrapped wholesale. However, I am also wondering what people are doing with all these servo motors without matching cabling and amplifiers.

[jacquesm]

Good point, amps are a bit harder to get by than motors, but then again, there are plenty of them on offer. I only paid full price once for a set of servo amps and that was because I wanted to have a particular type for a very special set of motors (pancake servos).

[formerly_proven]

How do you deal with the proprietary connectors on the motors? Replace them or only go for motors that come with stub cables? Proper replacement plugs probably cost about as much as a used motor... and most seem to be sold without cables/plugs. (Unfortunately it is hard to search for this stuff, because everything is "polluted" with model making servos)

[augustt]

https://odriverobotics.com/

[jiveturkey]

tormach doesn't seem to have a problem with it. it's only recently they started offering servo upgrades.

[ashtonkem]

IIRC, Servos also can provide feedback, which also helps with precision and reliability.