Links:
Description:
The OpenGrab EPM v3 is an electropermanent magnet, combining the advantages of electro and permanent magnets. The device creates a very strong magnetic contact with a ferrous target. It supports UAVCAN, RC PWM and push button operation. OpenGrab EPM v3 has been developed by NicaDrone in cooperation with Zubax Robotics.
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.
NicaDrone is announcing the 3rd generation of electro permanent magnet developed with Zubax Robotics with a bunch of new features.
First a crappy video:
The OpenGrab EPM v3 is an electropermanent magnet, combining the advantages of electro and permanent magnets. The device creates a very strong magnetic contact with a ferrous target. It supports UAVCAN, RC PWM and push button operation. OpenGrab EPM v3 has been developed by NicaDrone in cooperation with Zubax Robotics.
The NXP LPC11C24 MCU drives a mosfet connected to a transformer in a flyback configuration to charge the main PET capacitors up to 475 V.
A thyristor bridge is used to discharge the capacitor in either direction through the winding inside the AlNiCo material. This results in a short, 20 us 300 A pulse creating a 100 kAm field in the AlNiCo material. This causes the magnetic domains in the AlNiCo magnets to align in a particular orientation to form a magnetic circuit with a ferrous target.
An ON command results in the charging and discharging the capacitors 3 times to achieve full magnetization.
An OFF command results in charging and discharging the capacitors several times with changing direction and decreasing amplitude, effectively degaussing the AlNiCo material.
The diagrams below document the mechanical arrangement and dimensions (click to enlarge):
| Symbol | Parameter | Minimum | Typical | Maximum | Unit |
|---|---|---|---|---|---|
| Tcycle(ON) | Time to complete one cycle | 0.75 | s | ||
| Tcycle(OFF) | Time to complete one cycle | 1.2 | s | ||
| Fmax | Max holding force | 200 | N | ||
| Vsupply | Operating voltage | 4.75 | 5.0 | 5.5 | V |
| Isteady | Steady state current draw | 10 | mA | ||
| Ipeak | Peak current draw during cycle execution | 1000 | mA | ||
| m | Mass of the device | 65 | g | ||
| toperating | Operating temperature | -40 | +70 | °C | |
| RHoperating | Operating humidity (non-condensing) | 0 | 75 | % |
For debugging we recommend the Zubax DroneCode Probe, a multi-purpose debugger for STM32 and other Cortex-M based microcontrollers. It allows one to test and debug firmware on the microcontroller and is compatible with majority of IDEs (Eclipse and derivatives, CodeBlocks, etc.). Zubax DroneCode Probe is equipped with DroneCode-approved connectors which enables seamless compatibility with DroneCode projects such as Pixhawk and NicaDrones EPM V3.
We here at NicaDrone are testing out a new vacuum polyurethane conformal coating application method that should provide excellent water resistance for the GNSS and the Electro permanent magnet.
Here is the test video for the GNSS, the EPM test will happen over the next few days.
All Zubax GNSS are shipping with the enhanced conformal coating as of today.
TLDR: Zubax Gnss runs almost an hour completely submerged under water without losing GPS lock. Uart communication fails because of corrosion on the connectors. GNSS including barometer passes detailed testing procedure after being submerged.
Purchase (from Europa)
Purchase (from Americas)
Hello all,
we made some good progress and pushed out version 2.5, (actually it has been shipping for a few weeks)
The main change is that we only use Alnico magnets now and instead of magnetizing those fully in either direction go from full magnetization to completely demagnetize.
The advantage is a reduced air gab and shorter magnetic path length resulting in improved holding force.
It was a little tricky to find the ‘0’ point, or just how much of an external magnetic field needs to be applied to demagnetized the magnets but not more. Eventually we found a solution, magnetize them in alternative directions repeatedly while decreasing the amplitude of the field. This all happens in less than 1 second.
Git repository for Parts Drawing PCB Masks Pic12F source code
http://zubax.com/sites/default/files/zubax-gnss-bottom.jpg
