In multirotor drone design,the layout of motors and propellers directly determines the aircraft's performance,stability,and applicable scenarios.The most common multirotor structure is the conventional layout(one propeller and one motor mounted per arm),while another more specialized solution is the coaxial layout(one propeller mounted above and below on each arm,driven by two motors).
The two layouts differ significantly in appearance,but the real distinctions lie not only in the number of propellers but also involve multiple aspects such as aerodynamic efficiency,thrust-to-weight ratio,redundancy,occupied space,and maintenance costs.For drones used in aerial photography,surveying,transportation,or operations in special environments,choosing the appropriate layout can significantly enhance mission completion and flight safety.This article will detail the structural principles of coaxial drone motors and provide a multi-dimensional comparison with the conventional layout,helping you make more rational decisions in practical selection.
I.What is a Conventional Layout Drone Motor?
"Conventional layout"refers to each arm being equipped with only one motor and one propeller.Torque balance and attitude control of the entire aircraft are achieved by arranging propeller rotations in alternating CW/CCW directions across the arms.Typical models include quadcopters,hexacopters,and octocopters,which are currently the most widespread multirotor form,widely used in consumer,commercial,and industrial drone fields.
1.Working Principle
In the conventional layout,each motor directly drives its corresponding single propeller.The flight controller(FC)precisely adjusts motor speed to distribute lift and torque:
Overall speed increase/decrease→Changes total thrust,controlling climb and descent.
Differential speed adjustment→Changes thrust distribution across axes,achieving hover,forward/backward translation,lateral movement,and yaw rotation.
To counteract the counter-torque generated by propeller rotation,the conventional layout typically follows the"adjacent reverse rotation"principle(CW/CCW alternation),ensuring the airframe remains stable under balanced thrust without spinning.
In design,propeller diameter and pitch,motor KV value,and torque characteristics jointly determine the efficiency,response speed,and control precision of the powertrain.
2.Conventional Layout Drone Motor Matching
Powertrain matching for the conventional layout usually involves independently selecting motors,ESCs,and propellers to achieve performance balance.First,determine the required thrust based on the drone's total weight,then select the appropriate propeller.The propeller's size and pitch dictate the required motor KV value and torque–large props pair with low KV motors for efficiency,small props pair with high KV motors for responsiveness.Finally,select an ESC with a 20-30%safety margin based on the motor's maximum current under full load,ensuring its voltage matches the battery.
This independent matching approach allows free combination for specific tasks.Simultaneously,due to the independence of components,maintenance and replacement are more convenient and lower cost,making it the most mainstream configuration.
3.Conventional Layout Applicable Scenarios
Aerial Photography&Filmmaking:
Requires high image stability and platform responsiveness.Conventional layout has low vibration,fast attitude adjustment,enabling long hover times and smooth maneuvers.
FPV Racing&Freestyle:
Emphasizes lightweight and high maneuverability.Single-propeller direct drive reduces weight and rotational inertia,significantly improving acceleration,hard stops,and rapid turns.
Consumer&Recreational:
Simple structure,fewer parts,low production and assembly costs,easy maintenance,very suitable for beginners and mass-produced models.
Industrial&Surveying:
Paired with efficient blades and high-torque motors,can stably carry surveying cameras,sensors,etc.,ensuring flight stability and endurance.
4.Conventional Layout Advantages
Simpler structure,lighter weight:
Fewer motors and propellers reduce overall weight,benefiting endurance and maneuverability.
Less aerodynamic interference,higher efficiency:
Lower airflow interference between props improves propulsion efficiency and reduces vortex losses,aiding thermal management.
Cost and maintenance friendly:
Requires fewer motors,ESCs,propellers;replacement and repair are simple and low cost.
Faster response speed:
Low inertia of motor and propeller allows more sensitive FC adjustments,suitable for tasks demanding high control precision.
Good versatility:
A large market exists for motors,propellers,and frames of various specifications,providing rich choices for numerous applications.
5.Conventional Layout Limitations
Low redundancy:
For example,in a quadcopter,failure of one motor directly leads to loss of control,unlike coaxial layouts which can maintain flight with the remaining propeller set.
Large arm span required:
To accommodate large-diameter propellers,sufficient spacing between arms is needed,affecting takeoff/landing and operational convenience in confined spaces.
