Report on Hobbyking 40A ESC 4A UBEC 9261000003 / BC3540-14 brushless drive #2

Report on Hobbyking 40A ESC 4A UBEC 9261000003 / BC3540-14 brushless drive reported a set of measurements on a test on elements of a drive system which is the basis for one of my flying quads.

This article reports some interesting characteristics derived from the measurements.

Test configuration:

  • Gemfan 11×4.7″ SF propeller;
  • BC3530-14 1000Kv motor;
  • Hobbyking 40A ESC 4A UBEC 9261000003 (BEMF caps removed);
  • SimonK commit 02bd8e4ca36a06722efe51bc7cd5130d72a184b8 bs.hex with 2000ns dead time; and
  • 4Ah 4S Lipo battery.

Keep in mind that the application for this drive is a multirotor, and hover speed is around 3800RPM, so efficiency in that region is critical to battery endurance.

Measured data

Screenshot - 17_05_2015 , 08_35_27

Derived data

Thrust vs RPM^2

A first approximation of thrust is that it is proportional to RPM squared.

Clip 137

Above is the measured data and a linear regression. The measured data is a fairly good fit to a straight line passing through the origin (ie linear with zero intercept).

Input power vs RPM^3

A first approximation of input power is that it is proportional to RPM cubed.

Clip 138

Above is the measured data and a linear regression. The measured data is a fairly good fit to a straight line passing through the origin (ie linear with zero intercept).

Input current vs RPM^2

Since the drive is powered from a constant voltage source for these tests, it is also the case that a first approximation of input current is that it is proportional to RPM cubed.

Clip 139

Above is the measured data and a linear regression. The measured data is a fairly good fit to a straight line passing through the origin (ie linear with zero intercept).

Efficiency

A first approximation of output power of a propeller is that it is proportional to RPM cubed.

Clip 140

Above is the calculated relative efficiency based on measured RPM,thrust and assuming a cubic relationship between speed and power.

Clip 141

Above is the drive efficiency calibrated to the propeller characteristic in DriveCalculatorv3.4.

Thrust factor g/W

A figure sometimes used to express performance of a drive is the ratio of thrust to input power expressed in g/W.

Clip 142

Above is the thrust factor calculated from the measurements.