So I finally got started (and finished) with the testing of the FT Radial 2218 motor.
I used the thrust stand setup
previously described here.
I am using an arduino hooked to a laptop to record data from various sensors.
Thrust was measured via a 10kg load cell and the HX711 chip. The thrust is zeroed and calibration checked between each run.
RPM is an IR LED / Diode beam break setup.
Voltage was measured for each cell connected through an appropriate voltage divider.
Current is measured using a Hall Effect sensor and the factory calibration. This agrees well with my HK wattmeter
For power, I used 3 x 2200mAh batteries in parallel (for both the 3S and 4S testing). There was some drop in voltage as the testing progressed but I don't think it impacts the results (or their interpretation) significantly. Please note that because of the paralleled batteries, there is less voltage sag than you would observe with one battery, which means that the motors can reach higher RPM, pull more current, and generate more thrust than you might see in an actual plane.
Each run involved ramping up to 25%, 50%, 75%, and 100% throttle and holding at each throttle level for a defined number of seconds (these runs are controlled automatically by the software).
Props tested ranged from 8 to 10 inch in diameter and 4 to 6 inches in pitch. For 4S testing I did not go as far as the 10 inch props. There is a mix of genuine APC props (9 x 6 and 10 x 6), not-quite-genuine APC props from HK (8 x 4, 8 x 6) and generic Slow Fly (SF) props (8 x 4.5, 9 x 4.7). I point this out because the prop type can make a big difference to the performance and even similar props can produce different results - my 9 x 6 APC prop performs differently than my 9 x 6 not-quite-genuine APC prop from HK. The only "standard" prop I am missing is the 10 x 4.7 which was a pity because a lot of these motors are tested on a 10 x 4.7.
[Note: 10x4.7 data has been added]
I wanted to run a comparison against a similar motor. At one point early on in FT history they listed the NTM Propdrive 2826 1200Kv motor for use with their C-pack scale planes. I have a number of these on hand but they are not available anymore from HK. 2826 are the outer dimensions of the motor. I pulled the bell from an old one and confirmed that the stator is a 2211(22mm diameter, 11mm length) so probably not a great comparator for the 2218 FT Radial.
Given that there was some confusion as to the Kv of the FT Radial motor (the Item title in the store says its a 1080 Kv motor while the specs on the
same page say its a 1180 Kv motor), I had planned to run the NTM Propdrive 2826 1000Kv motor also.
I measured the Kv of all three motors using the drill and AC voltage method. Basically, you spin the motor at a known RPM and measure the AC voltage generated between the phases and using some math, calculate the Kv. These are the results for the three motors.
Based on these data the correct number should be 1180Kv, so I limited the comparator testing to the 1200Kv version of the NTM.
After testing was complete, I plotted all the prop RPM and Thrust data together, regardless of number of cells or which motor was used. This was just a reality check to make sure I didn't have significant issues with any particular run ( a given RPM for a given prop should produce a given thrust regardless of the motor, number of cells, etc).
You can see that all the curves are pretty smooth so there doesn't seem to be any testing problems between motors, props, or cells.
Below are the full set of testing data for the motors. I apologize that this data set is a bit dense. I am not going to interpret the data in any great detail, just to say the following:
(1) The FT Radial is a pretty powerful motor. Based on these results I am looking forward to installing it on my FT Edge and finally have some significant vertical power on 3S
(2) I did not see any significant increases in efficiency (grams/watt) for the FT Radial compared to the NTM - maybe the FT radial is a little better on 4S.
Is the FT Radial motor worth the higher price? That's a "How long is a piece of string?" question. You can pay a lot less
and a lot more for similarly sized motors and typically, you get what you pay for in terms or performance and quality. So far, this feels like a quality product but time will tell. It doesn't feel quite as nice as the E-flite Ultimate 10 motors I have (these were donated to me), but then again, that's a $60 motor.
Technically the FT Radial 2218 it should be tested against a similar configuration motor. But even the Emax C-pack motor is a 2215 and not a 2218.
The closest I can find is a 2218 1100Kv motor on Bangood for $20, this is about the same price I paid for the NTM with prop adapter (except for the ones that went on sale in 2017 for $5 a piece and I picked up four of them).
Although I would love to buy a better comparator motor, I just don't need to spend more money on a motor for testing.
Anyway - here are the numbers.
Enjoy!
3S Testing
Update 030619 - Data for 10x4.7 SF props added. Note that the batteries used were not fully charged for this test.
4S Testing