Thrust expansion limited:
Thrust increase relies mainly on switching to higher-power motors or larger props;further increases face structural and aerodynamic limits,encountering diminishing marginal returns.
Lower stability:
Relies on FC algorithms for attitude stabilization,but its response and resistance capability are relatively weaker compared to coaxial in sudden gusts or crosswinds.Especially during rapid vertical descent,it's prone to entering its own turbulent wake,causing airframe vibration and oscillation.
II.What is a Coaxial Layout Drone Motor?
Coaxial layout refers to mounting one motor and one propeller above and below on the same arm.Both propellers share the same axis and rotate in opposite directions:
the upper propeller is driven by the upper motor,and the lower propeller by the lower motor.Thus,a single arm can combine the lift of two propellers,significantly increasing the aircraft's available thrust density without increasing the number of arms.This layout is common in high-payload models like coaxial hexacopters(12 props)and coaxial octocopters(16 props).
1.Working Principle
The upper and lower propellers naturally counteract counter-torque by rotating in opposite directions,reducing the extra power allocation needed for attitude stabilization.The FC controls the speed of both upper and lower motors separately:
Lift adjustment→Upper and lower props accelerate or decelerate synchronously,changing total thrust for climb,descent,or hover.
Attitude adjustment→Upper and lower props can perform fine differential speed changes,cooperating with other arms for pitch,roll,yaw,etc.
Due to wake interference between the upper and lower props,the lower propeller operates in disturbed airflow,resulting in an overall aerodynamic efficiency loss of approximately 10-15%compared to a single-prop layout.However,this is traded for higher thrust density and control redundancy.This characteristic makes it more suitable for space-constrained,high-payload flight tasks.
2.Coaxial Drone Motor Matching
Because the lower propeller in a coaxial layout is affected by the wake of the upper propeller,leading to thrust loss and extra vibration,traditional independent component matching struggles to achieve optimal efficiency.Therefore,integrated powertrains(e.g.,T-Motor A-Series and T-Motor X-Series)are recommended.This solution involves precise pre-calibration and integration of motors,ESCs,and propellers at the factory.By optimizing parameters like upper/lower motor speed and power distribution,it minimizes efficiency loss and noise caused by"blade-vortex interaction"(BVI),solving the user's matching difficulties.
Integrated powertrains feature plug-and-play modular design,simplifying installation,reducing wiring and failure points.They integrate FOC vector control ESCs,efficient cooling structures,and multiple smart protection features(over-temp,over-current,etc.),ensuring reliability under demanding applications like heavy payloads and long endurance.Therefore,this solution is preferred in professional and commercial drone fields like agricultural spraying and industrial inspection,providing stability and performance assurance over independent matching.
3.Coaxial Layout Applicable Scenarios
Heavy Payload Transport&Multi-Sensor Tasks:
Increases total thrust without extending arms,capable of carrying multispectral cameras,LiDAR,surveying equipment,or heavy delivery payloads.
Shipboard&Confined Platform Takeoff/Landing:
More compact airframe on restricted decks,mountains,rooftops,etc.,enhances takeoff/landing safety and operational convenience.
Operations in Strong Wind Conditions:
Dual-propeller combined lift provides greater control margin,aiding attitude stability in turbulence or high winds.
Tasks Requiring High Redundancy:
If one propeller fails,the other can maintain limited flight capability to some extent,increasing safety.
4.Coaxial Layout Advantages
Higher total thrust for the same footprint:
"Dual-prop stacking"per arm significantly increases thrust density,suitable for high payloads and strong wind operations.
Compact volume,deployment friendly:
Maintains high lift output even with limited arm span,beneficial for shipboard,rooftop,and other space-constrained environments.
Improved stability and redundancy:
Counter-torque cancellation between upper/lower props enables more stable flight control;offers some safety redundancy under certain failure conditions.
5.Coaxial Layout Disadvantages
Efficiency and endurance penalty:
Wake interference between upper/lower props causes~10-15%efficiency loss.Under light loads,conventional layout is more power-efficient.
Increased power consumption and heat:
Dual motors operating simultaneously cause a significant rise in total current.Insufficient power systems may lead to voltage sag or overheating.
