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IndustryArena Forum > Mechanical Engineering > Linear and Rotary Motion > Differences between HTD, GT, AT and T pulleys?
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  1. #37
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    Re: Differences between HTD, GT, AT and T pulleys?

    Hi Mactec - The numbers indicate that an Alpha V will work in the given conditions and the consideration is the join life. It may last a month, a year or forever in Spoos application. An application or design engineer from the company would be able to help from experience to choose a belt, there are many out there and people have favorites. If a jointless belt is available then its clear thats preferable. All belts should be inspected regularly and replaced when deemed needed. We aim at infinite life but in reality this is not achieved.

    The exercise has been worthwhile to gain a better understanding of the belt design process (for me at least as I had not thought much about joins before) and gives Sploo the information to talk to a belt rep in confidence. Thanks for umpiring. Peter

  2. #38
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    Re: Differences between HTD, GT, AT and T pulleys?

    Peter/Mactec - thanks for the extra input.

    I've reproduced Peter's figures (I also realised the "25" in one of Peter's calculations is of course the belt width, not the number of teeth on the pulley).

    In terms of belt choice, my supplier has the Conti Synchroflex belts, and although I couldn't immediately find the same level of spec detail as the Optibelt catalogue, the supplier claims that the Optibelt AT5 is essentially a copy of the Synchroflex belt and "from what I can work out they just used the Synchroflex catalogue figures".

    That (hopefully) being true, our calculations should be applicable to the Conti belts. They also have a GEN III belt, which is rated as 25% better than the standard Synchroflex AT5. The only thing not clear to me is whether that translates to a 25% increase in running load. If true, that's great (as it takes the MN [load] and PN [power] figures of the belt above what the motor can provide). If the calculations are about whether the belt will slip on the small pulley then I guess that 25% improvement doesn't apply - but if I understand Peter correctly it is about fatigue on the belt due to load, so probably the GEN III will help.

    In short, with 7 teeth engaged on the 20 tooth pulley I get an MN of 9.46Nm, and a PN of 0.0595Kw. If I use idlers to get 10 teeth engaged that goes up to 13.5Nm and 0.085kW respectively. If the GEN III belt would increase those figures by 25%, that becomes 16.9Nm and 0.1kW (vs an input to the small pulley of 10Nm and 0.06kW). Should be OK?

    EDIT: Having just found a Conti Syncroflex data sheet with the figures; it appears my supplier is correct; their basic AT5 belt looks pretty much identical to the Optibelt in performance terms, with the GEN III having roughly 25% higher W/mm figures (though they use W/cm instead). I guess that bodes well for the GEN III for my application.


    PS As an aside, last night I knocked up a terrible hack with a smaller motor I have; ultimately it would have been providing around 2.25Nm to the small pulley; which was knocked up out of plywood on my lathe for use with an old SPZ belt. The ratio of the larger (also plywood special) pulley on the lathe spindle resulted in a further reduction of about 1.5x; for a "massive" 3.5Nm of torque at the lathe spindle. Even given that low torque figure it wasn't particularly pleasant trying to grab the chuck on the spindle to stop it, and the planned setup should result in something nearer 10 times the torque. As such, if the belt will hold up to it I'm hopeful it should do the job.

  3. #39
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    Re: Differences between HTD, GT, AT and T pulleys?

    Hi Sploo - How did the mod work out? Peter

  4. #40
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    Re: Differences between HTD, GT, AT and T pulleys?

    Fwiw..
    Even with HTD-8 profiles, about 3x and HTD-5, and 30 mm wide belts,
    the results are not good for 4th axis apps.

    Positioning, yes.
    Angular holding, no.
    With 10.000 count ac industrial 220V servos, 1:3 belts, 10 Nm cont, 30 Nm peak, 90 Nm at spindle.

  5. #41
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    Re: Differences between HTD, GT, AT and T pulleys?

    Quote Originally Posted by peteeng View Post
    Hi Sploo - How did the mod work out? Peter
    Hi Peter.

    Slowly getting there. There was an issue with the machining of one of the pulleys I bought so that had to do a round trip back to the supplier, then one of my servo drives packed up (doing a round trip back to the US).

    I have now sourced the servo motor size I wanted, and I'm using a 50:1 worm gearbox with huge amounts of backlash (so 50:1 from the motor, and 3:1 from the gearbox to the 4th axis spindle = 150:1 total). Having tried a few "air cuts" there's a lot of "slapping" due to the gearbox backlash, and that seems to be upsetting the servo drive. However, torque under load seems pretty good.

    I have a used 100:1 harmonic drive on the way, which (unless trash) should get rid of the backlash issue, and I'll make another judgement regarding the servo drive then.

    I'm using a 60mm idler on the outside of the belt to get more tooth engagement on the small pulley, and with moderate belt tension it all seems pretty good. The current shonky prototype looks like this (but it will get better!):

    Attachment 428278

  6. #42
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    Re: Differences between HTD, GT, AT and T pulleys?

    Quote Originally Posted by hanermo View Post
    Fwiw..
    Even with HTD-8 profiles, about 3x and HTD-5, and 30 mm wide belts,
    the results are not good for 4th axis apps.

    Positioning, yes.
    Angular holding, no.
    With 10.000 count ac industrial 220V servos, 1:3 belts, 10 Nm cont, 30 Nm peak, 90 Nm at spindle.
    With the absence of data to tell me what the forces would be from pushing an Nmm diameter bit with a Dmm depth of cut through wood at Xmm/s it's difficult to know what level of torque would be sufficient for my application. I've seen a few comments indicating that 27Nm is good for a rotary axis, but that lacked data on what was being cut.

    My motor is rated to 0.27Nm, and at 300:1 reduction (100:1 gearbox, plus 3:1 pulley), should in theory result in ~81Nm of torque at the spindle.

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