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48VDC or 24VDC for STEPPER MOTORS?

Discussion in 'General Talk' started by AR15DCM, Apr 23, 2016.

  1. AR15DCM

    AR15DCM Journeyman
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    Hello,

    Your typical newb here asking a fairly newb question. I did a couple searches and maybe I did not use the correct search terms, but I didn't find anything....

    When selecting a power supply to run the stepper motors should I use 48VDC or 24VDC ?
    Is there any advantage or disadvantage to running either one?

    Thanks!
     
  2. Joe Santarsiero

    Joe Santarsiero OB addict
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    If your drivers will take it then use a 48v supply. Motors will perform more desirable than at 24v. They may get warmer though. Don't exceed your drivers rated voltage.
     
  3. AR15DCM

    AR15DCM Journeyman
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    Okay so really I should shop for the electronics first and determine what the motor drivers will end up being, then shop for the motors?

    Do most systems take 48vdc or are they down around 24vdc?
     
  4. Joe Santarsiero

    Joe Santarsiero OB addict
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    Well, not quite the right order. If you're building one of the OB routers then you know you'll be using a NEMA 23/24. You'll choose that based on desired characteristics. I hear the OB NEMA 23 is a good start. So that's a shortcut. Also, your choice of control software has an effect on drive solutions.
    If you can afford dipswitch selectable DSP based drivers then go that route. There's less room for disappointment.

    There are systems that run off of various voltage ranges. Most hobbiest work in the 12-72v range. 12-48v is common in the printer/router arena. It depends on the needed motor requirements which depends on application. NEMA 17s for 3d printers and light load high velocity machines like laser engravers appear to run in the 12-24v range. Light to medium duty (like OX and CBeam) with NEMA 23/24s are mostly happy in the 24-36v. Some use 48v. 48v and up for medium to heavy duty machines like mill and lathe conversions and other beefy Diys. This is what I've mainly seen, but there are always exceptions.

    Joe
     
  5. AR15DCM

    AR15DCM Journeyman
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    Hi Joe,

    I will be building a beefy OX Tall Machine, 1000 x 1000 in size. I will mainly be using it for wood, but I can see some metal millwork in there too. I was expecting to use NEMA23 right off the bat, but I have not heard a lot about NEMA24 personally.

    I just bought a Lucent 48v 16AMP power supply for $80 on eBay. And if I add a module it will go up to 25AMP. So I am starting to gather parts here and there and its about time to start buying the T-Slot stuff, Motors, and Electronics.
     
  6. Joe Santarsiero

    Joe Santarsiero OB addict
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    Sounds like a fun build. 16amps should be plenty. General rule of thumb seems to be to spec a supply that provides at least 2/3 the sum of all steppers.
    Any software or electronics in mind?
     
  7. AR15DCM

    AR15DCM Journeyman
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    I was Leaning towards MACH4 Software. From what I have seen from some of the others they are not as robust or do have the support in place to back it up.

    The electronics... I have only really looked in depth at the Gecko. Gecko seems to be the only one that has put their information into a format that I can easily understand as an "off the street" newbie. I don't do Adruino, I don't own it, and I know nothing about it.

    There is still a lot that I do not understand about selecting the electronics/motors etc...

    Oh and update on the power supply... I figured in case I upgrade to do something with my metal mill that I also have... this afternoon I bought the module to fill the third slot of that power supply. So it will now be a 1200 watt/25 amp/48VDC supply. I will be able to use it for either machine now if I add stepper/servo's for the milling machine.

    Here is the link to it and the module :

    LUCENT 48vdc power supply 1200watt chassis with two 400watt supplies 48 volt
    Lucent Technologies RS0400AA100 48V 400W Power Supply
     
  8. Russell Zauner

    Russell Zauner Well-Known
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    I'm gonna hop on this thread as I just got done assembling the C-Beam actuator bundle and am trying to hunt down the datasheet for the motor (I'm learning as well - but I've got 20 years in as an engineering technician, just not deep in mechanical/motors...yet). Is there a repo of docs for the parts on OB?

    I'm also working out how to power this up and exercise it a bit while I'm waiting for some other parts.

    Second question - I'd like to know why 48V is better than 24V for motor operation. I need to learn enough to spec all the components from scratch for a given design/application, so these are exactly the observations I need to build up my "intuition" for motors. Some people may be born with it, but I've always had to work hard to develop it.
     
