A quad has four motors.... Sorry, couldn't resist a straight line...
I use a hex over a quad for its lifting capacity, I plan to carry a camera and gimbal system. I also feel that the hex is a more stable and safe platform. I had a prop failure at 100ft and was able to control the craft back to the ground. If that happened to a quad, I would have a box of parts.
Further to this (with aerial photography in mind):
Are Hexa's more stable?
As good motors/ESC's/props are so reliable nowadays, is the redundancy of the two extra motors really that important in a hexacopter?
Will a quad using the same electrical power (watts) as a hexa have the same lifting power of a hexa?
Or if for the same lifting capablity are hexa's more efficient than quad's?
Any other reasons not to choose a hexa over a quad?
Hovering efficiency requires a large lifting area, but electric multicopters rely on the ability to change the speed of the propellers for control. Rotational inertia increases with the square of the radius, and this is what we're fighting for control response. The only way to have a large area AND a short prop radius is to add more thrust units (prop/motor/esc combos).
The drawback of hex or octo is a higher probability of a failure with the added moving parts count, even if a single failure might have a smaller flight mission impact. Like Stephen said, it's hard to imagine a quad staying in the air after a single thrust unit catastrophe, whereas with a hex you stand a chance of having a controlled landing.
Hi guys I trolled the Russian site again and put the the numbers I could get in the comments on on vis astas 125 minute site blog I also got some other interesting information . Have a Great Day!
Thanks Brad, so going 6S battery, low Kv motors and large diameter props on a quad might not be such a good idea? (Lifting capability being primary and duration secondary).
Also I feel there are other risks greater than a failure of a single thrust unit especially if using good quality components which I'm planning, so for me the redundancy offered by a hex is less important.
There are many different parameters to consider, and lifting efficiency must be balanced against control-ability. With more disk radius comes more inertia and slower response. Lighter loading has a cost too, in that smaller perturbations in the air will cause more positional reaction (think of it as the dandelion seed effect). Like the Russian guy claiming two hours with LiPoly batteries; if his assertion has a modicum of veracity, a puff of wind will blow his ship into into somersaults. If your aim is long photography missions, take an extra battery with you.
With more disk radius comes more inertia and slower response.
Which is exactly what we want in a camera platform. I want slow, lumbering performance. Not a hot-rod aerobatic fighter-jet.
Actually, it is exactly what you DO want - the inertial guidance system to respond instantly to perturbations in the air to keep the platform stable. Slow,lumbering performance could easily lead to low frequency control oscillations as well.
I want the slower USER control response... Not a nudge on the stick and the hex is suddenly a block away and rocketing up.
I just want to go on station and stay there (and come back when finished taking photos or video). Inertial may help that, but all of the tuning threads that I've seen people discuss is for the super high-performance type of flying.
That is a good point. I've always been in the camp of thinking lumbering was the goal for a camera platform, but I see your point. It seems that the best solution is for the autopilot to be crisp while the operator input is a bit muted with some expo?