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    Default Stepper Optimal RPM Range?

    Hi Everyone!

    I have a basic question about what RPM range I should be aiming to use from a stepper to drive a ballscrew via pulleys.

    If we look at a torque curve example attached at 24V, we see in the <400RPM range the highest and roughly constant torque. Then >400RPM we see a downward slope develop where torque drops rather linear with RPM increase.

    Remembering that Power = Torque x RPM, to me this linear slope suggest maximum constant power has been developed and so torque drops as RPM increases.

    If we directly drive a ball screw from the motor I think it makes sense to use the highest torque range.

    However we have a pulley ratio in this system, that will convert RPM to torque, so I think I should be aiming to utilize the motors maximum power range, not maximum torque range. I should gear my system to use the >400rpm range.

    Is my logic correct?

    Stepper Optimal RPM Range?-torque-curve-jpg

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    Default Re: Stepper Optimal RPM Range?

    I thought to check my logic I would look at a Tesla power vs torque curve, because it shows both aspects. I think it confirms my thinking that maximum power is where the torque curve starts to drop off.

    Stepper Optimal RPM Range?-e98er-jpg



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    Default Re: Stepper Optimal RPM Range?

    Also, it seems to me that a motor which reaches peak power at the lowest RPM is desirable because it will take the least time to get to that point. Example: a motor that hits 50 watts output power at 100 RPM will reach that power sooner than a motor which produces 50 watts at 500 RPM. Acceleration of the machine will be better.

    I'm just looking for confirmation (or not) of my thinking here.



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    Default Re: Stepper Optimal RPM Range?

    Hi,
    comparing a Tesla motor to a stepper is incorrect. The Tesla motor is a synchronous motor whereas a stepper
    is a variable reluctance motor. The physics of torque generation is different.

    A synchronous motor will have near constant torque to its rated speed and therefater drops in the so called 'field weakening' mode.
    A stepper has its maximum torque at zero speed and essentially decreases thereafter.

    The principle determinant as to how badly the torque degrades is the winding inductance, the lower the better.
    Many steppers have good or even great torque but also have commensurately high inductance, so while they have great torque
    up to a hundred rpm or so they weaken badly at several hundred rpm. Manufacturers know that first time buyers look only at the
    holding torque figure and don't understand inductance. As a consequence they build steppers with great torque figures but are hopless
    at speed just to catch those first time buyers.

    In 23/24 size steppers look for 1-2mH, 1mH preferred and reject anything over 2mH.
    In 34 size steppers look for 2-4mH, 2mH preferred and reject anything over 4mH.

    Often times, for a motor of a given size, there will be different models, some with high torque and some with lower torque. The lower
    torque low inductance models are better for CNC and are often the high current versions of that motor size.

    The classic way to overcome inductance is to use the highest possible voltage drivers you can get your hands on. At the current time
    80VDC is about the practical maximum. A linear (transformer/rectifier/capacitor) power supply is preferred over cheaper switchmode supplies,
    they have way WAY better overload characteristics.

    This stepper has only 1.18mH and with an 80VDC drive could be expected to retain 45% of its rated torque at 1000rpm:

    Object reference not set to an instance of an object.

    Matched with this driver:

    Object reference not set to an instance of an object.

    With this power supply:

    https://www.antekinc.com/ps-10n80-10...-power-supply/

    You characterisation of a stepper as a 'constant power device' is reasonable. Consider however that a stepper is supplied with rated current
    at all times. Thus even when it it not turning, ie producing no mechanical output, it is still absorbing supply current. How does that fit with
    your characterisation? Your constant power characterisation is useful in the sense that it describes the torque/speed curve but is dubious
    for calculation purposes.

    Craig



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    Default

    Quote Originally Posted by joeavaerage View Post
    Hi,
    comparing a Tesla motor to a stepper is incorrect. The Tesla motor is a synchronous motor...
    Craig
    Thanks for your thoughtful reply Craig!