Increased weight and complexity:
Additional motors,ESCs,propellers,and structural parts increase overall weight and number of potential failure points.
Reduced maneuverability:
Higher inertia and extra aerodynamic losses make it unsuitable for high-acceleration,high-turn-rate competitive flying.
Noise issue:
The significant noise of coaxial systems stems not only from doubled motor count.The lower propeller cutting through the downwash and tip vortices generated by the upper propeller creates strong"Blade-Vortex Interaction"(BVI),resulting in noise 5-10dB higher than conventional structures.
Higher cost:
Doubled motors and ESCs,plus more complex frame design and wiring,lead to higher initial manufacturing costs and more potential failure points.
6.Coaxial Selection and Matching Tips
Define"Payload and Endurance"goals first:
Confirm the necessity of coaxial to avoid"using dual props just for the sake of it."
Account for the battery:
Increased power consumption requires upgrading battery capacity and discharge rate(C-rating),verified by real-world testing.
Include all structural and wiring weight:
Additional weights like brackets,quick releases,wire harnesses,etc.,must be included in power and thrust-to-weight calculations.
Modify cautiously:
Converting from conventional to coaxial requires coordinated optimization of FC parameters,ESCs,and power systems,plus aerodynamic testing.Avoid"crude add-on"installations.
Coaxial vs. Conventional Motor Pros and Cons Comparison Table:
Dimension | Conventional Layout | Coaxial Layout | Advantage Over the Other |
Structure & Complexity | Simple – fewer motors, props, ESCs; lighter frame; fewer failure points | Complex – double motors/props/ESCs per arm; heavier frame; more failure points | Conventional: simpler, lighter, easier maintenance |
Weight Impact | Lighter – benefits endurance and maneuverability | Heavier – extra components increase total weight | Conventional: better for long flights and agility |
Aerodynamic Efficiency | Higher efficiency – no prop wake interference; better thrust per watt | Lower efficiency – ~10–15% loss due to wake from upper prop | Conventional: more flight time for same power |
Thrust & Payload | Limited – depends on single motor/prop size; increasing power may require larger frame | Much higher – dual props boost thrust density significantly in same arm span | Coaxial: higher payload capacity in same size |
Space Requirements | Larger arm span – to fit large props for more lift | Compact – dual props stacked on same axis save footprint | Coaxial: better in confined spaces |
Stability in Wind | Lower reserve – strong winds reduce stability; low redundancy (motor failure = crash) | High reserve – more thrust margin; partial redundancy possible if one motor fails | Coaxial: more stable in harsh conditions |
Redundancy & Safety | Minimal redundancy – any motor loss often causes crash (quadcopters) | Partial redundancy – other prop on arm can keep partial control | Coaxial: safer for critical missions |
Power Consumption | Lower – more efficient, less heat, smaller battery needed | Higher – greater current draw; requires higher-C, higher-capacity batteries | Conventional: longer endurance, lighter battery |
Maneuverability | High agility – low rotational inertia; fast response (best for racing) | Sluggish – heavier, more drag, slower response | Conventional: better for speed & agility |
Noise Level | Quieter – depends mainly on prop design and RPM | Louder – wake interference adds 5–10 dB | Conventional: less acoustic disturbance |
Maintenance | Easy – fewer parts; quick turnaround; cheaper spares | Difficult – more parts, wiring, troubleshooting; higher cost | Conventional: cheaper & faster repairs |
Typical Use Cases | Aerial filming, FPV racing, mapping, light industrial tasks | Heavy lift, multi-sensor payloads, shipboard or rooftop take-off, military & rescue | Depends on mission: endurance vs payload |
III.Coaxial vs.Conventional Layout Drone Motor Comparison
Given differences in overall size,mission payload,endurance goals,and maintenance capabilities,coaxial(dual props per arm)and conventional(single prop per arm)present a clear trade-off relationship.The comparison below covers six dimensions.
1.Space Occupancy&Arm Span
Conventional Layout:
Requires larger prop diameter/pitch for sufficient lift with only one prop per arm,meaning longer arms and greater prop spacing.Long-arm-span models occupy more space and are more susceptible to obstacles during takeoff/landing in confined areas(e.g.,forest clearings,indoors,narrow roofs).