  9. GrayUK

    GrayUK Master
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    Whilst this video is probably not dealing with the electronics you plan to use, I suggest you watch it, and maybe the other videos by this guy,
    simply because it explains a lot of things simply. :)
    I used this as my "Idiots Guide" to CNC electronics. :banghead:

    Hope you find it useful. :thumbsup:
    Gray
     
  10. Russell Zauner

    Russell Zauner Well-Known
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    Thanks. Will do. I can buy all the parts I need, so I can select the components I want per application. If I have any more questions I'll pop on this thread if appropriate, or start a new one.
     
  11. AR15DCM

    AR15DCM Journeyman
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    Thanks for the heads up. I will watch them.

    I was also wondering... how do you size the motor's oz-in that is needed for the frame/router/spindle you will be using?
    For example, I will be building a 1000 x 1000 Tall Blue OX. At first I will be using a Dewalt DW660 however, that will be upgraded as money permits to a larger router so the weight will increase.
     
  12. Metalguru

    Metalguru Master
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    Professor Mode on

    Stepper motors operate on current. You must limit the current in the windings to prevent overheating the motor and burning out the windings. In the old days they used huge power resistors to limit coil current, which wasted a lot of energy as heat and took up a lot of space. Most modern stepper drivers use PWM (Pulse Width Modulation) to limit the winding current in the motor to a safe or specified value. They change the Duty Cycle (On time/Off time) of the incoming power to reduce the current into the motor to a safe value.

    How this works is that typically, a power supply will have a fixed voltage. The stepper motor controller circuit turns this voltage on and off at a very high rate, on the order of hundreds or even thousands of times per second. It can vary the on time/off time ratio, which then reduces the apparent voltage of the power supply by this ratio. So, if you have a power supply of 24v, and you PWM it's output by 50% ratio, you will have an apparent output voltage of 12v (only under load). The PWM ratio is actually reducing the power output of the supply and not the voltage. You still get the full supply voltage, but only for half the time, therefore half the average current.

    Stepper motors are inherently rather low voltage/low impedance/high current devices. If you have a stepper motor that requires a current of 2.4A at a voltage of 2.4V, using Ohm's Law it has a winding resistance of 1 ohm.

    Now, suppose you are using a 24V supply, and want to use PWM to limit the current into this motor, you would initially calculate that the motor current would be 24v/1 ohm or 24A. This is obviously way too high for the motor, so you would use the PWM to limit the current to 2.4A. The required PWM percentage to achieve this would be 2.4/24 or 0.1 or 10%. So, your stepper driver would be set to provide a 10% on and 90% off duty cycle. This would limit the average current into the stepper windings to 10% * (24V/1 ohm) = 2.4A, which it is designed to handle.

    Where the advantage comes in, is that the power supply voltage is still 24v. So, when the stepper driver turns on the coil, it will apply 24v to the coil for the first 10% of the cycle, and then turn off for the remaining 90% of the cycle. Since the stepper motor is actually an inductor, not just a straight resistor, it will take some time for the current to build up in the coil, and when the voltage is removed, it will take time for the current to fall back to zero. I don't want to get into inductive theory at this point, so you'll just have to take my word for it.

    This means that the stepper driver can deliver more energy to the coil initially, since the voltage is higher. The average current will still be the specified current for the motor winding, but the instantaneous current when the PWM is on will be much higher because of the higher voltage. This instantaneous application of high power causes the motor to accelerate faster and have more torque, while still keeping it within its specifications.

    So, the theory is that the higher the voltage you use to drive the motor, (while still limiting its current to specified levels via PWM), the more torque the motor will have and the faster it will accelerate. Of course, there are limits to this as to everything, so you will eventually hit a point of diminishing returns for one reason or another. Stepper motors are a very complicated bit of kit, and there are a lot of issues I simply left out for clarity.

    I hope this is a clear enough explanation.

    Professor Mode Off
     
  13. AR15DCM

    AR15DCM Journeyman
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    Okay that helped a great deal to understand how the motors work in conjunction with the motor drivers and power supplies. But going back to my original question, how does one calculate the amperage/oz-in needed to drive an x-type/size CNC router? Out of all of the stuff I read so far there has been nothing that says you need.. as an example;

    Based on the calculated weights for X,Y,Z
    An OX type CNC Router would need 2-NEMA23 420oz-in motors for the X-Gantry, 1-NEMA23 340oz-in motor for the Y-Gantry, 1-NEMA23 275oz-in motor for the Z router

    As a newbie oz-in doesn't tell me anything... it might as well be an Egyptian hieroglyphic.
     
