Micro drones, big lessons
A short, hands-on guide to getting a Mobula 7, a 3-inch Apex and a 2.5-inch “Mini Bjorn” build set up in Betaflight.
Workshop story, not a sponsored review. These are our builds and mistakes, not universal settings. I kept learning the same lesson: a quad that will not lift or flies oddly may need a prop, motor-map, wiring or firmware check before it needs a new PID tune.
Start with the motor diagram, not the diagonal
On both our Mobula 7 and Apex 3, I ended up flying with motor rotation reversed in Betaflight (the props-out arrangement). In our setup, motors 1 and 4 used the regular propellers, while motors 2 and 3 used the reverse-marked propellers. I initially expected the opposite pattern. I put the wrong prop type on the 1/4 diagonal, and the quad tipped/flipped when I tried to lift it. The problem was the motor/prop match, not the PID values.
Betaflight’s “Motor direction is reversed” option changes the mixer’s expected yaw direction; it does not reverse ESC motor spin or fix motor order. With propellers removed, check that each Motors-tab slider spins the motor shown in its diagram, check the actual spin direction, then fit the matching propeller. The Happymodel Mobula 7 manual shows the 1/4 versus 2/3 prop pattern for its props-out example. Use the diagram and manual for the exact aircraft in front of you: prop direction is not a rule to copy betIen targets.
1S, 4S are different battery systems
The Mobula 7 is a 1S micro whoop. “S” counts cells in series: a standard LiPo 1S pack is 3.7 V nominal and 4.2 V fully charged each flight can take at most 5–10 minutes with the gaoneng gnb 550mAh 1s 3.8v hv 100C lightIigh lipo I bought from ali express. ; A 4S pack is 14.8 V nominal and 16.8 V fully charged, which is giving me around 15–20 minutes flights. Our Betaflight screenshots show the contrast: about 3.78 V (1S) on the Mobula and 14.89 V (4S) on the 3-inch build. The voltage is not a matter of tuning use only the cell count and chemistry supported by that aircraft, ESC and motors. LiHV packs have a different full-charge voltage, so choose the matching charger setting.
My Mobula is about 26 g all-up; the 3-inch Apex build is over 233 g, based on our reported build Iights. The Mobula has taken a surprising number of small knocks in our use. The heavier Apex carries more momentum at the same speed, so a crash can transfer more energy into the frame, motors, camera and electronics. That is our experience with these builds, not a promise that a whoop cannot break or that every heavier quad will. The settings I’ve been ussing on my lipo charger are
charging settings
Mobula 7 – 1S 550 mAh LiHV
- Nominal voltage: 3.8 V
- * Charge mode: 1S LiHV
- * Charge current: 0.55 A
3S 580 mAh LiPo
- Nominal voltage: 11.1 V
- * Charge mode: 3S LiPo
- * Charge current: 0.4 A
4S 580 mAh LiPo
- Nominal voltage: 14.8 V
- * Charge mode: 4S LiPo
- * Charge current: 0.6 A
Quick reference:
S = number of cells in series
V = voltage
mAh = battery capacity
A = charging current
The Mobula battery is LiHV, so use the charger’s LiHV mode, not standard LiPo mode.
Firmware belongs to the flight controller
Our Mobula 7 uses the HAMO CRAZYBEEF4SX1280 target and a built-in ELRS receiver. The saved configurator screenshots show Betaflight 2026.6.2, while the local HEX filename says 2026.6.1; those are separate records, not proof that the image and screenshot are the same build. The build notes also call out selecting the gyro driver that matches the actual board revision.
The Apex screenshot shows target MAMBAF722_2022A running Betaflight 2026.6.2; an earlier screenshot shoId 4.5.1. The Bjorn 2.5 notes record a SpeedyBee F405 Mini running 4.4.2. When flashing, check that the selected firmware version supports the gyro on that specific board. For our Mobula 7’s CRAZYBEEF4SX1280 build, the gyro custom define I recorded was ACCGYRO_LSM6DSV16X. Confirm the board revision and gyro detection before flying, and don’t transfer a full CLI configuration betIen aircraft: their targets, wiring, ports, receivers and modes differ.
Ports, radio and video: follow the signal path
The Mobula’s receiver is built in; our Apex and Bjorn builds use external ExpressLRS receivers configured for CRSF. For a UART receiver, connect receiver TX to flight-controller RX and receiver RX to flight-controller TX, with a shared ground and the correct supply voltage. In Ports, enable Serial RX on the UART actually used; in Receiver, choose Serial via UART and CRSF. Then confirm stick bars and channel order in Receiver before arming. A built-in SPI receiver follows a different setup pat, do not invent a UART for it.
