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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  • We now have a wiki page for the EPM Gripper as well.


  • @Ken, very nice, PWM is coming in the next revision, it will have a PIC12F on board and will come with PWM support source code is available on github

    @John thanks! no litecoin sorry,....will add it of course if enough people ask for it

  • Way too tool! I would like one. I see you take bitcoin!!! How about litecoin?

  • Really nice stuff:)! I really like that you can lift that much with only 50grams penalty.

    ctech4285, I have a couple of comment about PWM control if you make any revisions to the hardware or software in the future:).

    It would be really cool if PWM control could be added since it gives a couple of advantages in my mind:). One, no extra code would have to be added to the already very limited free space on the APM 2.5/2.6. We could simply use the camera trigger function which is fully supported on automatic missions. You simply add a trigger event to the mission specifying RC channel output and PWM value if I remember correctly. Second PWM support would make it work with all RC transmitters out of the box ( only with manual control). 

  • Yeah I should add the test results in the wiki page, thanks for the reminder

  • Developer

    Really cool!

    During testing it looked like putting the open gripper within 5cm of the compass would cause about 30% interference but at 10cm there was almost no interference.  So basically somewhere between 5cm ~ 10cm from the compass should be fine.

    It can't can't be triggered as part of a mission yet (i.e. it can only be triggered from the ch7/ch8 switch) but I suspect that'll get added before the AC3.2 release goes out.

  • Sorry Euan you can not, the EPM needs logic high/low not PWM signal that your RC receiver would generate..you could use a PWM relay type switch that works off your RC PWM...

  • Brilliant idea...i take it you can run this (signal only) off a spare RC channel if you want to, rather than through the APM? I think youre saying you can, but i thought id confirm.

  • Yeab very true you could increase payload quit a bit with a proper cradle....

  • I'd imagine you'd be able to hold more weight if you made a mount that prevented the package from rolling along the EPM's axis.  Look at how bombs and drop tanks are mounted on airplanes:  http://i1030.photobucket.com/albums/y363/Sandancermo/Sandancer_FMSV...

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