  14. Rob Taylor

    Rob Taylor Veteran
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    This is where it gets tricky. There are two options:

    A) Get what you think you'll probably need, and then change it if it's not sufficient.

    B) Calculate the force values throughout your system to arrive at a required motor torque. This is a little bit "how long is a piece of string" unless you have access to commercial engineering CAD software and a workstation with the grunt to run it. Otherwise, it'll give you some ballpark figures based on some assumptions as you go, and then dump you back into option A above regardless. Same goes for figuring out how big you need your extrusion to be.

    If you want an idea, here's the chain:

    [Motor] drives [belt/chain/leadscrew/ballscrew] across [V-Slot/linear rod/linear rail], pushing a spindle of [mass/continuous power] (or in the case of the z-axis, pulling a spindle of mass [m] directly against gravity) which uses mills of [material, geometry] typically in the [diameter] range, and the [densest/hardest/grabbiest] material it'll be cutting at typical [feedrate] causes cutting forces calculated (or tabulated) to be [kickback/grab/continuous force/push-up], which transmit back through your system as outlined to produce a torque at your motor output of [T], which your motor needs to be bigger than.

    That's not quite technically right, but it'll get you started in the right direction. Look up "machine design". It's a whole field unto itself, and no one else can really tell you you NEED a particular motor, only what worked for them in their setup cutting particular materials with a particular spindle and milling bits. If your setup is going to be similar to someone else's, there you go, you're set. If not, well, gotta figure it out.
     
  15. Metalguru

    Metalguru Master
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    Yeah, the calculations for mass/inertia/speed/acceleration/tool force/friction/efficiency/etc are going to challenge a Mathematics professor to get an answer. And, when you are all done, it's still just pretty much a guess.

    Best way to go about it is to just experiment. Start with what everybody else uses, as Rob says. If the motor doesn't cut it, you can try a higher voltage. If that doesn't work, you can use the belt reduction setup. That doesn't do what you want, get a bigger motor.

    It's not really that much of an issue. If you motor is a bit too small, all it will do is limit your acceleration and maximum speeds. Not that important in the grand scheme. If it's WAY too small, you might have problems with missed steps etc. But, the OX size belt driven
    machines or the lead screw C-Beam machines will work just fine with the motors in the OpenBuilds store. Unless you are building a 4'x8' machine with a 200 pound gantry, you are probably barking up the wrong tree. You are tending to overthink things a bit.

    You don't have to know how the Ford Ecoboost engine was engineered to be able to drive a Ford pickup.
     
  16. AR15DCM

    AR15DCM Journeyman
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    Thanks guys I appreciate it. I don't want to overthink it, but I do want to understand more about what and why I am buying a certain product. Reading about the motors here on OB there is a statement "the motor is more powerful, compact and efficient than the standard motor on the market".

    Then I can go to another web site and read this about their motor: "They are also designed specifically with lower inductance for CNC applications to maintain higher torque throughout the RPM range, providing much better overall CNC machine performance when compared with many other common motors with higher torque ratings".

    Sort of similar statements...

    To make it simple and get through the marketing...
    Let's say that for a Tall OX Gantry load that there are two 345oz motors driving the gantry, one on the X and one on the Z. The motors themselves weigh 2.65 pounds each plus the gantry, belts, bearings, X parts and router. It is about 25lb total gantry weight. I came to that assumption this way;

    motors: 10.6 lb
    router: 4.6 lb (Dewalt DW611)
    X-Y Aluminum Parts/Bearings/Bolts Etc... 8lb-10lb ? Please correct me on this if wrong.

    Total Approx 25.2 lb.

    So I have already gotten the answer that these motors would be okay for this configuration in your replies. However, let's say without that guidance how would I know how much motor to buy in order to move that much weight at an appropriate speed? Is it just hit or miss, trial and error? Or is there some way to size the motors for a specific configuration?
     
  17. Metalguru

    Metalguru Master
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    As we said earlier, yes, there is certainly a method of calculating this stuff, but unless you are a mathematician or a seasoned mechanical engineer, it's probably beyond your math skills. Pardon, I should have said beyond my math skills, I have no idea what yours are. I'm not even going to attempt to explain how to calculate the required torque.