    Your point about motor types is well noted.

    I was asking quite generally without a specific design mentioned as I thought if I understand the logic I can apply it to my situation. But I'll give my specific circumstance.

    I'm making a very sturdy and well damped 3D printer. It doesnt have a huge amount of weight to shift but Inam hoping for rapid acceleration to some pretty fast speeds, like 500mm/s (40,0000mm/min).

    I haven't calculated the mass or built it yet, but let's say the gantry and head weigh 500g not including ball screw inertia. It has 20mm pitch ball screws. It will be driven by 45V 1.5A rms drivers.

    I know that's not a lot of current or voltage. But it is a really nice closed loop servo (uStepper S).

    I plan to use Nema 23 but obviously my current and voltage is limited.

    (On a side note, I would be happy to use closed loop stoppers from leadshine or others, but I worry about the quality of the drives. I know the drive signal purity directly reflects in the surface finish of the print. Trinamic driver ICs have a really clean output (stealth chip/ silent step) whereas many CNC router drivers are rather crude by comparison you can hear the drive signal in the motor coils. But maybe they have got better since 10 years ago when I built my router?)



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    Default Re: Stepper Optimal RPM Range?

    Hi,
    some of your target performance figures are very ambitious and I think are beyond steppers performance envelope.

    For instance you say you want to achieve 40m/min and you are using 20mmpitch ballscrews. That would require the ballscrew
    rotate at 2000 rpm. With direct coupled steppers thatis 2000rpm....which is achievable....just......but not with a 45V power supply.

    I use Vexta 5-phase steppers with genuine Vexta drivers that take 230VAC input for a DC link voltage of about 150VDC. That allows my steppers to spin
    at 2400rpm, but they have very little torque, that could not be direct coupled to a ballscrew. In my case the steppers go through a 10:1 planetary (low lash)
    gearbox.

    Achieving 2000rpm with a stepper AND still have useful torque is right at the very outside of stepper performance. If you use a gear or belt reduction
    such that the stepper is only required to do 1000rpm you might have more luck, but the stepper will require double the torque.....back in the too-hard
    basket.

    Manufacturers of closed loop steppers would have you believe that they are faster, more powerful and never lose steps....total BS. Closed loop
    steppers do have a couple of advantages (full step interpolation and realtime following error monitoring) but are bought at considerable price.

    From your description of your project you need AC servos. Delta (Taiwanese manufactured in China) and DMM (Canadian manufactuered in China)
    are two good quality brands that won't break the bank.

    A 400W Delta B2 series (160,000 count per rev encoder) has 1.27NM torque to its rated speed of 3000rpm, and has a ten second overload of 4Nm.
    In field weakening mode it will spin to 5000rpm. It'll EAT any stepper ever made. I got one of these and three 750W B2 series including one with a brake
    and they are superb. They really make steppers 'so last century'.

    Craig



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    Default Re: Stepper Optimal RPM Range?

    Hi,
    you may see in some other threads some calculations that predict the acceleration that a given torque can produce:

    https://www.cnczone.com/forums/servo...ml#post2372136

    If you follow the derivation and importanly the calculation that applies to my new build mill you will see that despite a very heavy axis (115kg) the acceleration
    is determined NOT by the axis mass but the rotational inertia of the ballscrews. As it turns out the mass of the axis is usually a small proportion
    of the acceleration potential....its more about the rotating components.

    Lets make a few assumptions and guesses and do some calculation that might approximate your machine.

    I suggest we take the D57CM31 Leadshine stepper I linked to previously. The spec sheet reveals a first moment of inertia:

    J= 0.84 X10-4 kg.m2

    Lets assume also that you have an 80VDC driver and supply such that the stepper can retain 50% of its rated torque at 1000rpm, ie 1.5Nm.

    Lets guess you use a 16mm diameter ballscrew of 20mm pitch and 400mm long.

