Custom GIANT multirotor - 25lbs payload, 20 minutes flight

[Raptortech]

Hope my title caught your attention!

It is true: I am building an aerial photography craft of epic proportions. Right now, I have a setup in mind, but before I go an throw down $7000, I thought I'd chat with everyone first.

So my plan (as of 6/29/15) is to build a custom X8 frame.

Motors: T-Motor U8-10 (170kv)
ESC: T-Motor 80A HV
Props: 22x6 CF
Batt: 12s 16000mAh

My calculations give me a 15 minute flight time if we load airframe up with about 20lbs of camera equipment (RED Epic, Movi M15 Gimbal, big lens, Connex FPV, etc). This is acceptable, but ideally I would like to reach my initial goal of 20min flight time with 25lbs payload.

If anyone knows of any comparable motors outside of the t-motor brand (I was unable to find any other than some data-less HK thing), please let me know! Also, ESC timing will likely be an issue, so if you have experience tackling that, any input is much appreciated.

I've done a fair amount of research into this and have found various configurations which could theoretically make the mark (for example using a conventional octo instead of an X8), but I am limited by cost and my transportablility. For the sake of discussion, let's say less than $8000 for the airframe and it should be able to fit in a decent size trunk of a car with the rear seat folded down. Another solution I have been considering is an X12, but I'm hesitant as that will significantly reduce the overall efficiency of the aircraft.

 

[Cyberdactyl]

It will certainly be grand. Hope you post some pics of it when done.

Getting ~15 minutes with an approximate AUW of close to 34lb sounds very doable. Getting 20-25min may be pushing your luck.

Haven't noticed you posting here in this section before. Have you flown extra large and heavy multirotors before? Just sayin', because stuff that size cannot land any other way but perfect, otherwise you're repairing expensive parts.

 

[Raptortech]

I hadn't done much heavy stuff until recently, but it's been my full time job for a few months now. Right now the biggest thing I fly regularly is a DJI S1000 (wasn't my choice but they bought it before I came onboard). I fly it roughly twice a week.

The piloting doesn't really worry me (it's going to have a pixhawk for safety), but building such a craft from scratch does. I've got a very solid background in all the EE, ME and RC required, but it's still a lot of $$$...

 

[nilsen]

Haha, good title!

Anyway, some back-of-the-napkin calculations and and ecalc show's you're correct, it's about 19 minutes of hover time however the motors at Max will be way over temp.

Although you will have 26kg of additional payload

 

[Cyberdactyl]

Yea, it'll fly, but getting upper teens in minutes with all the camera load will be optimistic. Most of these higher end AP birds want to at least have some transitional movement, so that will further drop the time. Lifting literally several thousand, if not double digit thousands in camera and lens isn't something I would find easy on the nerves to say the least.

 

[Ocean]

I added a few more figures to what Nilsen put in on ecalc. Made an estimation of around 15g AUW with camera gear and a wheel base of 1m.

AVRoto and Cobra sell some high quality motors, not sure if the KV is low enough though.

One thing to note is I noticed a change from 10.3min to 13.2min when changing from X8 to regular octacopter on mixed flight time. However again transportation is a key issue, unless you made a octa with arms that fold down, similar to the s1000.

These numbers might see not great, but ecalc has a habit of being conservative.

 

[Raptortech]

My rule of thumb is cut out 30% efficiency for coaxial motors and another 20% efficiency for movement. eCalc does this already, however.

Those are essentially the values I got, however I had specced a larger battery. I have a spreadsheet where the AUW and thrust is calculated for various configurations
https://docs.google.com/spreadsheets/d/1TdIcA1l0wtMuJZ9o5mrO-nvVpZK5wzRR8Sve66IkYvs/edit?usp=sharing

 

[jipp]

well im sure i speak for more than my self when i say. please share the build.. sounds rad.. more than most of us will ever fly but thats why it would be cool to see a build.

chris.

 

[Raptortech]

Ok. New configuration which could be suitable! Here's what I got:

Frame (1): Custom Hexacopter - $1500
Motor (6+1 spare): T-Motor U10 80kv - $2303
ESC (6+1 spare): T-Motor 80A HV - $839.93
Battery (1+2 spare): 12s 16Ah - N/A
Prop (3 pairs+1 spare): 27x8.8 Carbon Fiber - $1415.96

Total: $4948.87 (includes FC)
AUW with M15, Red, Zoom Lens, Connex: 18kg


The free version of eCalc doesn't really spec that high, so I'll just walk through my calculations here:

1. If our takeoff weight is 18kg, each motor needs to supply 3kg of thrust.
2. At 3kg of thrust, the U10 motor pulls 5A.
3. 5A per motor comes to 30A in a hover.
4. Add losses of 30% to account for inefficiency and lateral motion and we get 42.8A average current draw.
5. Take our capacity of 16Ah and divide by 42.8A to get 0.374h which is 22.4 minutes.

