A gimbal is a pivoted support that lets an object rotate freely about one or more axes while the surrounding frame moves independently. Its key component is the pivoted ring — usually a pair of nested rings on orthogonal bearings — that decouples the payload from outside motion. The purpose is isolation: keep a compass, camera, or rocket nozzle pointed correctly while the platform pitches, rolls, or yaws. The outcome is steady output from a moving base, which is why every drone, naval compass binnacle, and DJI Ronin uses one.
Gimbal Interactive Calculator
Vary platform rock angle and isolation efficiency to see the required pivot motion, residual payload tilt, and gimbal-lock margin.
Equation Used
The calculator treats the gimbal pivot as cancelling a percentage of the frame rock angle. With ideal two-axis isolation, eta = 100%, the pivot motion equals the frame rock and the payload tilt is 0 deg. The remaining travel to 90 deg is shown as a simple gimbal-lock margin.
- Two gimbal axes are perpendicular and remain orthogonal.
- Friction, bearing play, inertia, and flex are ignored.
- Isolation efficiency represents how completely the pivot motion cancels frame motion.
- Gimbal lock is approximated as occurring when pivot travel reaches 90 deg.
Inside the Gimbal
A gimbal works by stacking single-degree-of-freedom pivots in series. Take a two-axis Cardan suspension — the inner ring carries the payload on one bearing axis, the outer ring carries the inner ring on a perpendicular axis, and the outer ring bolts to the host frame. When the host pitches, the outer pivot rotates relative to the frame and the inner ring stays put. When the host rolls, the inner pivot takes that motion. The payload sees nothing. Add a third ring perpendicular to the other two and you get a three-axis gimbal — the standard pivoted ring suspension you see in inertial measurement units and camera stabilisers.
The geometry only stays clean if the three axes remain mutually orthogonal. If two axes line up — which happens when one ring rotates 90° and collapses its rotation axis onto another — you lose a degree of freedom. That is gimbal lock. The payload can no longer rotate freely in the locked direction until you back one of the rings off. This is why Apollo 11's IMU had a fourth redundant gimbal added after the engineers calculated lock would happen during specific re-entry attitudes.
Tolerances matter more than people expect. Bearing radial play above roughly 0.02 mm per pivot shows up as visible jitter on a 200 mm camera lens — the payload wags through an arc proportional to lens length. Ring imbalance of even 5 g at 100 mm radius produces a torque the stabiliser motors must constantly fight, draining battery and heating the windings. Get the centre of mass off the rotation axis and a passive gimbal will hunt instead of settling. Active brushless gimbal motors hide some of this, but only some.
Key Components
- Inner ring (gimbal ring): Carries the payload directly on a single bearing axis. Must be stiff enough that the payload's centre of mass sits within ±0.1 mm of the rotation axis, otherwise unbalanced torque drives motor current up and produces drift on a passive system.
- Outer ring: Carries the inner ring on an axis perpendicular to the inner pivot. On marine compass binnacles this is the heavy brass yoke; on a DJI gimbal it is a forged aluminium arm. Stiffness here determines yaw response — a flexy outer ring lets the inner ring nod under acceleration.
- Pivot bearings: Typically deep-groove or angular-contact ball bearings, sized for low friction rather than load. Radial play target is under 0.02 mm. On precision IMU gimbals you see jewel pivots with run-out below 2 µm.
- Slip rings or flex circuits: Pass power and signal across each rotating axis without tangling the cable. Slip rings handle continuous rotation; flex ribbons cost less but limit travel to roughly ±180°. Failure here is the most common gimbal field failure on production camera rigs.
- Brushless gimbal motors (active systems): Direct-drive outrunner motors sized for low cogging torque, typically 50-200 mΩ winding resistance and 14-22 pole count. They hold position against an IMU feedback loop running at 1 kHz or faster.
- Counterweights: Used on passive gimbals like ship compasses to keep the payload's centre of mass below the pivot point. A compass card with 50 g of counterweight 30 mm below the pivot is self-righting under any normal vessel motion.
Real-World Applications of the Gimbal
Gimbals show up anywhere a payload must keep its orientation while the carrier moves. The exact construction differs hugely — a brass marine compass binnacle and a 3-axis brushless camera stabiliser share the same kinematic principle but nothing else — yet the underlying nested-ring geometry is the same.
- Marine navigation: Ritchie Navigation magnetic compass binnacles use a two-axis brass gimbal to keep the compass card horizontal as the vessel pitches and rolls.
- Aerospace / inertial navigation: The Apollo Guidance Computer's IMU used a four-gimbal platform built by MIT Instrumentation Laboratory to avoid gimbal lock during lunar re-entry.
- Cinematography: DJI Ronin 4D and Freefly MoVI Pro three-axis gimbals stabilise cinema cameras up to 10 kg using brushless gimbal motors with IMU feedback at 4 kHz.
