Hi,
I'm planning to build a hexacopter and trying to find some motors which will provide good efficiency. The up in air weight will be around 3.6 kg(600-900g frame, 6x150g for motor + esc, 800g battery, 500g gimbal, 500g camera) give or take a few hundred grams. As far as I know, the key to long flight times is large props and low KV motors, given that all else remains constant. I've been looking at the rctimer HP4215 and sunnysky x4108 which provide about 600g thrust at around 3A according to test data. In my head that should give you 3600g thrust at 18A, giving a hoover time of 16min with a 5000mAh. In theory anyway. What I'm wondering is if using a motor like this would be overpowering the copter, giving control issues? It seems like the motor would be working at it's lower range when hovering. How about if I try to fly it without gimbal and camera, loosing another 1000g? On the other hand it seems to me that the key to long flight times is having a motor which provide alot of thrust with low current. From the test data I've seen, this seems to be related to high power motors with low KV. Am I missing something?
As a side note: for motors which lack test data but have test data for a higher KV motor of the same type, can I assume that the low KV motor will provide the same lift as the higher KV motor at same or less current?
regards
Håvard
Replies
Hi
Read this thread.
http://www.rcgroups.com/forums/showthread.php?t=1880665&page=1
As mentioned high efficiency = high voltage with low kv and large propeller.
Motor size/kv should be selected so that hover with payload is at or slightly below the RPM efficiency peak of the motor. This all sounds easy on paper, but can be very hard to achieve in reality. Data on motors from manufacturers usually is lacking or just plain wrong. Using eCalc you can get and idea of how it will work, but the only way to be sure is to test different motor and propeller combinations.
Hi Håvard.
also, for maximum efficiancy, don't forget to use high voltage, IE 6S.
This lets you send twice the power to the motors using the same Current, if you compare 3S and 6S and have ESC's and motors that tolerate both. The 6S motor market is quite small though.
I am flying an Octo Monster, 8x3536/9 motors (910kv-370W) at 4S. It can probably carry a lot of weight, but it really drains the batteries. For my self, I would choose a smaller setup next time, probably something like 250W motors to carry a Nex5-camera and allt he equipment I need. But that's just a gut feeling.
The HP4215's look very nice at 6S, giving you lots of power if you need it. You might get away with smaller motors though, but I would say that this is a nice, safe choice.