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
Comments
Does anyone know about an update to Brad Hugheys project constructing and testing his homebuilt multicopter 3 years ago 8/10/11? I would love to know about any further progress on his project. Is there another thread on this site to do with manned multicopters? Thanks for any help, Bill Costello, Annapolis
Ban of what! Banning it's testing in a public place is the likely outcome. Nothing wrong with building it. Lets not give the legislators at the FAA too much ammunition. They have us on the back foot already.
Just imagine if a police patrol car was passing at that time. Headline news and another step towards a total ban. Bad enough with the Hollywood scenario.
If you are gonna do that stuff. do it where no body can see it.
Small step for the man, a giant leap for the mankind !!!!
Well, fellow flight enthusiasts, I think this thread has run its course and I'm going to pull the video down. The next one you see will be a successful flight with hovering and maybe some maneuvering. Thanks to everyone for their support, particularly the APM/Mission Planner developers, upon whose metaphorical shoulders I shall be standing while hovering (this ground effect pressure bubble is much akin to standing on a beach ball). A very special shout-out thank you to fellow forum member Ole Moyer, who has been extremely helpful in redesigning the MOSFET power stages for the thrust units. And thank you Chris Anderson for spearheading this awesomely unique open-source control system.
@Denny Rowland: Here is a link to a copy of the Bell 412 official flight manual.
http://www.bellcustomer.com/files/Storage/412-FM-2_Rev_10.pdf
On page 1-12 is the height-velocity curve, and yes, it shows that the 412 has good recovery performance below 16 feet due to the high inertia blades and the advantages of ground effect. But the AVOID area of the curve starts at anything above 16 feet and out to an IAS of 40 knots. There is a reason Bell wants you to AVOID operation in that area. In fact, there have been experimental copters with very high inertia blades do some incredible things with stored energy, but they were never certified for production because of the other severe danger they represented - a very long, ponderous recovery from a low disk RPM condition.
Of course there are hundreds of model-scale multicopters out there, which is why I didn't bother building yet another one. The aerodynamic advantages of overlap are proven at a full-scale every time a CH-47 takes off, and verified in the lab by Dr. Leishman et.al. at the University of Maryland.
All helicopters have a safety curve known as deadmans curve however the Robo R22 has a very marginal one unlike the 44. Something like a 412 can autorotate, land and then take off again and fly for 100 feet and land again. I would check this out. Minsoo Kim has a ten rotor device that actually works. No overlap, just sound aerodynamics.
http://www.kkmulticopter.kr/index.html?modea=vieweng&mc_selecte...
@All, For the Record: This is not a helicopter. It has things that spin and make it go up, but the similarity ends there. The eCopter thrust unit blades are lightweight (the lighter, the better for control responsiveness) and when they strike something, they are designed to shatter and scrub off their energy very quickly. Notice the ones in the video striking the frame, which is made out of soft 6063 alloy aluminum channel - the blades disintegrated.
This is diametrically opposed to the rationale behind propellers and conventional rotors which are beefy as hell and made to hit things like birds and keep on going. In addition, conventional helicopter blades are made heavy on purpose because it is assumed that autorotation (and the blade momentum to give the pilot time to dump collective pitch) is the hope for salvation in case of an engine failure. A ship's "height velocity curve" aka "deadman's curve" is parochial helicopter aviation's dirty little secret. Just about every commercially-made chopper operating at an altitude of less than 300 feet and slower than 30 knots forward speed will splat like a pigeon dropping if the engine chokes. Every skycrane driver knows this for a fact. Also a fact - the Robinson R-22 pilot's manual doesn't recommend leaving ground effect (20 feet high or so) until moving at an airspeed of 50 knots. In other words, autorotation recovery is a myth in the typical flight envelopes that make helicopters the most useful. Ah, but I digress...
@Edward Strickland: No, it's nothing at all like a gyrocopter. The thrust and lift vectors go in the same direction, as opposed to a gyro where the thrust line is perpendicular and (typically) below the lifting plain. The thrust lines converge above.
If these are anything like gyrocopters in their stability, lowering the CogG will make it more unstable. Can I ask if the thrust lines converge above, below or not all?
I remember once seeing a model heli shed a main rotor during hover trails. It penetrated a car door as it came to rest twenty feet away. Apart from a full power inverted acceleration into culmula granite I wonder what else could have gone wrong.
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