Five33 UDL Spec Drone RTF (75mm)
Five33 (Happymodel Mobula7 V4 platform)
Underground Drone League spec-class 75mm race build
A hand-built 75mm 1S race whoop on the Happymodel Mobula7 V4 airframe, purpose-built for Five33's Underground Drone League Igniter spec class — the turnkey way to arrive race-legal with identical, RPM-limited hardware so racing comes down to pilot skill.
The SPI ELRS receiver is version-locked to Betaflight firmware (ExpressLRS 3.0, max 500Hz packet rate) and cannot be updated through the ExpressLRS Configurator; your ELRS radio must stay on compatible 3.x firmware to bind.
Made to order with a 2-4 week average lead time; battery and charger are not included.
Pre-built 'Hot & Ready' Friday drops of the same airframe sell for less than the made-to-order build but are usually sold out; the made-to-order listing is the dependable route.
The listing does not state the battery connector type; confirm the connector before buying 1S packs.
The full story
Each unit is hand-assembled in Five33's Maryville, Tennessee shop on the Happymodel Mobula7 V4 airframe. The electronics live on a single HDZero AIO5 board — flight controller, 4-in-1 , digital , and receiver on one thick PCB — paired with a RunCam HDZero Eco camera, EX0802 19,000KV motors, and 40mm HQProp props. Five33's in-house build team test-flies every drone before shipping, with a pro-level tune applied.
It exists for one job: UDL's 75mm Igniter class, which mandates identical, RPM-limited, LED-equipped builds at a class-minimum 40g all-up weight so racing comes down to pilot skill rather than hardware. That makes it deliberately slower than an open-class 75mm racer by design. The VTX output switches between 25mW and 200mW, and the linear-polarized antenna suits the indoor/track racing the class is built around.
Native HDZero video feeds straight into HDZero goggles like the BoxPro+ with no extra receiver module, and the feed keeps transmitting down to 2.5V so video outlasts the motors. The built-in SPI 2.4GHz receiver binds directly to any ELRS 2.4GHz radio with nothing external to mount. Because every component is an off-the-shelf catalog part Five33 sells individually, crash repairs are cheap and simple, and the single-board layout leaves minimal wiring to break.
Pros & cons
Pros
- Race-legal for UDL's 75mm Igniter spec class out of the box, including the mandatory LEDs (addressable or set-color options) and approved parts list
- Genuine HDZero digital video works natively with HDZero goggles such as the BoxPro+ -- no receiver module or conversion needed
- Hand-built and test-flown by Five33's in-house build team before shipping, with pro-level tune applied
Show all 7 pros
- Single-board HDZero AIO5 ( + 4-in-1 ESC + VTX + receiver on one thick PCB) means minimal wiring to break in crashes, and video keeps transmitting down to 2.5V so the feed never dies before the motors do
- Built-in SPI ExpressLRS 2.4GHz receiver binds directly to any ELRS 2.4GHz radio with no external RX to mount
- VTX output switchable between 25mW and 200mW
- Every component is an off-the-shelf catalog part (Happymodel V4 frame, HQProp 40mm props, HDZero AIO5, EX0802 motors, RunCam Eco camera) sold individually by Five33, so crash repairs are cheap and simple
Cons
- No battery or charger included -- 1S 450mAh packs are extra, and the listing does not state the battery connector type, so confirm before stocking packs
- Made to order with a 2-4 week average lead time; the cheaper pre-built 'Hot & Ready' Friday drops of the same airframe are usually sold out
- SPI ELRS receiver is version-locked to Betaflight firmware (ExpressLRS 3.0, max 500Hz packet rate) -- it cannot be updated through the ExpressLRS Configurator, so your ELRS radio must stay on compatible 3.x firmware to bind
Show all 7 cons
- Linear-polarized VTX antenna and 200mW ceiling limit range and multipath penetration versus circular-polarized, higher-power setups -- fine for the indoor/track racing it is built for
- RunCam HDZero Eco is the entry-level HDZero camera; the league's own build guides use the higher-end HDZero Lux
- Spec-class build by design: RPM limiter and 40g class-minimum weight cap performance, so it is deliberately slower than an open-class 75mm racer
- Warranty is limited to a 30-day defect claim window
Specs
Retailers & price history
| Retailer | Current | Stock | Lowest confirmed | Highest confirmed | Checked |
|---|---|---|---|---|---|
| Five33 (direct) | $251.99 | In stock | $251.99 (2026-07-02) | $251.99 (2026-07-02) | 2026-07-04 |
| Five33 (Hot & Ready drops) Limited pre-built Friday drops of the same airframe — usually sold out. |
$214.99 | Sold out | $214.99 (2026-07-02) | $214.99 (2026-07-02) | 2026-07-04 |
Current = cheapest ready-to-fly configuration (video system included, ELRS) tracked at that retailer; sold-out rows show the last listed price. Lowest/highest are from every confirmed scan since 2026-07-02 — the log grows with each stock check.
