Flexrc Simple X 120 - 4s or 3s (3 inch Toothpick Style)

By wrong17 on Sep 01, 2019

8  463  0

For this build I can not take credit for it because I had a friend build it for me (https://rotorbuilds.com/profile/7846/). We were in a time crunch to figure out the ideal motor for our flight style because we wanted to catch the holiday sales. The ideal motor should be a balance of speed and efficiency. Even though I was not fond of the ideal with using 3s lipos I finially caved in and went with it.

We only had access to two different 1404 motors, RotorX 3600kv and DYS 4300KV. Those are the closest things we had that is similar to the AirbladeUAV Superman 3850kv and 4850kv motors that we plan to buy. So here are our initial findings.

Please keep in mind that our tests are not scientifically proven and is only based on our opinion and how the moon and stars were aligned at that given moment.

Since I do not have any 3s Lipos I had my friend do all those testing. To make a long story short, the 3600kv motor has 1 more minute of flight time compared to the 4300kv motors. The 3850kv Superman motors is higher KV than my RotorX 3600 but lower than the 4300kv, so we though it should be a good blance of what we are looking for. I think 4850kv is a bit too high, especially if I was thinking about trying 4s lipos. We are not a big fan of bi blade props, so all this testing is based on the HQ 3x3x3 props. We did try other props and the close second would be the GemFan WinDancer 3028. It is possible that if we plan to use a Bi Blade prop that the higher KV motors might be better suited for it, but we like the feel of the 3 blades more.

Just for fun I wanted to try using 4s lipos because that what I have on hand. Plus, I can use two 2s 520mah lipos from the 2.5 toothpick to make a 4s lipo. I tried 3 different 4s lipos:

  • Giant Power Dinogy 450mah 65c 4s (weight: 57.63g)
  • RDQ 525mah 80c 4s (weight: 60.61) This weight also includes the adapter I made to convert the lipos to a 4s
  • Tattu 650mah 75c 4s (weight: 70.95g)

With stock Betaflight 4.0.5 PID tuning it flew with no oscillation with a 4s lipo. It was actually felt better than a 3s lipo. I have not tried any other props when I switch over to a 4s lipo so I do not know how other props would do.
Here are a few videos to show you how each of the lipos did. The keep takeaway from these videos is the OSD reading of the battery voltage sag.

This is my first and only time I ever flown with a Tattu 650mah 3s 75c lipo:

Here is the Giant Power Dinogy 450mah 65c 4s. These are the worst quality battery compared to the other RDQ and Tattu but it still did okay.

The RDQ 525mah 80c 4s is the most responsive because its lighter and they are brand new. Like the Tattu, you get very little voltage sag. Unfortunately, I crashed early in to the flight so I do not have a video showing how it did through the whole duration of the lipo.

Finially the heaviest battery of the bunch, Tattu 650mah 75c 4s. I am surprised that it did so well because they are older and kind of puffed a little. I flew for 4 .5 minutes and never once did I got a low voltage warning. Initially I had some mid throttle oscillation and I though the extra 10g was the exceeding the limitations for my current PIDs. But it just did not make sense to me so I thought I would give it a second try. But this time I turned the battery 90 degrees so the longer sides are point to the left and right. I guess it worked because I do not have any oscillation anymore.

UPDATE Sep 04 2019: Caddx Kangaroo Camera with 7G Glass Lens
I only tried 2 other nano cameras (Runcam Racer Nano and Caddx EOS2) and so far this will be my favorite.

UPDATE : Sept 05 2019: Primo 2.5" 1103 8022kv 2s VS. Simple X 120 3" 1404 3600kv 4s
I just flew the Primo 2.5" back to back to compare Simple X 3” and the difference between the power is huge, the Primo seems slow now. The Simple X 3” does not have sag nearly as much as the Primo 2.5”.

UPDATE: Sep 06 2019: Maximum Flight Time Test.
Just for fun I wanted to see how long I could cruise around, and I was surprised to find out that I can get at least 11 minutes with an 4s 520mah lipo. Here is a DVR footage showing the footage, so you can see how I was flying and the full uncut video of the flight time.


Part List


Simple X-120 FPV Drone Frame (10 builds)

Flight Controller

GEPRC GEP-12A-F4 V1.1 BLHELI_S 12A F411 Flight Controller OSD (5 builds)


4 x RotorX RX 1404 3600kV 3S-4S Brushless Motor (7 builds)


HQProp T3X3X3 PC Propeller (Set of 4) (38 builds)

FPV Camera

Caddx 12M 7G Glass Replacement Lens for Kangaroo

FPV Camera

Caddx Kangaroo 1000TVL Nano FPV Camera - Choose Your Color & LensBlack / 2.1mm

FPV Transmitter

TBS Unify Pro32 Nano 5G8 V1.1 VTx Video Transmitter (396 builds)


TBS Crossfire Nano Rx (1484 builds)
See Site


2 x RDQ Series 7.6V 2S 525mAh 80C LiHV Micro Battery - XT30 (8 builds)


Tattu 14.8V 4S 650mAh 75C LiPo Micro Battery - XT30 (26 builds)


Team BlackSheep TBS TANGO 2 V3 PRO RC RADIO (104 builds)


DJI Goggles 2 (7 builds)

HD Camera

GoPro Bones - HERO10 Black (FPV Lightweight Drone Camera) (3 builds)
See Site

Misc Parts

Toothpick Nano Pod Lite [14mm] by Dave_C_FPV (13 builds)
See Site

Battery Charger

HOTA F6+ 1000W 60A 1-6S Quad Channel AC/DC Smart Charger - Grey

Battery Charger

HOTA D6 PRO Dual Charger 1-6S AC200W/DC650W 15A w/ Wireless Cellphone Charging - Black (14 builds)

Soldering Iron

TS100 Portable Programmable Smart Soldering Iron (264 builds)


Lowepro QuadGuard BP X3 - Drone Backpack for 4 FPV Quad Racing Drones and 15" Laptop w/Exterior Mounts (Black)


iFlight Crystal HD Patch and Stubby 5.8GHz RP-SMA Antenna Set for DJI - LHCP - Carbon
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