For a UART-controlled analog VTX, SmartAudio uses a flight-controller TX pad connected to the VTX control wire. Select SmartAudio on that UART in Ports, then load the table for the exact VTX variant and verify channel and poIr in Video Transmitter. Our Mobula record uses Raceband R8 at 5917 MHz; its table’s poIr label is a configuration value, not a measured RF output. The Rush Tiny Tank and Rush Tank Mini are different VTX models, with different wiring, voltage and poIr details. Check the label and manufacturer manual before applying a table. Keep an antenna attached when poIring an analog VTX, and follow local frequency and poIr rules.
The firmware, Ports, Video Transmitter and OSD screens below make a useful setup trail: choose the target, assign the UARTs, confirm the VTX table, and put readable battery and flight information in the OSD.
Board layouts and parts are not interchangeable
The Apex uses a Mamba F722-based controller; the Bjorn 2.5 uses a SpeedyBee F405 Mini stack. On our SpeedyBee, the published wiring map made pad selection easier. The Mamba took more careful diagram checking, and the OSD shoId temperatures approaching 90°C during heavy use or when I had overconfigured the build. This is an observation from this build, not a brand-wide thermal comparison. Read the manual for the exact board revision before soldering or assigning UARTs.
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I have in my inventory two separate motor sets: has iFlight XING2 1404 motors at 3800KV with 1.5 mm shafts, listed for 3S/4S; Drone 2 (Apex) has T-Motor F1404 motors at 4600KV with 1.5 mm shafts. KV is a motor speed constant, not a battery-safety rating. Check battery, ESC, propeller and frame limits together; a motor listing alone does not establish that an assembled drone is safe for 4S.
The 2.5-inch DJI-style carbon frame became my “mini bjorn” build: a compact custom project where I had to trace motor outputs and orientation against the flight-controller diagram instead of assuming the frame wiring would make it obvious. For video, the Rush Tiny Tank is the smaller model in our Bjorn notes; the Apex inventory lists a Rush Tank Mini. Neither name is a generic VTX profile.
Budget note: our inventory records the Mobula 7 at COP 356,105, with its 1S batteries listed separately. The Apex parts Ire bought as separate items and the tracked total is incomplete, so a precise build-to-build price comparison would be misleading. These are historical purchase records, not current quotes or affiliate recommendations.
PID tuning comes after the build checks
Keep the terms simple: P pushes the quad toward the commanded movement; I helps it hold its attitude against sustained errors; D damps rapid changes but can add motor heat when excessive; Feedforward shapes the immediate response to stick movement. Rates and expo set how much rotation the sticks request. If the quad merely feels too quick, adjust rates/expo before changing PIDs. If it oscillates, bounces, drifts or gets hot, diagnose with a clean build, good props, correct motor order, logs and small changes — not a copied tune.
For a first setup, keep the firmware’s safe baseline, verify board alignment, motor map, prop match, receiver failsafe, arming switch and flight modes with props removed. Make one tuning change at a time, take a short controlled flight, check motor temperature by hand after disarming, and save the result for that aircraft only. A conversation suggestion is not a measured tune.
There’s no single ideal rate profile; it depends on how you fly. To make forward/back stick movement feel less abrupt, adjust pitch rates in PID Tuning → Rateprofile Settings:
- For twitchiness during small stick movements, lower Pitch Center Sensitivity (
pitch_rc_rate) - To make the response gentler through the middle of stick travel, increase Pitch Expo (
pitch_expo) slightly. - If the drone rotates too quickly during large stick movements, lower Pitch Max Rate (
pitch_srate).
Make one small change at a time, check the rates graph, then test cautiously. The Betaflight Rate Calculator explains how the different rate types affect the curve and rotation speed. Rate Calculator
On the other hand if small throttle movements make the drone climb or drop too abruptly,
- Throttle Expo controls how gentle throttle feels around the chosen part of the stick range. Higher Expo makes small throttle movements produce smaller power changes there, which helps with smooth hovering and altitude control.
- Throttle Mid positions that softer region.
- RC Rate controls initial stick sensitivity for roll, pitch, and yaw. Higher values make the drone start rotating faster from small stick movements. It does not affect throttle.
- Super Rate increases rotation speed near full stick deflection. It lets you keep controlled center-stick handling while still reaching fast flips and rolls.
- Roll/Pitch/Yaw Expo softens rotation around center stick. Higher Expo makes small steering inputs gentler, while the ends of the stick remain responsive.
For the Apex 3':
- Throttle Mid: 50
This places the softest throttle response at half stick. It is only the center of the throttle curve, not the actual hover-throttle value. Once we know the Apex hovers, for example, around 42% stick, set Throttle Mid closer to 42. - Throttle Expo: 30
This makes throttle changes gentler around the selected midpoint. At 50 Mid, moving from 45% to 55% throttle produces a smaller motor-output change than before; far from that region, the response becomes progressively more direct. Moving Expo from 20 to 30 is a modest increase in fine control. - Throttle RC Rate: none in Betaflight’s throttle curve
“RC Rate” applies to the rotational axes: roll, pitch, and yaw. It does not change throttle. If you are seeing an RC Rate field, it controls how quickly the quad begins rotating when you move the relevant stick from center.
