The brushless micro quad market has exploded, and there are suddenly a ton of options in a space where few existed just months before. Gearbest sent us an XF90 90mm Micro Brushless FPV Racing Drone for review: a 2S-powered machine at a competitive price point.
- The XF90
- 450mAh 2S battery
- 4 spare props
- USB charger
- 2-page info sheet
Compared to other offerings, there’s no manual, no prop guard, and no tools. (You’ll need a 1.5mm hex for props, and a Philips #1 for the camera mount and any frame adjustment.)
The frame is constructed of 1.5mm carbon plates with aluminum standoffs and screws. There are 4 plates and 6 standoffs. A dark green camouflage pattern is printed on the carbon. The camera is mounted with a 3D-printed bracket surrounding the lens. This allows for a wide range of camera tilt angles—though with such a wide lens, camera tilt isn’t especially necessary. The camera mount seems to easily work itself loose over time, so re-tightening will often be necessary. An excessively long battery strap completes the main structure.
The area where you strap in the battery could have been better designed. Mounting screws poke through where the battery is pushed up against. There’s no fore/aft support so the battery slides easily and feels like it will fall out any minute.
The XF90’s stack has a 4-in-1 ESC board on the bottom and an F3-based flight controller on top. The FC identified in Betaflight as a PIKOBLX. There’s a rather large notice on the included info sheet about not supporting DSHOT, and that the user should not attempt to update the firmware. As it turns out, it’s already running Betaflight 3.1.5 and has DSHOT150 enabled. The FC is oriented 45° off normal, reducing the motor-to-motor distance.
Four 0806 7500Kv brushless motors power the craft. There are big advantages to brushless motors, not the least of which is longevity. These have four threaded holes for screwing props directly to the bell. If you buy different props, you will want to be careful about the height of the prop hub and the length of screw you use. Screwing too far into the bell could damage the motor. Using 2 screws off-axis means there should be almost no problems with losing propellers in a crash. Gearbest tells us that though the ESCs support 3S, the rest of the quad isn’t designed for it.
The FrSky receiver on our version operates in D8 mode over SBUS and is just stuck to the side of a vertical plate with foam tape. It might look precarious hanging off the side, but is actually fairly well protected in a crash by the other parts hanging further outward. The single antenna also looks as if it will get sucked into the props at any time, but I folded it out of the way just a little, and didn’t have an issue. Telemetry isn’t supported.
The micro camera/VTx combo unit is the best I have seen. It’s a standard 40-channel with selectable power from 25, 100, or 200mW. Instead of tiny impossible dip switches we all hate, there’s a one-button interface and 7-segment display that is very easy to use. The included info sheet has a frequency table. The antenna isn’t copper and that seems to improve durability somewhat, but it will still bend under moderate pressure.
The camera is 800TVL, CMOS, NTSC only, with a wide FOV. The picture is impressive: great sharpness, pleasing color, (if slightly oversaturated,) and very good low-light performance. There’s no noticeable latency in flight. Finally, the camera has an extremely good dynamic range and light-to-dark transition. I could hardly believe how easy it was to fly between bright and dark areas—it even gives the venerable HS1177 a run for its money.
The cost of this performance seems to be zero tolerance for running under-powered. When the battery runs down, video is the first thing to give out. A crash is all but inevitable if you push this far. There’s also a minor issue that the mounting hardware and antenna get in the way of getting a finger in to press the button at all—so you might need a pointy object to change settings.
The USB charger was a bit of a surprise. Typically only 1S batteries are charged over USB. Some USB ports are capable of delivering 1.5A, which would result in a reasonable charge time. It’s hard to know which are and which are not, though, as they are often not labeled well. Use an older USB port that delivers only 500mA and you might be in for a long charge time. The charger appeared to provide an adequate charge but might ruffle feathers among those who take the tightest precautions: The cells don’t come out perfectly balanced, and it wasn’t unusual for it to charge one cell to 4.22V.
Despite not having a printed manual, getting the XF90 in the air for a first flight was very simple. First up, binding the receiver. The FrSky receiver is mounted externally, very easy to reach, and has a bind button. You still have to do the awkward 3-handed dance of holding the button while plugging in the battery to get into bind mode. (Manufacturers: could you give us a 5-second window instead of checking the bind button immediately on boot?) Once you’ve bound, it remembers your connection. Stick order is AETR.
Any other setup is optional. You can set up a 5th channel for mode change (Angle/Horizon/Rate) and a 6th to activate the beeper. If you want, you can adjust and confirm further settings with Betaflight Configurator, such as disabling the unused SERVO_TILT function. Doing so presents a small challenge, though: the USB port is directly in the path of the propeller. You may have to remove the prop each time you plug your cable in.
The frame itself seems pretty durable and the boards are all well protected inside the frame. Externally mounting the receiver seems like a little bit of a risk, but hasn’t been an issue in practice. The biggest potential for component damage is the FPV antenna, which is pretty typical for these micro quads. One crash wrecked ours pretty good, so we replaced it with a 1/4 wave linear (like we did on the QX70). Props are likely to bend and break in each crash. If you fly aggressively, or just aren’t very good at landing, you will go through a lot of them.
