Hello guest, if you read this it means you are not registered. Click here to register in a few simple steps, you will enjoy all features of our Forum.
This forum uses cookies
This forum makes use of cookies to store your login information if you are registered, and your last visit if you are not. Cookies are small text documents stored on your computer; the cookies set by this forum can only be used on this website and pose no security risk. Cookies on this forum also track the specific topics you have read and when you last read them. Please confirm whether you accept or reject these cookies being set.

A cookie will be stored in your browser regardless of choice to prevent you being asked this question again. You will be able to change your cookie settings at any time using the link in the footer.

Thread Rating:
  • 3 Vote(s) - 5 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Heavy Lifters
#1
Hello, my name is Bob and I am from Sydney Australia. I started flying models in 1950, R/c in 1955, Started my own R/C equipment manufacturing company in 1963 (Silvertone Electronics), autonomous flying in 1995, FPV in 2000, sold Silvertone in 2013 and am now retired. Restless, so am currently building an own design compound transitional aircraft of a rather radical design. I am however running into problems with the quad FC and associated components and so I need help. Thus my reason for joining "IntoFPV".
[-] The following 6 users Like Keyboard Kid's post:
  • Drone0fPrey, Oscar, unseen, Tom BD Bad, Carl.Vegas, fftunes
Reply
Login to remove this ad | Register Here
#2
My main problem at the moment revolves around a lack of take-off power. My quad is an own design heavy lift quad (6kg) intended purely for take-off and landing the compound aircraft. No forward flight, no aerobatics. During the design stages I tested various motors and prop combinations and finally settled on Scorpion 3026/710 and APC 12 x 6SF props which delivered 2.1 kg or more of static thrust.
Thus in theory I should have at least 8kg total thrust.
However in preliminary testing I can only lift about 3kg.
So my question is where is the power going?
I realise that some power must be kept in reserve for inflight corrections but 5kg missing thrust is a bit much in my opinion.
Is there a setting somewhere that adjusts the amount of power available for take off?
Reply
#3
Oops!! I forgot to mention the most important point of all.

I know absolutely nothing about quad electronics. Or at least I did not until about two months ago when I began the steepest learning curve of all. Now I know almost nothing.
Reply
#4
(07-May-2017, 09:26 AM)Keyboard Kid Wrote: My main problem at the moment revolves around a lack of take-off power. My quad is an own design heavy lift quad (6kg) intended purely for take-off and landing the compound aircraft. No forward flight, no aerobatics. During the design stages I tested various motors and prop combinations and finally settled on Scorpion 3026/710 and APC 12 x 6SF props which delivered 2.1 kg or more of static thrust.
Thus in theory I should have at least 8kg total thrust.
However in preliminary testing I can only lift about 3kg.
So my question is where is the power going?
I realise that some power must be kept in reserve for inflight corrections but 5kg missing thrust is a bit much in my opinion.
Is there a setting somewhere that adjusts the amount of power available for take off?

Hi Bob and welcome to the forum!

If a static thrust test gives 2.1kg of thrust at full throttle, then the actual thrust at full throttle will be about 70% of that. The full throttle thrust isn't really relevant either. The thrust you are interested in is what will be developed at 50% throttle.

So, if your all up weight is 6kg, you need to have 1.5kg of thrust per motor at 50% throttle.
[-] The following 1 user Likes unseen's post:
  • Aniket kumar
Reply
#5
That's a pretty high pitched propeller for that application. It's likely loosing some energy to lot of turbulence (does the craft tend to wobble at hover?). If your craft can handle it, I would suggest something like a 14 x 4 or 14 x 4.7.

EDIT: Just took a look at the chart. 14 x 4.7 would probably be too small. However the high pitch to diameter ratio (6 to 12 in your case) might cause issues. Something closer to 1 to 3 would be better. Maybe a 15 x 6?
[-] The following 1 user Likes sloscotty's post:
  • unseen
Reply
#6
Thanks Unseen. I am now realising that I just simply did not have the knowledge to undertake my design.
The question is what do I do now to rectify the situation?
One obvious answer is to increase the battery voltage from 11.1V to 14.8V but the problem there is I have no room for that size battery.
Back to the drawing board I am afraid.
[-] The following 1 user Likes Keyboard Kid's post:
  • unseen
Reply
#7
"That's a pretty high pitched propeller for that application. It's likely loosing some energy to lot of turbulence (does the craft tend to wobble at hover?). If your craft can handle it, I would suggest something like a 14 x 4 or 14 x 4.7. "[quote='sloscotty' pid='21539' dateline='1494160727']

