X650F can't figure out prop/motor combo

[Markeaye]

Hello all, I have a problem on a new quad build that's driving me nuts. First let me give you the build specs so we can be on the same page.

Frame: HK X650F 550mm fiberglass and alum
Motors: Banggood A4008 380kv high torque pankake motors.
Props: APC style 11x4.5, 12x3.8, and 13x8, have tried all three
ESC: 30amp Simon K
Controller: APM 2.6 vers. 3.1.5 with Ublox Neo 6m GPS/compass, and 3dr telem
BATT: 5000mah 3s lipo
Radio Turnigy 9x with Turnigy 9x8c v2 receiver
Weight: about 3 1/2 to 4 lbs
I tried to be as careful as possible with this build, and tried to do everything by the book. All the programming was done with Mission Planner. All indications appear to be good, 3d sattilite lock, Mavlink hooks in fine, calibrated esc's with the radio, and has a smooth linear throttle, all props turning in the proper direction, and not mounted upside down.

The problem: At full throttle it won't lift off. Pitch it forward or back and it will tip over. Yaw left or right and I get a strong twist. It looks like it's taking out the spring in the carpet, but just won't come up off the floor. As you can see from my specs, I have tried three different kind of props, with no change, allthough the smaller ones won't tip it over with pitch control.

I had originaly ordered 620kv motors, but the supplier shipped 380kv's in error. I'm still fighting with them over this, but getting those in charge of the proverbial slow boat from China takes so long it's has gone beyond stupid.

I really think I'm just not getting the thrust form the slower motors, and the 620 kv's I wanted in the first place would resolve the problem. If anybody can suggest an alternative answer, I would appreciate it.

Help, if you can, Markeaye

 

[Motopreserve]

The simplest check would be to make sure the motors and the props are all spinning in the correct direction. I know it sounds crazy - bit you'd be surprised how often they get mixed up. Do this without props. Then make sure the props are on there correct.

I couldn't find your motors (even searching bang good) - do you know what the specs are??? Maybe a link?

 

[Markeaye]

Thanks Motopreserve, Yes I checked all that several times. I even tried changing it to a wrong configuration just to try to get a different effect, no joy. If I could get someone to run the numbers and apply a calculation out of one of the many confusing methods I have seen, using the spec info that I stated, that might help. It just seems to me that with the equipment I have, it should, at least, lift off. The motor link: http://www.banggood.com/buy/a4008-motor.html

Thanks, Markeaye

 

[Motopreserve]

Thanks Motopreserve, Yes I checked all that several times. I even tried changing it to a wrong configuration just to try to get a different effect, no joy. If I could get someone to run the numbers and apply a calculation out of one of the many confusing methods I have seen, using the spec info that I stated, that might help. It just seems to me that with the equipment I have, it should, at least, lift off. The motor link: http://www.banggood.com/buy/a4008-motor.html

Thanks, Markeaye

Unfortunately there is no way to do a calculation because these motors don't have any specs (thrust, amps, watts etc). And the motor doesn't seem to be in ecalc. - and my ecalc is not working for some reason anyway....

You may be having some issues with the low kv motors and the 3S battery???

 

[Markeaye]

Hey thanks again. The low kv was my original thought. With what info I could glean about the motors I did some calculations. The nearest I could come to it boils down to this. With the 3s lipo I'm looking at about 4500 rpm max, giving me a total on the 4 motors and 13in props of around 6 to 7 lbs of thrust. 620kv motors, same props, comes in at about 12 to 13 lbs. Shooting for 2 1/2 times the thrust for a given weight, it should make it proper. The worry is that just increasing RPM may not provide the solution, because the power curve is not even. Max thrust may be achieved somewhere before the max estimated 7000 rpm of the 620kv motor. My hope is that the target of 12 to 13 lbs will be at about 4800 to 5500rpm. This will get it off the ground, then maintain a hover at around 4500rpm. I'm not an engineer, but I'm going by the old rule of thumb that says 70% more current to get a motor running than to keep it running. Of course just going to a 4s lipo might do the trick as well. Increasing rpm simply by adding the extra 380 rpm per volt. However, APM trys to warn you off of anything over a 3s. I know it sounds like I'm talking out of my ***. That's because I'm guessing. In other words, shotgunning. If you throw enough money at it buying stuff that don't work, eventually you'll trip over somthing that does. I don't have that much money. Given that Banggood had sent me the 620kv's that I ordered in the first place, we wouldn't be having this conversation. I would just like some solid advice on how to procede from this point. I'm sure that any one of several avenues might solve the problem. The operative word being "might." I would like to make the right choice as to which avenue to take, and not spend my way down another dead end.