Coaxial Layout:
Upper/lower props stack on the same axis,fitting two props within the same arm span,increasing effective disc area while keeping the body compact.More suitable for deployment on decks,narrow platforms,urban rooftops.
Selection Tip:
Prioritize coaxial for space-constrained sites;choose conventional for ample space and simplicity.
2.Lift&Thrust-to-Weight Ratio
Conventional Layout:
Available lift comes from one motor+one prop per arm.Increasing thrust requires higher-power motors or larger props,the latter sacrificing maneuverability and increasing arm span.
Coaxial Layout:
Two props stacked per arm can nearly double thrust(slightly less than theoretical due to wake loss).Significantly improves thrust-to-weight ratio without modifying arm span,supporting higher payloads.
Selection Tip:
Coaxial has the advantage when seeking maximum payload capacity within a limited airframe size.
3.Efficiency&Power Consumption
Conventional Layout:
Props work independently with minimal airflow interference;high aerodynamic efficiency;lower power consumption and longer endurance for the same thrust.
Coaxial Layout:
Lower prop operates in upper prop's wake,~10-15%efficiency loss.Significant current rise accompanies thrust increase,requiring higher C-rating and capacity batteries;otherwise,endurance is noticeably shortened.
Selection Tip:
Prioritize conventional for long-endurance missions;consider coaxial for short-duration,high-thrust missions.
4.Stability&Wind Resistance(Redundancy)
Conventional Layout:
Stability decreases in high wind or under heavy load if thrust reserve is insufficient;Low redundancy(e.g.,a quadcopter usually crashes directly if one motor fails).
Coaxial Layout:
Higher thrust reserve for the same airframe provides greater margin against strong winds.In some configurations,if one propeller set fails,the other can provide partial control force,offering slightly higher redundancy.
Selection Tip:
Prioritize coaxial in strong winds,complex airflow,or critical missions to enhance stability and safety.
5.Maintenance Difficulty&Cost
Conventional Layout:
Simple structure,fewer parts,intuitive wiring/installation;low maintenance and replacement cost,suitable for rapid support.
Coaxial Layout:
One extra motor,ESC,propeller,and bracket per arm;more complex wiring,increased weight;more failure points,longer troubleshooting time,higher spare part cost.
Selection Tip:
Conventional is more economical and easier to maintain for limited budgets or short mission cycles.
6.Typical Application Fields
Conventional Layout:
Aerial Photography/Videography,FPV Racing/Freestyle,Consumer/Recreational,Surveying&Light Industrial Operations.Characteristics:High efficiency,long endurance,simple maintenance.
Coaxial Layout:
Heavy Payload Transport,Industrial Inspection&Multi-sensor Tasks,Shipboard Takeoff/Landing&Urban Rooftop Deployment,Military&Emergency Response.Characteristics:
High payload capacity,compact footprint,high wind/stability resistance.
Comparison Between Coaxial and Conventional Drone Motor Layouts：
Comparison Dimension | Conventional Layout | Coaxial Layout | Selection Tip |
Space Occupancy & Arm Span | Single propeller requires larger diameter, leading to longer arms and greater spacing; larger footprint, less suitable for confined areas | Upper and lower props are stacked on the same axis, allowing higher total blade area while keeping the frame compact | For space-limited environments, choose coaxial; if space is ample and simplicity is preferred, choose conventional |
Thrust & Thrust-to-Weight Ratio | Thrust is provided by a single motor and propeller; increasing thrust requires higher-power motors or larger props, which may affect maneuverability and arm length | Two props per arm double thrust density (slightly less than theoretical due to wake interference), enabling higher payload without increasing arm span | For maximum payload within fixed frame size, coaxial is advantageous |
Efficiency & Power Consumption | Each prop operates independently with minimal airflow interference, resulting in high aerodynamic efficiency, lower power draw, and longer endurance | Lower prop works in disturbed airflow from the upper prop, losing ~10–15% efficiency; higher current draw reduces endurance unless battery capacity is increased | Choose conventional for long-endurance tasks; choose coaxial for short-endurance, high-thrust missions |
Stability & Wind Resistance (Redundancy) | If thrust reserve is low, stability suffers in strong wind; redundancy is low (e.g., quadcopters usually crash if one motor fails) | Greater thrust reserve improves wind resistance; partial redundancy—if one prop fails, the other may still provide limited control | For high-wind or mission-critical operations, coaxial improves stability and safety |
Maintenance Difficulty & Cost | Simple structure with fewer parts; wiring and installation are straightforward; lower replacement cost and quicker turnaround | Additional motor, ESC, propeller, and mount per arm; more complex wiring; heavier frame; higher spare part and repair costs | For limited budget or short mission cycles, conventional is more economical and easier to maintain |
Typical Applications | Aerial photography, FPV racing, consumer drones, mapping, light industrial tasks | Heavy-lift transport, industrial inspection, shipboard take-off/landing, urban rooftop operations, military and emergency missions | Choose according to mission needs |
IV.Selection Recommendations for Different Flight Scenarios
Layout selection must revolve around mission objectives,operating environment,and performance requirements.Executable selection advice and reasoning are provided below for common applications.