- Consumer drones: DJI Mavic 3 carries a three-axis gimbal with hall-effect position sensors to hold the Hasselblad camera steady to within ±0.005° during flight.
- Defence / electro-optics: FLIR Star SAFIRE gimbals on coast guard helicopters carry thermal and visible cameras on a stabilised four-axis platform.
- Spaceflight propulsion: SpaceX Merlin 1D engines use hydraulic gimbal actuators to vector thrust ±5° for steering during ascent.
- Entertainment rides: Disney's Soarin' Around the World ride uses a large-scale gimbal frame to pitch and roll seated guests in front of a domed screen.
The Formula Behind the Gimbal
The most useful design calculation for a gimbal is the motor torque required to hold the payload steady against an unbalanced mass offset. Get this wrong and the motors either saturate (payload drifts under acceleration) or run hot at idle (battery drains, windings cook). At the low end of the typical range — say a 200 g action camera with 1 mm of mass offset — required holding torque is trivial and almost any 2204-size brushless gimbal motor will do. At the high end — a 6 kg cinema camera with 3 mm offset on a moving vehicle — you need a 5208-size motor and you must rebalance every time you change a lens. The sweet spot for a handheld three-axis stabiliser sits around 1.5 kg payload and under 0.5 mm residual offset.
Variables
| Symbol | Meaning | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| τhold | Motor holding torque required at the rotation axis | N·m | lb·in |
| m | Payload mass | kg | lb |
| g | Gravitational acceleration (9.81) | m/s² | ft/s² |
| d | Offset of payload centre of mass from rotation axis | m | in |
| θ | Tilt angle of the gimbal axis from horizontal | rad or ° | rad or ° |
| I | Payload moment of inertia about the rotation axis | kg·m² | lb·in² |
| α | Angular acceleration the gimbal must produce to track motion | rad/s² | rad/s² |
Worked Example: Gimbal in a handheld cinema camera stabiliser
A documentary camera operator in Copenhagen is sizing the pitch-axis brushless motor on a custom three-axis gimbal carrying a Sony FX3 with a 24-70 mm zoom lens. Total payload mass is 2.4 kg. The operator achieves balance to within 0.5 mm of the rotation axis after careful setup. The gimbal must hold the camera level while tilted up to 45° and track angular accelerations up to 10 rad/s² during running shots. Payload moment of inertia about the pitch axis measures 0.018 kg·m².
Given
- m = 2.4 kg
- d = 0.0005 m
- θ = 45 °
- I = 0.018 kg·m²
- α = 10 rad/s²
Solution
Step 1 — compute the static gravity torque from the residual mass offset at nominal 45° tilt:
Step 2 — compute the dynamic torque needed to track 10 rad/s² acceleration:
Step 3 — sum to get nominal holding torque:
The dynamic term dominates by more than 20×. Now check the low end of the typical operating range — slow walking shots where α drops to roughly 2 rad/s²:
At this level a 5208-size brushless gimbal motor idles cool and the operator gets buttery footage with motor current under 0.3 A. Now the high end — a running shot with sudden direction changes pushing α to 25 rad/s²:
That is approaching the saturation torque of a 5208 motor. In practice, peaks above 0.4 N·m on this size motor show up as the horizon momentarily tipping during fast pans — the IMU loop commands more current than the motor can deliver and the payload lags by a few degrees before recovering.
Result
Nominal holding torque is 0. 188 N·m, which a properly-sized 5208 brushless gimbal motor handles comfortably with headroom for the IMU loop. At low-speed walking shots the motor sees just 0.044 N·m and runs cool; at running-shot peaks of 0.458 N·m the same motor saturates and you get a visible horizon tip during fast direction changes — the sweet spot for this rig sits between 5 and 15 rad/s² of commanded acceleration. If your measured holding current exceeds predicted by 30% or more, suspect (1) residual mass offset above the assumed 0.5 mm because you swapped lenses without rebalancing, (2) a dragging slip ring adding parasitic friction torque, or (3) bearing preload set too high during assembly causing the pivot to bind near 45° tilt.
