Your quad turns left faster than right. Pitch response is snappy but roll feels sluggish. You’ve tuned PIDs, changed rates, swapped props — and the problem persists. You’re fighting your center of gravity. Here’s how CG placement changes everything about how your drone flies, and how to get it right.
Why CG Matters More Than Most Pilots Realize
FPV quads are symmetric in frame geometry but rarely in mass distribution. The battery (typically 150-220g) sits on top or bottom, the HD camera (30-60g) in front or rear, and the stack (15-25g) in the center. A forward-heavy CG means the rear motors work harder to maintain level flight. A top-heavy CG means the quad pendulum-swings through sharp turns. Neither feels locked in.
When your CG is off, the PID loop compensates — but it compensates with motor authority, which costs you dynamic range. A quad with a perfectly centered CG uses less motor headroom for basic stabilization, leaving more for aggressive maneuvers. On a 5-inch build, moving the battery 15mm forward or backward changes the pitch moment of inertia by roughly 15-20%, which you absolutely feel in flight.
Finding Your Actual CG
Method 1: The balance test. With the battery strapped in and props off, balance the quad on two parallel objects (pencils, dowels) — one under each side, perpendicular to the arms. Slide the quad until it tips neither forward nor backward. The balance point is your pitch CG.
Now rotate the quad 90 degrees and balance it side-to-side. The roll CG should be dead center — if it’s not, your components are mounted asymmetrically (check RX, VTX, capacitor placement).
Method 2: The string test. Tie a loop of fishing line around a rear standoff and a front standoff. Lift from each attachment point separately. If the quad hangs level from both, your CG is centered. If the front hangs lower, you’re nose-heavy.
The target: CG should fall within 5mm of the flight controller center in both axes. Beyond 10mm offset, you’ll feel it in flight.
Battery Placement: Top-Mount vs Bottom-Mount
The battery is the heaviest single component. Its position determines the pendulum effect — the tendency of the quad to swing during sharp direction changes.
Top-mount (battery on top): Higher CG. The quad pendulum-swings in corners — it feels “floaty” and takes longer to settle after aggressive turns. Freestyle pilots often prefer this because the swing adds a sense of mass and momentum to flips. But it costs you cornering precision.
Bottom-mount (battery underneath): Lower CG. Snappier cornering, less pendulum. The quad stops rotating exactly when you center the stick. Racers overwhelmingly prefer bottom-mount — every millisecond of settling time matters in a race gate. The trade-off: landing on the battery pack means more battery damage in crashes.
The hybrid solution: Run a 20-25mm battery on top but use a low-profile mount that keeps it as close to the frame as possible. On a 5-inch frame, reducing the battery-to-frame gap from 15mm to 5mm noticeably reduces the pendulum effect without the crash-damage risk of bottom-mount.
CG and Flight Characteristics
| CG Position | Pitch Response | Roll Response | Yaw Behavior | Best For |
|---|---|---|---|---|
| Centered (ideal) | Symmetrical forward/backward flips | Symmetrical left/right rolls | Flat, predictable yaw | All-around, racing |
| Forward bias (nose-heavy) | Backflips faster than front flips | Minimal roll impact | Nose drops in coordinated turns | Cinematic (natural forward tilt) |
| Rear bias (tail-heavy) | Front flips faster than backflips | Minimal roll impact | Tail drops in turns, quad feels “loose” | Freestyle (helps with inverted hang time) |
| High CG (tall battery) | Slow pitch settling after flips | Slow roll settling | Pendulum in sharp corner exits | Freestyle flow |
| Low CG (slammed battery) | Quick pitch recovery | Quick roll recovery | Flat cornering, no pendulum | Racing, precision |
| Lateral bias (left/right) | Minimal | Asymmetric roll rates | Asymmetric coordinated turns | Avoid — fix component placement |
Practical CG Tuning
For racing: Bottom-mount the battery or top-mount with the slimmest possible strap. Run the HD camera as far back as the frame allows. Every gram you pull toward the center reduces settling time by measurable milliseconds. A 5g weight shift at the camera mount changes pitch CG by roughly 2-3mm.
For freestyle: Slightly rear-biased CG helps with inverted hang time. When the quad is upside down, a rear-heavy CG naturally pulls the tail up, which makes Matty flips and inverted yaw spins feel more controllable. Move the battery 5-8mm rearward from center. Test with 3 packs before committing — too far rearward and the quad feels “twitchy” in forward flight.
For cinematic/long-range: Forward CG bias works with the natural forward tilt of cruise flight. At 25-30 degrees of forward tilt, a slightly nose-heavy quad requires less pitch correction, which means smoother footage. The GPS module on the rear acts as a natural counterbalance — position the battery to offset it.
What Most Pilots Get Wrong
Mistake 1: Ignoring CG after a rebuild. You swap an ESC, move the capacitor to a different pad, or add a GPS module, and suddenly the quad flies differently. You retune PIDs without checking CG. The PIDs mask the problem but don’t fix it — you’re burning motor authority on compensation.
Consequence: Higher motor temperatures, shorter flight times, and a quad that never quite feels “dialed” no matter how much you tune.
Fix: Measure CG after any component change. Takes 30 seconds with the balance test. If CG shifted, move components to compensate before touching PIDs.
Mistake 2: Using a 6S 1300mAh battery where a 4S 1500mAh was designed. Different cell counts mean different battery dimensions and mass. A 6S pack is taller and often longer than a 4S pack of equivalent energy. The CG shifts up and possibly forward.
Consequence: Quad flies noticeably different after a voltage upgrade that “shouldn’t” change handling. You think it’s the extra power — it’s the extra 30g and shifted CG.
Fix: When changing battery format, re-measure CG. You may need to adjust battery position by 10-15mm forward or backward to compensate. This is especially true going from 4S to 6S — the battery is taller and the CG rises.
Mistake 3: Cameras mounted far forward on long standoffs. A GoPro on a 3D-printed mount extending 40mm forward of the frame nose shifts pitch CG significantly forward. At 60g for a GoPro Hero 11 Mini, that’s the equivalent of moving your battery 25mm forward.
Consequence: Rear motors run 5-10% hotter trying to keep the nose up. Flight time drops 30-45 seconds. Pitch response becomes asymmetrical.
Fix: Use the shortest camera mount that clears the props. TPU mounts that hug the frame nose shift CG less than rigid ABS extensions. Or counterbalance with a small weight at the rear — 15-20g of tungsten putty under the rear standoffs offsets a forward-mounted GoPro.
⚠️ Regulatory Notice: The flight recommendations in this article should be followed in accordance with the latest 2026 drone regulations in your country or region. Always verify local laws regarding flight altitude, no-fly zones, remote ID requirements, and registration before flying. Regulations vary significantly between the FAA (US), EASA (EU), CAA (UK), CAAC (China), and other authorities. Sub-250g builds have different regulatory requirements in many jurisdictions — weight distribution decisions that push your build over 250g may change your regulatory category.
Related Guides
CG affects motor loading, which affects sizing — our FPV Motor Sizing guide covers the torque requirements for different weight distributions. For frame geometry choices that interact with CG, see FPV Frame Geometry: Deadcat vs True X vs Squashed X. And when you’ve got CG dialed, Betaflight Rates Deep Dive helps you match rates to your quad’s actual rotational inertia.
Recommended Product
Getting CG right starts with a frame that gives you battery placement flexibility. The TBS Source One V5 frame, stocked at uavmodel.com, has adjustable battery mounting positions and enough top-plate real estate to shift components for perfect CG. Pair it with a low-profile battery strap and you can get the pack within 3mm of the frame top for minimal pendulum.