Death of a Draganflyer, Watching a $1000+ helicopter crash from 200+ feet Options

[Old Man Mike]

One of my Draganflyer helicopters has fallen and can't get up:

Death of a Draganflyer

Here's a picture of the crumpled mess:



Actually, I don't think you can blame my flying. You can hear the motors drop once and then a second time just before it starts to go into freefall. I've seen this happen a few times before but it had always been for less than one second and then recovered.

The only good news here is that my homemade custom camera mount protected the video camera. It survived without a scratch.

Old Man Mike

[Rommel]

Next time you should try to use a parachute as backup. It was awesome outlook !

[Shred and Burn]

Oh the humanity !

[Nemesis]

LOL I love the way the camera bounces around and then ends up facing the grass.

You should bring one of those to my house and get a video of the mountains.

[M@ster of Dis@ster]

I sure sounds like the engine let you down, not your flying. Any warrantee on that thing?

[flatliner]

Gimme a minute...


OK I have a video on photobucket to share.. how do I do it..?



This post has been edited by flatliner: 06/23/07 9:13pm

[Cross of Iron]

Ouch....I feel sorry for you OMM

[Ouch]

Well that really suxs.

[T/A6Pak]

I think GIJoe has a little duct tape...LOL



Sending you some super glue Mike. I know how much time and effort you put into it, if you want me to put it back together for you send it to me in Canada. Nothing a little welding can't fix.

T/A6Pak:(

[Clint]

ouch that looks painful.


here's a possible root cause analysis:
On that first glitch, it sounded like only one motor was cutting out. you can hear the rpms drop, and to
compensate, it started to pull too much current and a few seconds later fried one of the gyros/main esc
board. one possible reason for failure could be that the camera was a bit heavy and caused the motors to
pull more current than normal. Also high altitude summer air(thin air) also pulls more current/heat to the
motor. The brushes on 370's dont last too long under heavy load at 11.1v, they can overheat easily and
cause the situation above.

the only way to protect against this is a separate fuse for each motor. A benefit of this on a regular r/c heli
is, if the main motor/fuse dies, you can still autorotate the heli back down safely. if the tail rotor dies you can
hit throttle hold, and use the collective to lower the pitch of the blades to bring it down. Unfortunately with a 4
rotor, it's still going to crash if any single motor dies, but at least the electrics wont fry.

Using a single fuse on main v+ will not detect an overload on any single motor; ie 3 motors can be using 2
amps each and the failing 4th motor could be pulling 8 amps and still not cause a 15amp fuse to blow since
the whole system is using 8+2+2+2=14amps. whereas the Mosfets are most likely 5amp continuous/7amp
peak, so this situation would fry a gryo/esc. A single fuse setup only protects the Lipo from overdraw(which is
good too).

you may be able to salvage the main board if it's not physiclly broken from the crash(peizo gryos
can be damaged on impact.) If it's just some blown mosfets, then resoldering on some new mosfets isnt too
hard..and you can probably find replacement chips at newark.com or digikey for a buck or two each.
a few high res pics of the main board and i might be able to help.

The draganflyer is a really unique heli, sad to see it down.

[Old Man Mike]

ouch that looks painful.


here's a possible root cause analysis:
On that first glitch, it sounded like only one motor was cutting out. you can hear the rpms drop, and to
compensate, it started to pull too much current and a few seconds later fried one of the gyros/main esc
board. one possible reason for failure could be that the camera was a bit heavy and caused the motors to
pull more current than normal. Also high altitude summer air(thin air) also pulls more current/heat to the
motor. The brushes on 370's dont last too long under heavy load at 11.1v, they can overheat easily and
cause the situation above.

Ah, a fellow engineer. Actually power to all four motors initially dropped for aprox 800 ms. I, as well as others, have seen this dropout occur for no apparent reason every now and then. There has been much discussion about this in the R/C universe forums so I won't go into details here. Normally the draganflyer recovers from this "glitch" without problems. During this flight you can hear and see that it did recover from the first dropout. A little later the dropout occured again but this time you can hear only one or two start back up before it went into a freefall. This was only a little over 2 min flight which is much shorter than the typical 8 to 10 min flights I do with the camera. All the motors were fine after the crash and I have flown them with a second controller board with no problems. These are the heavy duty motors design for greater payload lift than the standard Draganflyer.

the only way to protect against this is a separate fuse for each motor. A benefit of this on a regular r/c heli
is, if the main motor/fuse dies, you can still autorotate the heli back down safely. if the tail rotor dies you can
hit throttle hold, and use the collective to lower the pitch of the blades to bring it down. Unfortunately with a 4

rotor, it's still going to crash if any single motor dies, but at least the electrics wont fry.

