New Build With New Builder

[TheMuffinMan]

Morning Guys

Today I'm here for some help with my first build. It's a tricopter with kk2.1, 750kv motors from David's build on a anycopter frame, wooden booms same as David's length and thickness , with 2 30amp Simonk esc and one multistar 30amp esc, a metal gear turnigy servo, and a traxxas 6400mah battery (yes it's big battery). I flashed the kk2 twice. Once with steveis 1.9S ( had a 2s flight time) and it's currently at Steve's 1.7pro (no flight). So it's been a month and I still can't get her up, It's was a long list of problems. All escs flashed to the kk2.(currently) I put my values at hallstudios and at full throttle just the tail would lift same for rc explorer settings, aswell as stock, even starting at zero and trying to dial them at full throttle no lift. I'm aware that I should be hovering at half throttle. (Previously) with these settings
http://youtu.be/jHN3FJBcFKc
With link roll pitch I could not lift but when it was off I had 2 seconds of flight time. I don't know what else to do I've read and tried so many things, I can't even remember the beginning.

 

[Craftydan]

hmmm . . . looks like you may have hit the high points, but something is still lurking in the details . . .

First obvious thing is the mis-matched ESCs -- they *might* be fine, but it's best to avoid a mismatch where you can. I'm assuming the Multistar is on the tail . . . have you tried moving it to other positions to see if it's the reason the tail isn't lifting?

Also a little more info might help -- prop size, setup pictures, video. These can sometimes show off that last detail that's hard to see if you don't recognize it, but hard to miss after you've built a few.

 

[TheMuffinMan]

Oh yeah I'm not to keen on mismatch esc myself but I cut the power on two of the multistar and can't get them to work even when I solder them back, yes the third is on the tail and when the new esc's came this Monday when I plugged them in I got this HUGE white smoke I almost thought that was the end for me, pics I'll have when I get home, props are 9"x4.6(or5) can't remember. For my receiver test there all at zero as we'll.

 

[TheMuffinMan]

Here's a vid http://youtu.be/tR1gmljRXCQ

 

[Cyberdactyl]

Those props are painfully small trying to lift a 6400mAh battery with 750's. I'll assume it's 3S. If it's 4S, it's almost over the top heavy.

 

[Craftydan]

I agree on the 9's -- I run 1200kv motors with 9's and they hover fine just below 1/2 throttle . . . but your motors are spinning nearly half as slow at full throttle and between the battery and motors, your airframe is at least 50% heavier than mine. You really should be looking at an 11-12" prop with a low pitch.

I'd also say when you've compressed the "hover" throttle toward one end (the top, in your case), there isn't much range left for the contorl board to keep the platform stable. I'd expect trouble getting airborne *and* trouble staying there.

Man! That's a shame about the fried ESC -- I hate it when that happens! Did you get the polarity backwards? (I've done that too many times, myself)

 

[TheMuffinMan]

Yeah 3s it weighs 625g but with each motor push 900 for total of 2700g the battery is heavy, and I didn't get them wrong just instant smoke. Okay so bigger props but if I turn off link pitch and roll if I go half throttle on elevator the front lifts almost instantly, just yesterday I accidentally reversed throttle while armed and it lifted just before crashing

 

[Craftydan]

Actually on an APC 12x3.8, it can push over 1500g/motor at Wide Open Throttle (WOT) . . . but you won't get anywhere near 900g at WOT on a 9x4.7.

http://www.rcgroups.com/forums/showthread.php?t=1708731

you're much closer to 700g/motor (assuming you're using APC -- cheaper props won't even do this). Frankly, to hold a 2:1 thrust/weight ratio, that means the All-Up-Weight(AUW), including the battery, would need to stay under 1050g -- kinda hard to do with a wood frame, DT750's and even an average sized battery.

With that battery and those props, it's beyond borderline.

Step up to some nice 12x3.8's and you should be able to have good flights with nearly 2300g AUW . . . or back off to 11x4.7's and keep your weight under 1860g.

 

[TheMuffinMan]

I have a question: when lifting off should I only need input from the throttle alone? Or is there more to it?

 

[TheMuffinMan]

You guys been great help so far, so I now need bigger props, and how did you figure out that ratio? Everyone please be advised I will try to pick your brain. Lol

 

[Craftydan]

We're like a Zombie buffet here . . . though some days it's just a dieter's special

Takeoff should be mostly throttle. On a dialed in frame, I launch by giving it a burst to about 3/4, then immediatly back to near half to catch it about 3-6" up. A touch on pitch/roll/yaw isn't uncommon, but more than a touch points to other problems.

The ratio is simple: total thrust/total weight. For the thrust, I add the thrust from each motor (3*1530g = 4,590g). 2:1 is a good ratio for multirotors -- It's a must, IMO, for quads, and higher is still great, but you don't want to go much lower for any multirotor. That means target weight = total thrust/target ratio (2:1 = 2/1 = 2, 4590g/2 = 2295g).

 

[Cyberdactyl]

I've found with a tri it's best to bump the throttle a bit. With my David W clone, mine tends to want to tip a bit if I baby it on take off. I'm not talking about slamming the throttle, but be a bit aggressive.

 

[TheMuffinMan]

Craftydani know you said 12x3.8 but what about 12x6 that's just the only thing I can get my hands on as of right now

 

[Craftydan]

Craftydani know you said 12x3.8 but what about 12x6 that's just the only thing I can get my hands on as of right now

understood, but I'd avoid them for two reasons:

- the 12x6 is WAY overpropped: if you look at the link I posted earlier, the DT750 w/ 12x3.8s top out above the rated 18A current at WOT. This isn't that bad, as long as you're sticking to the 2:1 ratio you won't go past that for more than short bursts, but . . . a 12x6 prop will require nearly 60% more power to swing . . . and you're already likely running your motors hot.

- the 12x6 is inefficient for multis: the second number -- the pitch -- is how fast fresh air needs to be fed into the prop for it to run efficiently, in inches/revolution (the typical way to look at it, how far the prop needs to move forward in one revolution to not eat it's own turbulance). How fast does the prop move upward in a hover? yeah, higher pitch works against multirotors.

It is an odd size . . . though 11x4.7-ish shouldn't be. A 12x4.5 should also be comon and good for Multirotor, but again, on the high side.

 

[TheMuffinMan]

okay good to know, okay I want to know what would be the best software to flash for my kk2 board and where can I download it

 

[Craftydan]

Google LazyZero and his flashtool should pop up -- It's hosted on his site in Germany.

 

[Cyberdactyl]

Here's a tutorial for location and flashing.

 

[TheMuffinMan]

Ok guys I did some number crunching and I estimate my weight to be 1400g to 1600g only because I can't account for the booms.i have the props on the way, but if I get a lighter battery it would put my weight to around 1200g could that be enough to lift her up with the prop I have now?

 

[Craftydan]

She won't be happy with three 9's lifting 1200g . . . but she should fly.

You'll be flying 1.75:1, so you should have headroom to control the craft, but she'll ride high on the throttle and might be a little extra droopy in a yaw.

 

[TheMuffinMan]

Oh I forgot to tell you on my kk2.1.5 m1 doesn't read the motor so m1 only has red and black and white is in m5 no matter what motor or esc m1 will not spool up. Would you guys know any reason why?