How to Make a Drone / UAV – Lesson 3: Propulsion - Robots

13 May.,2024

 

How to Make a Drone / UAV – Lesson 3: Propulsion - Robots

How to Make a Drone / UAV - Lesson 1: Terminology
How to Make a Drone / UAV - Lesson 2: The Frame
How to Make a Drone / UAV - Lesson 3: Propulsion
How to Make a Drone / UAV - Lesson 4: Flight controller
How to Make a Drone / UAV - Lesson 5: Assembly
How to Make a Drone / UAV - Lesson 6: Get it all working together
How to Make a Drone / UAV - Lesson 7: FPV & Long-range
How to Make a Drone / UAV - Lesson 8: Aircraft

If you want to learn more, please visit our website 10kg thrust brushless motor.

Now that you have either chosen or built a frame, the next step is to choose the right propulsion system. A complete propulsion system includes motors, propellers, ESCs and a battery. Almost all small multi-rotor drones / UAVs are electric, with almost none being gas-powered. For this reason, we will focus on implementing an electric propulsion using brushless DC motors.

The motors you use will have a huge impact on the payload (or maximum load) which your UAV can support, as well as the flight time. We strongly suggest using the same (propulsion) motor everywhere. Note that even if a pair of motors are the same brand and model, and from the same production run, their speeds may vary slightly, which is something the

Inrunner Motor

Brushless DC Motor

DC "Pancake" Motor

Brushed vs Brushless

Brushed motors spin the coil inside a case with fixed magnets mounted around the outside of the casing. Brushless motors do the opposite; the coils are fixed either to the outer casing or inside the casing while the magnets are spun. In most situations, you will be considering only

Inrunner vs Outrunner

There are a few types of brushless DC motors:
  • Inrunner - these have the fixed coils mounted to the outer casing and the magnets are mounted to the armature shaft which spins inside the casing (tend to be used on RC cars because of the high Kv)
  • Outrunner - these have the magnets mounted on the outer casing which is spun around the fixed coils in the center of the motor casing (the bottom mounting of the motor is fixed).
  • Hybrid outrunner - technically outrunners but have a static outer shell around them to make them look like they're inrunners
Inrunner brushless DC motors tend to be used in RC cars, airplanes and helicopters because of their high KV. They may also be geared down to increase the torque. Outrunners tend to have more torque.

"KV"

The KV rating / value of a motor relates to how fast it will rotate for a given voltage. For most multirotor aircraft, a low KV is desired (between 500 to 1000 for example) since this helps with stability. For acrobatic flight however, you might consider a KV between 1000 and 1500 and also consider using smaller diameter propellers. If the KV rating for a particular motor is 650rpm/V, then at 11.1V, the motor will be rotating at 11.1V x 650 = 7215rpm. If you operate the motor at a lower voltage (say, 7.4V), the rpm will be 7.4V x 650rpm/V = 4810rpm. It is important to note that using a lower voltage tends to mean that the current draw will be higher (power = current x voltage).

Thrust

Some brushless motor manufacturers give an indication of a motor's thrust corresponding to several propeller options (often presented in a table). The unit of thrust is often Kg, Lbs or N. For example, if you are building a

Additional Considerations

  • Connectors: Brushed DC motors have two connectors: one for positive, the other for negative. Reversing the wires reverses the rotation of the motor.
  • Connectors: Brushless DC motors have three connectors. Refer to the ESC section below to know how to wire them and reverse direction of rotation.
  • Windings: The windings impact the KV of a motor. When you want a lower KV but maintain the torque, you may need to consider a larger pancake-style brushless DC motor.
  • Mounting: Most manufacturers have a general mounting pattern for brushless DC motors which has allowed companies which produce frames to not have to design adapters. The pattern is normally metric, with two holes spaced 16mm apart, and another two holes spaced 19mm apart (at 90 degrees to the first).
  • Thread: The mounting thread used to secure a brushless motor to a frame can vary. Common metric screw sizes include M1, M2 and M3 and imperial might be 2-56 and 4-40.
Propellers for multi-rotor aircraft are adapted from

Propeller

Blades & Diameter

Most multi-rotor aircraft have either two and three rotor blades, with the most common being two. Do not assume that adding more blades will automatically mean more thrust; each blade must travel through the wake of the one which precedes it, so the more blades, the more prevalent the wake will be. A smaller diameter

