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Auto mission with NicaDrone's EPM cargo gripper documentation

Posted by Andreas Jochum on August 3, 2016 at 1:00pm

OpenGrabEPMV3_2.jpg

Hello all,

Cargo pickup / drop off in auto mission documentation using NicaDrone's EPM V3 and Pixhawk running APM :D

The OpenGrab EPM v3 (from NicaDrone.com) is a small (less than 4cm x 4cm x 2cm) Electro Permanent Magnet gripper capable of 200N of force meaning it can hold about 15kg of cargo securely. The gripping and releasing of the cargo is accomplished by delivering a short pulse to an electromagnet which reverses it’s field. Objects that it grips onto should be metal or have the included attached to them.
The device accepts a standard PWM servo input or UAVCAN and uses a 5V power supply. Significant amounts of power are only required for about 1 second when it first grips or releases the cargo.

Tags: epm, uavcan
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Comments

  • Anthony September 5, 2016 at 12:48pm

    Actually it seems to work rather fine in Plane.  As you mentioned MAVLink and mission item commands both work and can drive the EPM using servo-related commands.  I think when you say "The EPM is currently only in Copter", you really mean "the DO_GRIPPER command is only in Copter".  But that is orthogonal :-)

    The only thing that's slowing me down at the moment is the following: http://diydrones.com/forum/topics/fetch-servo-pwm-values-with-mavlink.  Essentially the following code seems unreliable, sometimes it works, sometimes not, sometimes it leaves the EPM in the turn-off sequence, etc.

    msg = v.message_factory.command_long_encode(

        0, 0, mavutil.mavlink.MAV_CMD_DO_SET_SERVO, 0,

        10,  # servo number

        1100,  # PWM value -- low

        0, 0, 0, 0, 0)

    v.send_mavlink(msg)

    time.sleep(3)

    msg = v.message_factory.command_long_encode(

        0, 0, mavutil.mavlink.MAV_CMD_DO_SET_SERVO, 0,

        10,  # servo number

        1500,  # PWM value -- neutral

        0, 0, 0, 0, 0)

    v.send_mavlink(msg)

  • Andreas Jochum September 5, 2016 at 12:47am

    Oh exactly what I wanted to hear thank you Tom! 

  • Developer
    Tom Pittenger September 4, 2016 at 10:17pm

    The EPM is currently only in Copter but it seems trivial to add it to Plane. There's no switches type feature in plane so it would only be the MAVLink and mission items commands. Pull requests welcome!

  • Andreas Jochum September 4, 2016 at 9:00pm

    @Anthony,

    Lets have a Skype chat with Pavel tomorrow about plane support 

    The EPM is not powered from the servo rail when using just the UAVCAN connector from the Pixhawk. 

    There is no problem if you are powering the EPM from the servo rail.

    Clarification is in this pull request

    clarification by ctech4285 · Pull Request #540 · ArduPilot/ardupilot_wiki
  • Anthony September 3, 2016 at 4:03pm

    @Andreas Jochum

    @Tom Pittenger

    Actually two more things.

    The doc mentions Copter but what about Plane?  This is for a QuadPlane.

    Second, the page says the following:

    - When Vin of the EPM drops below 5V the EPM will go into low power mode. Slowing down switching to prevent crashing the power rail.
    - When Vin drops below 4.5V the green status LED will blink fast indicating an error condition.
    - The Pixhawk power rail voltage is < 5V.

    I'm confused as I'm pretty sure the servo rail could definitely deliver 5V.  And since I'm powering the EPM with the rail (with a BEC), does that mean it will always go into low power mode?

    Electro Permanent Magnet Gripper (OpenGrab EPM v3) — Copter documentation
  • Anthony August 26, 2016 at 5:00pm

    Thanks guys that was quick! :-)

  • Andreas Jochum August 26, 2016 at 9:52am

    Thank you Tom!

  • Developer
    Tom Pittenger August 26, 2016 at 9:39am
    Clarification merged!
  • Andreas Jochum August 26, 2016 at 9:29am

    Hello Anthony,

    That is correct. The problem is that the voltage on the UAVCAN port drops below 5V @1A. The EPM will still work but it will go into low power mode reducing current consumption to <500mA and run very slowly. 

    The modified APM is only required if you are going to use UAVCAN and all the changes are in master 

    Clarification on this is in pull request #529 

    https://github.com/ArduPilot/ardupilot_wiki/pull/529/files

    EPM firmware update clarification by ctech4285 · Pull Request #529 · ArduPilot/ardupilot_wiki
  • Anthony August 26, 2016 at 12:38am

    @Andreas Jochum
    @Hugues

    Very nice! What's the recommended way to plug it in? Do I understand correctly that there are two "right" ways: a) UAVCAN to Pixhawk + external power source, or b) PWN to Pixhawk (and then make sure the servo rail is powered with a BEC) ?

    Also, do you still need to run a modified APM as stated here?
    http://ardupilot.org/copter/docs/common-electro-permanent-magnet-V3...

    Electro Permanent Magnet Gripper (OpenGrab EPM v3) — Copter documentation
This reply was deleted.