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Quad "A" Tail Design Questions.

SGrog

New member
#1
Quad "A" Tail Design Questions (Design Log)

Hello all!

I am new to Multi-Rotors and RC Aviation in general, the most experience I have is with Microsoft Flight Sim (most of the time in Helicopters).

I am looking at doing a Quad design that is essentially a modified V tail. The foam board prototype I am developing currently is laid out like a Tri Copter with three booms, but the rear has a structure literally shaped like an "A" with both motors tilted 30 Deg and spaced such that they can accommodate up to 10" Props. I am intending to use it initially to learn on, and eventually outfit with FPV gear, and possibly a Multi-Rotor recovery system. I could have probably stated the previous in fewer words, but here is the build list:

Booms: 1/2" x 1/2" Balsa - Updated to 3/4" x 3/4" 1/8"walls Aluminum
Electronics Mount: 1/8" Polycarbonate with spacers.
FCB: Hobby King KK2.1
ESC: Turnigy Multistar 30 Amp Multi-rotor Brushless ESC 2-4S
Motors: NTM Prop Drive 28-30S 800KV / 300W Brushless Motor
Props: 10x4.5 SF Props 2pc Standard Rotation/2 pc RH Rotation (In both Florescent Yellow and Orange)
Battery: ZIPPY Flightmax 2200mAh 3S1P 25C (X-Thin)

If I may ask for opinions on the selection it would be greatly appreciated! My Biggest concerns are the ESC and what battery I should use.

Thank you!
 
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Cyberdactyl

Misfit Multirotor Monkey
#2
Your choices are good.

However, 1/2" square balsa may be a bit too weak. Balsa is amazing stuff for the strength/weight, but you might want to consider cheaper fir or poplar. Those woods are slightly heavier, but considerably stronger if you're using 1/2"x1/2".

Oh, and the battery can be a generic and cheap Turnigy 2200 3S 25C. When you're just learning, a couple 'average' batteries is all you need.
 
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SGrog

New member
#3
Thank you for the reply and suggestions.

Would it be beneficial in terms of battery life to use 8" props in front, and the 10" in the rear to account for the minor inefficiency of the motor angle? I'm hoping that I can use this frame with upgrades for many years to come! At least in the development phase, I found I had some torque issues with the design but have plans to strengthen the rear boom.

Is there anything else that I am missing or concerns people have?

The following picture is what I have Prototyped so far, with minor modifications.

IMG_00000563.jpg

Im hoping to keep this site as a build log for the copter.
 
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SGrog

New member
#4
Would I need to have a Power Distribution board? I have also heard that the NTM are good motors when their bearings dont fail, would it be best to order some replacement bearings and swap them out before flight?

Other than that, I am almost ready for acquisition! ~$150 for everything!
 

cranialrectosis

Faster than a speeding face plant!
Mentor
#5
The power distro board is optional. You need to distribute power from your battery to your ESCs but how you do so is up to you. You can buy a breakout cable, a power distro board or build your own to suit your unique needs.

I had problems with the distro board I bought and no longer use it. As a result, I no longer trust Chinese solder joints even on the ESCs and motors. Cold solder joints are common and they really suk to troubleshoot. I trust my own and I build my own breakout cables.

The distro board made it simpler for me to be airborne faster. 90 days later when it failed, I had to rebuild my copter and it took me a week to figure out the problem.

When you build your own, you can mod it to power lights and/or to split off to a lipo alarm. The HK distro board has one JST connector. If you want two you have to mod it anyway. I find that breakout cables are smaller and more flexible than a distro board and so I find them easier to hide.

Here is how to build:
http://www.youtube.com/watch?v=tB3_L7do2QU

Quad XT-60 Breakout from HK:
http://www.hobbyking.com/hobbyking/...ullet_Multistar_ESC_Power_Breakout_Cable.html
 
#6
Another option is aluminum for the arms. I have used them on all my builds and I like how they look as well. Cost is not much at all. Just use some fiberglass at all the connection points. I would assume if you are making it out of wood the parts will be glued which will make it hard to replace broken parts. These were made on my CNC machine but I have also used solid tubing which works just as good, also makes them stronger. Quadcopter Arms.jpg Quad frame.jpg
 
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xuzme720

Dedicated foam bender
Mentor
#7
I have also heard that the NTM are good motors when their bearings dont fail, would it be best to order some replacement bearings and swap them out before flight?
I use a good bearing lube on mine before first time flying them and I have not had one fail yet. Check them regularly and add more as needed.
 

Craftydan

Hostage Taker of Quads
Staff member
Moderator
Mentor
#8
Why replace good bearings?

They won't go bad without symptoms, and if you've got spares on hand, why not swap it out *after* they've gone bad.

I have had bearings on one go bad from abuse (It's also the position that breaks the most props -- I'm not easy on my motors :p ), but even then, the vibe, motor noise, and resistance steadily increased. I had plenty of warning before I pulled it for maintenance, and likely a few more flights before it seized.
 

xuzme720

Dedicated foam bender
Mentor
#9
I'd agree, Dan. In my case, I already have the lube and adding it as I open the motor package is cheap insurance. I think a lot of the seizing might be from abuse or negligence. The NTM's have been treating me right, fwiw.
 

jhitesma

Some guy in the desert
Mentor
#12
I haven't tried NTM's on a multi...but I've abused the snot out of the one I use on my bigger power pod for swappables and it's still running great. And I mean I've ABUSED it. Since I fly in the desert most crashes result in a motor packed full of sand at best. That motor I've even managed to "land" in a mud puddle which by the time I got it home had hardened to a cement like consistency. And it's still still doing great.

