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Thread: BF30 Servo vs. Hybrid Stepper vs Stepper

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    Default BF30 Servo vs. Hybrid Stepper vs Stepper

    Hello!

    I would need help with selecting optimal drives for my Bernardo BF30 machine that I'm equipping with CNC stuff. First of all, I've gone through all builds on this site and found out that some of people run steppers like 3 and 4Nm on all axes directly, while others run 8 and 12Nm with reduction, which is kinda huge difference. I don't want to under-power the axes or get poor performance due to too large steppers. User "Ger21" warned people not to go into "too big motors" trap....

    I've also thought about getting servos, as I got quite good offer on them. So my first choice was:

    X and Y: Direct drive 86M-DHT-A6MK1 (750W servo) + DYN4 AC Servo Drive (directly on 230VAC) on 5mm pitch ballscrews
    Z: 1:2 belt reduction on same servo (with added brake!) and same driver.
    I know servos need fine tuning on each axis, but I'm prepared to do that, after all I'm designing PID controllers and doing PID tuning on tons of projects for last 8 years. I'm not sure about performance issues on Z because of drive belt. (I could also use direct drive stepper (closed or openloop) for Z to avoid belt)

    Second option was:
    X and Y: Direct drive Nema34 8Nm motors + EM806 + 60-70V DC power supply
    Z: Direct drive Nema34 12Nm + brake + EM806 + 60-70V DC power supply

    Third option was
    X and Y: Direct drive Nema34 4Nm motors (Closed loop!) + appropriate drivers + power supplies
    Z: Direct drive High voltage Nema34 8Nm (Closed loop!) + appropriate 230VAC driver

    As you can see, I'm really in trouble of finding out what's the "smartest thing" or which combo of X, Y and Z is going to work as it should. I don't want to invest too much, definitely don't want under-power or over-power -> to avoid performance issues.

    Can you please advise me what's best choice for that machine? I'll be eternally thankful for information!

    Best regards,
    Jure

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    Default Re: BF30 Servo vs. Hybrid Stepper vs Stepper

    Ger21 knows a damn sight more than I do.
    As far as I've read some use a 2:1 gear reduction using 4nm steppers to get the 8nm you mention. Not reductions using 8nm steppers themselves.
    I like the servo option because of the accuracy and speeds that can be achieved with the right units which is why you get a price tag with them.
    The BF30 is a lot bigger and twice as heavy than a G0704 that many have so my philosophy would be to go 30% bigger than what the average user has on them.

    Overall for me it's got to be option 2.
    Option 3 sounds too small without a 2:1 gear reduction. The saddle & table has got to be 60kg combined or close.
    As for option 1 I'm no way clued up on servos yet.

    The Syil X7 is only a little bigger in size (a lot heavier tho but that's including all the kit on it).
    That is fitted with 8nm motors.
    The Syil X5 is G0704 size and uses 4.5nm.

    So for a BF30 direct drive anything 7nm to 8nm should be near enough imo.

    Either way In terms of speed I can envisage a maximum rapid of 1500 to 2000mm/min with dovetail ways.

    Last edited by dazp1976; 10-06-2018 at 07:18 PM.


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    Default Re: BF30 Servo vs. Hybrid Stepper vs Stepper

    Quote Originally Posted by JKSniper View Post
    Hello!

    I would need help with selecting optimal drives for my Bernardo BF30 machine that I'm equipping with CNC stuff. First of all, I've gone through all builds on this site and found out that some of people run steppers like 3 and 4Nm on all axes directly, while others run 8 and 12Nm with reduction, which is kinda huge difference. I don't want to under-power the axes or get poor performance due to too large steppers. User "Ger21" warned people not to go into "too big motors" trap....