    Lets guess that you make the axis as light as possible, say 2kg.

    The first moment of inertia of the ballscrew is:
    mass= (0.016/2)2 x PI x 0.4 x 8000(kg/m3)
    =0.64kg
    J= 0.64 (0.016/2)2/2
    =0.205 x 10-4 kg.m2

    The first moment (equivalent) of the linear axis is:
    J= 2 (0.02/2*PI)2
    =0.203 x 10-4 kg.m2

    So the total first moment of inertia is:
    Jtotal= (0.81 + 0.205 +0.2) x10-4 kg.m2
    =1.21 x 10-4 kg.m2

    So you can see that the rotational inertia of the motor and the ballscrew dominate the acceleration equation with the mass of the axis
    representing less than 20%

    Continuing with the calculation:
    Angular acceleration = torque/ first moment of inertia
    =1.5 / 1.42 x 10-4
    =10563 rad/s2

    The linear acceleration of the axis:
    A= (10563 / 2.PI) x 0.02
    =33.6 m/s2

    Thus the stepper I've linked to could easily accelerate your axis but at 1000 rpm the torque is down to 1.5Nm even with an
    80VDC driver and supply. As a matter of practice I doubt you could go much faster without losing steps.

    Craig

    Last edited by joeavaerage; 05-23-2020 at 10:45 PM.


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    Default

    Quote Originally Posted by joeavaerage View Post
    Hi,
    you may see in some other threads some calculations that predict the acceleration that a given torque can produce:

    Craig
    Again, thanks so much for your reply and walking me though the math.

    I will give it some thinking over.

    I had not realised rotational inertia was such a big factor! Kinda wishing I orders 12mm dia. ball screws instead of 16mm now!

    There are a number of products offered by Delta and DMM, how much money are we talking for a basic 1.5nM drive and motor?



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    Default Re: Stepper Optimal RPM Range?

    I dont think I can afford AC servos and I also dont think I can easily incorporate them with standard 3D printer control boards designed for stepper drivers (?).

    So I see three options open for my design.

    1) High quality (Trinamic 2130) closed loop uStepper drive that has 16bit resolution magnetic feedback, but limited to 46V 1.5A rms.

    2) High quality (Trinamic 5160) open loop drive that has 4.5A rms 60V. Possibly opening door for Nema 34?

    3) Closed loop stoppers and drive such as Leadshine. Unkown quality of drive for me. Are they super smooth and silent? That smoothness of drive reflects in print quality.

    Last edited by ssashton; 05-24-2020 at 02:37 PM.


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    Default Re: Stepper Optimal RPM Range?

    Alright! I went for option 2! I'll have to give up closed loop and trust that well tuned stoppers and drivers will not loose steps.

    So now, with 4.5A and 60V what motors would be a good match? Again 20mm ball screws and minimal gantry mass (probably 1kg or less). I suppose I could even go with Nema34 for the gantry motors as they sit on the frame.



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    Default Re: Stepper Optimal RPM Range?

    Hi,

    So now, with 4.5A and 60V what motors would be a good match?
    These have only 0.75mH and may go fast enough for you.

    Object reference not set to an instance of an object.

    I suppose I could even go with Nema34 for the gantry motors as they sit on the frame.
    34 Size have even higher inductance and will go even slower....don't go there.

    Craig

    Last edited by joeavaerage; 05-25-2020 at 02:54 PM.


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    Default

    Quote Originally Posted by joeavaerage View Post
    Hi,



    These have only 0.75mH and may go fast enough for you.

    Object reference not set to an instance of an object.



    34 Size have even higher inductance and will go even slower....don't go there.

    Craig
    Thanks for all your help Craig!



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    Default Re: Stepper Optimal RPM Range?

    Slightly off topic but I didn't want to start a new thread if necessary.

    What type of belt is a good choice to connect my stepper motor to the ball screw, with the motor being right next to the screw? A lot of belts seem to be at least 300mm length!

