Reversing an electic engine?

Discussion in 'General Electronics Chat' started by Pumba, Mar 2, 2005.

  1. Pumba

    Thread Starter New Member

    Mar 2, 2005
    3
    0
    hey guys!

    i have this project for school in which i have to open a lid of a bin without using my hands. I have chosen to use a electic motor.

    heres my problem.. i can get the motor to turn one way yeh piss easy but getting it to turn the other way is the difficult part!

    i know its possible cause in a remote control car, u press forward and it goes forward and u press back and it does back..

    does anybody know?

    im in australia btw so if any1 knows of any shops here that would be great!
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    One common approach used to drive a motor in both directions involves the use of an H-bridge. So called because the driver is made up of four switching devices with the load (in your case the motor) bridging across the middle to form the "H" pattern.

    The h-bridge driver has two control lines. One control line enables and disables the motor while the other control line allows you to select the direction either clockwise or counter-clockwise.

    Google "h-bridge driver" and you will see what I'm talking about.

    Good Luck.
     
  3. harshana

    New Member

    Mar 2, 2005
    4
    0
    Easiest way is to have two battery power supply (two in sereis) so U can get GND as the mid point voltage. Then U can have +1.5V and -1.5V

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    +V GND -V
     
  4. harshana

    New Member

    Mar 2, 2005
    4
    0
    sorry see the attachment
     
  5. Firestorm

    Senior Member

    Jan 24, 2005
    353
    0
    yes that method works but i heard it wasnt always the bestway, I might have misread them but its seems it will work in theory. :D
    anyone kno what im talking about jump in plz...I might have just read something wrong..thx l8er

    -fire
     
  6. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    hi,

    you mentioned the use of an electric motor, but you didn't specify whether it's AC or DC and at what voltage you intend to use. then members maybe can draw up something for you like the H-bridge as suggested by "hgmjr". :)
     
  7. Pumba

    Thread Starter New Member

    Mar 2, 2005
    3
    0
    hey guys thanks for the replies

    this is all the info for the motor we are using:

    High Speed Torque Motor

    Voltage Range: 6 - 12V DC
    Nominal Voltage: 12V DC
    Speed (No Load): 18,400 RPM
    Current (No Load): 300mA
    Torque @ Max. Eff: 69.2g-cm
    Body Size: 27.5(d) x 32.6(l)mm
    Shaft Size: 2.3(d) x 2(l)mm


    Features: Shaft Diameter suits the various gears and cogs found in the value pack P-9040 Assorted Gear Pack.

    with that type of power would i need anything else?? obviously i need wiring, batteries and that 3 way switch watever ever it is but do i need resistors, chip, some sort of management..? anything at all?
     
  8. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    hi pumba,

    now i will assume that you do not need a speed controller.

    i can give you 2 options, you can use the H-bridge configuration or have a very simple circuit using relays and switches, of taking into account the back EMF of the motor.

    take your pick and i will provide the circuit design :)
     
  9. Pumba

    Thread Starter New Member

    Mar 2, 2005
    3
    0
    hmm a speed controller may be good actaully.. why did u say u assume I didn’t need one??

    As u could of guessed I don’t really know much about electrinics so spare with me ;)

    I have decided to go with using switches. Do u know of the ones which have 2 on’s? like the one I have in the picture I uploaded^^^

    If you could provide the circuit design that would be great thanks ;)

    Wats the EMF by the way?
     
  10. Firestorm

    Senior Member

    Jan 24, 2005
    353
    0
    so u want to use the H-bridge circuit...an EMF is the ElectroMagnetic Field. All electric motors have 1 of course. Moz said he could draw u a circuit but i think ill give it a try as well. Go with moz's since i havent made many circuits and mine will probly contain a couple errors if it even works lol :p ...hope this clears things up...l8er

    -fire
     
  11. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    [attachmentid=438]hi pumba,

    am attaching the circuit drawing of the relay switch and the H bridge.

    the relay control may look complicated but it has a good working principle.

    the H bridge design is basic with the use of PNP & NPN transistors. the high side drivers Q1 & 2 are PNPs w/c acts as your current source for the motor. PNPs, P Fets & P Mosfets are good providers of current source. the low side drivers Q3 & 4 are NPNs w/c acts as your current sink for the motor. NPNs, N Fets, & N Mosfets are very efficient in this regard.

    the Mosfets could have been my choice however due to high efficiency, but due to high trigger it would need a higher supply than your present supply. the 12v can still be used but another design has to be made like a cleaver circuit which would make things more complicated. :)

    for cost consideration you can use NPNs for the high & low side drivers. PNPs cost more that NPNs.

    the 2N6121 & 2N6124 can easily handle your 300ma motor (unloaded). if loaded you motor can draw as much as 2.5x your unloaded state. :)
     
  12. Firestorm

    Senior Member

    Jan 24, 2005
    353
    0
    nice job moz, on ur relay controller, can u go from forward to reverse w/o stopping? Most of the ones ive seen make u stop 1st. thx l8er

    -fire
     
  13. Nettron

    Member

    Jan 22, 2005
    29
    0
    You can also use 2 single pole relays to get forward-reverse control and the stop function happens automatically. Also the single pole dealy elliminates the possibilty of a short happening if the forward and reverse buttons are pressed at the same time ( the so called dis-allowed state).

    [​IMG]
     
  14. Erin G.

    Senior Member

    Mar 3, 2005
    167
    1
    This is a simple way of doing this. Sorry that it's hand drawn, but this would be an automatic system: Push either button, the limit switch will stop it when it reaches end of travel. Normally closed R & F aux-contacts act as interlocks to prevent R & F contactors from acting simultaneously. If I were building this for a practical device, I would use a manufactured reversing contactor that has a mechanical interlock as well.
     
  15. Erin G.

    Senior Member

    Mar 3, 2005
    167
    1
    I can't seem to get my schematic attached. Will work on this later: 'need some sleep,...
     
  16. Firestorm

    Senior Member

    Jan 24, 2005
    353
    0
    to get your pic attached make sure you save it as a GIF. or something along those lines. I think jpeg will work as well but bitmap wont. Just open your scan in paint and hit "save as" then click GIF under the bar with file name. then just browse with the uploading mod on this forum or use a free one such as www.imageshack.us
    You might know most of this but it never hurts to explain in detail :)...thx l8er

    -fire
     
  17. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    hi

    won't arcing occur when you throw the motor into reverse or vice versa? :)
     
  18. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    hi

    a running motor usually develops EMF which adds to a current flow in the opposite direction which causes arcing in the relay contacts. hence the stop mode. :)
     
  19. Nettron

    Member

    Jan 22, 2005
    29
    0
    Yes arcing is inevitable but you can help cut down on it by adding a damper capacitor across the motor terminals, left that out in the schematic for clarity along with the reverse biased diodes across the relay coils.

    Ive used this same relay scheme in a motor control project via the parallel port a few years ago, actually heres the entire schematic for the project for those interested.


    [​IMG]

    But to cut down on circuit complexity ( and PC board realestate) it'd prolly be better to go with a commercially available H-bridge IC such as a LMD18200.
     
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