    I've also thought about getting servos, as I got quite good offer on them. So my first choice was:

    X and Y: Direct drive 86M-DHT-A6MK1 (750W servo) + DYN4 AC Servo Drive (directly on 230VAC) on 5mm pitch ballscrews
    Z: 1:2 belt reduction on same servo (with added brake!) and same driver.
    I know servos need fine tuning on each axis, but I'm prepared to do that, after all I'm designing PID controllers and doing PID tuning on tons of projects for last 8 years. I'm not sure about performance issues on Z because of drive belt. (I could also use direct drive stepper (closed or openloop) for Z to avoid belt)

    Second option was:
    X and Y: Direct drive Nema34 8Nm motors + EM806 + 60-70V DC power supply
    Z: Direct drive Nema34 12Nm + brake + EM806 + 60-70V DC power supply

    Third option was
    X and Y: Direct drive Nema34 4Nm motors (Closed loop!) + appropriate drivers + power supplies
    Z: Direct drive High voltage Nema34 8Nm (Closed loop!) + appropriate 230VAC driver

    As you can see, I'm really in trouble of finding out what's the "smartest thing" or which combo of X, Y and Z is going to work as it should. I don't want to invest too much, definitely don't want under-power or over-power -> to avoid performance issues.

    Can you please advise me what's best choice for that machine? I'll be eternally thankful for information!

    Best regards,
    Jure


    Go with the servo option, you won't regret it. Power, speed and precision !!! Belt drive on the Z. For the Z axis use a motor with a brake built in.
    I updated a Denford NovaTurn to all Yaskawa servos, +-10V running PathPilot with a special pcie card I designed.
    Look for Denford NovaTurn.

    Hope this helps,

    Iron-Man



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    Default Re: BF30 Servo vs. Hybrid Stepper vs Stepper

    I think every option you've outlined will work, guess it depends on exactly the performance you want. I've been running my BF30 for many years now, direct drive open loop steppers with 3 Nm on all axes. Not a problem. If you rev the steppers they will lose torque rapidly, I honestly can't see the point of reduction drives on steppers because of this. If I did a 2:1 reduction on my setup, I think the only realistic outcome would be a reduction in reliable rapid speed by a factor of 2.

    LongRat
    www.fulloption.co.uk


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    Default Re: BF30 Servo vs. Hybrid Stepper vs Stepper

    Quote Originally Posted by LongRat View Post
    I think every option you've outlined will work, guess it depends on exactly the performance you want. I've been running my BF30 for many years now, direct drive open loop steppers with 3 Nm on all axes. Not a problem. If you rev the steppers they will lose torque rapidly, I honestly can't see the point of reduction drives on steppers because of this. If I did a 2:1 reduction on my setup, I think the only realistic outcome would be a reduction in reliable rapid speed by a factor of 2.
    All you do then though is then change your drivers and software. Half the number of both your steps per rev and steps per unit.
    Then your speed will stay the same but with extra torque.



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    Default Re: BF30 Servo vs. Hybrid Stepper vs Stepper

    Hmmm... I'm still in the quest for the best solution. As far as I know I don't want to run this machine over 2m/min or 80IPM due to the dovetail ways... Meaning with 5mm pitch ballscrews that's 400RPM.

    - Servos that I'm looking at will go up to 5000RPM with those drivers, meaning I won't use a lot of their speed capability. Maybe it would be better if I'd made 1:2 or 1:3 reduction on them and use higher RPM, but as far as I can tell belts will just make things worse performance wise, as I'll need to tune servos down due to belt slack. I'm not sure how well servos perform precision/acceleration/torque-wise in 0-400RPM range (limited max RPM).

    - If I than go to with steppers and I choose closed-loop hybrid steppers and I buy something like Leadshine 4NM fro X/Y and 8NM for Z, I'd probably be able to hit those 400RPM with them as they lose around 50% of torque at 400RPM. Meaning for X/Y = 2.5NM@400RPM will still be enough. 400RPM also means I can run them on 4000 ticks per rev microstepping and get around 0,001mm resolution per step, while max frequency is 27kHz which is probably great.

    But the funny thing is I can get those servos with direct AC drives (avoiding cost of DC power supplies) and really good paper specs, for THE SAME cost as closed-loop steppers kit. What is then a better choice?
    Stepper kit: https://www.damencnc.com/assortiment..._125_1244_NL_1

    Servo 86M-DHT-A6MK1:https://dmm-store-shopify.myshopify....ac-servo-motor
    Servo driver: https://dmm-store-shopify.myshopify....ac-servo-drive

    Best regards,
    Jure



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    Default Re: BF30 Servo vs. Hybrid Stepper vs Stepper

    Quote Originally Posted by JKSniper View Post
    Hmmm... I'm still in the quest for the best solution. As far as I know I don't want to run this machine over 2m/min or 80IPM due to the dovetail ways... Meaning with 5mm pitch ballscrews that's 400RPM.