Thanks again for the brainstorming, any ideas are welcome,

Markeaye

 

[Motopreserve]

You need to figure out what your total weight is (AUW) exactly - and if possible find the thrust value of the motors. The difference of 1lb can be huge! There is no way to guesstimate the thrust - because motors that are seemingly similar can be very, very different. I think for now you just want to focus on the AUW and the thrust you can create. Forget RPM etc until you can determine what you need for thrust, and what those motors can provide. For sure, a quad that size (even though that frame is overly heavy (I had one!), motors with Kv that low are overkill. You would probably be needing to swing an 18" prop

Off the top of my head, I think your options are new motors (preferably ones with known data) or a new frame and massive props.

Is it true that APM tells you to avoid 4S? That seems very limiting to me.

 

[Markeaye]

Hi again, Thanks for hangin in there with all advice and suggestions. Well, I stayed up late and sent an irate email to Banggood about sending me new motors. I even included a picture of the box, motor, and shipping label, per their request. What good that will do for them, I couldn't begin to know. I did, however, tell them, in no uncertian words, that if they didn't ship me four 620kv motors by express rush delivery, at thier expense, of course, that I would file a claim with PayPal to get my money back. It has been almost 8 months since my original order. If they don't, That's what I'll do too.

Regardless of their response, I'm in the market for some new motors, four to be exact. Not from China. The only reason I ordered these was because they were only $22 bucks each. So let me know what ya got, and maybe we can do a little business.

There's a new hobby shop that recently opened up in Vegas, and after talking to one of their staff, it sounds like they want to be in the multirotor business. There isn't much here for quads and such. Some fixed wing and boats, but that's about it.

Anyway, I'll keep you informed about the people in the mysterious land of CheeNaw.

later, Markeaye

 

[Motopreserve]

Maybe I missed it - but did banggood ship you the wrong motors from what you ordered???? I'm afraid if you ordered 8 months ago you are out of luck with PayPal recourse. They have a time limit I believe.

Before you dive into another motor choice - make sure you calculate your exact AUW - soup to nuts. Add everything up so you can determine the best motor for your rig. Once you have that completed, I would suggest looking into SunnySky motors. BuddyRC sells them here in the states. For the money, they are probably the best quality of the "cheap" motors.

 

[Markeaye]

Dear Motopreserve, Well I think that Satan is competing in the singles ice skateing championships. After threatning to file a complaint with PayPal, Ebay, and anybody else that would listen, Banggood has shipped, 4(four) 620kv motors to replace the 380kv's. They really were scrambling, as they tried to say that I originaly ordered 380's. I went back and looked at their documrntation, on their website, and lo and behold, it clearly said my original order, back in February was, in fact, 620kv motors. I couldn't get them to come out and say rush delivery, but they said they are being shipped as fast as they could get them here. 7 to 20 days. checked the tracking number as well as I could, and Elvis has left their building.
I'll let you know how they work. By the way, any ideas on what I can build with 5 380kv motors. I still have an old KK vers. 1 board. I thought I might build a rock crawler for my son.

Markeaye

 

[Motopreserve]

With 380kv you can basically build a rig that will have to swing 18" props - or something crazy like that. Look for some kryptonite booms and you'll be all set.

seriously, you could look to build a quad with wide arms and swing a large prop. You'll have to see if you can get some spec for what type of lift you'll get. Maybe build trust tester and determine it yourself.

 

[arh60]

I think is the board orientation (apm) , AHRS_ORIENTATION. after change it has to be calibrated again left, right up down on its back,