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(EPM) Electro Permanent Magnet Gripper V2.X
The EPM688-V2.X is an Electro Permanent Magnet, combining the advantages of electro and permanent magnets.
This Device comes with integrated electronics that can be operated with 5V PWM signal common on RC electronics.
The device is designed to hold 1kg of cargo. It is the user’s responsibility to verify that this can be achieved in each
Supported are RC PWM and CanBus with the CanAerospace daughter card. The EPM has an onboard PIC12F MCU with an in circuit programming header to allow easy reflashing.
Even lower power consumption; 400mA for 400ms at 5V per cycle or 800mJ.
On board tactile push button: Allows toggle testing the EPM on/off having only the power connected
Cycle time: The Cycle time is 400ms or 2.5Htz. This solves the problem when the EPM is turned on and the target does not make perfect contact, the majority of the energy is used to move the target into place rather than realign the magnetic domains, resulting in a much reduced holding force. With the fast cycle time one can turn the EPM on a few times in a row to make sure proper contact has been made.
Full bridge Thyrisotor drive circuit increases efficiency and reduces capacitor size .
Reduced magnetic interference allows mounting within 5cm of a magnetometer (please test it with your application)
Lighter- mass has been reduced to 47grams
Links / resources:
Git repository for Parts Drawing PCB Masks Pic12F source code
Shematics and PCB files
User Group (Help)
What is an electro permanent magnet?
- The Electro Permanent Magnet gripper safely holds on to a cargo payload using permanent magnets without consuming power.
- The EPM releases that load when desired by delivering a short pulse to an electro-magnet accomplishing short term field reversal.
- The safe cargo payload for a multicopter EPM is normally up to about 1kg with the magnets actually providing 7kg holding power.
- An appropriate iron or steel plate needs to be incorporated into the top of the cargo payload.
- The EPM Cargo gripper EPM-688-5 V2.X from http://NicaDrone.com is now supported by APM:Copter release.
- Check out this paper by Ara Nerses Knaian -: http://opengrab.googlecode.com/files/Electropermanent_Magnets_Knaia…
How to setup Manual RC control:
Seems to be broken on APM:Copter as of Feb 27 2014
Set RCXX_FUNCTION (i.e. RC6_FUNCTION) parameter
|RC6_FUNCTION to 1:RCpassthuw
Now setup your RC control to produce 3 PWM singals on the selected APM RC input;
1150ms for off,
1500ms for do nothing
1925ms for on
How to setup manual control RC receiver
Connect the EPM directly to the RC receiver and setup a 3 position switch or anything that produces 3 different PWM signals on the RC transmitter and your done!
1150ms for off,
1500ms for do nothing
1925ms for on
How To Setup A Mission:
The traditional way to control a PWM output only works as part of a mission (i.e. AUTO mode). Follow these instructions:
- Connect your APM to the mission planner
- On the Config/Tuning > Full Parameter List page, ensure that the RCXX_FUNCTION is set to zero for the servo (i.e. RC10_FUNCTION if the servo is connected to A10 on the left side of the APM).
- Press the Write Params button
- Create the mission you wish to fly and add a DO_SET_SERVO command and include the servo number (i.e. “10″) in the “Ser No” field and the PWM value, keep in mind if you constantly give the on command it will constantly turn on.1150ms for off,1500ms for do nothing1925ms for on
Note that the DO_SET_SERVO command is a “do command” meaning that it can only be run between waypoints so it must not be the first or last command in the mission. It will be executed immediately after the waypoint that precedes it.
On the Mission Planner’s Flight Data screen, there is a Servo tab that will allow servos to be moved in future versions of APM:Copter, Plane and Rover but it is currently not functioning.
Electrical Setup General:
- Magnetic interference has been reduced and mounting it with a minimum distance of 10cm of the magnetometer works fine. Mounting it closer is only recommended after testing magfield: Mission Planner->tuning->magfield->turn EPM on and off: Deviations over 30% interference (if it’s sustained) will make vehicles start circling but 10% should be fine.
- Current draw is 600mA with sharp rise, do not connect it to the analog output rail of the APM2, connect directly to the main 5V power rail and make sure the BEC can keep VCC stable to avoid brownouts. There is a 400mV drop in VCC when using the 20A 3DRobotics ECS on-board BEC
- When using a separate BEC or power source connect the ground to the PWM source ground.
Electrical Setup RC Receiver:
Cable Color codes:
- Yellow: PWM
- Black: Ground/Gnd/Negative
- Red: VCC/Positive
Electrical Setup APM aux channel (Mission Control / RC Pass-thru)
Servo outputs from RC5-RC8 can be used if they are available or AN10 or AN11. Note If that the power supply of the EPM is connect to the main servo rail and not to the AN power rail. Again make sure that the BEC can supply adequate power to avoid brownouts.
- The EPM688-V@ is designed to hold a cargo of 1kg securely and switch on and off effectively with low power consumption. 600mA at 5V for 400mS or 1200mJ per cycle.
- The on board bush button allows toggling between on and off..
- When PWM signal of >1750ms is supplied the EPM will switch on and keep switching on every 400mS (V2.05 or lower)
- When PWM signal of >1750ms is supplied the EPM will switch on a minimum of 3 times to ensure proper contact with target and keep switching on as long as the PWM is >1750ms (V2.06 or higher)
- When a neutral PWM between 1250 and 1750ms is supplied the EPM does not do anything
- When a off PWM <1250 is supplied the EPM will switch off and keep switching off every 400ms so long as the PWM is <1250
- The on board LED will blink rapidly 4 times when a switching cycle is being excecuded
The on board LED will blink once ever few second if no PWM signal is detected