65mm Build: Happymodel SE0702 28000KV + Gemfan 1219 3-blade

This combination sits at the aggressive end of 65mm. The SE0702 at 28000KV is a high-RPM motor for this frame class; the Gemfan 1219 3-blade is a high-pitch (1.9") 31mm tri-blade that loads it harder than a low-pitch or 2-blade prop would. The result is strong punch for indoor ripping, with a penalty in efficiency and heat. Plan your tune and filtering accordingly.

Hardware Checklist

• Frame: 65mm whoop frame — inspect duct integrity (no cracks or ovaled duct rings; a warped duct costs thrust and adds vibration), confirm canopy fit over the AIO stack, and prefer injection-molded nylon/PA12 over brittle materials that crack at the motor mounts. Keep all-up weight near the ~28g class target with battery
• Motors: Happymodel SE0702 28000KV — verify stator temp after first hover; these motors run warm under load
• Props: Gemfan 1219 3-blade — inspect hub fit on motor shaft; 1mm and 1.5mm shaft variants exist, confirm before ordering
• Battery: 1S only — the SE0702 at 28000KV is a 1S motor; on 2S it would spin toward ~235,000 RPM theoretical no-load and destroy itself. Typical packs for this class are 1S 260–450mAh (300mAh is the calculator preset); use HV cells with low internal resistance
• FC/ESC: AIO boards rated for the cell count; solder joints on a 65mm chassis carry high pulsed current — use quality solder and short wire runs

Measured Flight Time

First-hand numbers from this build, not model output. Source: data/bench/mobula6-2024-hdzero-se0702-28k.json.

One cruise run, 2026-08-05. The onboard current sensor read about 25% hot and is corrected by a 0.79 factor calibrated against a full-discharge anchor, so the current figure carries roughly 8% uncertainty. Hover and freestyle runs are not yet measured — those numbers are absent here rather than estimated.

For context, the same pack and props on a 25.42 g analog 65mm running VCI 0702 PRO 30000KV gave 233 s at 4.2 A — this HDZero build costs about 34% of the flight time. The video system is the dominant difference; the 2.3 g of extra airframe weight is secondary. See data/bench/air65-analog-vci0702-30k.json.

Betaflight Setup

Reference: betaflight.com — use the current stable release.

Configuration Tab

• ESC/Motor protocol: DSHOT300 minimum; DSHOT600 if FC supports it cleanly at this loop rate
• Gyro and PID loop: 4k/4k is a safe starting point; 8k/8k only if your FC handles it without scheduler overload
• Motor direction: props-out (recommended for whoops — better washout handling in tight spaces)
• Bidirectional DSHOT + RPM filtering: strongly recommended with high-KV motors — reduces noise without aggressive static filters

Filtering

High KV + 3-blade props generate substantial mid-to-high frequency noise. Start with RPM filtering enabled and dynamic notches active. Avoid over-filtering — excess filter delay will make fast direction changes feel mushy and hurt propwash recovery.

• Dynamic notch: medium width, count 3–4
• Gyro lowpass: keep as high as the noise floor allows — lower only if motors get hot
• D-term lowpass: tune after P is settled; lowering this is the first move if motors warm quickly

Tune Direction

This is not a beginner-tune combo. The high KV and 3-blade load mean the quad responds quickly and amplifies tune errors into oscillations fast.

• Start P lower than you think you need — increase until you see roll/pitch tracking sharpen, back off at first sign of oscillation
• D should be enough to dampen P, not so much that motors overheat within a pack
• I: use the Betaflight iterm_relax feature; anti-gravity helps on throttle punches
• Check the tune database for submitted 65mm SE0702 baselines before flying blind

Maiden Flight Protocol

1. Hover at 30–40% throttle for 30 seconds; land and check motor temperature by touch
2. If motors are hot immediately, reduce D-term lowpass cutoff before any other change
3. Progress to short indoor runs — full throttle punches against ceiling clearance, not wide-open outdoor flights
4. Log blackbox from the first pack; examine gyro vs. P-term trace before adjusting anything

Known Gotchas

• Prop shaft fit: loose props on 28000KV motors strip hubs fast — check torque fit before every session
• Battery sag: high-KV, 3-blade on 1S will sag a weak cell hard; use cells with low internal resistance
• Heat: back-to-back packs without cool-down can demagnetize small stators — let motors cool between packs
• AUW creep: every gram matters on 65mm; weigh the finished build in the calculator to verify thrust-to-weight before tuning