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Help! Tricopter flies well, but then suddenly loses control and crashes

thedoble

Junior Member
#1
Hi folks

I've been flying for a while and recently got into multirotors, built a tricopter to David's design, then made a few changes and now I am up to version 3 of my own take on David's tricopter.

It flies great and is the most stable and responsive tricopter I've built yet. However, I've had a problem in that the last two flights it has unexpectedly crashed.

I've put probably 5 batteries through the tricopter testing hovering, going up and down and general flight, with no problems. However when you fly FPV you do tend to fly further away! My suspicion is that my radio link is dropping out which is causing the crashes. I'd like to confirm this by checking with some experts here :)

The tricopter flies fine and then suddenly spins out of control.
In both crashes, I was at approx. 90 degrees to myself, eg:

---------------------
---------------------
-----me------Y-----
---------------------
(Y is the tricopter)

In both cases I think I am less than 250m away from myself, and with no obstacles.
I think this is relevant because my DX6i antenna points at 90 degrees.

Here is a video of the most recent crash - it was a fairly windy day but the tricopter seems to fly quite well until it suddenly crashes. Listening to the audio, the motors sound like they just switch off. As I was flying, once the tricopter had rolled over upside down, I killed the throttle so as to avoid flying into the road or some other obstacle. I'd rather have a crashed tricopter than someone hurt!


Currently I am using a DX6i with an OrangeRX R620 and Satellite receiver.
Motors are 888kv CarbonBird from MultiWiiCopter
Props are 9"x5 Triple Bladed Props from MultiWiiCopter
ESC's are 18A Turnigy Plush as recommended by David
Control board is a KK2 board running firmware 1.2 I believe
Battery is a 4S 3700mah

Here's a picture of my tricopter which shows the placement of the receiver. The FPV transmitter is on the rear tail boom.

photo(2).JPG

If anyone can give me some idea of if they think it is the OrangeRX receiver that is the problem, or if it could be something else that would be great, as I don't want to replace the receiver and then have to rebuild my tricopter for a third time!

Thanks for your help!
 
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Craftydan

Hostage Taker of Quads
Staff member
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#2
I agree, your description sounds like what that RX would do on a lockout.

What FPV freq are you using? How far back is the antenna? Linear or CP?

The crash in the video appeared to have the tail pointed at you, is this common to all your lockouts?
 

thedoble

Junior Member
#3
Hi Dan - thanks for your response

FPV Frequency is 5.8ghz, my radio is 2.4

The antenna is probably 20cm from the receiver, and 30cm from the satellite receiver.
Regarding Linear / CP - I think it's just linear? My FPV antennas are skew planar but the controller is just a di-pole antenna like this one .

Here's another photo of the tricopter before I mounted the gopro properly:

tricopter2.jpg

In the video the tail is actually aligned with me, as follows:

----------------------------
----------------------------
---------^--------------Y--
----------------------------

The 'up arrow' is the direction I was facing relative to the tricopter.
In the previous crash, the tricopter was at roughly the same position relative to me, however it was facing the other way (inverted Y)

Thanks
 
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Craftydan

Hostage Taker of Quads
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#4
hmmm . . .

Shoudln't have problems from the FPV rig so scratch that -- off frequency, out of polarization (by a little), and the RX wasn't in it's shadow during the crash.

Might be placement -- On closer inspection, your master RX's antenna is routed horizotally right next to ESC #2, and your satelite is also mounted horizontally. either would degrade performance, together it's a problem. It's likely you dont' have much range at all on the master antenna (try unplugging the satilite and do a range check at mid throttle -- props removed, of course), and when the satilite drops into it's null or the shadow of the motor, it stops hearing the transmitter as well.

Dont' have a silver-bullet fix for you, but three suggestions with minmum impact on the setup:

- remount the satilite to the front of the boom, not the top -- that will put the null in that dipole antenna's pattern directly down -- point your DX6i antenna skyward to match.

- move that coil of extra wire on that boom away from the satilite-- that's a big inductor with a strong AC current flowing through it, and you're satilite is almost right on top of it. best to remove it entirely, but moving it right up against the ESC will give you seperation -- hopefully enough to help. BTW wavelenght at 2.4g is ~12.5 cm. Anything in reach of that might interfere to some degree, but every CM farther away is a huge percentage of that -- small changes in distance can help a lot!

- move the master antenna away from those ESCs! don't nescisarily need to move the rx, but if you loosly tied off the antenna (with string! don't knot the wire!!!) to the base of the gopro mount, it would be away from the ESCs, mostly clear of the battery's shadow, and at enough angle that when you're in the satilite's antenna null, it should still have a clear view.

BTW, if your Gopro has WIFI, *TURN IT OFF*! It also transmits at 2.4 and has been known to step all over the control signals.
 

thedoble

Junior Member
#5
Great advice, thanks Dan, appreciate the time you've taken to outline those tips

As an aside, I did have the gopro wireless switched on ... will make a point of turning it off from now on.

I think I will make the changes you suggest, and will also look into some long-range gear, as I think I will be out-flying my 2.4 pretty easily based on what I've seen so far.

If anyone else would like to weigh in as well, I'm all ears!
 

thedoble

Junior Member
#6
One other thing - with regards to the satellite - do you mean stick it to the front of the boom, or rotate it so it is pointing downward?

Thanks again
 

Craftydan

Hostage Taker of Quads
Staff member
Moderator
Mentor
#7
no sweat, Thedoble

The Satilite's antenna should point down. If it's got two, angle them in a V shape with one pointed mostly up the other mostly down.

Dipole antennas (linear polarized, BTW) have a null looking down the lenght of the wire -- think of it this way, the more wire surface you see, the more RF that antenna can transmit in that direction. by orenting it vertically, the null is straight down, and shoudl have great visability all along the horizon. directly above, where a vertically orented satilite is weak, the master should have good visabiility.
 
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thedoble

Junior Member
#8
Great - thanks

Does that also mean that I should orient my transmitter's antenna directly up at 90 degrees? In theory then the null spot would be right above me ... which I shouldn't be flying in very often :)
 

Craftydan

Hostage Taker of Quads
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#9
Pretty much. Pont the TX antenna skyward, and it'll have good brodcast all along the horizon.

Also don't know about you, but when I go overhead I naturally tend to lean back as well, so the TX null leans back too -- probably won't happen in FPV as much as LOS, but even then, you'll have far greater range flying on the horizon at altitude than when you're overhead at altitude.

That, and your video antennas have the same vertical null . . .