    Most designers just design in a motor with more power than is needed, to compensate for stuff like wear and friction increasing with age, etc.
    This is called "seat of the pants" design and is rampant in the DIY mindset. And, it's certainly valid if you have the experience to back it up. There are lots of other variables besides motor torque that affect things, like lead screw pitch, # of starts, # of teeth on belt pulleys, etc.

    All I know is that IMHO the 175 oz-in motors running at 24V are generally good enough for the OX and C-Beam type machines. Keep in mind that you are typically using 2 of them together to run the Y axis, (that moves the gantry) so you have double the available torque.

    The 345 oz-in motors running at 48V would likely be way overkill and a waste of money for this size machine. And, stepper controllers that handle 48v are quite a bit spendier than 24v ones as well. They are something you might use on a 4x4' or 4x8' machine.

    Personally, I would not do a 1000mm x 1000mm OX build. Not stiff enough. But, that's my opinion. Lots of other guys have done it, and even larger. Depends on your application.
     
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  18. AR15DCM

    AR15DCM Journeyman
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    In Google I trust... I actually found the first link while browsing Google, however when I was reading the second link it is also mentioned there.
    The second link Estimating Stepper Motor Requirements for CNC is an excellent document which clearly helps you to understand what is going on with the motors etc..

    Drive Motor Sizing Tool

    Estimating Stepper Motor Requirements for CNC

     
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  19. AR15DCM

    AR15DCM Journeyman
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    I have already committed to 48v and have found a fantastic deal on a power supply. It's a 16amp supply for $80. The supply has three hot swap slots, two of which have supplies in them. Those two provide 48vdc @ 16amps. Add the third supply and it becomes a 25amp supply. So I found the other amp for $35 on eBay and added it in the empty slot and now I have a total of 25amps 48vdc.

    The reason I went with this is I will be doing wood and metal milling on this which is why I want to make sure it is a little beefy. From what I read, if you're doing metal work the demands on the system increase a bit. Also I have a mmilling machine and I may get stepper/servo's for it as well. I will be using the power supply to run those motors as well. And, those motors will be significantly larger in order to turn the milling machine.

    Back to the CNC Router, the X will have two 20x80's plus I will be adding a rectangular tube with 1/4" walls to add stiffness.
    On the Y I will be using 6" x 6" aluminum angle cut in 4" pieces which will bolt onto the side rails and anchor them just like this 1000x1000 machine ...

     
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  20. Joe Santarsiero

    Joe Santarsiero OB addict
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    The second link will get you in the ballpark.
    Adding, lead screw efficiencies are 60-70% sometimes higher. Depends on nut material, pitch, type of lube or dry. orientation is another consideration. Breakaway torque is often negligible on fine pitch ballscrews under 1" compared to any leadscrews. One should still take a look at it.
    Higher voltage will overcome resistance to change inherent to the motor and change its direction faster. That be slowing down and speeding up. This results in better torque performance and higher rpms. Metalguru did a pretty decent job explaining all this. You can only push a motor so hard though. One may find that the increase in performance is negligible from one voltage to another. There's a write up floating around that examines the performance characteristics of a couple of motors at different voltages. Interesting read. Will post if I can find it again. Here's a discussion from the zone on this. Of course it references Gecko ;)
    www.cnczone.com/forums/stepper-motors-drives
    Regarding your motor questions. Your going to see more force from the motors than their ratings. They're rated at 1". If you're translating force at less than 1" then the force will be greater and visa versa. Here's a post from last October explaining this: Stepper specs and their meanings? | OpenBuilds
    If using belt and pulley then you'll use the pulleys belt pitch diameter to determine the force at the belt.

    Joe
     
  21. AR15DCM

    AR15DCM Journeyman
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    Thank you Joe,

    I briefly read over it just now... will give it a thorough read later tonight. Been spending this afternoon going through inventory and trying to see what I have and ordering what I don't for my upcoming OX build.
     
  22. Metalguru

    Metalguru Master
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    Yeah, a calculator is just the ticket. Nice find AR!
     
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  23. AR15DCM

    AR15DCM Journeyman
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    I figured it couldn't hurt :thumbsup:
     
  24. Bob K

    Bob K Journeyman
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    Joe - that calculator was a big step forward for me.

    After a lot of calculating I was ready to start looking at steppers but I couldn't find any torque curves. :(

    While looking for torque curves I ran into a motor sizing spreadsheet that doesn't need the torque curves:
    What size stepper motor do I-need.

