Help With Heavy Lift Hexacopter

A

aricolton

Member
Hi, I am working on designing a hexacopter for a competition. I am new to multirotors and have a few questions. I need it to be able to carry as much weight as possible and due to size limitations we are limited to 8" blades. I don't want to spend much more than $600. Here is what I am thinking about buying:

1450KV 1600 Watt Motor
http://hobbyking.com/hobbyking/store/__8485__Turnigy_3648_Brushless...

60 Amp ESC
http://www.hobbyking.com/hobbyking/store/__45503__Turnigy_Multistar_60_Amp_Multi_rotor_Brushless_ESC_2_6S_OPTO_.html

8x4.5 Carbon Fiber Props
http://www.hobbyking.com/hobbyking/store/__45040__8x4_5E_Multistar_...

Battery 5s 8000 mAh (I might need 2 of these to get the required current)
http://hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=16227

Naza-M Lite Flight Controller
http://www.hobbyking.com/hobbyking/store/__30901__DJI_Naza_M_Lite_M...

We will be constructing a wooden frame ourselves.

I ran it through an online calculator and will attach the results

So here are my questions:
Will 8 inch carbon fiber props be able to handle all that power?

Is there anything you would change to maximize the amount of payload we can lift with 8 inch props? (based on the online calculator, it looks like we can lift about 9 Kg including the weight of the vehicle)

Finally, is it realistic to expect 5 mins of flight time from that battery?

Thanks for all your help!
1 more thing, is the Naza really worth the money? or would something like a KK2.1 be easy enough to control. It will primarily be flow indoors, so wind should not be much of an issue.

View attachment 16210
 

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A

aricolton

Member
We are limited to about 27" rotor to rotor. I didn't think of doing a Y6, off the top of my head I could probably get 10" props if I do that, or maybe 9" props on an X8......

I just put together the parts for each of them and ran them through the online calculator, it looks like I only get a little more lift out of the Y6, but I can get alot more out of an X8. What do you think of this parts list for an X8 build?

ItemQuantityWeight (g) PriceTotal Weight (g) Total PriceLink
1450 KV 690W motor8130 $ 18.851040 $ 150.80http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=18230
60 Amp ESC662 $ 22.12372 $ 132.72http://www.hobbyking.com/hobbyking/store/__45503__Turnigy_Multistar_60_Amp_Multi_rotor_Brushless_ESC_2_6S_OPTO_.html
9x5x3 Rotors810 $ 1.0480 $ 8.32http://www.hobbyking.com/hobbycity/store/uh_viewItem.asp?idProduct=5248
Naza-M Lite Controller125 $ 69.0025 $ 69.00http://www.hobbyking.com/hobbyking/store/__30901__DJI_Naza_M_Lite_Multi_Rotor_Flight_Controller.html
Battery 4s 8000 mAh2845 $ 61.651690 $ 123.30http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=20823
Transmitter/Receiver10 $ 53.820 $ 53.82http://www.hobbyking.com/hobbyking/..._module_8ch_receiver_mode_2_v2_firmware_.html
Battery Charger10 $ 23.000 $ 23.00http://www.hobbyking.com/hobbyking/store/__7028__Turnigy_Accucel_6_50W_6A_Balancer_Charger_w_accessories.html
Connectors10 $ 4.750 $ 4.75http://www.hobbyking.com/hobbyking/store/__21758__10cm_male_to_male_servo_lead_jr_26awg_10pcs_set_.html
Power Breakout Cable151 $ 4.8051 $ 4.80http://www.hobbyking.com/hobbyking/store/__25484__HXT_4mm_to_6_X_3_5mm_bullet_Multistar_ESC_Power_Breakout_Cable_.html
Remote Battery10 $ 12.790 $ 12.79http://www.hobbyking.com/hobbyking/store/__16529__Turnigy_2650mAh_3S_1C_LLF_Tx_Pack_Futaba_JR_.html
Wood frame110001000 $ -
TOTAL4258 $ 583.30

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J

jes1111

Active Member
You really need to give more detail of the brief! Is the sole object to lift the greatest amount of weight? For how long? What are the "limitations" exactly?

I strongly recommend using eCalc with the weight field set to "without drive", i.e. only enter the weight of the frame and electronics, etc. Also, if it's a weight lifting contest then add your payload to that figure. To hover with a minimum degree of control you'll need to be at around 75-80% throttle or less. Remember too that ultimate lift will be determined by the diameter of the props, not the motor, so start at that end first: work out the largest props you can fit (an X8 configuration, presumably), then find a motor that can drive them efficiently, then ESCs, then battery, etc. You could even consider overlapping the props. In an X8 config, use a bigger pitch on the bottom prop - unfortunately eCalc can't handle that so use an average of the two pitch values.
 

A

aricolton

Member
So basically what we have to do is lift a payload that weighs as much as possible and carry it through a few gates (each gate has an opening of 2 meters wide by 1.5 meters tall). Then we have to drop the payload on a target and return to the start. This all has to be done in under 5 min, so to be safe we should shoot for maybe 7 min of battery run-time. As for limitations, the only real limitations they gave us were: it must be battery powered, radio controlled, and fit within the size limitations (they measure this my making sure you can pass a 28 inch hoop around the vehicle). The weight they use for the scoring is actually the payload + the weight of the vehicle, so making the vehicle light weight is not really a priority.

