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  1. #337
    *Registered User* JoergS5's Avatar
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    Default Re: Best belt drive ever! (If I do say so myself)

    Quote Originally Posted by ger21 View Post
    There's always a small amount of play where the belt teeth fit the pulley, to keep it from wearing too fast.
    Agree. I meant the backlash at the top-to-bottom belt right and left of it.

    There is backlash at the stepper gear and inside the stepper/servo.



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    Default Re: Best belt drive ever! (If I do say so myself)

    Why is this belt on belt type of drive better than just using a single belt that is properly tensioned? The second is exactly like the first but without the bottom belt.



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    Default Re: Best belt drive ever! (If I do say so myself)

    Quote Originally Posted by tkms002 View Post
    Why is this belt on belt type of drive better than just using a single belt that is properly tensioned? The second is exactly like the first but without the bottom belt.
    A simple "omega" belt varies in stiffness from end to end, with the least stiffness being the stretch of almost the full length in belting. In tuning high performance servo loops, you must tune to this rubbery case, and are basically detuned everywhere else. Adding the bonded lower belt makes the stiffness of the drive consistent, and equivalent to one leg of belt between pinion and idler, an inch or two of belt stretch.

    Mike Visit my projects blog at: http://mikeeverman.com/
    http://www.bell-evermannews.com/ http://www.bell-everman.com


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    Default Re: Best belt drive ever! (If I do say so myself)

    Quote Originally Posted by JoergS5 View Post
    In my understanding all belt solutions have no backlash, if you have tension at the servo/stepper gear, because the tension on the left side presses the teeth to the right flank, and the right idler presses the right teeth to the left flank. So when you change direction, nothing has to move = backlash.

    T5 has a trapezoid tooth profile, GT2 has round teeth, so T5 will be better to transfer forces.
    Yesss, but there is lost motion. It is true there is no "zero stiffness deadband" with belts like you'd see with a rack and pinion (installed with the proper clearance). What there is, is lost motion. The trapezoidal teeth do not wedge flanks of the teeth, so when we move the motor up, as was mentioned, the teeth are in pre-contact in the driving direction under both idlers. That's part of it.

    Where the lost motion comes in is on reversal. It acts like a traction or flat belt drive and is zero backlash, but the traction contact and the reinforcment line are at a different radius. The steel belts are the actual pitch line we use for calculations, not the tooth pitch line/circle. What this means is that for a small bit of the pinion rotation on reversal, the teeth on the pinion will march to the opposite flank of the groove it was in contact with before, just because they are moving at a different tangential velocities. If you design or plate or otherwise build up the teeth for interference, then the next batch of belting may not snug down into the grooves.
    There are two classes of T5 that we deal with "low clearance" and "zero clearance". What it means is that "low" will have a lost motion (total) of 150 microns or so, and "zero" has 50. You could plate your pinion so it's a sweet fit if it matters, at the risk of having a matched set, pinion to a specific bit of belt.

    Mike Visit my projects blog at: http://mikeeverman.com/
    http://www.bell-evermannews.com/ http://www.bell-everman.com


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    Default Re: Best belt drive ever! (If I do say so myself)

    Thank you for your information, Mike. I will think about it.

    For rack and pinion, I found the Nexen roll and pinion interesting. But I expect your solution more maintainable and easier to implement.

    Last edited by JoergS5; 09-27-2018 at 02:47 AM.


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    Default Re: Best belt drive ever! (If I do say so myself)

    Quote Originally Posted by Mike Everman View Post
    There are two classes of T5 that we deal with "low clearance" and "zero clearance". What it means is that "low" will have a lost motion (total) of 150 microns or so, and "zero" has 50. You could plate your pinion so it's a sweet fit if it matters, at the risk of having a matched set, pinion to a specific bit of belt.
    Did you measure how much the backlash varies? If the backlash is software corrected, there will be some variation left. Is T5 better than GT e. g. in this respect?



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    Default Re: Best belt drive ever! (If I do say so myself)

    Sorry, being lazy but I didn’t want to read through all 29 pages of this thread. Is there a website where this is sold?
    Thanks!



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    Default Re: Best belt drive ever! (If I do say so myself)

    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Quote Originally Posted by JoergS5 View Post
    Thanks a lot, Mike.

    So for GT2 I will need to use 40 teeth, this is diameter 25 mm then, similar to your T5 15 teeth 24mm. I will try it with steel. And I will need a gear unfortunately.

    For 3D printer this will maybe work, but for the 35-linear guide of the CNC machine I will use T5 then.

    I can keep you informed about the acceleration and speed I can achieve. I will post here.

    Regards,
    Joerg
    What gear down ratio are you planning on using?


    I am considering GT2 10mm in both sides, 20 teeth and those motors with a 5:1 ratio.
    Freies schiff 3 stücke 4-Blei NEMA 23 reduktion getriebe Stepper Motor, Getriebe verhältnis 15:1, 20n. m
    https://s.click.aliexpress.com/e/b834MfFE
    The second option is just one 3nm stepper in the middle of the gantry driving both sides, geared down with a belt at the motor.

    I might try a direct driven pinion first, maybe I don't need that power anyways.



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    Quote Originally Posted by Scot808 View Post
    Sorry, being lazy but I didn’t want to read through all 29 pages of this thread. Is there a website where this is sold?
    Thanks!
    Thank you for putting the link, Ger.
    Scott, generally no, we do not sell to the public. Our main focus is OEM sales, but we do sell one-offs rather regularly to OEM customers.

    The reason I am here is that I am happy to help DIYers with their own implementations. You would not be happy with the price of how we do it, and the whole concept is rather simple for you to apply.

    We unfortunately can’t currently sell bits and pieces, which is what you will end up wanting.

    Mike Visit my projects blog at: http://mikeeverman.com/
    http://www.bell-evermannews.com/ http://www.bell-everman.com


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    Default Re: Best belt drive ever! (If I do say so myself)

    Quote Originally Posted by heavyweather View Post
    What gear down ratio are you planning on using?


    I am considering GT2 10mm in both sides, 20 teeth and those motors with a 5:1 ratio.
    Freies schiff 3 stücke 4-Blei NEMA 23 reduktion getriebe Stepper Motor, Getriebe verhältnis 15:1, 20n. m
    https://s.click.aliexpress.com/e/b834MfFE
    The second option is just one 3nm stepper in the middle of the gantry driving both sides, geared down with a belt at the motor.

    I might try a direct driven pinion first, maybe I don't need that power anyways.
    The advantage to use GT2 over T5 is that it's nearly backlash free. You will loose this advantage with a gear again, so I would avoid a gear and try to find a stepper with 0.9 angle per step and high torque and try to use it without gear. An alternative is to use a harmonic drive as gear, which has low/no backlash. Cost is about 150$ used. It depends on what precision and speed you want to achieve. (e.g. high precision, low speed => harmonic drive 1:50).



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