    - Servos that I'm looking at will go up to 5000RPM with those drivers, meaning I won't use a lot of their speed capability. Maybe it would be better if I'd made 1:2 or 1:3 reduction on them and use higher RPM, but as far as I can tell belts will just make things worse performance wise, as I'll need to tune servos down due to belt slack. I'm not sure how well servos perform precision/acceleration/torque-wise in 0-400RPM range (limited max RPM).

    - If I than go to with steppers and I choose closed-loop hybrid steppers and I buy something like Leadshine 4NM fro X/Y and 8NM for Z, I'd probably be able to hit those 400RPM with them as they lose around 50% of torque at 400RPM. Meaning for X/Y = 2.5NM@400RPM will still be enough. 400RPM also means I can run them on 4000 ticks per rev microstepping and get around 0,001mm resolution per step, while max frequency is 27kHz which is probably great.

    But the funny thing is I can get those servos with direct AC drives (avoiding cost of DC power supplies) and really good paper specs, for THE SAME cost as closed-loop steppers kit. What is then a better choice?
    Stepper kit: https://www.damencnc.com/assortiment..._125_1244_NL_1

    Servo 86M-DHT-A6MK1:https://dmm-store-shopify.myshopify....ac-servo-motor
    Servo driver: https://dmm-store-shopify.myshopify....ac-servo-drive

    Best regards,
    Jure
    I run my little Sieg X2 on 425oz/in (3nm).
    With tight gibs I couldn't run at 4000 microsteps, the torque dropped off massively and could barely rapid 700mm/min.
    I now have it at 2000micro/400per unit for 5mm screws (0.0025mm res) and can now hit 1200mm/min.

    If you want accuracy you want tight gibs, with tighter gibs more torque is needed.

    Most of the hobby cnc's I see like the Syil only have a res of 0.01mm (so they can use less microstepping to give them better speed)
    I actually don't think you need less than 0.005mm res on a mill to be honest.

    Seems the torque drops off with the more microstepping you use as well as with rpm,s.
    There's no way I'd get less than 7nm on a 30 when talking steppers.
    I'm getting 8nm ones for my 25 when it comes

    For that kind of res and high microstepping you want as flat a torque curve as poss on the motor. The flattest torque curves are on servo's.
    Just my opinion.



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    Default Re: BF30 Servo vs. Hybrid Stepper vs Stepper

    Hey!

    Thank you for your input! I know there is limited resolution or accuracy to the machine, but with 4000steps/rev I was actually reading out this 8NM closed-loop stepper graph...
    https://www.damencnc.com/userdata/artikelen/1614-3.jpg

    Based on your writing it seems better idea to go for at least 8Nm stepper motors, closed or openloop ones. But I'm still thinking about those servos Don't want to spend 1000$+ on some non-optimal drive

    Best regards,
    Jure



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    Default Re: BF30 Servo vs. Hybrid Stepper vs Stepper

    Quote Originally Posted by JKSniper View Post
    Maybe it would be better if I'd made 1:2 or 1:3 reduction on them and use higher RPM, but as far as I can tell belts will just make things worse performance wise, as I'll need to tune servos down due to belt slack.
    If you get the correct belt and tension, belt slack is a non-issue.



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    Default Re: BF30 Servo vs. Hybrid Stepper vs Stepper

    Quote Originally Posted by Stigoe View Post
    If you get the correct belt and tension, belt slack is a non-issue.
    In case of belt, is 15mm or 20/25mm wide HTD belt with 5M pitch okay?



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    Default Re: BF30 Servo vs. Hybrid Stepper vs Stepper

    What do you guys think of this combo:

    3x direct drive 8Nm Closed-loop Leadshine 3phase "easy-servo" = stepper
    Leadshine Technology Co., Ltd.

    3x ES-DH2306 direct 230VAC Closed-Loop driver (no need for DC power supply)
    Leadshine Technology Co., Ltd.