Propeller Diameter

Pitch / Angle of Attack / Efficiency / Thrust

The thrust produced by a propeller depends on the density of the air, on the propeller's RPM, on its diameter, on the shape and area of the blades and on its pitch. A propeller's efficiency relates to the angle of attack which is defined as the blade pitch minus the helix angle (the angle between the resultant relative velocity and the blade rotation direction). The efficiency itself is a ratio of the output power to the input power. Most well-designed propellers have an efficiency of 80%+. The angle of attack is affected by the relative velocity, so a propeller will have different efficiency at different motor speeds. The efficiency is also greatly affected by the leading edge of the propeller blade, and it is very important that it be as smooth as possible. Although a variable pitch design would be best, the added complexity required as compared to a multirotor's inherent simplicity means a variable pitch propeller is almost never used. Additional information regarding the theory behind blade design and thrust generated can be found online at sites such as the

Propeller Pitch (one revolution)

Propeller Angle of Attack

Rotation

Propellers are either designed to rotate clockwise (CW) or counter-clockwise (CCW). It is important to know which part of the propeller is intended to face upwards (the top surface is curved outward). If the design of your multirotor inverts some of the motors (as is the case for a Vtail, Y6, X8), be sure to change the orientation of the propellers so the thrust is still downwards. The top of the propeller should always face the sky. The documentation associated with the

Counter Rotating Propellers

Material

The material(s) used to make the propellers can have a moderate impact on the flight characteristics, but safety should be the primary consideration, especially if you are new and inexperienced.

The motors you use will have a huge impact on the payload (or maximum load) which your UAV can support, as well as the flight time. We strongly suggest using the same (propulsion) motor everywhere. Note that even if a pair of motors are the same brand and model, and from the same production run, their speeds may vary slightly, which is something the flight controller will take care of.Brushed motors spin the coil inside a case with fixed magnets mounted around the outside of the casing. Brushless motors do the opposite; the coils are fixed either to the outer casing or inside the casing while the magnets are spun. In most situations, you will be considering only brushless DC motors . Brushless DC motors are used extensively in the hobby RC industry for products ranging from helicopters and airplanes to the drive system in RC cars and boats. "Pancake" brushless motors have a larger diameter and are essentially flatter and often allow for higher torque and lower KV (details below). Smaller UAVs (usually the size of the palm of your hand) tend to use small brushed motors because of the lower price and simpler two-wire controller. Although brushless motors come in a variety of different sizes and specs, selecting a smaller brushless motor rarely means it will be less expensive.There are a few types of brushless DC motors:Inrunner brushless DC motors tend to be used in RC cars, airplanes and helicopters because of their high KV. They may also be geared down to increase the torque. Outrunners tend to have more torque.The KV rating / value of a motor relates to how fast it will rotate for a given voltage. For most multirotor aircraft, a low KV is desired (between 500 to 1000 for example) since this helps with stability. For acrobatic flight however, you might consider a KV between 1000 and 1500 and also consider using smaller diameter propellers. If the KV rating for a particular motor is 650rpm/V, then at 11.1V, the motor will be rotating at 11.1V x 650 = 7215rpm. If you operate the motor at a lower voltage (say, 7.4V), the rpm will be 7.4V x 650rpm/V = 4810rpm. It is important to note that using a lower voltage tends to mean that the current draw will be higher (power = current x voltage).Some brushless motor manufacturers give an indication of a motor's thrust corresponding to several propeller options (often presented in a table). The unit of thrust is often Kg, Lbs or N. For example, if you are building a quadcopter and find that a specific motor can provide up to 0.5Kg of thrust with an 11 inch propeller, that means that four of these motors (with that given prop) can lift 0.5Kg*4=2Kg at maximum thrust. Therefore if your quadcopter weighs just less than 2Kg, it will only take off at maximum thrust. You need to either choose a motor + propeller combination which can provide more thrust, or reduce the weight of the aircraft. If the propulsion system (all motors and props) can provide 2Kg of thrust (max) then your entire copter should be at most about half this weight (1Kg, including the weight of the motors themselves). The same calculation can be done for any given configuration. Let's assume a hexacopter 's weight (including frame, motors, electronics, battery, accessories etc) to be 2.5Kg. Each motor should therefore be capable of providing (2.5Kg/6 motors) x 2:1 = 0.83kg of thrust (or more). You can now calculate the specs of your motor(s) but suggest reading through the sections below before making a decision.Propellers for multi-rotor aircraft are adapted from propellers used in RC airplanes . Why not use helicopter blades? Although it has been done, imagine the size of a hexacopter which used helicopter blades. Note that a helicopter-type system also requires that you vary the pitch of the blades which significantly adds to the mechanical complexity. You may also ask why not use a turbojet, turbofan, prop-jet etc? These are incredibly good at providing a lot of thrust, but also require a lot of power. If the objective of the drone was to move really fast rather than hover in confined areas, one of these may be a good option.Most multi-rotor aircraft have either two and three rotor blades, with the most common being two. Do not assume that adding more blades will automatically mean more thrust; each blade must travel through the wake of the one which precedes it, so the more blades, the more prevalent the wake will be. A smaller diameter propeller has less inertia and is therefore easier to speed up and slow down, which helps in acrobatic flight.The thrust produced by a propeller depends on the density of the air, on the propeller's RPM, on its diameter, on the shape and area of the blades and on its pitch. A propeller's efficiency relates to the angle of attack which is defined as the blade pitch minus the helix angle (the angle between the resultant relative velocity and the blade rotation direction). The efficiency itself is a ratio of the output power to the input power. Most well-designed propellers have an efficiency of 80%+. The angle of attack is affected by the relative velocity, so a propeller will have different efficiency at different motor speeds. The efficiency is also greatly affected by the leading edge of the propeller blade, and it is very important that it be as smooth as possible. Although a variable pitch design would be best, the added complexity required as compared to a multirotor's inherent simplicity means a variable pitch propeller is almost never used. Additional information regarding the theory behind blade design and thrust generated can be found online at sites such as the MDP project . There are also several online tools which help calculate a propeller's thrust. Certain sites list a variety of motors such as eCalc for the thrust calculationsPropellers are either designed to rotate clockwise (CW) or counter-clockwise (CCW). It is important to know which part of the propeller is intended to face upwards (the top surface is curved outward). If the design of your multirotor inverts some of the motors (as is the case for a Vtail, Y6, X8), be sure to change the orientation of the propellers so the thrust is still downwards. The top of the propeller should always face the sky. The documentation associated with the flight controller (discussed in the next lesson) normally shows you which way each propeller is intended to turn for each multi-rotor it supports.The material(s) used to make the propellers can have a moderate impact on the flight characteristics, but safety should be the primary consideration, especially if you are new and inexperienced.

