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    Discussion in 'The main mechanical design forum' started by lilduka, Nov 8, 2010.

    1. lilduka

      lilduka New Member

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      Hello my friends,
      i want to design a system that lifts 30kg to 80cm vertically up and down. i want to drive it with a DC motor. what is your advices about the lifting mechanism, it can be worm screw and a nut or rack and pinion mechanism. do you have any experience about the advantage and disadvantage of these mechanisms. cost is so important.
      thanks very much..
       
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    3. AndrewNew

      AndrewNew Well-Known Member

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      Lead screws and nuts are robust and compact, but not very mechanically efficient, so you might end up needing a bigger motor. Ballscrews are better, but more expensive. With a rack and pinion, you will probably need to gear down your motor more. Which is the best depends on your budget (for the whole system, including motor, controller and power source, not just the final drive) and other constraints you have (for example, does the system have to fit into a restricted space). I've done a bit on lifting systems, if you can give more details I might be able to offer some more specific suggestions.

      Cheers

      Andrew
       
    4. lilduka26

      lilduka26 Member

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      Hello Andrew,
      Thanks for your candid reply. As every projects cost is so important, we are doing this system for end user. Our restrictions are; be quiet (<30Bd), travels 80cm up and down and lift 40kg by 30mm/sec. I saw that from my search rack and pinion mechanism will cheaper than lead and ballscrew solutions as you said, so i eliminated screw solutions. it can be also belt drive solution but i dont know about it is efficiency and prices.

      have a nice day

      ?brahim
       
    5. AndrewNew

      AndrewNew Well-Known Member

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      30dB is really quiet (a whisper across a room!) I think you will struggle to meet that unless the mechanism is enclosed, and I suspect the noisiest device will be the motor/gearbox. In general, belt drives tend to be quieter than geared (e.g. rack and pinion) drives. Have you thought about using a cord/tape system running on pulleys (something like a block-and-tackle)? You could then play around with number of cord/tape runs vs. motor capacity/speed vs. lift speed.

      Cheers

      Andrew
       
    6. lilduka26

      lilduka26 Member

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      i am suspicious about the safety of cord/tape system? and thinking that when i lift my mass and turn the electricity, is the mass goes downward or save the last position before the motor shut. the mass must save the position when the system is off.
       
    7. AndrewNew

      AndrewNew Well-Known Member

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      I have seen tape systems used on 1000kg fork lifts - like this one for example http://www.advancedhandling.co.uk/produ ... c-stacker/. The tape I am talking about is similar to the sort used for seat-belt webbing in vehicles (but thicker) and is incredibly strong. You would need to check the load capacity of the tape you chose but your application is pretty low load so you won't have a problem finding something suitable. If the tape is being wound onto a drum driven by a motor, for example, you would need to check how much torque you can apply to the motor shaft before it back-drives with the power off in order to work out whether the mass will hold it's position. Again, given the gearing that you will need in the motor-gearbox assembly, this is not likely to be a problem, but you will of course need to check.

      Cheers

      Andrew
       
    8. lilduka26

      lilduka26 Member

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      now some alternative design solutions are awaking. we need a tape that is wrasping a drum and guide bars left and right of the system by linear ball bearings.are you agree with me about this tape and drum alternative is cheaper, silent and a robust system than rack and pinion mechanism alternative. our design have to be a integrated solution and anyone can assemble this system to their mass.
       
    9. AndrewNew

      AndrewNew Well-Known Member

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      I would think so, yes. With a tape and drum system, you have eliminated most of the noise sources except the motor, which you are probably going to need regardless of the rest of the system design. Although they will probably give the lowest friction, especially under loads, linear ball bearings can be a bit noisy, so I would suggest you consider plastic plain bearings on your guide bars (Igus make an extensive range). The plastic bearings also don't need lubrication, which means they are maintenance-free, possibly another benefit, and they are tolerant of dirt and corrosion resistant. Hope this helps!

      Cheers

      Andrew
       
    10. lilduka26

      lilduka26 Member

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      Thanks very much Andrew, your suggestions will powered us. If you give permission we can speak progressive phases of the design.
      Thanks very much

      have a nice day
       
    11. AndrewNew

      AndrewNew Well-Known Member

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      Yes, absolutely, it would be good to see what you come up with. I hope to do some more work in this field in the future - next time you might be able to help me!

      Cheers

      Andrew
       

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