1.Aerial Photography&Filmmaking
Core demand:
Stable footage and long-duration smooth maneuvers.Light camera/gimbal setups usually prioritize conventional layout for its simplicity,high efficiency,and low prop interference,benefiting long hover and slow-motion shooting.
If carrying cinema cameras,dual gimbals,or other heavy payloads,consider coaxial for higher thrust and redundancy.
Recommendation:
Light payload AP→Conventional(Quad/Hex);Heavy payload AP→Coaxial(e.g.,Coaxial Octo).
2.Cargo Transport&Logistics Delivery
Priority:
Safety under full load and climb/wind resistance reserve.Coaxial provides greater lift within a given airframe size,especially suitable for medium/large payloads,mountainous/high-altitude,or maritime routes.
If payload is small/medium(≤5 kg)and route prioritizes range,conventional layout can be used.
Recommendation:
≤5 kg→Conventional;>5 kg or High Altitude→Coaxial.
3.Industrial Inspection&Surveying
Light single-sensor tasks often prioritize endurance and trajectory stability.Conventional layout extends flight time with high efficiency and low power consumption.
When carrying multiple sensors(e.g.,visible+thermal+LiDAR)or operating in strong winds,coaxial provides more stable attitude control due to greater thrust reserve and redundancy.
Recommendation:
Endurance priority/Light payload→Conventional;Multi-payload/Strong wind→Coaxial.
4.Shipboard&Confined Environment Takeoff/Landing
Decks,rooftops,mountain platforms,etc.,require a more compact airframe profile.Coaxial maintains thrust while reducing arm span,favoring deployment and recovery.
Recommendation:
Choose coaxial for significant space constraints.
5.FPV Racing&Freestyle
Ultralight weight and high maneuverability are paramount.Conventional layout has advantages in weight and responsiveness.
Coaxial's added weight and aerodynamic interference hinder acceleration and turning.
Recommendation:
Racing/Freestyle→Conventional.
Flight Scenario Applicability Table:
Application Scenario | Recommended Layout | Main Reason |
Aerial Photography & Filmmaking | Conventional for light payload; Coaxial for heavy payload | Conventional is simpler, more efficient, with less vibration—good for long hovering and smooth tracking; Coaxial provides more thrust and redundancy for heavy cinema cameras |
Cargo Transport & Delivery | Conventional for ≤5 kg; Coaxial for >5 kg or high-altitude | Conventional offers better endurance for small/medium loads; Coaxial delivers higher lift in same frame size for large/heavy payloads |
Industrial Inspection & Mapping | Conventional for light, single-sensor missions; Coaxial for multi-sensor or strong-wind environments | Conventional has longer endurance; Coaxial offers greater thrust reserve and stability for heavy payloads |
Shipboard & Confined Take-off/Landing | Coaxial | Compact frame and short arm span allow safe operation in restricted spaces |
FPV Racing & Freestyle | Conventional | Lightweight and fast response improve acceleration, cornering, and agility; Coaxial weight and drag hinder performance |
V.Common Coaxial Misconceptions
During layout selection and actual use,many teams have incomplete understanding of the performance trade-offs between coaxial(dual props per arm)and conventional(single prop per arm).Minor impacts affect range and efficiency;major ones bring safety risks.Misconceptions are explained below in"Myth-Truth-Avoidance Advice"format.