    Is HTD 3mm width belt enough? Seems rather thin, but the 5mm HTD belts don't seem to be available in such short lengths.

    Then we have GT2 as well, I'm not sure what the difference is really?



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    Default Re: Stepper Optimal RPM Range?

    I just bumped into this thread....and skimmed through the posts, so please forgive me if I missed anything in the discussion.

    I'm really interested in this thread because I am also making a 3d printer.

    Quote Originally Posted by ssashton View Post
    Also, it seems to me that a motor which reaches peak power at the lowest RPM is desirable because it will take the least time to get to that point. Example: a motor that hits 50 watts output power at 100 RPM will reach that power sooner than a motor which produces 50 watts at 500 RPM. Acceleration of the machine will be better.

    I'm just looking for confirmation (or not) of my thinking here.
    One big thing to consider when selecting steppers, lead, gearing, etc is how fast you want to go, what that equates to in RPM at the stepper, and how much torque is available at that RPM to DECELERATE. That's the weak point, not acceleration, because at zero RPM you have more torque. Usually you want to find a stepper with a fairly flat curve if you can for CNC applications, that is to say that many people have bought steppers that have 1200 Oz in for example, only to realize later that the 800 Oz in performs better because there is more torque at higher RPM's where they need it to decelerate.

    That's why joeaverage is talking about mH. The lower the mH the flatter the torque curve of the stepper, more torque at higher rpm. Personally, I ignore the mH and look at the torque vs RPM graph, but if you can't find one, then you are stuck guessing based on mH. In the first link joeaverage provided, if you go into specifications, then speed torque curves, you will find this:

    Stepper Optimal RPM Range?-leadshine-d57cm31_torque-curves-jpg

    This stepper also doesn't have much difference across the voltage range, that's nice. Thanks joeaverage, I might buy some of these myself . Of course, the graph may change a bit depending on what drivers and microstepping are used.

    I'm not sure that's what you're asking though? You are asking if you should gear the system so that at your top speed you are still in the lower RPM range of the stepper? So you would want your ballscrew to spin faster than your stepper motor? That seems kind of backwards to me. Yeah, I don't think it's a good idea. It also makes the mechanical resolution, microstepping aside, worse.

    If you want to gear it, IMO, you are looking at a servo, with perhaps 3:1 or 2:1 gearing (ballscrew spins slower) even though for your application you could easily direct drive with a smallish servo.

    So what extruder are you planning on using that will print at 500 mm/s? And for that top speed to mean anything you need some really good acceleration. I have been looking at the hemera, formally known as hermes extruder to get started on my project, but I don't think there's any way in heck that will keep up with high acceleration and 500mm/s? Eventually I want to go with a full on pellet extruder.

    So what are your plans for the extruder?

    Quote Originally Posted by ssashton View Post
    I dont think I can afford AC servos and I also dont think I can easily incorporate them with standard 3D printer control boards designed for stepper drivers (?).
    I'm trying to figure this out myself in more detail. Duet 2 or Duet 3 with an expansion board to access step/dir outputs fed into additional servo drivers than can accept those inputs. Leadshine has an AC servo driver and a couple brushless DC servo drivers, also they have low voltage AC servos. Would also require a separate DC power supply running at a higher voltage than the board.

    Or any servo driver and servo that can accept step/dir inputs from a Duet expansion board, running from a separate higher voltage power supply, either AC or DC, depending on the servo driver.


    Quote Originally Posted by ssashton View Post
    1) High quality (Trinamic 2130) closed loop uStepper drive that has 16bit resolution magnetic feedback, but limited to 46V 1.5A rms.
    Are you talking about a Duet 2 board?

    Quote Originally Posted by ssashton View Post
    2) High quality (Trinamic 5160) open loop drive that has 4.5A rms 60V. Possibly opening door for Nema 34?
    Are you talking about a Duet 3 board?

