T-Rex 700/800 on Hydrogen: Some Technical Questions

[karllovesmercedes]

Hey guys,
(Excuse the essay)
I've been meaning to upgrade to a T-Rex 700 or 800 for aerial photography.

In the next year I will be launching an aerial photography business catering to the commercial sector; specifically long-distance Search and Rescue, commercial surveying and videography/inspection, and as such have the exciting opportunity to build a rig in whatever configuration suits best.

With all our camera and radio equipment and intended power unit, we will be sitting around 11~12kg (24~26lbs)
Our mission requirements are high flight times (20~30 min+), high payload capacity (approx 3.5~4kg in equipment) and ideally; low noise

I initially looked at pure electric....and soon discarded it as flight times are incredibly short. Gas was the next, but high noise, smoke and vibrations wrote that off. Third was a Wren turbine with long range tanks, this seemed a viable option however we need huge fuel capacity and this increases weight drastically.

Recently I came up HES Aeropak systems.
http://www.hes.sg/#!in-the-air/c15wk

This company specialises in high-output, low weight hydrogen fuel cells. I've made an enquiry and they are able to produce a fuel cell package of around 2kw at a total weight of 4.5kg including 6L carbon fibre fuel tank, controller etc. operating comfortably within 12S voltage
What I need to provide him to get a complete price estimate and work out the size and feasibilty, are the power demands on such an AP ship to work out if the power output of the fuel cell will be up to the tasks I'm asking of it and how they will engineer it to suit my application.

So, to come to my question:
How much power are you drawing on your heavily loaded AP T-Rex 700, 700 Stretched or 800 ships? In amps and in what voltage configuration (6S/12S)?

I'm admittedly not an expert in electric helis, however I am learning avidly. If anyone can recommend an efficient motor and pinion combo in 12S with a rough amp draw, that would be brilliant. I am looking at a 44.4V 800 or 700-stretch with asymmetric blades running a (somewhat) low headspeed.

The hydrogen cells are not high-amp champions, so I am after the lowest amp draw possible. I believe it's maximum amp cutoff will be around 90~100 with nominal amps about half this and on-demand burst power provided by a separate Lithium pack.

If my workings are correct, a 22.2V setup drawing 90A will be the same as a 44.4V / 45A setup - totalling 1998W, meaning a "12S" voltage is the only option (unless someone knows of a higher voltage setup that can draw less amps - Hydrogen gives high voltages)) given the max nominal amp output of the fuel cell. However hydrogen wouldn't be worth it, if the heli is operating at the verge of it's maximum output doing lazy circuits and definitely wouldn't be suited in a search and rescue environment where wind will most definitely be a factor. Theoretically a 2kW fuel cell with a 6L tank at 45A will comfortably fly for an hour or more - if amp draw is around 20-30, this may well be a viable powerplant.

This is an experiment in feasibility and completely new territory for me. I know hydrogen isn't energy rich, I'm just looking into it's potential use for long flight times. I have no clue on amp draw at this weight, as I've not owned an electric AP ship yet - though I imagine it to be high, even with asymmetric blades and the right motor and pinion combo and am leaning toward a gas or turbine powerplant for the application, but would like to look at hydrogen before discounting it completely.

I'm looking to draw on your experience in this and find out what your average amp draw is in an 800-size ship doing general videography with the occasional maneuvers.

Your knowledge would be greatly appreciated

[nightflyr]

With all our camera and radio equipment and intended power unit, we will be sitting around 11~12kg (24~26lbs)
Our mission requirements are high flight times (20~30 min+), high payload capacity (approx 3.5~4kg in equipment) and ideally; low noise.

How much power are you drawing on your heavily loaded AP T-Rex 700, 700 Stretched or 800 ships? In amps and in what voltage configuration (6S/12S)?

I'm looking to draw on your experience in this and find out what your average amp draw is in an 800-size ship doing general videography with the occasional maneuvers.

Without knowing whatplatform or configuration your attempting to use.....

I can say that a properly configured 800, 900 or 1000 class can easily obtain your flight time requirements.