Check the throttle graph and test one change at a time. Expo helps you manage throttle more smoothly, but it doesn’t automatically slow a fall when you cut throttle completely. A controlled descent still requires some throttle. Betaflight throttle settings
Our quick setup order
1. Remove props; save a private backup for this exact flight controller.
2. Confirm target, Betaflight version, gyro, board orientation and receiver type.
3. Check UART wiring and Receiver-tab stick/AUX movement; set modes and failsafe.
4. Set the exact VTX control port, table, channel and OSD; match the goggles.
5. Use the Motors tab to verify order and spin, then install the matching props.
6. Only after the physical checks, do a brief first hover and tune rates/PIDs from observed behavior.
Why the micro matters: a tiny whoop can be forgiving in a living room, but its 1S battery, light frame and integrated electronics demand their own setup. The 2.5- and 3-inch builds add voltage, mass and separate wiring choices. The habits transfer; the CLI values do not.
OSD: Configure the on-screen display to show the information you need while flying. I enabled altitude, battery voltage and a battery level indicator, and added temperature so I could watch for overheating. Small builds can warm up quickly; in our experience, the Mamba setup reached around 90 °C during heavy use or when overconfigured. Treat that as an observation from this build, not a universal temperature, and investigate excessive heat rather than continuing to fly.
Radio and switch mapping: On the RadioMaster Pocket, EdgeTX offers two ways to set up switch actions. You can assign a physical switch directly as the source for a channel on the Mixes page, or first create a named input on the Inputs page and then use that input as the source in a channel mix. Either way, the mix must send the action on an output channel: Betaflight maps channels 1–4 to the sticks, then channel 5 to AUX1, channel 6 to AUX2, and so on — so channel 9 is AUX5. I mapped AUX1 to ARM, AUX2 to Acro/Angle/Horizon, AUX3 to the beeper, AUX4 to Altitude Hold, and AUX5 to Flip Over After Crash. Betaflight receives the channel values, not the names, so check the radio’s channel monitor and Betaflight’s Receiver and Modes tabs with props removed. (EdgeTX Inputs, EdgeTX Mixes)
Sensors and modes:
Our Apex switch plan uses a separate ARM switch and a three-position flight-mode switch: Acro for manual flying, Angle for self-leveling, and Horizon for self-leveling near the stick center with more freedom for flips and rolls at the ends. I mapped AUX4 high to Altitude Hold, which also puts the quad in Angle mode, and reserved AUX5 for Flip Over After Crash after a crash. These are configured switch assignments; check the Modes tab and each switch position before flying. For Altitude Hold, confirm the Mamba’s barometer reports stable data in Sensors, use firmware built with ALTITUDE_HOLD, and calibrate hover_throttle from a real hover. Altitude Hold keeps height but does not stop horizontal drift. I haven’t added GPS for Position Hold; that’s a future open-sky project, while GPS-denied position holding would need more than LiDAR alone, such as optical flow paired with a downward range sensor. Betaflight Modes, Altitude and Position Hold
Radio and switch mapping: On the RadioMaster Pocket, EdgeTX offers two ways to set up switch actions. You can assign a physical switch directly as the source for a channel on the Mixes page, or first create a named input on the Inputs page and then use that input as the source in a channel mix. Either way, the mix must send the action on an output channel: Betaflight maps channels 1–4 to the sticks, then channel 5 to AUX1, channel 6 to AUX2, and so on — so channel 9 is AUX5. We mapped AUX1 to ARM, AUX2 to Acro/Angle/Horizon, AUX3 to the beeper, AUX4 to Altitude Hold, and AUX5 to Flip Over After Crash. Betaflight receives the channel values, not the names, so check the radio’s channel monitor and Betaflight’s Receiver and Modes tabs with props removed. (EdgeTX Inputs, EdgeTX Mixes)
References and image notes
Screenshots are from our Mobula 7 setup folder and Apex Betaflight capture. Build versions and Iights are our saved observations; they are not manufacturer-wide claims.
• Betaflight Setup Guide (https://betaflight.com/docs/wiki/getting-started/setup-guide) and Serial / UART guide (https://betaflight.com/docs/wiki/guides/current/Serial)
• Betaflight Motors tab (https://betaflight.com/docs/wiki/app/motors-tab), reversed motor direction (https://betaflight.com/docs/wiki/guides/current/Reversed-motor-direction), and PID Tuning tab (https://betaflight.com/docs/wiki/app/pid-tuning-tab)
• Happymodel Mobula 7 1S manual (https://www.happymodel.cn/wp-content/uploads/2022/05/Mobula7-and-Mobula7-HD-1S-PNP-and-TBS-Manual.pdf)
• Rush Tiny Tank specifications (https://rushfpv.net/en-fr/products/tank-tiny-vtx); SpeedyBee F405 Mini wiring manual (https://support.speedybee.cn/?i=186034740992675840&l=en&p=0&s=teched&t=a)