But to be totally fair it does seem that multis can dish out more abuse than FT swappables. I have two 24g 1300kv pods and both of them have seen the same kind of abuse as my NTM pod and are still going strong...one of them is starting to show signs of some issues but they still fly after almost 2 years of crashes. On the other hand since the beginning of Nov when I first got my quad in the air I've already managed to break windings on 4 24g motors and bend shafts on 3. I'm guessing it's the extra weight of the quad compared to the foamies because most of my quad crashes are much lower and slower than my foamie crashes :D
 

SGrog

New member
#13
Good points with the motors, why spend more then needed, when nothing is wrong with them. I will definitely pick up a lubricant for the motors. I have heard good things about the NTM's, and like that with the 10" x 4.5 props they have about 1.25 kg of lift, which I believe should be enough for future goals.

As for power distribution, I think I will end up making my own. I have soldered some and know they can survive a trip up to 110,000 feet and back. I would also like to incorporate a LiPo alarm, and Nav lights right into the breakout cable.

In terms of the frame, I am leaning towards the aluminum frame as I have worked a lot with aluminum in the past and am familiar with it. So I can hopefully save the motors during the inevitable crash, I will use zip ties to secure the motors.

Here is the design for the frame that I have settled on. It is tail heavy, but I hope to counteract that with the battery.
IMG_00000566.jpg
 

Fooman

Junior Member
#14
Fascinating idea with the A frame tail like that, have to see how it flies and if the board can compensate for (what is probably) a tail heavy condition like that.
Foo
 

SGrog

New member
#15
The tail is definitely heavy, but with the fork set up in the front arms, I hope to use the battery to counteract the tails weight. In the actual design, the front arms should both fold back upon impact. they are just glued here such that they can help me get measurements.

Another thing that will be interesting to see is if the material I will be using will be to heavy. Ill be using Aluminum as it is commonly available, and should be able to withstand the torque on the rear boom. But with the rigidity, I gain some weight. The wood available to me was to small to withstand much so I had to move to aluminum, but I already have the tools to work with it. For fastening, Ill be using rivets.

We will see how it works out!
 

SGrog

New member
#16
Another question I had was for the motors; As I understand it a lower Kv allows for slower rotation, meaning that you can have larger blades thus increasing lift. On the other hand, the higher Kv indicates higher rotations per volt and you have a smaller blade, but higher performance. My question is, would the 800 motors be sufficient for lifting a rather heavy frame, and potentially a full FPV set up? I see a lot of people use the 1200Kv motors, and was just wondering. I figure based off of the information given, I should have on the conservative side, 10 lbs of lift. and dont plan on going over half that weight.

Thanks!
 

Craftydan

Hostage Taker of Quads
Staff member
Moderator
Mentor
#17
most folks running 1200kv are lifitng 1.5-3lbs airframes, and leaning more toward areobatic performance

Now by 10lbs, is that total thrust or the lifing capacity you want? For any quad, you need *at least* a 2:1 thrust to weight -- might be able to get away with a little less on a V-tail, but I wouldn't recommend it.

If you want to lift 10lbs of airframe and payload, that's well into the heavy lift catagory and you might want to look even lower Kv, longer props, higher voltages.

If you just want that much thrust to lift ~5lbs weight, the strongest 1200's can do it at higer voltage, but if you don't want the aerobatic perfomance (with 5lbs worth of momentum to deal with, why would you want that?!?) a strong 800kv motor should work out better for you.

Edit: re-read -- sorry about that. a strong (250-350W) 700-800kv motor should treat you well.
 
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SGrog

New member
#18
That makes sense. The 10 lbs is in thrust, per specs the motors I'm looking at are: "10x5E - 18.5V / 315W / 17.3A / 1.27kg thrust". for all 4 motors, Im looking at about 11.19 lbs total thrust, but would like to keep the ratio higher then the 2:1 that had been stated.

The frame I am figuring is going to be around 2.5 - 3 lbs total, and then I would have the electronics which would be around 1.5 - 2 lbs I am figuring (all estimates are on the high end hopefully).

Near term goals are to just get it flying with out FPV or any other gear, then once I am flying more then crashing (If thats even possible?!) I'll add on some FPV gear. Long term goals are to add on a multi-rotor recovery system (MRS) in which I can essentially be an R/C Skycrane.
 

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SGrog

New member
#19
One follow up question I have is for the FCB, would the ArduPilot, or KK2 board be best? I finally have the funds available to start purchasing the electronics and my frame is nearly complete, so Im one step closer to the A Tail maiden flight. To help narrow what best is referring to, I am looking for something that would work well with a GPS module, for Return to home, or automatic way point identification. According to my research, the ArduPilot would fit the bill best, but I do not know if that is the right choice for starting out?

Until recently, Ive been leaning KK2, but have thought that maybe if I go with the more versatile board now, I might save the cost of a KK2.

Thank you again!
 

Dumpster Jedi

The One Who Speaks
#20
I've seen a few of these rescues and it always seems that getting a grip on the downed craft is the most difficult part. It is way cool to be able to retrieve an otherwise irretrievable model.