    You feed it your system/design specs, the desired motor voltage, and the candidate motor data sheet specs and it generates the following (along with a bunch of other stuff):
    • needed torque
    • expected motor performance
    • recommendations
    It's recommendations are based on a 3X safety factor. At first I thought this was overboard but then I got to thinking that the spreadsheet had to make a lot of assumptions when

    It's needed torque comes in at about 2/3 of the numbers generated by the "Estimating Stepper Motor Requirements for CNC" website.

    I've attached two files:
    • MotorCalcs example.xls - my system entered into the "What-size-stepper-motor-do-I-need" spreadsheet
    • motor sizing 31 Jul.xlsx - my calcs on what I'll need to mill aluminum including results from the "Estimating Stepper Motor Requirements for CNC" website. Some of the numbers I used in "MotorCalcs example.xls" came from this sheet.
    The "What-size-stepper-motor-do-I-need" spreadsheet's is protected so I have no way of knowing if the motor numbers are reasonable. I'm hoping some of our master builders can give us feedback.

    Bob
     

    Attached Files:

  25. Joe Santarsiero

    Joe Santarsiero OB addict
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    Hey Bob,
    AR15 posted the calculator links.
    The steppers offered in the Openbuilds partstore now have the torque curves in the picture section. I am aware that some outside suppliers do not have torque curves available. In some cases you can request the torque curves by providing a list of the motors you're interested in. There have been cases where I required a specific torque at a given rpm and voltage supply and have had suppliers provide me with a short list of motors to narrow down my search. I have noticed more suppliers providing the curves on their product pages as of late. For instance, Automationtechnologies formerly keling (quality motors and drives btw) used to lack the curves on their pages. Now they have them for just about every motor. So, it's getting better. Oriental motor doesn't play around. They want your business. lol. They'll probably give you curves if they haven't posted them already.
    Regarding your spreadsheet issues, what type of system are you running? Generally, the 345 oz-in motors are more than adequate for the OX and C-beam systems. Higher the voltage the better (usually. 48 isn't much better that 36 in some instances). I don't recommend 12v anyways. The motors in the parts store are recommended 24v minimum anyways. Steppers aren't really that expensive (subjectivly). If you have great electronics to start then the failings of a motor may not be as apparent. If you purchase a set and you have semi-decent electronics then you'll just start to learn where the failings of your motors lay. You might start to avoid certain feedrates because of known resonances and because of stallings (things present in all of them). Most importantly, you'll be machining and moving on. Don't get too caught up in the details. Sometimes the experience points us in the right direction much faster than getting caught up in the planning stage. One benefit to this is that we are learning in other areas at the same time. Order a dang set of motors, hook them up, and move on :D By the time you figure out the characteristics of your machine and the motors you installed, you'll have a much better understanding of what you really need. That is if you aren't happy already!

    Good Luck Bob. Keep us posted

    Joe
     
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  26. Bob K

    Bob K Journeyman
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    AR15 - sorry for the mis-attribution.

    Joe - I've just gotten my motors hooked up and have been playing with feed rates and micro stepping. Sure gets noisy when you're not at the sweet spot.

    I definitely have a lot of learning on stepper motors and system performance.

    I'll take my questions back to my build discussion area.

    Thanks

    Bob
     
  27. AR15DCM

    AR15DCM Journeyman
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    you can continue here... I do not mind and I would like to see the Q&A because I am learning too :)
     
  28. Julius

    Julius Veteran
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    too many variables here, but with my 2 175oz-in Nema 23s, on 24V I can push my 25lb gantry at 150ipm through a 3/4 DOC into MDF. Im using ballscrews. People told me to get 48V, but i cant stall my motors if I try! The 375oz-in Nema's are also overkill unless you intend to cut 1" hardwood in a pass or mill hard metals.
     
  29. Joe Santarsiero

    Joe Santarsiero OB addict
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    Yeah. That's a lot of variables. Well, the efficiency of ballscrews over lead and the mdf def help your case. I'm using 52v, 425s, ballscrews, digital drives, and I'm gonna have to give that 3/4 cut a try myself at 150ipm. What magic tooling are you using for that?
     
  30. Julius

    Julius Veteran
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    I just used a 6mm 2 flute cutter. My issue now is Z slop with the C beam, the variance in cut is almost 1/8".

    PLEASE Dont start the test at 150ipm. Try it at 25 and go in 10ipm increments if you're still comfortable. Youre spindle will most likely become the limiting factor in that test. I used it at 24k rpm instead of my usual 16.
     

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