# How to Fix Mid-Throttle Oscillations on Your FPV Drone
You’re cruising at 40% throttle and your quad suddenly develops the shakes — a rapid buzzing that appears at mid-throttle, disappears at higher or lower throttle, and makes your HD footage look like it was filmed during an earthquake. Mid-throttle oscillations are one of the most common and frustrating tuning issues in FPV, but they have a well-understood set of causes and fixes.
## What Are Mid-Throttle Oscillations?
Mid-throttle oscillations are rapid, small-amplitude vibrations that appear at roughly 30-60% throttle and vanish outside that range. They’re distinct from propwash (which happens during sharp drops and is low-frequency) and distinct from full-throttle shakes (which are usually bent props or bent motors).
| Issue | Frequency | Throttle Range | Feels Like |
|——-|———–|—————|————|
| Mid-throttle oscillation | High (150-250Hz) | 30-60% | Fine buzzing, image looks “fizzy” |
| Propwash | Low (20-50Hz) | During rapid descent | Wobble, quad bounces |
| Full-throttle shake | Medium (100-150Hz) | 80-100% | Coarse vibration, visible in camera |
| Yaw twitch | Low-medium | All ranges | Random yaw kick, usually one direction |
| I-term windup | Very low (<20Hz) | After fast moves | Slow drift, then sudden correction |
## Root Causes (Ranked)
1. **D gain too high** (most common) — 60% of cases
2. **P/D ratio imbalance** — 20% of cases
3. **Motor/prop resonance at specific RPM** — 10% of cases
4. **Frame resonance** — 5% of cases
5. **Noisy gyro / bad FC soft-mounting** — 5% of cases
## Step-by-Step Fix
### Step 1: Identify Which Axis Is Oscillating
Before changing anything, identify whether roll, pitch, or yaw is the culprit.
1. Enable Blackbox logging at 2kHz with GYRO_SCALED debug.
2. Fly a throttle sweep: hover, then slowly increase throttle from 20% to 60% and back down. Hold at the oscillation point for 5 seconds.
3. Open the log in Blackbox Explorer and look at the gyro graph for each axis separately.
4. The oscillating axis will show a thick, fuzzy trace during mid-throttle while the other axes remain clean.
5. If ALL axes oscillate simultaneously, it's likely a frame resonance, not a PID issue.
### Step 2: Reduce D Gain on the Offending Axis
D gain amplifies high-frequency noise. If D is too high, it magnifies tiny gyro fluctuations into motor commands that create more vibration, which creates more gyro noise — a feedback loop.
1. In the PID Tuning tab, note your current D gain for the oscillating axis.
2. Reduce it by 5 points (e.g., from 35 to 30).
3. Fly the same throttle sweep. Oscillation reduced? Continue decreasing by 3-5 until it's gone.
4. Stop reducing when you notice propwash becoming sluggish — that means D is now too low.
5. Find the sweet spot: the highest D that doesn't cause mid-throttle oscillation.
### Step 3: Adjust the P/D Ratio
P and D work as a team. A common cause of mid-throttle oscillation isn't high D in isolation — it's the ratio of P to D being wrong.
| P/D Ratio | Symptom | Fix |
|-----------|---------|-----|
| P too high relative to D | Bouncy stops, ringing after flips | Raise D or lower P |
| D too high relative to P | Mid-throttle buzz, mushy feel | Lower D or raise P |
| Both too high | Tight but oscillates mid-throttle | Reduce both proportionally |
| Both too low | Loose, poor tracking, drifts | Raise both proportionally |
**Rule of thumb**: D should be roughly 0.6-0.8 × P on pitch and roll for most 5-inch builds. For example, if P = 55, D should be around 33-44.
### Step 4: Apply TPA (Throttle PID Attenuation)
TPA reduces PID gains as throttle increases. It's designed specifically to address mid-to-high throttle oscillations.
1. In the PID Tuning tab, find the **Throttle PID Attenuation (TPA)** section.
2. Set **TPA Breakpoint** to the throttle level where oscillations begin (commonly 1250-1350 for 30-40% throttle).
3. Set **TPA Rate** to 0.15 (15% reduction at full throttle) as a starting point.
4. If oscillations persist, increase TPA Rate to 0.20-0.25.
5. Do not exceed 0.30 — excessive TPA makes the quad feel loose at high throttle.
### Step 5: Dynamic Notch Filter Tuning
If PID tuning doesn't resolve the issue, the oscillation is coming from a mechanical resonance that needs filtering.
1. In the PID Tuning tab → **Filters** section.
2. Ensure **Gyro RPM Filter** is enabled with 3 harmonics.
3. Set **Gyro Notch Filter 1** frequency to 0 (auto) and cutoff to 200Hz as a starting point.
4. Set **Gyro Notch Filter 2** frequency to 0 (auto) and cutoff to 100Hz.
5. Set **Dynamic Notch Filter** range to `LOW` (80-330Hz) for 5-inch builds, `MEDIUM` (160-660Hz) for smaller builds.
6. Set Dynamic Notch Width to 1.5 (wider notch catches more noise but reduces PID authority at that frequency).
7. Fly and check the spectrogram. If the mid-throttle noise band is now dim or gone, filters are working.
### Step 6: Hardware Fixes
If software tuning exhausts all options, address the mechanical source:
1. **Add a capacitor**: A 35V 470-1000µF low-ESR capacitor on the battery pads filters electrical noise that the gyro picks up. This is the single most effective hardware fix.
2. **Soft-mount motors**: Place a thin TPU or silicone pad between each motor and the arm. Some frames include these — if yours doesn't, cut them from 1mm silicone sheet.
3. **Replace props**: Even new props can be unbalanced. Try a different brand or pitch.
4. **Check arm stiffness**: Twist each arm by hand. If one arm is noticeably more flexible (delamination from a prior crash), replace the frame.
| Capacitor Type | Capacitance | Voltage | Best For |
|---------------|-------------|---------|----------|
| Panasonic FM | 1000µF | 35V | 5-7 inch builds, best overall |
| Panasonic FC | 470µF | 35V | 3-4 inch builds, space-constrained |
| Rubycon ZLH | 1000µF | 35V | Equivalent to Panasonic FM |
| No-name electrolytic | Any | 35V+ | Avoid — high ESR, ineffective |
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