Plastic

Injection-Molded Plastic (ABS / Nylon etc.) is the most popular choice when it comes to multi-rotor aircraft. This is largely because of their low cost, decent flight characteristics and respectable durability. Normally in a crash, at least one propeller ends up broken, and while you are calibrating the drone and learning to fly, you will end up with a lot of broken propellers. A plastic propeller which has been reinforced with carbon fiber is arguably the best overall choice because of its high rigidity and low cost.

Fiber-Reinforced Polymer

A fiber-reinforced polymer propeller (carbon fiber, nylon reinforced carbon etc.) is “cutting edge” technology in more ways than one. Carbon fiber parts are still not very easy to produce and as such you pay quite a premium for them over a plastic propeller with the same specifications. In the event of a crash, a carbon fiber propeller is harder to break and flex and as such will cause more damage to whatever it contacts. This having been said, if you want to consider a fiber-reinforced propeller, they are normally well made and rarely require balancing, are stiffer (so fewer losses in efficiency due to flexing etc) and are lighter weight than other materials. We suggest considering these high performance propellers only after you are comfortable flying.

Natural

Natural materials such as wood are not used often to make propellers for mulitirotors as they require machining to produce and therefore cost more than plastic. The main advantage heere is that wood is quite strong and will not bend. Wood propellers are still used for RC airplanes.

Propeller Materials

Folding

Folding propellers have a central part which connects to two pivoting blades. When the center (which is connected to the motor's output shaft) spins, centrifugal forces act on the blades, forcing them outwards and essentially making the propeller "rigid", with the same effect as a fixed propeller. Because of lower demand and higher number of parts required, folding propellers are less common than fixed propellers. As expected, a folding propeller makes transporting the aircraft quite a bit easier, and combined with a folding frame, the "retracted" size of the UAV can be significantly smaller than in flight. Folding propellers also have a nice advantage of only having to change one blade in the event of a crash.

Folding Propeller

Mounting

Since aerial vehicles can come in a wide range of sizes, so can propellers. As such, there are a few somewhat more "standard" sized motor shaft diameters in the industry. Propellers often come with a small selection of these adapter rings (which look like washers with various different diameter holes in the middle) to press into a cutout of the propeller so it centers it on the motor's shaft. If you find that the center ("bore") of the propeller you are using is way too large for the shaft of your motor, you will need the spacer / adapter ring. Don't assume that the propeller you are purchasing includes the adapter; check the bore and compare it to your motor's shaft diameter.

Folding propellers have a central part which connects to two pivoting blades. When the center (which is connected to the motor's output shaft) spins, centrifugal forces act on the blades, forcing them outwards and essentially making the propeller "rigid", with the same effect as a fixed propeller. Because of lower demand and higher number of parts required, folding propellers are less common than fixed propellers. As expected, a folding propeller makes transporting the aircraft quite a bit easier, and combined with a folding frame, the "retracted" size of the UAV can be significantly smaller than in flight. Folding propellers also have a nice advantage of only having to change one blade in the event of a crash.Since aerial vehicles can come in a wide range of sizes, so can propellers. As such, there are a few somewhat more "standard" sized motor shaft diameters in the industry. Propellers often come with a small selection of these adapter rings (which look like washers with various different diameter holes in the middle) to press into a cutout of the propeller so it centers it on the motor's shaft. If you find that the center ("bore") of the propeller you are using is way too large for the shaft of your motor, you will need the spacer / adapter ring. Don't assume that the propeller you are purchasing includes the adapter; check the bore and compare it to your motor's shaft diameter.

