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  1. #11
    Rich's Avatar
    Lives in Warrington, United Kingdom. Last Activity: 08-04-2015 Has been a member for 5-6 years. Has a total post count of 30. Received thanks 1 times, giving thanks to others 0 times.
    Thanks for those three points Jazz, they help a lot!

    I've corrected my calculations and marked them down as 'guidance only'. The main issue I was focused upon within the calculation was the effect of microstepping on the available holding torque. It appears with a 2.8 gear ratio, set at 4 microsteps, the machine retains 100% peak holding torque.

    Having used your original recommendation as a starting point for the research, I now see that I have the option to spec the machine according to what is required, circa 1.5Nm Nema 23 low inductance or over spec the machine and carry the electronics forward. More reading to be done!
    Last edited by Rich; 04-11-2014 at 12:11 AM.

  2. #12
    Don't forget to take into account the screw pitch, it's the resolution at the tool you want to calculate
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  3. #13
    Rich's Avatar
    Lives in Warrington, United Kingdom. Last Activity: 08-04-2015 Has been a member for 5-6 years. Has a total post count of 30. Received thanks 1 times, giving thanks to others 0 times.
    On the z-axis using a TR12x3, resolution will be 0.015mm at 1 microstep. This assumes no backlash, deflection of the carriage or issues with the table. If I'm out by a factor of 10, then the starting point would be 0.15mm. As the majority of any variation will arise as a result of deflection, the option to gear the z-axis is on hold.

    The z and y axis are belt driven, the gear ratio is 2.8, so the starting point for mechanical resolution at 1 microstep is 0.1339mm. I will have issues with positional accuracy when cutting longer lengths, but I can compensate within Mach 3.

    I'm guessing you started you build with better figures?

  4. #14
    Quote Originally Posted by Rich View Post
    I'm guessing you started you build with better figures?
    I didn't calculate them as such but obviously had an idea of what I needed. I used the best components I could and the best design I could build myself with the tools at hand. Having plenty of engineering experience I knew it would be achievable, but having no experience with cnc, I initially relied heavily on the advice from members of this forum on the mechanical side.

    The actual figures after the machine was finished are here; http://www.mycncuk.com/threads/7155-...6572#post56572
    that is with a 200N force applied as described.
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  5. #15
    Rich's Avatar
    Lives in Warrington, United Kingdom. Last Activity: 08-04-2015 Has been a member for 5-6 years. Has a total post count of 30. Received thanks 1 times, giving thanks to others 0 times.
    Great number Eddy. Your log is one of many logs I have been reading )

    So after further research I found this website:

    http://www.orientalmotor.com/support/motor-sizing.html

    The numbers offer a guide to the amount of torque required to move at specific feedrates.

    The issue now is what will the available torque curve will actually look like. I am unable to get hold of the torque curve for the motors I have in mind ( This is fine, as the torque curve is stepper specific ... so I have read.

    On the X-axis – if I remember correctly, I have a theoretical ratio of 1:10, required v’s available. In practice, when testing the X-axis using an oversized drive pulley and a poorly tensioned section of belt, one side worked really well, the other was satisfactory. As the belt was being held in palce without correct tension this was a good result. A confidence builder! Once the pulleys and belts are in place, I can run a second test, adjust etc and then attach a line and weight to the gantry and let gravity tell me how much force is required to move the gantry, in particular the friction coefficient.

    Steppers, after bit more reading, I realised this isn’t the place to start when thinking about building the circuit ) I need to be thinking in terms of ripple, electrical noise, and clean/dirty sides of a circuit.

    http://www.mycncuk.com/threads/6696-...machine-wiring

    http://www.mycncuk.com/threads/7450-...ical-behaviour

    Stripping back on some of the technical detail, I think I need to focus on segregation, shielding, filtering and then follow best practice, as detailed within the document and many of the build logs. I will write something up, best way to avoid mistakes.

    As per the second link, it looks like Leadshine is ‘the’ brand and they offer an anti stall feature, which is important feature when slaving motors on such a light rail.

    Next steps, take the frame apart and PU the mdf. Order a few non-essential elements, write up the outline for the electrical circuit, order the pulleys and belt.
    Last edited by Rich; 15-11-2014 at 04:26 PM.

  6. #16
    Quote Originally Posted by Rich View Post
    So after further research I found this website:

    http://www.orientalmotor.com/support/motor-sizing.html

    The numbers offer a guide to the amount of torque required to move at specific feedrates.

