I have followed the technology advances like farm drones observing water drainage to crop decay, construction degradation monitoring, and potentially drones placing building frames instead of people. But the other day, something caught my eye with DJI Mavic Pro and its sibling DJI Mavic Pro Platinum. What was interesting, is that the flight time between the two drones, (27 minutes increased to 30 minutes) and how they drive their motors. See the below diagrams.
According to the the above picture they say the propellers and the motor ESC drivers improve noise control and stability. It is true that if the motor commutation is done with Sine drive (right diagram) vs trap-drive/6 step drive (left diagram), the system will have improved stability. An improved shape and material can also improve noise reduction also. But what also happens is that the motor will perform more efficiently giving the motor more thrust for the same amount of current commanded.
What is the different between trap-drive and sine-drive?
In a brushless motor that is in most drones, there are 3 phase lines. Each will be controlled independently but in combinations.
-Commands the next phase combination to turn the motor when the motor state changes, usually by reading hall effect devices or x-y sensor data.
-Easy to implement in code quickly and effectively
-Does not need extra hardware to read voltage on the phase lines of the motor.
-Does not necessarily need hall effect devices or xy sensors to move the brushless motor.
-Does not command the motor at the right time. This won’t allow optimal torque out of the motor.
-Less efficient = More heat and Less flight time.
-Less consistent with torque output.
-Continually commands the phase lines of the motor to allow the current and Voltage to follow the back EMF curves (see right diagram from above) of the motor to provide optimal torque at all times.
-Makes the use of a motor very efficient by allowing the same amount of current to be used and achieve the best torque the motor can provide.
-Better efficiency = less heat on board and more flight time possibly less weight.
-Near perfect consistency with torque output.
-Less current ripple on circuit board means less noise getting on radio lines which means farther flights.
-Harder to implement in code.
-Need more components because more information is needed to be able to commutate in sine-drive.
-Motors can be sensitive if not coded correctly.
It is cool to see commercial companies start putting in software and hardware architecture to improve flight times, reduce weight, and increase flight distances.
Even though the Mavic Air just came out which has some pretty cool features, I am probably going to get the Mavic Pro Platinum with the FPV Goggles because of the farther flights and longer flight time. Hope I can get a hold of one and get flying again soon.
Credit: All pictures are from DJI.com website and not of my own making.
Disclaimer: This blog is solely Tinee9’s opinions through electrical engineering experience and does not have exact knowledge of the inner workings of DJI products that would compromise IP, or patent infringement. DJI is not a sponsor of Tinee9 but Tinee9 is apart of DJI affiliate program to help earn revenue to keep the website going.
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