So it sounds like we need to build an X8 copter with the largest props possible within our size constraint, what props would you recommend for an X8 configuration?

I didn't realize overlapping props was an option, how much can the props overlap? Also, how much vertical clearance is needed between overlapping props?

Thank you so much! I really appreciate your help
 


J

jes1111

Active Member
aricolton said:
the size limitations (they measure this my making sure you can pass a 28 inch hoop around the vehicle).
Click to expand...
Be more precise - 28 inches to the tips of the props lined up with the arms or 28 inches to the outside of the motors. Big difference ;)

aricolton said:
I didn't realize overlapping props was an option, how much can the props overlap? Also, how much vertical clearance is needed between overlapping props?
Click to expand...
I haven't tried it myself but see this thread: http://www.multirotorforums.com/sho...pping-Propeller-Designs&highlight=overlapping
 


A

aricolton

Member
We want to stay under 28 inches to the tips of the props.

I skimmed through the overlap thread, and it looks like overlapping would be instead of coaxial (It does not look like you can overlap and X8 as that would essentially be 4 props on top of one another)

I did some drawings and it looks like the biggest props we can fit on an X8 within those size limitations would be an 11". How far apart do the prop tips have to be from one another, right now it looks like we will have about a third of an inch when they are closest together, will that cause any problems?

Right now I am looking at doing an 11x5 on top and an 11x6 on bottom, how does that sound?

Here is my new calculation with the standard battery and temp/elevation

Also, That battery life is pretty bad, is there any way to improve it without strapping 4 batteries to the copter?

Thanks again for all your help!

View attachment 16233

And here is a quick Cad drawing I did for an X8 with 11" props to visualize the size of everything:
View attachment 16234
 

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J

jes1111

Active Member
Yes - 20% more pitch on the bottom is about right. Tips being that close might give you some trouble (airflow is "flung" off the tips) - overlapping slightly may actually work better - "interleave" the props a bit so you might be able to squeeze 12" props in there and avoid tip problems. All this is very weird (and interesting) as an exercise because of the size limitation - normally you'd be considering at least 16" props to carry this sort of weight. Since the total weight is what counts, you can get your flight time up by substituting batteries for payload - smaller capacity (and C rating) will be cheaper, so just pile 'em on there!

Not guaranteeing this will work, but it achieves your target flight time at 14150g AUW:
 

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A

aricolton

Member
Alright, I have been playing with the idea of 12 inch props. In order to get them to fit in our size constraint they have to overlap by just over 1 inch (there is a drawing of this below). Do you happen to know how much clearance I need between the overlapping propellers?

I like your idea about using a pile of cheap batteries. I was able to get it up to a about 4 min with an AUW of over 15KG. 4 min should be fine because it will only be carrying the payload for no more than half the time, so the battery life should be much much better once the payload is dropped.

The only worry I have with this design is that it does not leave much room for the batteries and other various components that need to be mounted somewhere on the frame..... But since we are building the frame ourselves we should be able to figure something out.

Here is where I am at now:
View attachment 16236View attachment 16237
 

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A

aricolton

Member
One more stupid question I just thought of: Do I need 5 battery chargers? Or can I put the pack of 5 batteries, wired in parallel, into one charger?

Thanks!
 

J

jes1111

Active Member
No - one charger will do - but you'll want to slow charge them to make sure you have the maximum energy in them so, presuming you'll need to do more than one run during the competition, you really want to have multiple battery sets already charged and ready.
 

JoeBob

JoeBob

Elevation via Flatulation

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A

aricolton

Member
So I just found out that we can actually have the tips of the props extend out beyond the 28 inches. In that case we can extend the arms a bit and not have to worry about overlapping props. It also will give us much more space in the middle to mount the electronics.

As for landing gear, we have access to a 3D printer and will probably design the landing gear on there.

I really like your idea for the overlapping props, if we do end up needing to overlap them, I will consider having one set of arms on top like that.

Thank you so much, I really appreciate all the feedback I am getting
 

J

jes1111

Active Member
Well - 28 inches to outside of motors - that means you could go up to 19" props - get some serious lift! If you overlapped you could go 20" inches or more. You'd need some big-*** low-kV motors.
 

A

aricolton

Member
20" sounds like we could get some really serious lift. The only thing I am worried about is the budget.... I dont want to spend more than $600-$700 on components, and we are already pushing up against that with the 12" props. Roughly How much more would it cost to up to 19" props and low kV motors?
 

A

aricolton

Member

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A

aricolton

Member
JoeBob said:
There goes the budget!

$52.40 for 100amp ESCs ( http://www.hobbyking.com/hobbyking/...00A_2_6S_SBEC_Brushless_Speed_Controller.html )
$39.80 for the NTM Prop Drive Motors
$92.20 per
x 8 motors
$737.60 for motors and controllers alone...
Click to expand...

Ya If I want to do that I am going to need to find a little more funding.....

I did find these ESC's that cost quite a bit less, anything wrong with them?
http://www.hobbyking.com/hobbyking/store/__18012__HobbyKing_Red_Brick_100A_ESC_Opto_.html
 

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