Rated torque and stall torque

  1. i need to get a 12V DC motor which is used to operate a vertical acting ram movement ( rack and pinion assembly ) ........ i 'm confused between the specs of the motor ........ the motor should have a high torque value and i'm not sure how much torque should it be there ..... considering the mass of ram and rack and pinion assembly to be 10 kg approx. what is the necessary torque value of the motor required ???
    anticipating many responses ...... thank you
     
  2. jcsd
  3. Baluncore

    Baluncore 2,576
    Science Advisor

    Some idea of the pinion size is needed before answering the question.
    How many gear teeth are there on the pinion? What is the pitch of the gear teeth on the rack.

    The pitch radius of the pinion converts the torque of the motor to a linear force against the rack.
    Use the smallest pinion available to get the best low speed response, with the least torque.

    It would be good if the vertical weight of your system could be balanced to remove the continuous torque requirement from the motor. The mass of system components is then only important during acceleration.

    You might be better using a ball screw since one turn of the motor can advance the ball nut a shorter distance than will one turn of the pinion on a rack. Another advantage is that only the nut needs to move which reduces the inertia and space requirement.
     

  4. thank you :) can a heavy compaction force be produced in a ball screw arrangement ????? and can a heavy ram be fixed in the ball screw arrangement ??????
     
  5. Baluncore

    Baluncore 2,576
    Science Advisor

    Heavy is a relative term. Ball screws are available in many sizes and lengths. A ball screw is self aligning and makes a stronger press than an equivalent sized rack and pinion, but nowhere near as small and strong as a hydraulic ram or jack.
     



  6. heavy compaction force ..... i.e., a compaction force of 350 - 400 kg can be produced using a ball screw ???? how to select the ball screw arrangement for producing this compaction force ????
     
  7. Baluncore

    Baluncore 2,576
    Science Advisor

    A 16mm diameter ball screw can generate an axial force of about 1000kg.

    What length of movement do you require?
    What is the repetition rate?
    How are the ends of the ram anchored, or is one floating?
    What guides the ram and can that stop the ram rotating?

    Motor selection requires torque with movement, so stall torque can not do any work, except that it makes it possible to calculate the relationship between speed and torque for the motor. A DC motor will get hot if operated too slowly for too long. You will need to operate at say 20% of the motor's “no load RPM” which should give you a torque of about 80% of the specified “stall torque”. Your motor may be reduced in size by using a gear reduction when driving a pinion or ball screw, but that will depend on speed and repetition rate requirement.
     
  8. length : 600 - 700 mm
    repetition rate : 4 times a day
    ends of the ram attached to the screw assembly
     
  9. Baluncore

    Baluncore 2,576
    Science Advisor

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