Compared to similarly sized micro quads, flight performance out of the box is a bit disappointing. The first flight was wobbly and lost of oscillations could be heard. The stated flight time of 4 minutes is flatly unrealistic. I may fly more aggressively than most, but I had a 2 minute flight time at best. After the very first flight the battery was very hot and even a but puffy—though it returned to normal after a rest. Acro flight is certainly possible; there’s enough power to launch and flip over trees yet the small size makes hitting gaps feel effortless. The props certainly don’t “bite” like a larger quad, though; acceleration isn’t the greatest and along with that comes a recovery time from dives that leaves you just a bit nervous that you won’t pull out. The handling has quite a bit of drift—that lack of “bite” makes for wide corners and a several-second recovery time on a hairpin turn at speed.
Possibly the most annoying, though, is that almost every flight comes to an abrupt end. Because of the short battery life and intolerant minimum voltage on the camera/VTx unit, each flight—almost without fail—ends when the video simply drops out and you crash as a result. You need to be very vigilant with your timer to avoid this.
Make no mistake, though: the XF90 certainly outclasses the Tiny Whoop, Hubsan, and their ilk. Without a great increase in size, the 2S battery and brushless motors offer a significant improvement in thrust and stability. It might be hard to call this an ‘indoor’ product as it’s too powerful for many to fly inside their homes (and lack of a prop guard would also be a concern for many). Larger indoor spaces like lobbies, atriums, and the like would be fine, but most owners will be flying outdoors. It’s a nice size to be able to fly in places that aren’t large enough for a full-size racer: those green spaces around the edges of parking lots and in front of buildings, for example—and the non-threatening size means it is less likely to become a cause for concern to onlookers.
Modifications and Upgrades
Something should be done to prevent the battery from sliding around and pressing against the screw heads. I added a piece of single-sided foam tape to create friction. This helps use up some of the excessive strap length as well, but I still double-wrap around the battery.
Running Betaflight means a number of flight improvements can easily be enabled in software. It’s a matter of preference, but full-time Airmode and disabling Motor_stop are obvious changes for me. Betaflight is also very chatty by default when there’s a beeper attached. Currently, these are only adjusted via CLI commands. The “beeper” command is about as simple as they come, though. If you start with “beeper -all” then make sure you turn on “rx_set” at minimum so the switch on your controller still works.
Change motor direction
It’s suggested that using a non-traditional motor spin direction helps improve performance. We’re exploring this in greater detail, but felt that it did improve flight performance on the XF90. Because it uses BLHeli_S, the process to switch direction is simple.
- Use BLHeli Configurator to set each ESC’s “Motor Direction” to “Reversed”. This will get them spinning the way you want.
- Change out your props, replacing each with one of the opposite kind.
- These changes will cause Betaflight to yaw backwards. Open the CLI and enter “set yaw_motor_direction = -1” to correct for this.
68g seemed like a pretty hefty amount of weight, so I went looking for improvements. There’s quite a bit that can be done without reducing functionality. First, the vertical plates had to go. They easily unscrew. A little rubberized glue holds the LED/Beeper board in place but pulls off easily. The 3D printed camera mount also unscrews easily.
Getting the top plate off is again just a matter of unscrewing it, but the camera and LED board were soldered through the holes in the middle. The LED board can fit through sideways but the camera will not. The leads are held down with a rubberized glue that needs carefully cut with a hobby knife. Afterward, those pads are at the edge of the board and can be unsoldered fairly easily. Once done, the top plate and all four remaining standoffs can be removed and the camera soldered back into place.
Re-mounting components is made somewhat simple by the tabs on the bottom plate previously used for the standoffs. The LED board can simply be hot-glued down to the rear tab, while the right and left tab are perfect for strapping a rubber band around. I used a tiny amount of hot glue under the camera to help settle it into place.
In all, I reduced the dry weight to 56g, which is a 20% improvement. You could further reduce weight by leaving the LED/buzzer off completely, but I’ve found it very helpful for finding the quad after a video dropout.
Performance After Modification
After these modifications, the XF90’s flight characteristics definitely improved. It felt zippy, far more stable, and fun to fly. There was far less wobble, reduced only to the hardest of turns. Some enthusiasts will still complain of a sluggish dive recovery, and the drift still exists though less pronounced. It makes for an enjoyable flight.
Many parts don’t have direct replacements readily available, but there are many compatible parts.
The XF90 has a good feature set with current-generation hardware and the Camera/VTx unit is a standout among micros. Heavy weight and “drifty” flight performance reduce its appeal somewhat for aggressive pilots. It’s neither perfectly suited for beginners nor for expert pilots—instead aiming somewhere in between. All of these features are pulled together at a price point that edges out most other brushless micro offerings today. Even with our modifications, the XF90 will never be the fastest, best quad available—but you do get an awful lot of value for the price.