Kook needs help with motor size?

Discussion in 'General Electronics Chat' started by Mark Rountree, May 9, 2017.

  1. Mark Rountree

    Thread Starter Member

    May 9, 2017
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    Just joined up to ask a question. I have developed a machine that runs on a 18 volt cordless drill, its a prototype and need more motors for other actions but the main working motor will need the torque of a drill as above {18 volt}. I will need to be able to reverse this motor and have it timed accurately with the other motors to do the job then a robotic arm takes the product out of the machine. so there will be this motor and maybe 5 other smaller motors all in sequence. Im thinking stepper motors will be fine for the 5 easier operations but im stuck with the main power motor and was looking for any ideas or direction from people in the know, i want slow and powerfull for this motor. Also i want to get info on how to controll all these motors best. Will i need to learn some coding?

    Cheers

    Mark
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    For slow and powerful motor you need a motor with reduction gear.
    Look at automotive motors for possible solutions. Window motors and windshield wiper motors are good candidates.
    For smaller motors, look at mirror adjustment motors. Scrap yards are a good source for cheap parts.

    Yes, you will have to learn to code. Any type of robotics will need sensors, feedback, decision making and control.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    It appears you need a form of CNC positioning control, if using non stepper style motors, this requires accurate feedback from each motor, Robotics usually involves interpolated motion, then the (PID) design constraints are even higher.
    As to motor/GB size you will need to measure the approximate torque required at each axis.
    Max.
     
    Last edited: May 9, 2017
  4. Mark Rountree

    Thread Starter Member

    May 9, 2017
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    Brilliant, after working automotive for most my life, I didn't even click. Do you think I can mix a window motor and some other small steppers ? Then controlled all with an arduino?
     
  5. Bernard

    Expert

    Aug 7, 2008
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    All Electronics, plain & gear reduced DC motors, inc. window raisers like 12V, 3.8 A, 88 RPM. I use CAT# DCM 470, 6V DC 150 mA, 25 RPM.
    Surplus Center, wide selection of DC motors. I've been a customer since 1952.
    The Electronic Goldmine, DC motors, low on gear reduced motors.
     
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  6. Picbuster

    Well-Known Member

    Dec 2, 2013
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    Define:
    the max speed of your object to move.
    The max time/ distance to bring this mass to a halt.
    This will produce the power and torque needed.
    Now you have to find an engine able to do that.
    Next step is to convert the motor refs into the wanted movement.
    Gearbox ok but there will be a play on the gears.
    Belts no play and when teeth belts are used no slip.
    Stopping a gear down is also something to give attention to.
    Your whish to have a power full slow running motor calls for how power full and how slow?
    Picbuster
     
  7. MrChips

    Moderator

    Oct 2, 2009
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    Stepping motors do not have as much holding power as DC servo motors.
    I worked for a major German robotics company and all the motors used were DC servo motors. They require very complex S-curve velocity and PID control using DSP software,
     
  8. Mark Rountree

    Thread Starter Member

    May 9, 2017
    51
    4
    I think I'll do some homework on teeth belts and the cogs to hold them too. I don't know the torque but an18 volt cordless drill does the job at the moment,
     
  9. Mark Rountree

    Thread Starter Member

    May 9, 2017
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    4
    Will a servo motor have as much torque as an 18 volt cordless drill, and where is a good source for powerful used ones, just fired prototyping? Is a electric car window motor a servo? No obligation questions lol
     
  10. Mark Rountree

    Thread Starter Member

    May 9, 2017
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    Cheers mate, but I'm in new zealand
     
  11. MrChips

    Moderator

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    Window motors are not servo motors. Servo motor has closed-loop control, that is, it has a position encoder to relay information back to the controller. Window and wiper motors use simple limit switches to know when to stop.

    Cordless drill, window and wiper motors have reduction gear. This is where you get the increased torque with accompanying speed reduction.
     
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  12. MrChips

    Moderator

    Oct 2, 2009
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    For maximum holding power you want a motor with a worm gear.
    For a maximum torque, look at a 12V winch motor.

    Have you checked out Pick-A-Part?
     
  13. Mark Rountree

    Thread Starter Member

    May 9, 2017
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    Do you think the winch motor can be controlled with arduino ? At the same time the arduino is controlling steppers for a fairly accurate sequence
     
  14. MrChips

    Moderator

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    It really depends on your application. A stepper motor can be used with no position encoder (i.e. blind or open-loop control). However you have to ensure that the stepper never misses a step.

    For feedback, stepper or DC, you have to have position encoders (closed-loop control).

    Any motor can be controlled by an MCU such as Arduino. You need proper interface to the motor.
     
  15. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Your OP mentions 5 axis, this will be quite involved if using a 5 axis robotic unit.
    Typically robots have absolute encoders instead of the customary quadrature for position registration at switch on/off.
    upload_2017-5-10_20-28-47.jpeg
    Max.
     
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  16. MrChips

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    Good point. An alternative is to do a calibration on start-up where you seek to a home position, like they do on printers.
     
  17. MaxHeadRoom

    Expert

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    That is how the traditional CNC M/C registers home, but for some reason robotics has always tended to use absolute .
    Max.
     
  18. strantor

    AAC Fanatic!

    Oct 3, 2010
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    @Mark Rountree It is unclear to me if you are actually trying to build a 5-axis robotic arm, or something that works in conjunction with such an arm.

    If you are indeed trying to build an arm, you should know that this is a very complex operation. Read up on inverse kinematics to get an idea what you are getting into. The companies involved in making these arms commercially have invested millions to develop controls that work, and as far as I know, there is no open-source control that works. Maybe LinuxCNC can do it, but I am not sure (I doubt it). I will be very surprised if you can make an arduino do anything more than canned cycles that each have to be programmed from start to finish, which each axis programmed separately, to bypass the need for inverse kinematics - much fussing and trial/error involved in programming each cycle just right.
     
  19. MaxHeadRoom

    Expert

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    Many modern multi-axis robots are programmed using a 'Teach' unit or tablet, you jog the axis to each consecutive final position and hand or gripper function and press Enter, the program is then stored.
    So no programming in G code like most any other CNC M/C.
    Max.
     
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  20. MrChips

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    Correct.

    Simple pick-n-place demo of 5g objects using stepping motors salvaged from old computer disk drives is one thing.

    Moving payloads over 100g with any amount of precision and speed is another thing altogether.

    PID control for real world kinematic applications is extremely difficult and demanding. On top of that, you need to program for S-curve velocity profiles where you accelerate the movement from rest, maintain a constant speed, followed by deceleration at the ending point.

    A robot arm is multiply complicated because every time you strengthen one axis, the additional load means all underlying axes have to be strengthened to handle the increased load.

    It is like a spiraling positive feedback. You attempt to build a battery-powered mobile robot. You put a heavier motor on the robot and then you need bigger batteries. This in turn calls for an even bigger motor. The cycle continues.
     
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