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Relay and DC motor help and info needed

Discussion in 'Sensors and Actuators' started by Karokis, Jan 21, 2010.

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  1. Karokis

    Karokis

    3
    0
    Jan 21, 2010
    I am needing help on what part I need to make a 3 to 6 volt DC motor run for 7 to 10 seconds and shut down for around 5 seconds then kick back on again and repeat.
    I got a local Radio Shack and would like to know what part number I need or even a link to a website with the part would be very much appreciated.

    And what is a good medium torque and about 2000 RPM DC motor if any is available in the 3 to 6 vold range.

    Also, Do they make an adapter to make the shaft longer on the motor?

    Thank you . Kar
     
  2. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Define medium torque. Or hint us on the power (or the current). I'd believe anything can be had (maybe not from the shack).
     
  3. Karokis

    Karokis

    3
    0
    Jan 21, 2010
    I posted more details on another forum. I will repost it here. Sorry for lack of info.


    I need help with a set up for a forward reverse motion DC 3 to 6 volt motor.
    I will be useing the motor to go back and fourth between 9 and 3 O clock.
    Like wipers on a car.

    The motor needs to be quiet and be able to lift about 8 onces and have atleast a 1.5 inch shaft with a flat side. The speed between 3 and 9 should be 1 second.

    Thank you for the reply back to my first post.
     
  4. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    With a motor speed of 2000 RPM & an output speed of 30 RPM you'll need a gearbox with a ratio of around 67:1.
    The weight lifting ability says nothing w/o including the length of the lifting arm.
    The noise level can be kept down by using a 12 or 24V motor on the voltages you mention.
     
  5. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Ok, so yours will be a little slower than that one, and have an arm length of about 30cm (12in, 1ft)? 8oz=227g btw. That gives a needed torque of at least 6lb-in (= 678Ncm).
    Running a motor on 1/4 of its rated voltage also means you only get 1/4 of its rated torque, so choose for example a 24V 8000RPM (or a 12V 4000RPM) 10W motor with a 67:1 gearbox & an output torque of at least 24lb-in (= 2.7Nm).
    You know you'll have to mount end-stop switches to reverse the rotation at the required points?
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,362
    2,757
    Jan 21, 2010
    Perhaps a typo, but isn't the relationship based on a squared law? I thought that operating at 1/4 the voltage would result in 1/16 torque.
     
  7. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    No, not the torque (as it's directly related to current draw), but I figure the power output would be down to 1/16 (as the speed would also be 1/4, related to the voltage).
     
  8. Karokis

    Karokis

    3
    0
    Jan 21, 2010
    Thank you all for input.
    I am now in need of a start (run for 8 seconds) then stop for 5 then start again and repeat small compact relay (or?) The highest voltage it would see is the use of 4 AA batteries.(6 volt low amps) SOmeone got a part that I could pick up from radio shack or online? Thanks again for all the help.
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,362
    2,757
    Jan 21, 2010
    A fairly simple design would be using a 555 and an appropriate transistor to drive the motor.

    Google for "555 lamp flashers" and you should find something that can be made to flash a lamp at that rate. Replace the lamp with the motor (or a relay) -- remembering to place a reverse biased diode across the motor (or relay) and you should be set to go.

    You need a circuit where you can alter the mark/space ratio, but that should not be too hard to find.

    Whilst checking that advice <grin> I found the following:

    http://www.schematica.com/Schematica/files/555_Timer_PRO_Setup.exe

    it's not free, but here is a design for a 555 circuit that has the right timings:

    http://img269.imageshack.us/img269/7198/555wo.gif

    The resistors are impossibly large (which in itself means I'm probably not going to buy this software), but if you reduce them by a factor of 1000 and increase the capacitor by a factor of 1000, you'll have a workable circuit.

    43 M ohm becomes 43 k ohm
    72 M ohm becomes 72 k ohm (closest E24 value is 75k)
    100 nF becomes 100 uF

    The frequency is 0.077 Hz (which is the reciprocal of the period -- 13 seconds) and the duty cycle is 61.5% which is 8/13). Note that changing the resistor from 72 to 75k will change these values a little.

    The output could directly drive a relay (connect between the output and ground) or maybe your motor as long as the current required is low (check the 555 specs)
     
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