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

## Derived data

### Thrust vs RPM^2

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

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.

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.

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.

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

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.

Above is the thrust factor calculated from the measurements.