What soft mounting does
Oscar Liang describes soft mounting as isolating the gyro from frame vibration. The usual payoff is fewer mid-throttle oscillations and twitching, room for a cleaner tune, and sometimes less video noise when mechanical vibration couples into the electronics. It will not fix a bent motor shaft, a chipped prop or electrical noise on the power bus. Those still show up on the gyro. Soft mount is for systemic frame resonance, not a single broken part.
Betaflight's soft-mounting notes (ctzsnooze) add an important caveat: real dampers act a bit like springs. Ideal isolation is viscoelastic and cuts high frequencies without a strong resonant peak. Hard rubber foam and stiff silicone can pass less noise overall and still ring near the cutoff. So soft mount is not "the softer the better." Too soft, or stacked with too many layers, can introduce a slow wobble that feels like too much I-term. Too hard, or overtightened, behaves like a solid standoff.
Oscar Liang's 2024 update is blunt: software filtering is good enough that most clean builds with a decent gyro do not need exotic motor soft mounts anymore. Almost every FC already includes gummies. The remaining skill is not buying more dampers. It is using the ones you have without defeating them.
How modern gummies fit
Most 30.5 x 30.5 mm boards use oversized holes so an M3 silicone grommet sits in the board and an M3 screw passes through the soft centre. The ESC usually hard-mounts to the frame. The FC sits above it on the gummies. That is the common stack: rigid ESC, soft FC.
Oscar Liang's stack advice from his tuning guide:
- Use metal screws for the stack. Nylon screws and nylon standoffs break easily and can add their own vibration.
- Lock the long stack bolts into the frame with metal nuts (or use the frame's pressed inserts) so the bolts themselves cannot wiggle.
- Soft-mount only the FC with the rubber grommets. Put nylon or plastic nuts on top and tighten by hand until the gummies are slightly compressed, not crushed.
If the gummies bulge sideways into a flat pancake, you have gone too far. IntoFPV builders describe the same rule of thumb: a little squish so the board cannot rattle, still enough give that the FC can move slightly. Crushing them hard can make the accelerometer drift and, in extreme cases, confuse Angle mode.
Details that defeat a soft mount
ctzsnooze's Betaflight write-up stresses that soft mount only works when the board really floats:
- If the screw holes are a tight fit on the bolts, the hole edges bind on yaw and transmit vibration. Older advice was to open the holes to about 4 mm and bevel the edges so the board recentres on the O-rings or gummies. Modern gummy holes are already oversized for that reason.
- Stiff wires act as vibration bridges. Use fine silicone wire with slack between the FC and the ESC. A ribbon cable pulled tight defeats the gummies.
- Nothing else should press on the FC: zip ties, camera wires, VTX leads, a battery strap rubbing the board.
Oscar Liang makes the same point: keep wires and zip ties off the FC so they cannot reintroduce frame vibration.
Motors: soft mount only when you have to
Motor soft mounting (TPU pads, rubber sheets, tape under the bells) attacks vibration at the source. In 2017 Oscar Liang tried it and concluded it was a hassle: you cannot fully tighten the motor screws, you must check them every session, and uneven tightness across four motors makes results inconsistent. His 2024 update is clearer still: with modern filtering, you generally do not need to soft-mount motors. Soft-mount the FC with the supplied gummies and keep the motors hard-mounted and Loctited.
Keep motor soft mounting as a last resort for a build that still rings after props, bearings, capacitors and FC gummies are sorted.
How to check that it helped
Before you loosen filters or raise D, confirm the hardware change did something.
- Props off. In Betaflight Configurator, open Motors (or Sensors with Expert mode). Spin each motor and watch the gyro. A bad bearing or bent shaft will stick out on one motor. Soft mount will not hide that.
- Fly a short pack with Blackbox at a high logging rate and look at the raw gyro spectrum before and after you change the mount. You want a lower noise floor and less broadband junk between motor harmonics, not a new low-frequency wobble.
- Only then consider easing filters. Soft mount that makes the log cleaner is permission to filter less. Soft mount that changes nothing means look elsewhere: props, motor shaft, ESC capacitor, or a damaged gyro.
Unmanned Tech's gyro troubleshooting note is useful here: most "bad gyro" symptoms are frame resonance, chipped props, wrong mounting or electrical noise. A motionless FC on the bench with a smooth Sensors graph and a noisy log in the air points at the airframe, not a dead IMU.
Practical order of work
When a new build feels harsh at mid throttle:
- Fresh, undamaged props. Try another set before you touch hardware.
- Confirm FC gummies are installed and only lightly compressed. Remount if the board is hard against carbon or another board.
- Add or check the low-ESR capacitor on the ESC/battery leads if it is missing (covered in the ESC capacitor article on this site).
- Soft-mount motors only if the log still looks ugly after the steps above.
- Replace the FC or gyro if soft mounting is correct and the yaw axis still twitches the way ctzsnooze describes for certain chip samples.
Soft mounting is cheap and usually already in the bag with the FC. Treat it as part of the build, not an optional afterthought, and do not crush the gummies when you tighten the stack.