Replacement parts & batteries
Crash spares that fit this model, checked against the shops like everything else. Batteries show three price tiers — $ lowest, $$ middle, $$$ highest — among compatible in-stock packs.
Batteries
| Part | Price | Availability |
|---|---|---|
| BT2.0 550mAh 1S Battery (4PCS) $ 1S 550mAh 40C/80C LiHV · BT2.0 · 13.99g |
$15.99 | In stock at BetaFPV (direct) |
| LAVA 1S 450mAh 75C Battery (4PCS) $$ 1S 450mAh 75C LiHV · BT2.0 · 12.5g |
$17.99 | In stock at BetaFPV (direct) |
| LAVA II 1S Battery — 480mAh $$$ 1S 480mAh 95C LiHV · BT2.0 · 12.6g |
$21.99 | In stock at BetaFPV (direct) |
Props
| Part | Price | Availability |
|---|---|---|
| HQProp Ultralight 40mm Bi-Blade (1.0mm shaft) 40mm bi-blade · 1.2 pitch · 1.0mm shaft · 0.2g · set of 4 (2CW+2CCW) |
$2.25 | In stock at Five33 (direct) |
Motors
| Part | Price | Availability |
|---|---|---|
| Happymodel EX0802 19000KV motor EX0802 19000KV · 1.0mm shaft · unibell · 1.7g (4-pack at Five33, singles elsewhere) |
$12.99 | In stock at Pyrodrone |
Frames
| Part | Price | Availability |
|---|---|---|
| Happymodel V4 75mm Whoop Frame (Moblite7/Mobula7/Mobula7 1S) V4 75mm ducted whoop frame · max 40mm props · 5.4g |
$4.49 | In stock at RaceDayQuads |
Camera
| Part | Price | Availability |
|---|---|---|
| HDZero Eco camera HDZero Eco · 1/3in sensor · 720p60 4:3 · 98° vertical FOV · HD composite out |
$32.99 | In stock at HDZero.us |
Flight controller
| Part | Price | Availability |
|---|---|---|
| HDZero AIO5 (FC + ESC + HDZero VTX + ELRS RX) AIO5: F411 FC · 5A BLHeli_S 4-in-1 ESC · HDZero 5.8GHz VTX 25/200mW · SPI ELRS 2.4GHz · 25.5mm mount |
$114.99 | In stock at HDZero.us |
Chargers
| Part | Price | Availability |
|---|---|---|
| BT2.0 Battery Charger and Voltage Tester V2 1S BT2.0 charger + voltage tester (V2) · LiPo/LiHV |
$6.99 | In stock at BetaFPV (direct) |
| 6 Ports 1S Battery Charger & Adapter (BT2.0/PH2.0) 6-port 1S serial charger · BT2.0 + PH2.0 ports · LiPo/LiHV |
$11.99 | In stock at BetaFPV (direct) |
Other spares
| Part | Price | Availability |
|---|---|---|
| Five33 Adjustable Whoop Mount for Eco & BeeEye Camera TPU adjustable whoop camera mount for the Eco camera · $3.50 printed or free STL download |
$3.50 | In stock at Five33 (direct) |