Hi Sloscotty, the quad flies very smoothly with no apparent wobble and it would appear with very little turbulence.
I can hover at two feet for extended periods in still air without setting up a down-wash vortex by using a little sideways movement from time to time.
One peculiar thing I noticed is that if I advance the throttle very slowly even to full throttle I cannot get off the ground, but if I rap the throttle to full it jumps off the ground easily.
I must admit I had a lot of trouble at the beginning (broken arms, broken props etc) until I started to get the hang of flying it and then I started to fine tune the PID settings after which it all settled down nicely.
So at the moment my only complaint is lack of lifting power.
[-] The following 1 user Likes Keyboard Kid's post:
  • sloscotty
Reply
#8
I added a bit to my post above. I still think one of the first things I would try is different propellers. The 13 x 4.7SF looks pretty good. You also might consider some of the triblades. I haven't flown one as large as yours, but I have a 10" that I experimented with a lot of different propellers and it can make a huge difference.
Reply
#9
Thanks everybody, those tips are very helpful.
But most encouraging of all were the prompt answers and just knowing that there are people out there willing to help.
Sadly I now realise that because the design was laid down with insufficient knowledge I face limitations on props size, battery size and weight which may call for physical changes to the aircraft.
Live and learn as they say!
It is now bed-time here in Sydney so I am off to bed and will not be back for the next 18 hours or so.
Thanks once again for the help.
[-] The following 2 users Like Keyboard Kid's post:
  • pips, sloscotty
Reply
#10
Sloscotty, I may be able to squeeze in 13 x 4.7SF props with a bit of surgery so I will give that a try first thing.
One thing I must stress is that my quad is unlike anything that you have every seen.
It is called "Wooden It" because it is made of heavy blocks of wood (mainly 2" x 1") and it is just simply a test bed for the motor/props and their lifting power. No effort was made to save weight because in the end I have to weight it up to 5.6kg. At the moment it weighs 3kg
The heavy wooden structure largely eliminates resonant vibration which I suspect contributes to the smooth  flight characteristic.
Now I am off to bed.
Reply
#11
I'm not convinced that 13x4.7 slow fly props will deliver the extra thrust needed at 3S to fly a 6kg AUW safely.

Those are impressive motors looking at the specs, very beefy and capable of tolerating up to 1kW of power!

The specs say the 12x6 props will give 2075g thrust at full throttle which is probably more like 1450g in reality. The 13x4.7 give 2194g, which is a minor improvement. Then again, none of this tells us much about what they'll do at 50% throttle, which is what really matters.

Realistically, 4S is going to be what gets you the thrust that you need. Out of interest, I'll see if eCalc has those motors listed and see what might work with an AUW of 6kg.

Bob, I'm puzzled by what you said about being able to go to 100% throttle without lifting off if you raise the throttle slowly. What flight controller and firmware are you using on this craft?
Reply
#12
(07-May-2017, 07:53 PM)unseen Wrote: ...
Bob, I'm puzzled by what you said about being able to go to 100% throttle without lifting off if you raise the throttle slowly. What flight controller and firmware are you using on this craft?

Was wondering too... now, the battery shouldn't sag that much, though it maybe could happen if it went into some sort of "invisible mid-throttle oscillations" ...
[-] The following 1 user Likes fftunes's post:
  • unseen
Reply
#13
OK, eCalc has the motors, so I configured a generic quad with an all up weight of 6000g and calculated a few scenarios.

As I suspected, eCalc says that even with the 13x4.7 SF props, 3S simply won't provide enough power to hover. Even 15x5 SF props would need 78% throttle just to hover and that's not really safe as there's not enough thrust left over to control the craft adequately.

Even with 4S and 15x5 props, you'd just scrape by with a hover needing 58% throttle.

If you absolutely can't use anything else than 3S, the smallest props that will get you in the air at under 60% throttle would be the MAS 16x8 triblades, but they would want 20A per motor just to hover and 70A at full throttle!

I'm afraid that once you get up to the 6kg class, lower kv, higher voltage and much larger props are the only things that will really do the job.

(07-May-2017, 08:07 PM)fftunes Wrote: Was wondering too... now, the battery shouldn't sag that much, though it maybe could happen if it went into some sort of "invisible mid-throttle oscillations" ...

Yeah, something isn't right there is it?
Reply
#14
hey there Bob, welcome to the forum.

I have no useful input for your problem and it looks like you got the pros on it already, I just wanted to send an extra welcome Smile
carl.vegas
Current Quads: Operational: Diatone GT2 200 In need of repair: Bumble Bee, tehStein,  Slightly modified Vortex 250 
[-] The following 1 user Likes Carl.Vegas's post:
  • unseen
Reply
#15
(07-May-2017, 08:21 PM)unseen Wrote: As I suspected, eCalc says that even with the 13x4.7 SF props, 3S simply won't provide enough power to hover. Even 15x5 SF props would need 78% throttle just to hover and that's not really safe as there's not enough thrust left over to control the craft adequately.

What does eCalc say bout the 12 x 6 SF that he's trying to use now?
Reply



Login to remove this ad | Register Here