Power: 6S setup
Current: 17 - 18A
Wattage : 800
ESC temps: 48.8*C (120*F)

[karllovesmercedes]

Nightflyr, thanks for your post, that's been extremely helpful.
(I love the camera sticking through the cowling!)

Our platform has been estimated to be on the heavy side, to factor in extra weight as a safety margin.

The main heavyweights are the Photoship One gimbal (590g)
Sony A7S (480g) + lens (200g+ depending)
Ammion Connex Video Downlink (130g)
Flight battery (300~450g depending on power consumption from equipment)
2x Go Pro Hero 3s (180g) (one for FPV, the other side-by-side gimballed and separately controlled, with a FLIR Vue 120g thermal camera)
DragonLink, Pixhawk, Pixhawk GPS module, assorted wiring and lighting required for night flying and legalities and a Mars 120 UAV parachute add on to this weight. I added together 2500 grams as a generous estimate, with 1kg thrown in for any extra payload bringing it to the 3.5kg figure. 4.5kg being a worst case, absolute maximum weight I'd like to be flying on top of the chassis weight (3.1kg) and H2 Fuel Cell (4.5kg). The blades will be Spin Blades 800 size asymmetrical, though much larger is something I'd like to avoid - 800 is already quite large enough haha.

Depending on the mission, the A7S really won't be required most of the time, other than surveying and certain site inspections which will cut weight down a LOT.

For most SAR missions this gives an equipment weight of 1,500~1800 grams without the A7S, and likely the opportunity to run a lighter flight battery as well.

If I can draw somewhere around in the 20A region on 12S in average flight I would be over the moon.

Am reading the chart correctly? Are you running an 800rpm head speed? How are you finding the responsiveness? I've not yet seen anyone venture anywhere near that low yet.

Thanks again, Karl

[nightflyr]

Actually I run 760 rpm HS ...
Responsiveness is fine....
I set it up specifically for LHS and long flight time.

As I see it, your setup will need to have a major weight reduction.
I can tell you that from many hours of trial and error.
Might also consider a strong light weight frame

But then again, I do not use any gimbal, electro/mechanical stabilization or post production software

All my video is raw, straight out out of the onboard cameras.

GOPR0 Clean Raw Footage (6 min 33 sec)

[R_Lefebvre]

Hi Karl,

I think I have the solution for you.

http://www.suasnews.com/2016/04/proc...t-1kg-payload/

This could easily be reconfigured to have only a single battery, and 3.5-4kg payload on the front. Currently there is 2.5kg battery and 1kg dummy weight on the front. Flight time like this is 40-60 minutes depending on airspeed.

The mechanics are based on the Protos Max V2. Since it is all-belt drive, it's extremely quiet. All you can hear are the rotors. In forward flight, it's extremely quiet. Eerie actually.

I am glad to hear you like the Pixhawk. I am the lead developer of the helicopter code, but in fact I am a mechanical engineer, and will be marketing these soon. I will have a Beta test program open to qualified buyers in May.

[helicek]

Hi nightflyr,
your 760rpm head speed have my attention.
my setup is:
trex 700, 12S, Scorpion 4035 350kv, Kontronik Heli Jive, dji AceOne flybarless, SpinBlades 71 assym, align 110mm tails, 12t pinion on the motor and 112 main gear. AUW inc a D700 and brushless gimbal is 10,5kg. For flight, main rotor speed is governed to 1,300rpm. At 6˚ pitch draws 23amps at hover near ground. Current goes down to 17amps during forward flight. With 2x 6S 5,300mahs my safe flight time is near 10 mins. After landing battery packs and motor are warm. The esc is cool, even though it is setup near %60 throttle governor.
It flies nicely around 1,200 but tail looses hold when hard pitch is applied.

I will be very happy if tell us your setup for comparison:
auw?
choice of main blades?
main blades angle during hover?
motor?
gear ratio?
6S / 12S ?
where is your throttle curve for hover?