    If so, "Power supply (min. 12V. max 32V, recommended 24V)"

    https://duet3d.dozuki.com/Wiki/Getti...ed_With_Duet_3

    I'm of the understanding, that you could run a stepper at 60V, only with an external driver via an expansion board from the duet. Am I mistaken? Is this what you bought, a Duet 3? I am thinking of buying one myself, and need to learn more about it. Is there a different board that runs at 60V with the trinamic 5160's, or did I totally miss something here?

    Quote Originally Posted by ssashton View Post
    3) Closed loop stoppers and drive such as Leadshine. Unkown quality of drive for me. Are they super smooth and silent? That smoothness of drive reflects in print quality.
    I'm of the understanding that you could still run these from a Duet board, using an expansion board to get your step/dir outputs to the drivers.



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    Default Re: Stepper Optimal RPM Range?

    I put the acceleration calculation in a spread sheet so I could make fast comparisons between motors and other parameters. It might be helpful for others so here is a link: https://docs.google.com/spreadsheets...VkfnxZ99E/copy

    Doing this I found that comparing a Nema 23 and Nema 34 option I got almost identical acceleration. This seemed to be that despite higher torque from the Nema 34, it also has significantly higher rotor inertia and adds some extra mass to the moving gantry. So I went with the physically smaller Nema 23. Leadshine 57CM13

    I don't have space for the longer body motors, but you will see the longer Nema 23 also has higher rotor inertia that dominates the equation when gantry mass is low.

    The driver I went for are Big Tree Tech TMC2160 external drivers. They can handle 60V with 4.5A rms current. I like the TMC drivers as they have 'StealthChop2' mode which gives a really smooth drive waveform.

    I was strongly considering the uStepper S, which has nice high resolution magnetic feedback, not a granulated optical encoder. However I just don't think it has the grunt for my application.

    I plan to use a control board with these external drivers so it seems a shame to go for a Duet with a lot of money spent on built in drivers. I'll probably use an SKR GTR board. It has the option to use 'step stick' drivers for the extruder while also breaking out pins for external drivers. The main CPU is quite powerful, 168MHz ARM M4. More grunt than the Duet 2, but not quite on Duet 3 terms.

    Regarding pulley ratio for the motor to ball screw I was thinking that I would be better having the motor spin slower than the ballscrew to keep it in the maximum torque range. My 20mm ballscrews would need to spin at 1,500RPM to move at 500mm/s, but if I used a 2:1 pulley ratio the motor would only need to spin at 750RPM.



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    Default Re: Stepper Optimal RPM Range?

    Quote Originally Posted by ssashton View Post
    I put the acceleration calculation in a spread sheet so I could make fast comparisons between motors and other parameters. It might be helpful for others so here is a link: https://docs.google.com/spreadsheets...VkfnxZ99E/copy
    I tried to have a quick look at what you did, but I just can't bring myself to make a google account. LOL.

    I do my calculations a bit differently, by inputting the acceleration I want and working backwards to see how much torque is left over, and then converting that into available cutting force.

    FYI, I haven't done any calculations myself in regards to this thread.

    Quote Originally Posted by ssashton View Post
    I don't have space for the longer body motors, but you will see the longer Nema 23 also has higher rotor inertia that dominates the equation when gantry mass is low.
    Here's the thing that I was trying to allude to in my previous post by asking about the extruder. You are trying to make a printer that prints extremely fast. 500 mm/s, what you're talking about is comparable in performance to the best industrial 3d printers on the market. To do this usefully, you need really good acceleration. This is more important for a printer, because compared to a router or a mill, you have lots of small jerky movements.

    For me, my plan is to end up with a pellet extruder eventually. So the extra weight of that, an extruder that can keep up with those speeds, isn't really as much of a problem when you are considering inertial math, but it could be a huge problem when you now have very high accelerations and your machine isn't rigid enough to handle all of this weight being slammed around. The lengths of your axis also have a huge impact as the deflection of a beam is proportional to the length cubed.

