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Results of testing 15 props for 250 size quad racers.

Background--A 250mm diagonal quad racer is becoming the emerging standard for FPV racing.

Requirements--The requirements for a quad racer are:

  - speed

  - acceleration

  - (not efficiency as time margins exceed rotor efficiency margins)

Test Measures

Rotor speed is a direct function of max net-thrust (excess thrust available after accelerating the ESC, motor, and prop). Thus max net-thrust is measured as maximum thrust less the mass of the:

- ESC (naked) & wires

- Motor & attachment bolts

- Prop & prop-to-motor attachment plates/hubs/bolts

- Structure (ignored since only 6" props were tested)

Rotor Acceleration is a direct function of how fast the rotor system can achieve throttle level commands.

- measured by net-grams thrust

- criteria is the % of commanded thrust level achieved

- categorized in Hz

For example, if the command is full throttle, then zero throttle, which is then repeated 10 times per second, a rotor that can achieves max throttle and 40% throttle before the end of each cycle would achieve a 100% score for the up command and a 60% score (1 - 40%) for the down command at 10Hz. A score of 80% in either direction is acceptable for high-quality control.

For this test, to compare various rotors, we used the extreme limits of 0 to full throttle (like a drag race at the start of a lap) using response rates of 1.67 Hz to 13.33 Hz (the latter being the approximate limit of human twitch rate; you only need a system that responds faster than it can be commanded).

The following chart shows two of the better rotors that show small but significant differences. First, the chart shows the acceleration of a DAL and GemFan prop when mounted on a T-Motor MN2206-13 motor + DYS 30A ESC.

1) The max thrust is similar with the DAL being a few net-grams higher

2) There is a consistent lag in the DAL reaching the top as compared to the GF

3) The GF is quite steady once the targeted thrust is reached

4) The DAL seems to waiver once the peak is reached

5) On down throttle, the GF consistently gets closer to target and does so faster

6) Not shown is that these props beat the heck out of all comers (except other branded same props)

Note of caution about this summary table. For accurate data, sample size of the tests needs to be increased as there are variations between props, which can affect max thrust. In most cases, only one prop was tested and only tested once. If i really get into 250 racing, i may repeat these tests with 8 props each for the most promising (4L + 4R).

Test Device--The test device is repeatable to +1% that uses:

  - a controlled DC Power Supply in this case set to 14.8 VDC

  - a professional quality load cell connected to a DAQ

  - an amp meter connected to a DAQ

  - a voltage meter connected to a DAQ

  - a DAQ connected to a computer with direct feed to Excel

  - a Mega Arduino board to precisely control/repeat PWM and Hz rate for each test

  - a non-contact thermocouple reading the base of each motor

Test Results

A note to Manufacturers and Racers: The tests were conducted at FQRPL, a proprietary test lab that does not receive pay for public testing of OTS products. If you want FQRPL to test OTS products, please contact me to send products for test.