It sorta scares me to buy propellers that cost $329 per pair, but if that's what it takes...

This actually comes out a bit cheaper than the first configuration, because it's a hex instead of an octo.

 

[joshuabardwell]

It sorta scares me to buy propellers that cost $329 per pair, but if that's what it takes...

It'd scare me to put a $30,000 camera on a multirotor that I built. A $300 prop is nothing.

Definitely, definitely find a way to simulate motor failures and see how the FC responds before you put the camera up.

 

[Raptortech]

Definitely, definitely find a way to simulate motor failures and see how the FC responds before you put the camera up.

Unfortunately I don't think anyone has such a simulator. However, I do plan to log at least a few hours of air time before I load it up with anything other than jugs of water.

 

[joshuabardwell]

Unfortunately I don't think anyone has such a simulator. However, I do plan to log at least a few hours of air time before I load it up with anything other than jugs of water.

Just un-plug an ESC or something and see how she flies. Intentionally put a broken prop on to destabilize it. That sort of thing.

 

[Raptortech]

That's a good idea. The reason I went flat hex over flat octo is for larger prop clearance. I might jump back to the X8 for redundancy and prop clearance, drop to 6s on the U8 motors, and prop way up. I'll run those calculations tomorrow.

 

[nilsen]

Ok. New configuration which could be suitable! Here's what I got:

Frame (1): Custom Hexacopter - $1500
Motor (6+1 spare): T-Motor U10 80kv - $2303
ESC (6+1 spare): T-Motor 80A HV - $839.93
Battery (1+2 spare): 12s 16Ah - N/A
Prop (3 pairs+1 spare): 27x8.8 Carbon Fiber - $1415.96

Total: $4948.87 (includes FC)
AUW with M15, Red, Zoom Lens, Connex: 18kg


The free version of eCalc doesn't really spec that high, so I'll just walk through my calculations here:

1. If our takeoff weight is 18kg, each motor needs to supply 3kg of thrust.
2. At 3kg of thrust, the U10 motor pulls 5A.
3. 5A per motor comes to 30A in a hover.
4. Add losses of 30% to account for inefficiency and lateral motion and we get 42.8A average current draw.
5. Take our capacity of 16Ah and divide by 42.8A to get 0.374h which is 22.4 minutes.

It sorta scares me to buy propellers that cost $329 per pair, but if that's what it takes...

This actually comes out a bit cheaper than the first configuration, because it's a hex instead of an octo.

Look what I came up with:



Looks like an excellent option, the only thing assumption I made was 2kg frame weight.

At hover you only have 78% efficiency but it's not bad, but you would crack the 20 minute mark.

Where would your get a 16000mAh 12S battery?

2 x 8000 in parallel?

 

[Raptortech]

Where would your get a 16000mAh 12S battery?
2 x 8000 in parallel?

I have an S1000 currently that I fly with 6s 16000s and 6s 22000s. They are made by Pulse. Just take two 6s 16Ahs in series.

 

[nilsen]

Nice.

What are you thinking for the Custom Frame?

 

[Raptortech]

Nice.

What are you thinking for the Custom Frame?

Simple sandwich construction with carbon fiber plates, aluminum hardware, and 40mm carbon fiber booms. The reason I'm going custom is in part for the weight, but mostly for the gimbal mounting requirements.

 

[Raptortech]

Thought I'd give you guys a quick update on this project. On Thursday, I finally nailed down our parts list. I decided to buy an FX8 Pro Elite frame from AerialPixels rather than build my own simply because we need this thing flying sooner.


I chose the X8 over a flat 8 or a hex because we needed a more compact airframe both for maneuverability and transport.

The AUW should be 45-50lbs with a 12s 22000 + camera payload, and AerialPixels assures me that I can expect flight times nearing 25 minutes with my configuration (though my more conservative calculations showed several minutes less).

To my knowledge, we will be placing the order tomorrow, with plans to do a maiden flight before August!

PS - the props are 26" carbon fiber beasts!!!! If you buy from T-motor, each pair costs over $300!!!

 

[Cyberdactyl]

Wow! 22,000g for AUW

Looks like a beast. Heck it IS a beast.

I haven't run the numbers like you, so it's just a gut feeling, but my guess is it will get air time in a static hover, closer to your conservative estimate of the mid, maybe upper teens. But it will be awesome if you get the 25 minutes you're calcualting. Can't wait to see some video of it in the air!

 

[cranialrectosis]

Video with audio please.

Those props are gonna sound AWESOME!

Thank you for posting this.