    Many diy type printers use unsupported round rods for rails, in various configurations, and people try to reduce as much mass as possible. IMO, that only works when you are trying to get the most out of tiny Nema 17's, you have light components, and your acceleration settings are relatively low. Sure, I've seen videos of some of these types machines flying around, but I haven't seen them printing anything reasonably at super high speeds and accelerations.

    I'm probably saying things you already know, but for the benefit of whoever else may read this thread, what I'm trying to communicate, in essence, is that I don't think that lighter is necessarily better if you want to go fast.

    I don't know anything about your design. But we're only talking about one axis being driven by a single ballscrew, hypothetically, in this thread. What about the rest of the printer? I don't need to know what your design is, I just see some potential problems that could arise, and I thought I'd mention it and open it up for discussion.

    Many of the videos on YouTube I've found that claim high speed printing have the accelerations set so low that they never reach those speeds.

    But I found these ones interesting




    Quote Originally Posted by ssashton View Post

    The driver I went for are Big Tree Tech TMC2160 external drivers. They can handle 60V with 4.5A rms current. I like the TMC drivers as they have 'StealthChop2' mode which gives a really smooth drive waveform.
    I'll have to check those out, thanks for the link!

    Quote Originally Posted by ssashton View Post
    Regarding pulley ratio for the motor to ball screw I was thinking that I would be better having the motor spin slower than the ballscrew to keep it in the maximum torque range. My 20mm ballscrews would need to spin at 1,500RPM to move at 500mm/s, but if I used a 2:1 pulley ratio the motor would only need to spin at 750RPM.
    Just so you're aware, if you are using gearing:

    Jref = [(Jload + Jballscrew + Jcoupler2 + Jgear out) / (i^2)] + Jmotor + Jgear in + Jcoupler1

    Jref = The total moment of inertia (I'll just call this "inertia") as seen by the motor

    Jload = The inertia due to the moving mass

    Jballscrew = The ballscrew inertia

    Jcoupler2 = The inertia of any coupler to the ballscrew at the output of the reducer

    Jgear out = Only really important if using a dual stage planetary gear

    i = the gear ratio

    Jmotor = The motor rotor inertia

    Jgear in = The gear reducer inertia (for planetary gears, usually the manufacturer will give you this and will specify that it is as seen by the motor)

    Jcoupler1 = The inertia of any coupler attached from the motor to the reducer input

    That equation doesn't account for preload torque, bearing friction, ballscrew or reducer efficiency, etc.

    When you divide by the gear ratio squared, things can change significantly. Belt driven gear reducers are good because they have less inertia.

    Also important

    AAm / i = AAbs

    AAm = The angular acceleration of the motor

    AAbs = The angular acceleration of the ballscrew

    i = The gear ratio

    In your case, wanting the ballscrew to spin slower than the motor, the i value would be less than 1.

    Here's a video I found on YouTube that explains it





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    Default Re: Stepper Optimal RPM Range?

    Thanks for the gear calculation. I think I will use a drive ratio of 1:1 after thinking it through with your calc.

    My motor choice 57CM13 (that I already bought) has the rotor inertia as approx 1/3 of the rotor/ballscrew/gantry inertia sum, which seemed balanced to me. If I use a pulley ratio, the rotor inertia will stay the same, but the ballscrew/gantry inertia will be significantly higher which may not make much sense; wasting that low inertia motor. On the other hand if I had bought the larger motor 57CM31 mentioned earlier, it might make a lot of sense to use a drive ratio.

    FYI, my motor and ballscrew are parallel to each other and connected by a short belt. Hence I asked what the difference between HTD and GT2 belts is?

    I absolutely agree that light weight at all costs is not the answer for fast printing. I took inspiration from PCB pick and place machines which only need to move tiny electronic components around. Despite the tiny parts smaller than your finger nail, good ones have heavy steel or cast iron frames and gantry, large pitch ball-screws and servo motors. This Manncorp MC384 in the YouTube video weighs about 650Kg.