    The issue now is what will the available torque curve will actually look like. I am unable to get hold of the torque curve for the motors I have in mind ( This is fine, as the torque curve is stepper specific ... so I have read.
    Can I say after reading your initial first post outlining the simple usage of router style machine that your going far too deep into what will in practice make very little difference to how simple router works.

    Don't get me wrong there's nothing wrong with learning about the technical side of things but honestly in practice for this type of machine there's not much to decide on the stepper side other than size and drive selection.

    In practice what will Make or Break the machine will be YOU and YOUR skills and ATTENTION to DETAIL in how you build the machine rather than if the motor speed curve is optimum.!! . . . Poor build quality can make a perfectly suitable sized motor/drive /psu setup perform like bag of nails.

    With typical stepper systems in basicly boils down to if you run on 50Vdc drives or 80Vdc drives. With voltages around 36/44Vdc and 60/70vdc respectively.
    If 50Vdc then lower sized <2nm steppers are often used and on smaller size machines.
    If 80Vdc then >2nm steppers are used and on Medium to large-ish(4x4) size machines.

    Personally I mostly use 3nm motors running at 68Vdc with Digital drives on any size machine larger than A3 upto 4x4 as the money differance between smaller setup is nothing and the performance of this combination covers a large range.
    For those with little engineering skills or tools they also offer a safety net to account for less than ideal build and will transfer to the inevitable next build.!!

    It's really not rocket science regards steppers and doesn't need to be turned into it for straight forward router style machine. IMO DON'T try to re-invent the wheel just go with a setup what's proven to work.

  7. #17
    Rich's Avatar
    Lives in Warrington, United Kingdom. Last Activity: 08-04-2015 Has been a member for 5-6 years. Has a total post count of 30. Received thanks 1 times, giving thanks to others 0 times.
    Thanks Jazz. I hear what you are saying. A bit of research is just a way of ensuring that any good advice I receive is not wasted and I avoid losing too many steps )

    The build quality is good. All the holes are drilled accurately, helped by the use of a USB microscope, unfortunately they are not always drilled in the right place.
    Last edited by Rich; 15-11-2014 at 04:38 PM.

  8. #18
    Quote Originally Posted by Rich View Post
    The build quality is good. All the holes are drilled accurately, helped by the use of a USB microscope, unfortunately they are not always drilled in the right place.
    Ah ah isn't the point of accurecy to be that holes are in the right place. . . . . . No drill makes an accurate hole.!

  9. #19
    Rich's Avatar
    Lives in Warrington, United Kingdom. Last Activity: 08-04-2015 Has been a member for 5-6 years. Has a total post count of 30. Received thanks 1 times, giving thanks to others 0 times.
    Per an earlier post, I’d run through ‘Gecko: Step Motor Basics’ and put the details into a spreadsheet, the results reflect the numbers quoted by Jazz. As the basics of building a dedicated PSU have been clearly stated, I will give it a go.

    I will follow the PSU circuit provided by Irving, except for the safety circuit, which will be adjusted to include things I already have hanging around:

    - NVR Switch, removed from a 240v hobby router table
    - Zig CF-8 charging and distribution unit 12v http://www.zig-electronics.co.uk/products.htm#
    - 240vac, 25 amp Consumer Unit
    - STAC, AC voltage regulator, ST500W (Type D) http://stac-japan.jp/portable/

    Zig unit will be used in the safety circuit, in place of the 24vdc transformer. The NVR switch is an option, but more probably a 12v momentary push button switch.

    The Consumer Unit can be used as the primary switch (C or D rated MCB). The AC regulator can be wired into the safety circuit, using a third relay. It will take power from the 240v garage supply. I’m assuming I can break into the cable between the mains and the unit, so the unit and the spindle will be isolated when the e-stop button is pressed.

    I'm still roughing things out and will need someone to review the completed PSU before I turn it on?

  10. #20
    The methods described in your link from Oriental Motors are essentially the same as my script here. Mine is a bit more detailed in some areas, for what it's worth...It's also to get a qualitative feeling for the system.

    If you don't have the torque speed curve for a particular stepper motor, a reasonable assumption is that it outputs 2/3rds of the rated holding torque up to the corner speed, then assume constant power from that point. This is essentially the method used in Irving's spreadsheet. This is of course an assumption, so it's safest to design for just below the corner speed, unless you're very confident about what you're doing. I guess I could add a plot of the stepper motor torque speed curve and machine torque requirement to my scrip, then look for the intersection to find the maximum speed... but nobody seems interested.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

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