How to make/find a "pecking motion" arm

Discussion in 'The Projects Forum' started by Duckinabearsuit, May 14, 2014.

  1. Duckinabearsuit

    Thread Starter New Member

    May 14, 2014
    10
    0
    [​IMG]

    How can I make or buy a device like this?

    It needs to move up and down, anywhere from a 10 to 90 degree range... pause for a few seconds on the "up" before it goes back down.

    Is there a servo-like motor or something that already comes with such a programming?

    I want a "pecking" motion like a bird. I don't mind taking apart something that is already made to get to the electronics.

    Any ideas?



    Update : I found a little servo on ebay that sounds almost exactly what I'm looking for, but how do I make it pause for a few seconds before moving again?

    [​IMG]

    Item Description:
    - 9g Micro Servo for RC plane helicopter ,This product fits for RC helicopter and airplane.
    - Micro Servo 9g servo
    - Gear Type : All Nylon Gear
    - Dead Band Width : 2 usec
    - Stall Torque : 1.5kg/cm at 4.8V
    - Operation Voltage : 3.0 - 7.2Volts
    - Dimension : 23mm x 12mm x 29mm
    - Connector Wire Length : About 248mm
    - Operating Speed : 0.12sec / 60 degrees (4.8V no load)
    - Temperature Range : -30 to +60 Degree C

    It looks like it goes 60 degrees in .12 of a second, but I want it to pause, then move, then pause.
     
    Last edited: May 14, 2014
  2. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
    315
    First thought for simple is a synchronous gear motor.

    [​IMG]

    Use mechanical stops and a timer.

    If you need random stops (10-90) then the servo type you show is the only type I can think of. With programmable controller.

    Do you just need one?

    If you incorporate limit switches, a hobby servo can be driven without a special PWM circuit.
     
    Last edited: May 14, 2014
  3. Duckinabearsuit

    Thread Starter New Member

    May 14, 2014
    10
    0
    It only needs to move upward to a set position, not multiple degrees of stopping.

    For example, it moves upward and stops at 60 degrees.
    Then waits some amount of seconds before moving back down to "peck" a flat surface.

    I'm trying to avoid a controller, just a simple mechanism powered by a 5 volt supply.

    And yes, just one. I want to recreate exactly what is in that picture.

    Here is a video of it:
    http://youtu.be/Pxn9p_Yqg2U
     
  4. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
    315
    Can't tell from the video if there are two or three wires going to it. Or what the device on the end of the arm is.:confused:

    A simple control will require limit switches and a timer.

    A mercury switch from a Honeywell heat/cool thermostat mounted on the arm might work.:eek:

    See what ideas others come up with.

    I have some boards from a 20 year old project that moves a servo xx degrees and back with a spdt switch.
    It's not a difficult circuit to build.
     
  5. Duckinabearsuit

    Thread Starter New Member

    May 14, 2014
    10
    0
    Could you point me in the direction of a simple control like you recommend?

    It looks like if there is a control of some sort it's inside the servo.
     
  6. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
    315
    I'm betting not. Unless it's a special design servo.
    Have you looked for that exact device.

    For me, it's a simple servo drive circuit with two or three 555 timers.

    Are you up for an electronic circuit build?
    If yes, a servo guru on here (not me :D ) will design and simulate a circuit for you.


    http://www.555-timer-circuits.com/servo-tester.html
     
  7. Duckinabearsuit

    Thread Starter New Member

    May 14, 2014
    10
    0
    Thanks again for your tips and suggestions, I'm totally new to servos and such.

    You mentioned it might be a special design servo...
    It's just interesting that the servo in the video looks almost exactly like the servo I posted above from eBay. Not even any bigger. I wonder how they were able to get it to move like in the video... possibly without adding anything to the servo?

    I'd like to make this instead of buying it though.
     
  8. Duckinabearsuit

    Thread Starter New Member

    May 14, 2014
    10
    0
    I just read that you can use a 555 timer chip to make this move:
    [​IMG]

    Where would the chip be placed in relation to everthing else?
     
  9. ErnieHorning

    Member

    Apr 17, 2014
    67
    17
    It would help to know what your end objective is.

    Here's a video showing mechanical pecking that may spur your own idea's.
    http://www.youtube.com/watch?v=BT-DydUtkO8

    Instead of the string, a simple solenoid would do the job. A coil, with an iron core, attracting another iron part could work too.

    Just idea's.
     
  10. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
    315

    You need an external circuit.
    The three wires from motor connect to board.
    A dc supply connects to board,

    Circuit to move servo is only on 555 timer. The complete circuit will need at least one more to control off time and reverse.
     
  11. Duckinabearsuit

    Thread Starter New Member

    May 14, 2014
    10
    0
    Video: http://youtu.be/Pxn9p_Yqg2U
    The point of the "robot arm" in this video is to continuously tap the screen of an iPhone in order to prevent the phone from turning off (like sleep mode) without actually having to touch the phone with your finger every minute or so. You can walk away from your phone, allowing the game to continue on. It's like setting up a macro for a computer game to keep it doing something, cheating at the game basically ;)

    It is powered by USB and uses conductive foam on the tip of it to react with the touch screen of the iPhone.
     
  12. Duckinabearsuit

    Thread Starter New Member

    May 14, 2014
    10
    0
    Okay maybe this isn't the correct route with a 555 timer... it's like they built the little machine without a board since it powers straight from 5v USB.

    Like this, without the board:
    [​IMG]
     
  13. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
    315
    http://www.pc-control.co.uk/control/products/packs/servo-pack.php

    prices

    https://www.pc-control.co.uk/ocart/index.php?route=product/category&path=59

    All that is required to get the servo up and running under PC control are four AA
    size
    batteries. N
    o soldering
    is required. All you need to do is plug in the servo cable to the
    MotorBee
    , connect the battery pack to the screw terminals on the motor bee
    and then
    connect the MotorBee to a free USB port using the lead supplied

    3.3 Automatic Operation
    In manual mode above we have seen
    how each of the controls can be used to
    turn motors on and off and vary their speed and direction and also how to position a
    servo. This combination of on/off speeds and positions we call a configuration. To
    make automation more useful we need to be able
    to “program” a set of these
    configurations by specifying their duration and the order in which they occur. This is
    the function of automatic mode.
    This mode provides the user with a means to edit, save, restore and run a
    sequence of “configurations”
    that will be used to directly control the devices attached
    to the Motor
    -
    Bee adaptor board. This is known as Directed Sequencer Control. The
    sequence is made up of up to 10000 individual configurations or “steps”. The number
    of the current step being edite
    d is always shown in the “Step” box. Each step has all
    of the following elements
    -
    A duration (from 0.1sec up to 99hours)
    -
    A speed for each of the 4 motors
    -
    A direction for each motor (when only 2 motors used)
    -
    On/Off for each motor
    -
    Position of the servo (to ap
    prox 1 degree resolution)
    -
    A pattern of outputs (on or off for each of the 4 digital outputs)
    -
    The number of the next step to be executed
     
    Last edited: May 15, 2014
  14. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,004
    1,523
    For what you want it can be done purely mechanically, no electronics. Thes a mechanism called a "scotch yoke" that does this exact movement, a linear movement with a 'dwell' at both ends. And the motor just rotates in one direction, no start and stop. Have a look at this example - http://www.robives.com/blog/scotch_yoke_dwell_more_animations
     
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