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  1. #321
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    Default Re: Best belt drive ever! (If I do say so myself)

    Low-Alloy,

    That is what I show in post #306. An angle with the static belt is mounted to the bottom of the X-axis carriage and the dynamic (endless) belt is mounted to a reduction drive mounted to the frame. The motor is stationary.

    Stan



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

    Thanks for the answers guys!



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

    Howdy Mike, I was looking through this discussion and had some thoughts on self tracking of belts.
    Have you considered something like the Brecoflex SFAT or ARC-Power belts?
    Another potential self-tracker would be the goodyear eagle PD herringbone, or Continental silent-sync.



  4. #324

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

    I only read up to page 3 for now but this is the most usefull thread regarding servo belt drives I stumbled across.

    I guess I will be ok with a belt in belt HDT5m 20mm on both sides of my X axis butI have an idea for DIYers regarding backlash.
    (Don't know if someone has come up with that one already here).
    I was thinking about a second belt and two pulleys if you run two belts (4 when belt in belt) side by side and offset the pulleys a little you get something like a split pinion.
    This could be done with cheap steel reinforced PU gt2 6mm hardware or HDT5m belts.



  5. #325

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

    Here is another diy copy of the servo drive (without the lower belt) on a German board.CNC filament winding maschine.
    CNC Faserwickelmaschine Reloaded - Seite 4



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

    Backlash is not really an issue if you use the T5 belts.

    Gerry

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    WOW! Eighteen months silence.
    Does using 2 of these belts on either side of a dual driven Y axis pose tracking issue? How to ensure perfect sync between the two? The two Belts need to be pasted with exactly equal stretch or there'll be tracking errors. How's this accomplished?

    Last edited by ajaytanna; 05-30-2018 at 11:01 PM.


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

    Quote Originally Posted by ajaytanna View Post
    WOW! Eighteen months silence.
    Does using 2 of these belts on either side of a dual driven Y axis pose tracking issue? How to ensure perfect sync between the two? The two Belts need to be pasted with exactly equal stretch or there'll be tracking errors. How's this accomplished?
    Apologies, my notices were going to spamalot.
    So far, many gantries down the road, there has not been an issue with small differences, leg to leg. The BrecoFlex belting is extremely good wrt pitch accuracy. I did a laser measurement over 20', and the linearity was +/-60um. Even so, most gantries are going to be able to absorb quite a bit of mismatch, as it boils down to tiny angles of bridge to base. That said, I've also done a double drive where the two belts were only 180mm apart, and didn't have much infighting to speak of, though I was expecting it.
    The joy of elastomers!
    Mike

    Mike Visit my projects blog at: http://mikeeverman.com/
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    Default Re: Best belt drive ever! (If I do say so myself)

    Quote Originally Posted by ajaytanna View Post
    WOW! Eighteen months silence.
    Does using 2 of these belts on either side of a dual driven Y axis pose tracking issue? How to ensure perfect sync between the two? The two Belts need to be pasted with exactly equal stretch or there'll be tracking errors. How's this accomplished?
    Mike Everman,
    please comment on this question!!



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

    Quote Originally Posted by tkms002 View Post
    Mike Everman,
    please comment on this question!!
    I did 11 days ago.

    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)

    Mike, thank you for your wonderful idea of the ServoBelt.

    I'll try it for a 3D printer with GT2 9 mm belts. But most users of those belts avoid steel based belts and use glass fiber ones, because if the diameter of the pulley is too small, the steel breaks.

    I wonder why you use steel based belts. Do you use special ones?

    Another idea is to use steel based belts as rack to provide precision and use glass fiber ones for the upper belt to avoid breaking.



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

    Quote Originally Posted by JoergS5 View Post
    Mike, thank you for your wonderful idea of the ServoBelt.

    I'll try it for a 3D printer with GT2 9 mm belts. But most users of those belts avoid steel based belts and use glass fiber ones, because if the diameter of the pulley is too small, the steel breaks.

    I wonder why you use steel based belts. Do you use special ones?

    Another idea is to use steel based belts as rack to provide precision and use glass fiber ones for the upper belt to avoid breaking.
    Hi Joerg,
    The reason for steel reinforcement is the back-bend that is going on. We can get up to 50 million cycles with steel, and Kevlar would not make it through the weekend. I do not know about glass. We observe a minimum tooth count of 15, and a minimum back-bend diameter of 40mm for extreme life with T5 belting. You will not have to observe those minimums, but if you did, it would last forever, properly sized. The chances that any enthusiast CNC would be applying accel/decel forces in the same exact place even 5 million times is very remote.
    We however, have to design for the worst case, as when it is an actuator that does the same move 24/7.
    GT is great, but will have far less force capacity given a size than T series. T has a little lost motion, though. It's a trade-off. I use GT for most of my rotaries, or reducers that need zero lost motion on reversal.
    Mike

    Mike Visit my projects blog at: http://mikeeverman.com/
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    Default Re: Best belt drive ever! (If I do say so myself)

    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



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

    Quote Originally Posted by Mike Everman View Post
    Hi Joerg,
    The reason for steel reinforcement is the back-bend that is going on. We can get up to 50 million cycles with steel, and Kevlar would not make it through the weekend. I do not know about glass. We observe a minimum tooth count of 15, and a minimum back-bend diameter of 40mm for extreme life with T5 belting. You will not have to observe those minimums, but if you did, it would last forever, properly sized. The chances that any enthusiast CNC would be applying accel/decel forces in the same exact place even 5 million times is very remote.
    We however, have to design for the worst case, as when it is an actuator that does the same move 24/7.
    GT is great, but will have far less force capacity given a size than T series. T has a little lost motion, though. It's a trade-off. I use GT for most of my rotaries, or reducers that need zero lost motion on reversal.
    Mike
    ANd I thought you were using T5 because it had NO backlash??



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

    Quote Originally Posted by tkms002 View Post
    ANd I thought you were using T5 because it had NO backlash??
    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.



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

    There's always a small amount of play where the belt teeth fit the pulley, to keep it from wearing too fast.

    Gerry

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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/
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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/
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