    So far this is my design. Over-all size is about 550mm^3.

    Frame is welded 40x40mm steel with concrete and SBR (laytex) admixture core for damping.
    1mm Steel panelling (not pictured) welded on all sides for bracing except front and top.
    Gantry is two aluminium tubes with a constrained (layer damping) PU core.
    16mm dia. 20mm pitch ball-screws with 4-start thread.
    MGN 12mm profile linear rails on X and Y.
    X and Y drive is Nema 23 Leadshine 57CM13 with 60V TMC2160 drivers.
    Bed is 10mm or maybe 16mm cast ali tool plate, face machined for flatness.
    Z rails are 16mm round rail.
    Z drive is dual Nema 17 0.42Nm with integrated T8 lead-screw.

    You might wonder why no profile rails and ballscrews for the Z axis? I didn't want the difficulty of creating 4x flat and aligned vertical rail supports if I had used profile rails. I would also loose a lot of vertical headroom if I used ballscrews that need BK / BF mounting blocks and then a way to couple a motor too - all for very little gain. The print surface doesn't need to move fast, nor handle any cutting forces. It just needs to be super flat.

    As for the extruder, I expect to use a Hemera with either a volcano or super-volcano hot end. Only the super-volcano can manage 500mm/s but I only set that as a target because I Googled 'fastest FDM printer' and that was the figure to match. Really I just want the fastest printer with great quality.

    Have you seen the Lily pellet extruder? https://www.recycl3dprint.com/

    Why not a pellet extruder for me? I don't actually print a lot and don't waste a lot. Primarily I want the highest print quality, want it fast for rapid prototyping and hate stringing. The Hemera appeals to me for its tight control on the filament path for reduced stringing and ability to do flexibles. Are there any pellet extruders to consider that have a really tight control on the extrusion path for low stringing?



    Stepper Optimal RPM Range?-3d-printer-4-jpg

    Last edited by ssashton; 06-05-2020 at 07:37 PM.


  18. #18
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    Default Re: Stepper Optimal RPM Range?

    Hi,

    16mm dia. 20mm pitch ball-screws with 4-start thread.
    Did I read that correctly, 4 starts at 20mm pitch so 80mm linear travel per revolution??

    I've certainly heard, seen in fact, multi start leadscrews but don't recall ever hearing of multi start bllscrews.

    Craig



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    Default Re: Stepper Optimal RPM Range?

    Hi Ssashton - I see you have two drives on the centreline and 4 bushes at the corners of the platen. Its usual to drive these at all four corners. If one side goes up a little more then the other side the platen will jam. This is called "stick slip" behavior. Have you made a platen like this before so you know it works? I have designed/built a few 4 poster machines (presses and patient lifters) and one suffered this so badly we had to convert it to square cars and rails...

    are these plain bushes or linear bushes with ball bearings? If ball bearing type then stick slip is nearly zero...

    Re: 40x40 tube what thickness? The concrete you are adding provides mass for damping (which is a valid approach) but it does not dampen via friction or viscous damping or material hysteresis. So you may as well go to a thicker tube to create the same mass gain and its stiffer vs concrete filling and cheaper. There's a lot of discussion on damping in the forum...

    The gist of it is that in these sort of structures the strain delta from the steel to the core is so small (due to the steel being so stiff and being on the outside of the structure where the strain is, the core does not internally deform enough to contribute to hysteritic damping. It does dampen via added mass but this is better achieved by adding steel (cheaper and stiffer) Peter

    Last edited by peteeng; 06-06-2020 at 03:07 AM.


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    Default Re: Stepper Optimal RPM Range?

    This has really moved away from the original topic of stepper choice so I think I'll start a new thread. I'd welcome your input there.



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Stepper Optimal RPM Range?

Stepper Optimal RPM Range?