Using a single fuse on main v+ will not detect an overload on any single motor; ie 3 motors can be using 2
amps each and the failing 4th motor could be pulling 8 amps and still not cause a 15amp fuse to blow since
the whole system is using 8+2+2+2=14amps. whereas the Mosfets are most likely 5amp continuous/7amp
peak, so this situation would fry a gryo/esc. A single fuse setup only protects the Lipo from overdraw(which is
good too).

I'm not sure why you think that a gyro could be fried since they are not involved in the high current path of the motors. The micro controller interfaces with the gyros and then controls the motors via the power MOSFETs. The power MOSFETs are LZ44NS which can acutally handle 33 Amps continuous and 47 Amps peak! Of course they are never stressed at that level in this design.

you may be able to salvage the main board if it's not physiclly broken from the crash(peizo gryos
can be damaged on impact.) If it's just some blown mosfets, then resoldering on some new mosfets isnt too
hard..and you can probably find replacement chips at newark.com or digikey for a buck or two each.
a few high res pics of the main board and i might be able to help.

The draganflyer is a really unique heli, sad to see it down.

Althought the four sensors used for the thermal intellegence (TI) were damaged beyond repair, I was able to get it flying in the non TI mode after about 4 hours of repair. So the mosfets are fine but unfortunately it does appear that the gyros are damaged since it was very unstable. Spectrolutions repairs the boards for a flat $55 fee so I'm just going to mail it back to them. My second draganflyer is flying well so things are not so bad.

It was a pleasure to see a response from someone with an electrical engineering background. Few R/C guys have that level of knowledge about their equipment. By the way, you can see some of the best videos and pictures I've taken with the Draganflyer as well as some of the other hobbies I'm involved with at:

Old Man Mike's Website


Eventually I will have a helicopter that will go to a designated position in the sky, hang in that spot for 5 mins taking video or pictures and then return back home using GPS. I should be involved only with the take off and landing.

Old Man Mike

[flatliner]

COME ON!!! TELL ME HOW TO POST A VIDEO!!!

i SYNC'ED THE OH THE HUMANITY AUDIO TO THE OMM VIDEO, IT IS HILARIOUS!!!

[Clint]

Ah, a fellow engineer. Actually power to all four motors initially dropped for aprox 800 ms. I, as well as others, have seen this dropout occur for no apparent reason every now and then. There has been much discussion about this in the R/C universe forums so I won't go into details here. ...

Wow, it's crazy to hear that it's a common occurrence. Since it's a hot topic, I wont dig into it, but in my
experiences, All-in-one boards can be a disaster waiting to happen. Having the RX circuitry in close proximity
to the high power leads....Maybe someone can recreate the glitch while probing around with a scope to get to the bottom of it.

I'm not sure why you think that a gyro could be fried since they are not involved in the high current path of the motors. The micro controller interfaces with the gyros and then controls the motors via the power MOSFETs. The power MOSFETs are LZ44NS which can acutally handle 33 Amps continuous and 47 Amps peak! Of course they are never stressed at that level in this design.

I normally work with separates, so when I saw the pic of the board having the gryo/esc/rx/bec all on one
unit, I just lop it together and call it a gyro/esc mainboard. I do know the power going to gyro and rx
components is regulated and the mosfets are part of the esc circuitry. My bad for referring to it as the gyro unit. Bad habit I guess for having owned helis with flaky 4in1 units.

When I see r/c's offered with the standard $10 motor, it usually means the mosfets are rated specifically for
that motor. When you spend $1000 on a setup, It's nice to know that they give you room to
grow. I really need to check out the specs in more details on the Draganflyer, the TI
mode sounds like something out of star wars or MIT.

$55 for a repair job is not bad at all. Considering you can drop about $120 on a replacement heading
hold gyro for a 200$ heli. Makes you think about the entry price/repair/maintenance costs of this hobby.
It all costs $1000's in the end. Just dont tell the wife.

Old Man Mike's Website


Eventually I will have a helicopter that will go to a designated position in the sky, hang in that spot for 5 mins taking video or pictures and then return back home using GPS. I should be involved only with the take off and landing.

Old Man Mike

Whoa, I'm sure I've been to that site before. I'm always searching for different nebula pics for my desktop.
There's too much city light in my area for anything other than looking at the moon, so I'm stuck with my
old tasco-at least it has an eqmount. Definitely jealous of your setup, it's amazing what you are able
to come up with after processing. Oh and GPS guided heli.. you are sick.