Choosing the Gimbal: Pros and Cons
A gimbal is one of several ways to keep a payload pointed correctly on a moving platform. The alternatives — fixed mounts with electronic image stabilisation, or pure software stabilisation in post — trade mechanical complexity for compute and cropping. Pick based on payload mass, required pointing accuracy, and how much real-time correction you need.
| Property | 3-axis Mechanical Gimbal | Electronic Image Stabilisation (EIS) | Optical Image Stabilisation (OIS) in lens |
|---|---|---|---|
| Pointing accuracy | ±0.005° (DJI RS class) | ±0.1° equivalent after crop | ±0.02° but limited to small angles |
| Payload capacity | 0.1 kg to 50 kg depending on size | Sensor only — no payload | Lens element only, sub-gram |
| Correction range | ±180° per axis (full hemisphere) | ±2-5° before crop becomes visible | ±1-2° typical |
| Cost | $300-$15,000 for handheld; $50k+ for ENG/military | Software only — built into camera | $50-$500 added to lens cost |
| Latency | 1-2 ms (1 kHz IMU loop) | 1 frame minimum, often more | Sub-millisecond |
| Failure mode | Slip ring wear, motor saturation, gimbal lock | Crop artefacts, rolling-shutter wobble | Lens element drift over temperature |
| Best application fit | Cinema, drones, marine compass, missile seekers | Smartphone video, action cams | Telephoto stills, low-light handheld |
Frequently Asked Questions About Gimbal
A still gimbal should draw near-zero current. If yours is hot at idle, the payload's centre of mass is not on the rotation axis — the motor is fighting gravity continuously to hold the offset. Loosen the axis lock, let the camera find its natural rest position, and adjust the sled until it stays put at any angle you release it. On a properly balanced rig, motor current at idle should sit under 0.1 A per axis.
The other common cause is bearing preload. If you over-tightened a pivot during assembly, the motor fights friction the whole time. You should be able to flick a balanced gimbal axis by hand and watch it coast for several seconds before stopping.
Two axes (pitch and roll) are enough if the platform's yaw motion is either irrelevant or already controlled — a marine compass does not need yaw stabilisation because it measures yaw deliberately, and a fixed-mount drone camera that always faces forward only needs pitch and roll cleaned up. Add the third axis (yaw/pan) only when the operator needs to look in a different direction than the platform travels, or when platform yaw is unpredictable, like a handheld walking shot or a helicopter EO turret.
The cost is real — the third axis adds mass, a slip ring, another motor, and roughly 30% more battery draw. Don't add it just because the marketing photos look cooler.
Gimbal lock occurs when two of the three rotation axes align, collapsing three degrees of freedom down to two. Once locked, you cannot rotate freely in the lost direction without first un-aligning the rings. On a typical handheld camera gimbal it almost never happens because the operator does not point the camera straight up or straight down for sustained periods. On a drone tilting fully nose-down to inspect rooftops, it can — which is why some drones use a fourth redundant gimbal or quaternion-based control to slew through the singularity.
Apollo 11's IMU had this exact issue. Mike Collins added a fourth gimbal to avoid the lock condition that would have occurred during specific re-entry orientations.
Running adds high angular acceleration peaks that the motor cannot deliver. The IMU is commanding more torque than the motor can produce — at saturation, the payload lags the command by a few degrees until the disturbance ends. Two fixes: rebalance more carefully so the static term drops to near zero (giving you full motor torque headroom for dynamics), or move up to a larger motor size. A 5208 motor handles roughly 0.4 N·m peak; a 6208 handles closer to 0.9 N·m.
The other thing to check is IMU mount stiffness. If the IMU board is on a flexible bracket, it sees its own ringing during running steps and over-corrects.
You can, but you shouldn't for any precision application. Brushed motors have cogging torque from commutator switching that telegraphs into the payload as visible jitter — typically 0.5-2° peak-to-peak at low speeds. Brushless gimbal motors are wound specifically for low cogging (high pole count, distributed windings) and are direct-drive, so there is no gear backlash. The only place a brushed motor with a gearbox makes sense is a slow-tracking platform where the payload moves rarely and steady-state pointing accuracy below 0.5° is acceptable.
For a 2 kg cinema rig, residual offset above about 1 mm starts forcing the motor to draw measurable continuous current. Above 3 mm the motor will saturate during normal panning and you'll see the horizon tip on direction changes. The professional benchmark — DJI Ronin 4D auto-tune passes — is roughly 0.3 mm offset, which puts the gravity-torque term well below the dynamic-torque term at all reasonable accelerations.
Quick check: with the gimbal off, set the camera at 45°. If it holds position without falling either way, you are under 0.5 mm offset. If it falls, calculate how fast it falls — angular acceleration of free-fall under 0.5 rad/s² means you're roughly within spec.
Slip rings carry power and signal across a continuously rotating joint through sliding contacts — typically gold-on-gold or silver-graphite brushes on a metal track. Every rotation generates contact wear and microscopic debris that eventually shorts adjacent tracks or opens a connection. Production camera rigs commonly see slip-ring life in the 500-2000 operating-hour range, much shorter than motor or bearing life.
If you are seeing intermittent video dropout or HDMI handshake failures during pan moves, the slip ring is the first place to look. Replacement is straightforward on most professional gimbals; on consumer units the slip ring is usually integrated and you replace the whole arm.
References & Further Reading
- Wikipedia contributors. Gimbal. Wikipedia
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