Myth 1:Coaxial=More Lift,Therefore Definitely Better
Truth:
Coaxial does make stacking total thrust easier within the same size,but mutual wake interference between upper/lower props typically reduces efficiency by~10-15%vs.single prop.If payload isn't high,conventional often excels in efficiency and endurance.
Avoidance Advice:
Quantify"mission payload and target endurance"clearly before deciding on coaxial.Avoid"using dual props just for the sake of it."
Myth 2:Ignoring the Link Between Power Consumption and Endurance
Truth:
Coaxial's thrust increase comes with significant current and power consumption rise.Using the original capacity/C-rating battery will noticeably shorten actual flight time.
Avoidance Advice:
Upgrade battery capacity and discharge rate(C-rating)simultaneously.Verify with real-world full-load tests before finalizing the solution.
Myth 3:Only Considering Motor&Prop,Not Calculating"Total Weight"
Truth:
Coaxial adds a whole extra set of motors,ESCs,props,and brackets.Structural parts and wiring also increase overall weight,affecting takeoff/landing conditions,transport,and handling.
Avoidance Advice:
Include brackets,quick releases,wiring harnesses,fasteners,etc.,in thrust-to-weight and energy budget calculations before assessing endurance and safety margin.
Myth 4:More Complex Structure Always Means Better Performance
Truth:
Complexitycanbring higher performance,but maintenance difficulty and potential failure points increase proportionally.For teams with average support capabilities,conventional layout is easier to maintain and offers higher operational readiness.
Avoidance Advice:
Factor maintenance capability and spare parts support into selection.Balance performanceandmaintainability,don't blindly pursue"high-spec."
Myth 5:Simply Adding Dual Props to a Conventional Frame Makes it Fly
Truth:
Directly adding dual-prop components to conventional arms without coordinated adjustment of FC parameters,ESCs,and power systems can cause uneven thrust,amplified vibration,or even unstable flight.
Avoidance Advice:
Modification requires system-level design and validation:Coordinate upgrades of FC/ESCs/Power.Conduct ground and aerial aerodynamic testing before operational flights.
VI.Frequently Asked Questions(FAQ)
Q1:Can motors with different KV or different brands be mixed on the same coaxial arm?
Not recommended.Differences in KV,torque constant,or rotor inertia can cause imbalance between upper/lower motors on the same arm,leading to unpredictable torque coupling and heat differences.Use motors and ESCs of the same model and batch,calibrated as a set.
Q2:Which rotation direction is more stable for coaxial?
Follow the principle of"opposite rotation,controllable overall torque."The key lies in the yaw response and wind resistance of the whole aircraft.Perform step-response tests on a ground rig,comparing yaw overshoot and settling time for both pairing orientations before finalizing.
Q3:Is coaxial noisier?How to reduce noise?
Coaxial can have more pronounced noise peaks in specific frequencies due to wake superposition.Suppress noise through propeller optimization,reducing tip speed,adding noise-damping feet and vibration pads,and optimizing arm-end resonance.
Q4:Is coaxial suitable for quick-release props?
Yes,but pay close attention to axial clearance,locking reliability,and dynamic balance after repeated assembly.Minor looseness in quick-release mechanisms can be amplified under upper/lower prop resonance coupling.
Q5:Do high-altitude/high-temperature environments affect the two layouts differently?
In thin air,achieving equivalent lift requires higher disc loading and more power.Coaxial more easily compensates for thrust within a given size,but thermal management pressure is higher.Conventional is more efficient and thermally balanced.
Q6:Can a regular quadcopter be converted to an X8 coaxial configuration?
Yes.The conversion mainly involves:Replacing the single motor mount on each arm with a dual motor mount for top/bottom motors;Upgrading ESCs and the Power Distribution Board(PDB)to handle current for eight motors;Finally,reconfiguring the flight controller firmware for the X8 layout to correctly control eight motors.
Q7:Can a coaxial drone truly continue flying after a motor failure?
Yes,this is a core advantage of coaxial designs(e.g.,Y6,X8).When one motor,ESC,or propeller fails,the FC immediately detects thrust imbalance and rapidly adjusts the speed of the remaining functional motors to restabilize the aircraft.While performance is degraded,sufficient attitude control is maintained,allowing the operator to safely fly the drone back and land it.
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