    This drive should be matched together nicely, offers good torque and reliability and it probably suffice for all 3 axis directly driven.
    Price is a bit higher than 3x 0.75kW servo drive though...

    Thanks!



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    Default Re: BF30 Servo vs. Hybrid Stepper vs Stepper

    Quote Originally Posted by dazp1976 View Post
    All you do then though is then change your drivers and software. Half the number of both your steps per rev and steps per unit.
    Then your speed will stay the same but with extra torque.
    Not convinced on that, for a given travel speed the motor will be spinning twice as fast. In many setups that will place the motor well down on the torque curve which will not be compensated for by the reduction ratio.
    My machine is heavy for a BF30, with the large motor on the head and other additions. The motors are quite low inductance (can't remember the numbers now) but I rapid all axes at 1400 mm/min. If the motors were bigger, with more inductance, the torque would be higher at low speeds but the fall off rate much greater, with the same supply voltage. I built this setup in 2006 but I'm not actually sure I would do anything different now if I did it again, the reliability has been excellent. Running 5mm pitch ball screws all round.

    LongRat
    www.fulloption.co.uk


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    Default Re: BF30 Servo vs. Hybrid Stepper vs Stepper

    Running those servos at 400 RPM will only use 100W of their power, so kind of a waste. You could save some money by going with the DYN2 drivers rather than the DYN4, as all you lose is top speed with the DYN2 (limited to 2k RPM.) 2 or 3 to 1 belt drives on X,Y and 3:1 on Z would get you better acceleration and still be able to run 666-1000 RPM for faster rapids if you decided on it later. X,Y rapids on Tormach's 1100 are 110 IPM, and on their little 440, 135 IPM and those are dovetail machines (scraped ways though.)



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    Default Re: BF30 Servo vs. Hybrid Stepper vs Stepper

    Quote Originally Posted by LongRat View Post
    Not convinced on that, for a given travel speed the motor will be spinning twice as fast. In many setups that will place the motor well down on the torque curve which will not be compensated for by the reduction ratio.
    My machine is heavy for a BF30, with the large motor on the head and other additions. The motors are quite low inductance (can't remember the numbers now) but I rapid all axes at 1400 mm/min. If the motors were bigger, with more inductance, the torque would be higher at low speeds but the fall off rate much greater, with the same supply voltage. I built this setup in 2006 but I'm not actually sure I would do anything different now if I did it again, the reliability has been excellent. Running 5mm pitch ball screws all round.

    You're right. I confused myself somewhere. Looking at it again I worked out, leave your drivers step per rev the same and half your step per unit in the prog. Might be wrong but:

    I was just going by what mine did. My machine is way to tight anyway which needs addressing.
    Direct drive on 1605 screws, driver/stepper settings 4000/800, resolution 0.00125mm per step, stepper 425oz/in, ind of 3.1.
    Stalled at a rapid of 900mm/min. 180rpm.
    Changed settings to 2000/400, resolution 0.0025mm per step.
    Torque went up using less steps and now didn't stall until 1500mm/min. 300rpm.

    So as a guess: Say if I fitted a 2:1 belt drive the screw would spin half the speed of the motor so would be like having a 10mm pitch instead of 5.
    So if I kept the driver at 2000 I would now need 200 per unit giving a resolution of 0.0025mm again. Correct? So the motor will now only rotate 180 degrees per full rotation of the screw. So for 1500mm/min I'd now need 600rpm?!

    I wouldn't change the way I did it either (direct drive) these hobby machines with dovetail ways limit your max rapid speed anyway imo.

    If I had a linear machine and wanted fine resolution & speed with steppers then I may think differently. Having said that though if you're going linear then you'd prob go for servo's without question.

    Last edited by dazp1976; 10-16-2018 at 08:09 PM.


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    Default Re: BF30 Servo vs. Hybrid Stepper vs Stepper

    Unless I am missing something, 2:1 drive ratio means you'd halve the pitch, not double it. 2 turns of the servo means 5mm of movement, or 1 turn is 2.5mm.



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BF30 Servo vs. Hybrid Stepper vs Stepper

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