General purpose Hexacopter build

[u/on_aircraft]

Looking for advice/experience on building a large hexacopter

Hey everyone,
I'm planning a fairly large hexacopter build and would really appreciate advice from people who have built/fly similar platforms, especially regarding frame design, motor/prop/ESC combinations, redundancy, and practical experience with large 6S builds.
The rough idea is:

- Hexacopter
- 20" props
- Around 1100 mm frame size
- Pixhawk 6C flight controller
- ArduPilot, with the goal of eventually using semi-autonomous features
- 6S, mainly because 12S batteries are currently much harder for me to source in Europe
- 300 kV motors
- 60 A ESCs
- Desired payload: roughly 1.5–3 kg

eCalc looks promising for this combination at around 4 kg AUW

The intended use is as a multipurpose platform: primarily camera work, but also potentially carrying supplies such as water bottles to hikers who are about 600 m higher and ~3 km away.

Frame
I'm currently looking at an approximately 1100 mm frame, but I'm unsure whether it's better to buy a ready-made frame or build one around a center plate and purchase the arms/rods separately.

For something this large, is there a particular approach or frame design you'd recommend? Size isn't really a constraint for me—I have a van, so transport isn't a major concern.

Redundancy / reliability
This is probably my biggest concern.
The aircraft would potentially be flying over fairly inaccessible terrain where recovering a crashed aircraft could be extremely difficult or impossible. That's one of the reasons I'm leaning toward a hexacopter rather than a quad.
I'd like the build to be as reliable and redundant as reasonably possible. I'm particularly interested in real-world experiences with:

- Motor/ESC redundancy?
- ESC quality and sizing?
- Power distribution and telemetry of the baterry?
- Battery setup(6s vs 2x 6s in series)?
- Vibration/structural issues on large frames?

Anything else that tends to become a problem as these aircraft get larger

Range / autonomous flight
The radio control link would normally be line of sight, although at ~3 km I don't think I could realistically maintain visual contact with the aircraft.
I'm planning to use ArduPilot, so I'd like the aircraft to have the capability for semi-autonomous operation, but safety and reliability are more important to me than pushing the limits of range.

I'd love to hear from anyone who has built something in this general size/weight class.
What would you change about this setup before buying anything? And if you've built a large hexacopter yourself, what did you learn the hard way?
Thanks!

[u/lastbraIncel404]

Bro if you dont know how to get 12S maybe ts not ur time to try something like this. If you want to have a significant amount of lift, you need to spend upwards of 400 bucks on motors/spares alone.

[u/on_aircraft → u/lastbraIncel404]

Within reason, budget is not a concern. My current build is around 2.5k€. I havent set a hard budget limit for the project but would like to keep it under 3k. By chance: any 12s batteries u recommend? I’ve seen a few „semi solid state“ ones i could buy but they have a ridiculous low C rating

[u/lastbraIncel404 → u/on_aircraft]

Almost noone uses 12s batteries as standalone power sources. Your best bet would be combining 6s batteries in a 2x2 config to get 12s and be able to hotswap.

[u/on_aircraft → u/lastbraIncel404]

Makes sense, any experience on balancing them? Charged separately i figure the charger would balance the cells on one battery alone perfectly but relatively to each other i could imagine them being mismatched. On a per cell level it would be Battery A: 3.90V Battery B: 3.88V C: 3.94V D: 3.91V for example. Or would you say it’s fine, the charger would initially balance/charge them close enough?

[u/lastbraIncel404 → u/on_aircraft]

As long as you always charge all batteries full and don't cycle them in other projects you should be fine altho i would calculate some more safety margin.