motor reversing

Discussion in 'General Electronics Chat' started by DROID, Feb 8, 2008.

  1. DROID

    Thread Starter New Member

    Feb 8, 2008
    5
    0
    Hi everyone.
    I've spent the last couple of days trying to design a simple circuit that will control a linear actuator - and failed miserably. The actuator is a powered by a six volt motor. The actator lifts and lowers one corner of a large perspex ball bearing maze (there will be four of these acting independantly). I would like a switch to activate up and down on each motor. The problems arise when the actators reach the end of their travel. I have fitted some limit switches so that when say the maze gets to its highest position it hits the limit switch and reverse the action of the operators switch (so up now becomes down). I have tryed to design a circuit using switches and relays, without success. Even if I could get this working there is still the problem of reversing the switch. Am I going about this all wrong, is there a simople solution I just can't see.
    Any help appreciated.
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Are the operator switches simple on/off, or are they directional? Single pole or double pole?
     
  3. DROID

    Thread Starter New Member

    Feb 8, 2008
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    I've tryed it with both types and have lots available.
     
  4. h.d

    Active Member

    Oct 22, 2007
    150
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    you can do it with double position limit switch
    in the N.O posithion the motor in FWD circuit
    in the complement the motor in BWD circuit
    if your motor is dc its easy to reverse by flip the source.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Hello Droid,

    The idea of having an actuator in each of the four corners is interesting, but will mean your project will require complex electronic controls. If the linear actuators are "out of sync" with each other even a little bit, there will be a great deal of twisting force applied to the maze and tension/compression forces on the actuator's mounts, tending to tear the structure apart.

    Your concept is actually used in aircraft simulators, where it is necessary to have movement in three or more axis. However, I suggest that for a marble maze, you only need pitch and roll. Moving the maze in the Z axis (up and down) may actually cause the marble to depart the maze surface. While possibly amusing, this would generally be considered undesireable.

    You could implement pitch/roll control by using a single actuator for pitch, and another for roll, if you mount your maze in a gimbal. While the mechanical structure may seem to be more complex, it will greatly simplify your control requirements, as the actuators for pitch and roll will have no effect on each other.

    Another thing to consider is how one actually gets the ball moving in a direction when manually manipulating such a maze. Generally, the maze is tilted for a brief period of time in order to get the ball rolling due to gravity, and then returned immediately to the level to stop the ball from continued acceleration. The ball continues on it's path due to inertia. To stop the ball, the maze is tilted briefly in the opposite direction, and then leveled.

    To duplicate such actions, you would need buttons to cause the actuator to move in or out, tilting the maze field, and when the buttons were released, to automatically return the maze field to level. This may not be as simple as it sounds, as DC motors usually don't immediately stop when power is removed.
     
  6. DROID

    Thread Starter New Member

    Feb 8, 2008
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    Thank you SgtWookie, lots of food for thought. I was originally contemplating attaching the actuators to each corner by some form of ball joint and as the actuators (based on a screw thread principle) don't spin terrible fast, I had not considered the ball lossing contact with the surface. The Maze idea came about as a practical way of trying to improve communication and team work skills in some of my Engineering pupils (14-16 yrs old). Four pupils one on each control.
    The maximum travel for the actuators is approximately 50mm (2") with the deck being 1000 by 1000mm. I figured that the base of each actuator leg would be a large round pad which could slide to a certain extent to limit the chances of structural damage.

    I'm sure your pitch and roll idea would work (for two students), but wouldn't I still have the problem of having to create some sort of limit switched reversing circuit to stop the turning actuator when it gets to the extent of its travel.

    Thanks for your patience.
     
  7. techroomt

    Senior Member

    May 19, 2004
    198
    1
    i would recommend initially designing a ladder logic circuit, using double pole relays for the (directional) control of each motor, such that you have rise in one relay position and fall in the other, and 6vdc removal when powered off. then put the travel limit switches, as well as any other control switches, in the rungs with the relay control.
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    Yes, you would still need to have a maximum travel limit - but rather than having the limit reverse the direction of the motor, it should simply open the circuit for continued travel in that direction, rather than striking the end of travel and having the motor stall.

    If striking the limit switch caused the reversal of the motor direction, it would result in oscillation back and fourth, which would likely be very hard on it.
     
  9. chuckey

    Well-Known Member

    Jun 4, 2007
    75
    10
    One way to go is to use a diode across each limit switch. The idea is that if it is the "up" end switch, hitting the switch, causes the diode to be switched in, so only a reverse voltage can power the motor else it stops. Needs a centre tapped PSU. Can't see why you want to reverse the controls.
    To reverse the controls and to stop the motor. Wire each limit switch to the coil of a relay with 2 DPC/O contacts. Use a third relay to actually control the "controls" direction. Choose to have this relay energised or de-energised for the controls direction. The two relays have one set of contacts for the motor feed. The other set of contacts are arranged in series so that if either relay de-energises (hit end stop) the controls relay changes its state. Hence controls changeover.
    Frank
     
  10. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    Ok, I've thrown together a couple of reasonably easy circuits to get you started.

    Have a look at the attached. Try experimenting with the first one before moving on to the next. If you don't have SPDT pushbuttons, you're going to need to use relays, which will require more wiring and complicate things.

    I'm just trying to keep things as simple as possible for the moment.

    Getting the maze to automatically return to center will add another couple of levels of complexity, so it's important that you get what these circuits do first, and make them work.
     
  11. DROID

    Thread Starter New Member

    Feb 8, 2008
    5
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    Thanks again SgtWookie (techroomt and Chuckey),

    SgtWookie - I understand how both circuits work. The second circuit seems to do everything I need and it's nice and simple too. Returning the actuators to the start or central position would be a nice touch but I cannot begin to think how to go about this!
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    Here's the last step - auto return to center. :)

    It took some noodling to get it worked out. :rolleyes: It was necessary to resort to the use of 3-pole double-throw relays to ensure that the motor would be able to move in either direction with auto-return, without having the possibility of any shorting of the supply to ground.

    It looks more complex at first glance than it actually is.

    If you can't find 3PDT relays readily available locally, this one should fit the bill:
    KUP-14D15-6
    http://catalog.tycoelectronics.com/TE/bin/TE.Connect?C=1&M=BYPN&TCPN=1-1393118-8&RQPN=KUP-14D15-6
    The coil is 6V, contacts rated @ 10A.
    Newark has them for $12.47 each:
    http://www.newark.com/24F2623/elect...POTTER-BRUMFIELD-KUP-14D15-6&_requestid=71046
    Allied is even cheaper @ $10.13 each:
    http://www.alliedelec.com/Search/Se...&Ntt=KUP-14D15-6&Source=&sid=47ACED006450617F
     
  13. DROID

    Thread Starter New Member

    Feb 8, 2008
    5
    0
    Cheers SgtWookie for your much appreciated help. Sorry It has taken so long to reply, but I've been on my Holidays and only just returned. I will try the new circuit over the next few days and let you know how it works on a mock-up. Thanks again
     
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