About this project
Well this is it folks…on to the next stage. As this page will be frozen as of tomorrow here are our contacts: andreas´s e-mail is –ctech4285 at gmail dot com…anything to do with design/technical stuff goes to him…jeff´s email is –jeffniccca at gmail dot com…anything to with admin/shipping/payments etc. goes to him…luis´s email is-lmontoya.rk@gmail dot com..luis is our nicaraguan partner who has extensive business experience here and can help us navigate the sometimes aggravating bureaucratic hurdles..he will also be helping us with the funding for phase two. We have set up a google project page at code.google.com/p/opengrab/ ... you will find all the updates on the project there..we will try to keep it as current as possible but initially we´re going to be stretched pretty thin so bear with us.. As you may have seen from this site we´re still in the process or ordering parts and having some of the components fabricated…some of this stuff, for example the parts that are being laser cut like this one: part 1259 revision b are coming from China, they should be here four or five days after fabrication if we have no problems in customs. We are constantly reviewing the design to see if there are any improvements before committing to fabrication, but no radical changes so far. Here is the latest rendering of the open grabber:
Plug and play support for the R10 project is a done deal! go to http://www.kickstarter.com/projects/1101297082/r10-quadrotor-powerful-inexpensive-and-customizabl For other frames, send me a picture of the frame where you would like to mount it and i´ll see what can be done.
NICKEL PLATING FOR RECHARGING OPTION
Nickel plating contacts, pledge $7 more and you get plated contact so you can use your OpenGrab to recharge your quad. You can pass current from the 'cargo metal' to a plug on the board.
Envision for a moment a simple mechanism that enables a quadrocopter to pick up and drop a cargo such as building hardware like seen in the video below. http://youtu.be/JnkMyfQ5YfY?t=40s I stumbled upon this idea by reading this great article by Travis Deyle about electro-permanent magnets. These magnets are programmed (on off) with a current pulse. No static energy is required. Changing the magnetic field does require energy and is around 1 Joule for our purposes. These electro-permanent magnets are just as strong as Neodymium magnets. I am proposing to manufacture a simple open source hardware device to do just that, aiming at sub $50 retail released under something similar to the GPL. All prints and design files are available on request, and if there is enough interest i would move all documentation online. The target markets are hobbyists, students and the larger DIY community The device is simple enough to appeal to a large audience.
ELECTRO PERMANENT MAGNETS
What are Electro Permanent Magnets? Ara Nerses Knaian: "An electropermanent magnet is a solid-state device whose external magnetic field can be modulated by an electrical pulse. No electrical power is required to maintain the field, only to do mechanical work or to change the device's state." If you like to read more Ara Nerses Knaian has this really great paper available here on which i based this design. Hizook.com has kindly asked me to stop abusing their server, so here is the link to their article containing a link to the paper. http://www.hizook.com/blog/2010/12/07/electropermanent-magnets-programmable-magnets-zero-static-power-consumption-enable-s
Power consumption? About 1 Joules for switching, none in static state. About 40 Amps for less than a millisecond from the capacitor bank. Switching once per second would consume 1-2W of power taking ohmic losses into account. Switching: Switching the gripper on is done by aligning the poles of the Alnico magnet with the Neodyium magnet by discharging 1Joule into coil one via a 3V and 5V logic level compatible Mosfet (Solid state switch). The capacitor bank recharges via a charge resistor in about half a second at which time one can turn on Mosfet two to discharge the capacitor bank into coil 2 turning the gripper off. The capacitor bank provides a nice fail-safe feature; you won't be able to crash the power supply (battery on your quad) if for some reason a Mosfet is left on.
WEIGHT AND CAPACITY
The complete device will have a mass of about 50 grams capable of holding a mass of 10kg in optimal conditions, in practice it should securely hold 1kg of cargo on a quadrocopter
In order to keep the electronics simple two opposing windings are to be used with two Mosfets discharging a capacitor through either coil. A capacitor is not necessary if the power supply (battery) can handle a peak current of 40 amps.
Design principle verification: Done
Design characteristic selection: Done
Mechanical drawing: Done
Bill of materials: January 15th
PCB eagle files: January 15th
Supplier selection: January 15th
Risks and challenges
edit: there where concerns that the magnetic field cause interference with the compass on a 3dr APM board. it turns out it is a problem so magnetic shielding has to be added a minor increase in complexity.
edit: 12V will work verified with prototype
edit: Magnets available on the market do not require remagnetizing
Going from prototype to production problems may well arise. In this particular case 12 volts might not be enough to keep the capacitor size reasonable and a boost converter to raise the voltage to 36 volts might be necessary. Another problem might be that the Neodyim magnets is not magnetized to the correct level determined by the Alnico magnets and would have to be adjusted and this would add to the complexity of the production stage. Although I have a strong background in electronics I have made arrangements with a professional electronic engineer with over 20 years experience to consult on this project. As the project is being executed in Nicaragua design changes will result in greater than normal delays due to lack of technical and comercial infrastructure.Learn about accountability on Kickstarter
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