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Thread: Nema 34

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  1. #1
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    Nema 34

    Hi,
    As a student of mechanical engineering im trying to do a project which involves shredding\ grinding plastic bottles.
    I wonder if i can take a Nema 34 or even Nema 24 stepper motor with high torque and connect it to baldes such as electric blender/meat grinder blades and let it run.
    If not, id like to know which motor should i use for a purpose like this? one thing is that i need it to be controlled through Arduino board.
    Thanks!!

  2. #2
    Community Moderator Jim Dawson's Avatar
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    Re: Nema 34

    Look at the torque curves for your chosen stepper. The stepper torque drops off rapidly as the RPM increases. It depends on the torque required to run your proposed machine.

    There are other motor options that could be controlled by an arduino board. The real question is: Does the motor need to be variable speed? If not, then any motor with sufficient torque can be used. The arduino would then only need to turn the motor on and off.
    Jim Dawson
    Sandy, Oregon, USA

  3. #3
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    Re: Nema 34

    Im still new at this field so i dont really know how to calculate the torque required for my machine. all i need is to shred the plastic bottles. also time is not important.
    and no, it does not need to be variable speed it can be constant speed. i just need a good motor that will do the work.
    for instance, i tried using my one of Anet A8 3d printer stepper motors and connected to the tip of the motor blades like i have mentioned and it didnt work at all.
    thanks for helping!

  4. #4
    Community Moderator Jim Dawson's Avatar
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    Re: Nema 34

    Well, maybe think in terms of a food blender. About 12,000 RPM and maybe 0.75KW or so.
    Jim Dawson
    Sandy, Oregon, USA

  5. #5
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    Re: Nema 34

    Try putting some of those bottles in a blender and see how well the shredding action really works. My guess is - not well. I'd think you need to think of a process that will deal with them more effectively, like a series of rollers that entrain and flatten the bottles and feed them into a series of parallel fine-tooth sawblades. Once you've got an effective process, then you can start worrying about the type of motors you need. I don't think steppers are what you'll end up with, though. 3D printers typically use tiny little NEMA 17 motors, which are nowhere near big enough. I'd think in terms of multi-horsepower motors for a machine like this.
    Andrew Werby
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  6. #6
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    Re: Nema 34

    Hi Saar - You are going to need much more torque then a small stepper can provide. There are lots of videos of plastic shredders on the net. Look up "precious plastics'. Usually a medium size electric motor with a gearbox. Steppers are used for displacement/motion control not for brute force applications. Cheers Peter

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    Re: Nema 34

    Thanks you all for replies!!
    thats the thing i was worried about.. those medium size electric motors are way out of my budget and cost from 300 to 500 dollar. i was trying to find cheaper solution :\

  8. #8
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    Re: Nema 34

    Hi Saar - Some people start with scissors, some have used bicycle power but soon realise a person can't put out a kW unless your an Olympic cyclist. I'm sure if you look around you will find a free one somewhere off of an old machine. The junk yards are full of them. Unfortunately you can't scrounge at the tip like when I was a kid... Put an ad in the paper for a free motor I'm sure someone has a machine in the garage they want gone and you can do that and get the motor.... I was in my local electrical repairers place a few months ago and he had some stacked up in the corner. Time to get creative, there out there...Peter

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    Re: Nema 34

    Quote Originally Posted by peteeng View Post
    Hi Saar - Some people start with scissors, some have used bicycle power but soon realise a person can't put out a kW unless your an Olympic cyclist. I'm sure if you look around you will find a free one somewhere off of an old machine. The junk yards are full of them. Unfortunately you can't scrounge at the tip like when I was a kid... Put an ad in the paper for a free motor I'm sure someone has a machine in the garage they want gone and you can do that and get the motor.... I was in my local electrical repairers place a few months ago and he had some stacked up in the corner. Time to get creative, there out there...Peter
    Hi Peter,
    first of all, thank you for you help.
    Let me rephrase my question.
    I need the motor for my university project, and for some reasons, I can’t take a motor for free from people.
    maybe you can help me with this question:
    I am trying to determine what motor to use. I understand from your and other people answers that I can’t use stepper motor because of the low torque. what is the minimum torque you think is good enough?
    Lets say i wanna use 250 RPM, if I will know the torque I need I will be able to decide what motor and gears to buy for this use.
    Thanks you very much!
    Saar

  10. #10

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    Re: Nema 34

    How about a treadmill motor, you can find varying sizes with variable speed controller for next to nothing on Craigslist

  11. #11
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    Re: Nema 34

    Quote Originally Posted by whodwho View Post
    How about a treadmill motor, you can find varying sizes with variable speed controller for next to nothing on Craigslist
    ok those one are less than 100$ which is good but how can i know for sure that they will do the work and i wont buy them for nothing?

  12. #12
    Community Moderator Jim Dawson's Avatar
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    Re: Nema 34

    You are starting at the wrong place. Design and build your shredding system first. Then measure the torque required to run it. Then choose a motor/gearbox combination that will produce the required torque and speed.
    Jim Dawson
    Sandy, Oregon, USA

  13. #13
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    Re: Nema 34

    Hi Saar - Putting my Mechanical Engineers hat on, there are at least 3 ways to do this:
    1) Research similar machines and take advantage of their experience. Precious plastics say 70rpm and 1.5kW minimum. They have been building plastic shredders for years so know a lot about them
    2) Agree with Jim, build the shredder put a torque wrench on its input and figure out the torque required, then select motor to suit
    3) Design from first principles, estimate friction (see bearing manuals and contact friction - static and kinetic), estimate cutting force (get scissors and measure forces) , estimate motor required....
    4) your motor requirement will depend on the length of the machine, if its 1000mm long it will require twice as much power as a 500mm long shredder etc so if you build a 50mm long one you may be able to turn it by hand at 1:3 gearbox or more....

    So this is a design exercise? The Uni would not expect students to pay out for these machines but they do want to know what things cost? and they are looking for innovation so if you own a car, it has a jack so you jack the powered wheel take off the wheel and plug the shredder onto it. Do the work rebuild car.

    250rpm is a bit fast for a shredder. Even the really big ones that eat cars go slow... Shearing plastic is a slow process, blenders just knock the things around. I keep coming back to scissors...a shredder is just a big multiple blade scissor. Hat off Peter

  14. #14
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    Re: Nema 34

    Thank you all for your answer. it really helps me!

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