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  1. #1
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    Default atypical use

    Hello,

    My usage of a spindle is atypical. I’m an musician, and I want to use it to turn (spin) an elastic jump rope (length: 5meter), slightly tensioned (maximum tension 10kg), with a 50mm offset from the axis.
    I first tried a washer motor (14000rpm), it's working but far too loud.
    Then, I've tried a system with a shaft (10mm) passing in 2 pillow blocks bearing coupled with a brushless outrunner motor. (1rst photo)
    It's working but the bearings, which are not angular ones, don't support well the offset from the axis (then certainly a shorter lifespan), and it still makes too much noise (due to vibrations, mis-alignment between the 2 pillows). I am still thinking about optimizing this system ( with some mistakes on 2nd photo), and machining different parts (or maybe use a cartridge kit), with better bearings, but complexity comes with precision, and sometimes it's not so good to reinvent something already well-engineer (plus I'm not an expert).

    I’m looking for a robust system (5 to 8 hours running), and silent (as it will be on stage).
    I need to vary the speed between 100hz and 200hz (6000 rpm and 12000rpm) (I think the speed limit has to exceed 200Hz, as it will run long hours..)

    for example, I saw this spindle:
    http://www.automationtechnologiesinc...cooled-spindle
    but I'm not sure that it is low noise and support the forces from the offset-tension.

    Can you advice me or share experiences?

    thanks

    Pamal

    Attached Thumbnails Attached Thumbnails atypical use-testb-jpeg   atypical use-testc-jpg  


  2. #2
    Community Moderator Jim Dawson's Avatar
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    Default Re: atypical use

    If you are really turning at 6000 to 12000 RPM then with a 50mm offset the system is going to be out of balance and would destroy itself . I question the RPM because you state that you were using a washer motor and were turning it at 14000 RPM. This is not possible, the washer motor would explode at that speed. 1400 RPM would be about correct for washer motor running at 50Hz. Even running in the range of 600 to 1200 RPM, the system is going to have to be somewhat balanced to compensate for the 50mm offset.

    The pillow block bearing setup would work OK for RPM ranges of 600 to 1200.



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    Default Re: atypical use

    I didn't measure precisely, but for sure the motor was far above the 1400 rpm (I post the spec of the motor here)
    ... but anyway, as it was too loud, this couldn't be a solution.



    I really need to vary the speed between 100 and 200 hz (so 6000 to 12000rpm) for interaction with light (fast led flashing).

    So ok, I note that the the spindle from automationtechnology isn't a solution.

    I saw some headstock and spindle on sherline but only speeds below 10000rpm are possible. And maybe it's also not enough robust...

    Attached Thumbnails Attached Thumbnails atypical use-img_5247-jpg  
    Last edited by pamal; 03-09-2017 at 03:35 PM.


  4. #4
    Community Moderator Jim Dawson's Avatar
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    Default Re: atypical use

    That being the case, maybe something like this would work for you. 2.2KW ER20 WATER-COOLED SPINDLE MOTOR AND 2.2KW VFD MATCHED INVERTER DRIVE | eBay



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    Default Re: atypical use

    thanks Jim for your answer.
    With the one from automationtechnology, is the main difference about bearings, or the price and quality?
    water cooled seems difficult to implement on stage, but they have also equivalent air-cooled for 4$ more!

    have you experienced it? noise and robustness...



  6. #6
    Community Moderator Jim Dawson's Avatar
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    Default Re: atypical use

    I chose the water cooled because it runs with much less noise than the air cooled. The air cooled spindles have high speed fans that are very noisy, 90+db. The water cooled spindle can be equipped with a small heat exchanger for cooling, something like this. JEGS Performance Products 60374: Transmission Cooler 26,000 GVW | JEGS does not require an external water source.

    I have no personal experience with any of the spindles. I think that any of the spindles would be robust enough for your application, if you balance the rope attachment. If you do not balance the rope attachment, the bearings will be destroyed in a short time.



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    Default Re: atypical use

    Quote Originally Posted by Jim Dawson View Post
    I think that any of the spindles would be robust enough for your application, if you balance the rope attachment. If you do not balance the rope attachment, the bearings will be destroyed in a short time.
    but how is it possible to balance the rope attachement?
    The action of a counterweight isn't the same direction than the tension of the rope.



  8. #8
    Community Moderator Jim Dawson's Avatar
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    Default Re: atypical use

    Removing material from the opposing side of the attachment would be a start. But you are correct, it will be difficult. You should be able to get it in radial balance, but I have no idea how to get it in axial balance. But I think radial balance is most important.



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    Member awerby's Avatar
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    Default Re: atypical use

    This sounds like a bad idea to me. A normal jump-rope would go at about 60 rpm. Trying to spin something like that a hundred or 200 times faster with a high-speed spindle intended for small tools is a recipe for disaster. You will destroy the spindle in short order, but you also run the risk of hurting people seriously when the mechanism flies apart. There's no way that little wooden machine you picture can handle speeds like that, especially with ropes attached. Hire some kids to turn the rope for you; they're good at that.

    [FONT=Verdana]Andrew Werby[/FONT]
    [URL="http://www.computersculpture.com/"]Website[/URL]


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    Default Re: atypical use

    The term "jump rope" was just an image to illustrate the movement of the rope. It is not intented to play here.
    As I said before, the 6000-12000 rpm are needed for interaction with light flashing....
    Ok, I've heard the precision about the limitation of this spindle, and the security risk (there will be 2 men near this installation, myself included!)
    Then this spindle is not really appropriate....
    have you other propositions, robust and as silent as possible?



  11. #11
    Community Moderator Jim Dawson's Avatar
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    Default Re: atypical use

    I understand what you are trying to do. And I am going to disagree a bit with Andrew, I think the spindle will be robust enough to survive the load if you can balance the attachment point. But, I am not sure about the system as a whole. I would expect the rope to fail before the spindle.

    What I would do is build the system, install it in a safe location, then turn it on from a safe location and run it at various speeds for at least an hour. Since you are in the entertainment industry, maybe talking with a special effects or lighting effects guy would be a good idea.



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    Default Re: atypical use

    I agree with Jim about the safe location. Having 2 men standing around while this thing is being spun at high velocity doesn't make it safe - especially for them. It will be interesting to find out what fails first, but none of the components in your picture are balanced for high RPMs, so expect it all to vibrate a lot before flying apart.

    [FONT=Verdana]Andrew Werby[/FONT]
    [URL="http://www.computersculpture.com/"]Website[/URL]


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    Default Re: atypical use

    The last test was good: running for 40min, with nothing broke... the little bearings at the elastic attachements work.
    My system is always too noisy, and the bearings are not appropriate, so I seem to hear a bit more vibration.
    To return to the idea of an existing solution, and as it is difficult to balance the offset tension or diy a good angular bearing assembly, maybe the solution is to choose a pre-built system little bigger.
    Also the outrunner motor works and is not too loud, finding a spindle with no motor could be a solution. I'm looking at sherline product, but speed limit is 10000rpm.
    Do you know other product?
    Thanks
    Pamal



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