[nightflyr]

Hi nightflyr,
your 760rpm head speed have my attention.
my setup is:
trex 700, 12S, Scorpion 4035 350kv, Kontronik Heli Jive, dji AceOne flybarless, SpinBlades 71 assym, align 110mm tails, 12t pinion on the motor and 112 main gear. AUW inc a D700 and brushless gimbal is 10,5kg. For flight, main rotor speed is governed to 1,300rpm. At 6˚ pitch draws 23amps at hover near ground. Current goes down to 17amps during forward flight. With 2x 6S 5,300mahs my safe flight time is near 10 mins. After landing battery packs and motor are warm. The esc is cool, even though it is setup near %60 throttle governor.
It flies nicely around 1,200 but tail looses hold when hard pitch is applied.

I will be very happy if tell us your setup for comparison:
auw?
14 lbs. (6.35Kg)
choice of main blades?
SAB


main blades angle during hover?
Good question: never actually measured it, but I have it set for a total of -2 to +8, so a reasonable guess would be +3 ~ +5 degrees... Lots of lift on those blades
motor?
Scorpion 5020-450
gear ratio?
8.92, I believe, I'd need to double check my main gear.
Lowest would be 8.61, highest would be 9
6S / 12S ?
6S
where is your throttle curve for hover?
I'm set at FIXED RPM on my ESC govener ....NORMAL 760, IU 1 825, IU 2 900

Current draw is 17 - 18A
Wattage ~ 800W
ESC temps 115*F - 120*F (46.1*C - 48.8*C)
Motor and packs are at ambient.

JMHO...
I believe you would have better results by using a different motor ...
A 4035 series..works nice on a stock build 700, 800 or even a light 900, but not so well when you start loading it up on a AP rig.

If you have a soft tail at your required head speed ...
You have several choices on how to correct it.
1) Larger tail blades
I tried the largest I could find, but they didn't really help.
That is when I cut down a set of 450 main blades.
Made up sets from 140mm up to 180mm you'll need to CG and balance them.



2) If your handy and a bit creative a stacked tail rotor will solve the issue with standard length blades.



An offset may also help:









3) Tinkering with the gear ratio for the tail is another way, though I never had to go that far.

4) Now if your really into tinkering ...
Might think about a direct drive tail.
A bit more involved, but a useful solution

[helicek]

Hi Nightflyer, are you satisfied with flying Ace One flybarless? I am not happy with mine and considering going back to flybar rotor.

[nightflyr]

Never tried ACE ONE ...
Run HC and NAZA-H

[helicek]

Hi nightflyr,
I have just read your 05-07-2016, 02:09 PM reply. What an awesome job you did and thanks for taking the trouble of putting into words and pictures.
I am happy with 4035 III 350 so far. Have not noticed anything -ve. I want to keep things as simple as possible so lengthening the tail blades I did. When I am careful with pitch feed this thing manages the tail at 1,250 main rotor rpm. I try to keep hovering pitch around 6,5˚ +ve. With 10,5kg auw the flight has to be smooth with no abrupt controls.
Best regards,
Ahmet

[Mapoff]

I was running an Align 800 with the 700mx at 470kv, 10t/112t carrying a gimbal and camera weighing 11lbs, and two nanotech 8000's to counter balance, with Edge 815 blades. I do NON beauty shots, and require the ability for fast movement, so I keep my headspeed up. I've noticed that if I run around 1450-1500 the control is very squishy and wind will push me all over the place. 1550 is good and I've even been running 1600 rpm which provides a very very solid lock on flying.

Recently the motor bearings were noticably worn so I pulled it, replaced bearings and found some things I didn't like so for an upcoming shoot, I swapped to another MX that was rewound to 520kv. Both my MX's had been rewound but the 520 was for 3d. The previous current draw was typically 30amp with the 470, and the 520 has been pulling between 50-60amps, with peaks of 95. The peaks on the 470 were usually 50 amps with a hard climb. I'm looking at an Xnova 400kv 4035 now which should give me better than 30amp and still have the high headspeed. I'm also thinking about a 3 blade setup.

https://www.youtube.com/watch?v=VPUXcU1iOQ4

I'm still battling vibrations. I have a friend working on a wire rope isolator setup. Before the shocks worked perfect with a GH2/GH4/Sony A7x, but with this large Blackmagic Production camera, the shocks just don't do it. I also have gimbal tuning and such. As much as I dislike DJI, I'm thinking about the Ronin MX for quick change of cameras, and cleaner install.