Inductive charging hack

After the LED hack we are back with an inductive charging hack!

The idea of charging Crazyflie inductively is almost as old as the copter itself. Last week we received a Palm Touchstone charging kit that we ordered. Like many phone hacks using this inductive charger we dismounted the receiving coil and electronic and attach it to the Crazyflie:

As the Crazyflie has a power-management circuit, any supplied voltage above ~4.5V will make it charge, and as we have made some soldering pads available for things like this it was a simple task. The coil is very thin and light (about 3g) so the flight performance are not affected a lot by the change. The charger is working very well and provides enough current for charging. We charge with a little less then 500mA and we think the Touchstone can supply up to 1A. One possible problem though is that the copter has to be placed exactly in the middle of the charging station to be able to charge. The phone has magnets to align it to the charge station and on top of that the charge station is not straight but tilted. The magnets are way to strong to let the Crazyflie take off so we are trying to find a landing area design that would permit the copter to land in the right spot and still be able to take off again without the magnets, any ideas?

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21 Responses to “Inductive charging hack”

  1. VR says:

    If the magnets are too strong, how about using an electromagnet on the Crazyflie? It would turn on and hold the copter in place while landing and turn off to allow for take off. Just an idea.

  2. EF says:

    Switcable electromagnet on the base so when the flyer stops drawing charging current it switches off and comes on ‘x’ seconds later to allow realignment
    Or make the base into a cone shape so the flyer’s landing gear will slip down the sides. Or make the bottom the other half of the cone.
    Same idea as the cone only a negative sloped valley the same shape as the flyer’s PCB.

  3. Richard Russell says:

    Wow, just had to shout out a huge thanks for posting info about this induction hack, less than $10 for dock and back plate, and looks like the coil and pcb is very easy to get at, so many projects I’ve wanted to add inductive charging to, super cheap hack!! Patiently awaiting the Crazyflie’s release!!!

  4. Connor says:

    Could you make a sort of a upside down half pyramid so that when you land gravity pulls the copter down and at the same time aligns it?

  5. tobias says:

    Thanks for the suggestions. We are also thinking about using the gravity to align the Crazyflie. We will try to make a bowl that will make it slide into the centre. The angle can’t be that steep though as the propellers wouldn’t clear but by applying a little thrust I think the vibration from the propellers will take care of that. Will come back with an update when we have done an actual test.

  6. DJ says:

    I think it’s a cool feature, but shouldn’t the normal version without inductive charching be finished first? :P Can’t wait to get my hands on one!

    • tobias says:

      Yep, I totally agree but there are some lead-times we are waiting for so we might as well do some fun stuff while we wait :-)

      • DJ says:

        True that… Ignore my message then! Do you have a deadline set for first shipping to testers/buyers?

        • tobias says:

          As the timetable looks now we will run a very small pre-series to test out the sourcing and production. It is estimated to take 6 weeks. If that turns out OK we will open for pre-ordering and the first batch should be ready 5-6 weeks after that. But again it is just estimates. We have been wrong many times before :-(

          • DJ says:

            Sounds good. So a test-sample could be on my doormat just before X-mas? ;-)

  7. Fabian says:

    an official addon section would be cool later so you can design moutable addons, like cameras, lights, or charging modules…
    maybe even combine them.

  8. Richard Russell says:

    Wow, that’s not much lead time 11-12 weeks for 2 cycles? Would love to send some money your way that soon!
    And with all that time, 6 weeks waiting on the first test run, plenty of time for R&D to go full UAV, right ;) lol
    I got to say, the induction hack is my favorite to date!
    I do have a question, unless I missed it in one of your post, how many grams payload can she effectively carry. I know you said the weight of the induction coil is 3g, does that include the pcb. I didn’t see a weight listed on the LED hack, but from the looks of it, I would think 15g+?
    As always patiently awaiting release / pre-order!!!

    • tobias says:

      Hi Richard!

      The coil and the PCB weights about 3-4g. I don’t have very accurate scale but it shouldn’t be to far off. The Crazyflie can carry at maximum 8-10g but then it can’t do much more then hover and fly slowly around. Keeping the weight below 4-5g is preferred to have better maneuverability and stability.

      And yes 12 weeks might be a bit optimistic but most of the engineering is done and it is mainly production related work left so it is not impossible :-).

  9. Norbert says:

    Nice hack, just reminded me of this one:
    http://www.youtube.com/watch?v=ee4Ab3w2hl8

  10. Stenny says:

    ‘The phone has magnets to align it to the charge station and on top of that the charge station is not straight but tilted.’

    Would it not be easier to level out the charging station and use the upside pyramid idea to centre it?

    Wicked project by the way :-)

  11. Thomas Howard says:

    So amazing! I fall in love with it ,I can not help doing another one. Could you share your Schematic with me?

  12. randomizer says:

    Nice hack :) If you go as far as the electromagnets, though, why not just make a contact charger instead of the induction one? It can use electromagnets to snap into place while it’s charging, and turn them off to undock. That might even work on a wall or a ceiling mount, which would be pretty awesome!

  13. Juhu says:

    Hi guys,Try to bypass the station on/off mechanism, so you can hover over it an charge. In this way, no land is needed.
    May be you also can use a mangnometer to gude te approach….

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