Powertrain & flight time
Compared to racing drones we do not aim for high speed and acceleration values. A camera drone needs as much flight time as possible while still being able to get the job done. All other characteristics like range, quality, speed just need to be as good as necessary. This assumption allows us to reduce the complexity of the problem a little. It leaves us with an optimization problem where we want to have the max. flight time while keeping all other components “just good enough”. The definition of “just good enough” is different for every project. Sometimes it is necessary to adjust your definition slightly in order to get better system performance.
With this project, my aim is to get a flight time of somewhere in between 22min and 30min. This drone will be very similar to a DJI Phantom, so Phantom components are a really good starting point.
Motors & Battery
We choose the T-Motor 6th Anniversary MN2213. All four of these cost around 70€ (which is really cheap!). Looking at the specs they are a good choice for our project (if we wanted to spend more money there might be better alternatives):
They produce around 600g to 700g of thrust each, running on 3S with the included 9″ propellers. So the current draw is somewhere around 3A while hovering. Tests by other users show that they can easily handle a bigger propeller (~10″). That will increase the efficiency and will give us a hover current of around 2.5A running at 3S.
Using a 4S battery would give us a lot more thrust but efficiency will be lower thus flight time will decrease. This is not something we want, but worth to keep in mind in case we want to have a heavier payload someday.
At this point, we do not know the exact numbers since we just use thrust data gathered by people of the internet. A 3S 5200mAh LiPo (similar to what’s inside the Phantom) will most likely give us the flight time we want.
It took a lot of iterations till I found a good motor, propeller and battery combination. Looking at existing builds or specifications of commercial products definitely helps and speeds up the process. Especially the pre-estimated weights of the battery and overall UAV really help.
Sometimes it can be hard to find proper motor thrust/power consumption data. It is not worth looking at motors that do not come with detailed thrust stand data.
Just pick whatever gets the job done. I choose 20A Bel-Heli ESCs. “All in one” or not does not really matter.