3D Robotics

 

This may be the most amazing thing we've ever posted here. DIY Drones member Brad Hughey built an electric multicopter capable of carrying a person (him), and then actually tried to fly it in his driveway (without a helmet!). Let's just say it didn't end well. But he's figured out what went wrong and he's going to give it another go.

 

In an email to me, he explains:

History was indeed made on August 10th, 2011 when the Revelation PoC prototype crashed unceremoniously in my driveway.  It did briefly leave contact with the Earth, and one could argue that you have to fly in order to crash, but I do not have the audacity to declare a success out of this debacle.  A root cause analysis has determined that multiple Magically Obliterating Smoke and Fire Emitting Transistor (MOSFET) failures are to blame.  If you listen real closely, you can hear the power rail line inductance ringing (a bit of electronics levity).  I wasn't laughing at the time, but an important lesson is finally learned; MOSFETs fail shorted (full throttle).  One failure in the back started the pitch forward, then three in the front failed, catapulting me down the drive perilously close to a parked car, missing a rotor strike by mere inches.

 

The resolution isn't great due to the use of USB instead of FireWire to copy it off of the camcorder.  That said, I'd rather this didn't go "viral", as it is a bit embarrassing.  Such is the nature of invention.  I proffer it mainly as a veracity enhancer; this effort is real and very close to success.

 

It is interesting to note that half the array out of ground effect managed to push the whole craft with me in it dragging against the asphalt for almost 20 feet before I managed to shut everything off.  The power is certainly there.  It's all a matter of control now, and the first thing to do next is make the power MOSFET stage for each thrust unit "bullet-proof".

 

The damage isn't as bad as it looks.  The real work involves a total redesign of the power stage including FUSES for each thrust unit.  There are much better MOSFETs around now, considering this iteration is seven years old. 

New changes frantically being applied include:

  • Higher current and more modern MOSFET devices
  • A resistor-capacitor snubber network across every MOSFET to help mitigate ringing overvoltages
  • Transient voltage suppressors (zener diode-based technology) across every MOSFET
  • A complete rewiring to minimize power rail inductance
  • FUSES on each motor as a fail-safe
  • Larger decoupling capacitors on the outrigger thrust units

We're a couple weeks away from another run at it. 

Yours in Daring Invention Progress,

 

Brad

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Comments

  • I forgot to mention. Low KV and Very fine pitch is the way to go!

  • I think the first step would be to start making some motor prop. tests to see where you are with efficiency. Basically you need to absorb your available power into the largest swept area. Motor KV will tell you what RPM you should be aiming for. PID settings come well after that has been finalised and could be done with a simple balanced beam and a motor at each end. Once you have two motors working properly then move on. 

  • Yes, about that...

    Anyone have any suggestions about how to scale up the configuration settings for a much larger than normal application?

  • Need to adjust your PID settings :)

  • Ah, magic smoke. It's what makes electronics work, and once it comes out of the chips...

     

    You should check out the combat robotics community (www.robotcombat.com is a good supplier) for speed controllers. We push our controllers to the ragged edges (when someone claims their controller is bulletproof, they mean it -- literally!), and many of them have features like current limiting that might be useful. The ones you will probably want are the one-way weapon controllers.

     

    I'm a noob, but I would be concerned about that many points of failure on the device; what happens when you lose a motor at altitude? Especially if that has the possibility of triggering a cascade failure.

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  • good try but safety is first

  • The crash was a direct result of my cavalier disregard for the effects of power loop inductance.  I have already capitulated to using an APM system to do the actual piloting.  My creativity in that area is relegated to PID tuning now.  Experience trumps theory, so feedback or extrapolated "rules of thumb" for that are welcome.

  • I would also suggest talking with your local EAA chapter (if you haven't already) to learn how to conform to  FAA Part 103 rules and regs for your craft, insurance coverage, etc. They have a lot of practical experience and knowledge in that area.

  • Brad,

     

    My comment wasn't meant to disparage your piloting skills. The airframe looks light enough to meet Part 103 and those licensing requirements. Without the classic rotorcraft controls it could be much easier to fly, but hasn't been certified in any category yet. What I meant to convey was "cover your butt": it's got rotors, so to the FAA it's currently a rotorcraft. Had the damage been worse any insurance companies involved (medical, liability, your own or your neighbor's) would quickly drag you into court. Good luck with the project and be safe.

  • @Jan Detlefsen: A preferred embodiment would be a 12-rotor system.  The Revelation airframe is 7-years old, and the selection of >> 1 KW motors back then was very limited.  The ground certainly stopped having an effect after pitch up of more than 30 degrees or so.  Here's a link to the patent with associated background and embodiment descriptions. 

    http://tinyurl.com/eCopter-Patent

    All the APM can do is change the MOSFET gate PWM duty cycle (through the ESC translator).  If the MOSFET drain is shorted-circuited to the source, the gate signal is ignored (and often becomes shorted too, toasting the driver chip).

    @Kevin Breen: I am working diligently to insure that the prototype and the first production versions of the eCopter are FAR Part 103 (ultralight category) compliant.  Therefore, neither the operator nor the airframe would require any certifications, saving the FAA-type from having to form a material opinion on my qualifications.  :-P  That said, this doesn't have the classic cyclic-collective-tail rotor pitch controls of a standard helicopter, nor does it behave like a gyrocopter; eventually LSA or larger versions will likely need their own type category. 


    United States Patent: 7699260
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