The EPM Cargo gripper EPM-688-5 V1.21  from http://NicaDrone.com is now supported by APM:Copter master branch.

Master branch != widely tested! Wait for the 3.2 release if you´re not comfortable with that.

This setup has only been tested by the author.  

All this is open source, check out the resource section at the bottom


What is an electro permanent magnet?

Check out this paper by Ara Nerses Knaian -: http://opengrab.googlecode.com/files/Electropermanent_Magnets_Knaian.pdf

Or watch the completed kickstarter project videos  that go over the working principle


Very cool eh? I thought so...


How to setup:

Get the code: http://dev.ardupilot.com/wiki/where-to-get-the-code/

Open APM_Config.h and un comment line number       35 so your left with

#define EPM_ENABLED           ENABLED             // enable epm cargo gripper costs 500bytes of flash

Build the code: http://dev.ardupilot.com/wiki/building-the-code/

Upload the code: http://dev.ardupilot.com/wiki/load-the-code-ontoapm2x/

Complicated ehh?? If we can justify using an extra 500bytes of flash we could include the code in 3.2 RC1 which is due to come out in a couple of weeks


Connect with Mission Planner

Go to Config/Tuning->Full Parameter List->Find: EPM

Set either Channel 7 or 8 to '19' "EPM", This will allow you to control the EPM with that channel from your RC or Joystick

Set EPM_Enabled to '1', This will enable the EPM

Restart the APM Mission Planner: ->Actions->Preflight Reboot->Do Action






Hardware setup:

Mount the EPM with a minimum distance of 10cm from the magnetometer, make sure to check out the section "Magnetic Interference".


Prepare the cable assembly

Cable Color codes:

Yellow: Signal S_on/S_off

Black: Ground/Gnd/Negative

Red:   VCC/Postivie

The EPM has two redundant Positive and Negative Pins, only one set needs to be connectedvkteLjs.jpg?width=350APM2_ARDUPLANE_analog_pinout.jpg?width=300

The Two Signal have to be connected to A7 And A8 on the APM2.X see APM2_analog_pinout as reference

The Analog output rail has power supply pins next  to the signal pins but it is not recomended to use these pins because the current draw of the EPM during it's 3 second charge cycle exceeds the capacity of what the APM can supply on these pins. You are probably going to blow the onboard fuse or cause random brown outs, creating a flying Schrödinger's Cat.

















Mount the EPM:


Connect the cables:




and we are ready to play- hahahaha





The EPM688-5 is designed to hold a cargo of 1kg securely and switch on and off effectively with low power consumption. 800mA at 5V for 3S or 3.4J per cycle.


Under the capacitor discharge condition pull either S_on or S_off high  Via RC channel 7 or 8 for 3 seconds and then low. The capacitor is fully charged and the device is ready to cycle. Pulling either S_on or S_off high via Via RC channal 7 or 8, causes the magnetic field to move either in the on or off state.




The complete device will have a mass of about 50 grams, and is capable of holding a mass of 7kg in optimal conditions, in practice it should securely hold 1kg of cargo on a quad.


Magnetic interference:

So the APM uses a compass that is sensitive to the surounding magnetic field. The EPM can produce a sizable field that can interfere with the compass when it is in its on state, without a target metal attached ,if mounted closer then 10cm. Please be carefull since this has not been widely tested.



Order The EPM: http://Nicadrone.com

EPM Cargo Gripper Datasheet: http://code.google.com/p/opengrab/wiki/Datasheet

Drawings of parts and models V1.X and 2.X: https://github.com/ctech4285/EPM

Schematics and gerbers: https://upverter.com/eda/#tool=schematic,designId=aee8e8e33e656dad

Ara Nerses Knaian paper: http://opengrab.googlecode.com/files/Electropermanent_Magnets_Knaian.pdf

Original Kickstarter Project: http://www.kickstarter.com/projects/412473553/opengrab-open-hardware-electro-permanent-cargo-gri





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  • A brief intro using it :-)

  • I just bought it to try it with my lady Pixhawk !
  • Theoretically with my mount the user won't have to worry about the 40 vs 45 thing - as long as they can take a 4 post mount under their craft it'll work.

    My design means they can reuse their gimbal mounts too; if I can find a secure but quick release bolt in M3, it'll mean "plug and play" payload swapability!
  • Ah nice,

    I would love to see some pictures!

    Hmm if i hear from more people that they like 45mm form factor I'll be happy to accommodate this.

    >Question is - if it comes with a 1mm silicon target square, can we order spares?

    Yeab, just added it http://nicadrone.com/index.php?id_product=15&controller=product

    If you like to add this to your order just order it and select "pick up in store" so you don't get charged for shipping again and I'll ship it out with your order

    Can't wait to see you do something cool with it!!!



  • I just ordered version 2 - with the PWM input ;-) At last I can build my commerical payload dropper!

    I have already designed a CF load carrier frame for this, complete with a mount for a downfacing pinhole FPV cam, and a 1400 lumen LED light, and space/mounts for the BEC(s). Payload size is aimed to be 2kg maximum, and I have geared it to SAR application. Will post some pictures once I get the cut CF back from China.

    The only grumble I had was that the 40mm form factor, rather than a 45x45. With a 45x45 my module can be retrofitted onto a lot of the common gimbal mounts which use this form factor. Instead, I needed to offset it a little and drill a 2nd set of holes for it.

    Actually, no, that's not the only grumble - the other grumble is the 8.4V requirement for the high power LED, which means another BEC to wire in.

    Question is - if it comes with a 1mm silicon target square, can we order spares?

  • There is a 1mm steel plate under the PCB, I did a lot of experiments and never been able to cause damage to the PCB

  • So, at a max payload of 7kgs... is all that weight supported by the mount attached to the pcb board?  Is there worry of the pcb breaking?

  • Thank you Ken!

    @Alex, you just need a metal target on your package. It comes with a 1mm silicon steel target square, you could also use transformer iron or most other ferromagnetic materials....

  • What kind of magnet do you have on the box?

  • @ctech4285, Really nice to hear:)! I hope you have great success with your project!

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