Certain manufacturers further customize the way the propeller mounts to the motor. Some have D-shaped (single or double) cutouts on the motor, and the propeller has the missing material; this ensures that the propeller will not loosen itself in flight. Other manufacturers have been known to include other types of specific “male / female” motor to propeller connections as well. Newer propellers have a thread rather than a hole which is opposite to that of the rotation, and the motor’s shaft has the same thread, essentially tightening the propeller when rotating.

Prop savers

Prop savers replace the normal propeller adapter on a motor and have a small part (such as an O-ring) which keeps the propeller in place. In the event of a crash, the propeller is normally prevented from rotating (ex it contacts an object) and since the motor is still rotating and high speeds, it causes the O-ring to either rip apart of fly off, ideally saving both the motor and the propeller from damage. As great as this might be, there are a few disadvantages:
  • The propeller sits higher on the shaft
  • If the design of the prop saver is off, or not properly centered center it can lead to vibration
  • Check O-rings periodically since they may become brittle and crack in flight

Prop guards

Propeller guards ("prop guards") connect to the main frame and provide a fixed ring / cushion around the propeller. Should the UAV contact an object, ideally the propeller guards will contact the object first and withstand the impact so the propellers are not touched. Small toy multi-rotor UAVs often have removable plastic prop guards included. As always, there are some compromises to using prop guards:
  • They can be a high source of vibration
  • Only good for low force impacts
  • Can lower thrust if there are too many supports directly under the propeller wash

Prop Guard

Balancing

Most inexpensive propellers are not very well balanced, which can be seen by simply balancing the center on a pencil (one side will likely be heavier than the other). As such, it is always good practice to balance your propellers before fixing them to the motors. It is very important that the propeller be balanced because if not, the vibrations caused by an unbalanced propeller often propagate to the

Propeller Balancer

An ESC (acronym for "

Brushless ESC

An ESC might initially be confusing because it has several wires exiting on two sides.
  • Power input: The two thick wires (normally black and red) are to obtain power from the power distribution board / harness which itself receives power directly from the main battery.
  • 3 bullet connectors: These pins are what connects to the three pins on the brushless motor. There are some standard sizes in the industry, but if you find the two are mismatched, you will need to replace one set.
  • 3-pin R/C servo connector: This connector accepts RC signals, but rather than requiring 5V on the red and black pins, most of the time an internal BEC provides 5V to power the electronics.
In certain instances, the manufacturer does not want to assume which connectors you are using, and leaves the wires for the motor connection and power input bare (they may provide bullet connectors in the packaging which you may or may not want/need and would have to solder onto the wires). The bullet connectors you received with the motors may also not match those of the ESC, so in this case, it's simply best to replace one or the other. Your next question is obviously given three bullet connectors, which one plugs into which on the motor? As far as the connector for the power, this is entirely up to you - ideally you would use connectors to make the ESC easily removable in case of failure, or if you want to use it on a different project, but be sure that the positive on the ESC goes to the positive on the battery, and same for negative. In order to reverse the direction of rotation, swap any of two of the three connectors between the ESC and the brushless motor.

BEC

Most ESCs include what is called a "Battery Elimination Circuit" or BEC. This comes from the fact that historically, only one brushless motor was needed in a given RC vehicle, and rather than splitting hte battery, it would just need to be connected to the ESC, and the ESC would have an onboard voltage regulator to power the electronics.It is important to know the current which an ESC's BEC can provide, though it is normally in the range of 1A or above and is almost always 5V.

Prop savers replace the normal propeller adapter on a motor and have a small part (such as an O-ring) which keeps the propeller in place. In the event of a crash, the propeller is normally prevented from rotating (ex it contacts an object) and since the motor is still rotating and high speeds, it causes the O-ring to either rip apart of fly off, ideally saving both the motor and the propeller from damage. As great as this might be, there are a few disadvantages:Propeller guards ("prop guards") connect to the main frame and provide a fixed ring / cushion around the propeller. Should the UAV contact an object, ideally the propeller guards will contact the object first and withstand the impact so the propellers are not touched. Small toy multi-rotor UAVs often have removable plastic prop guards included. As always, there are some compromises to using prop guards:Most inexpensive propellers are not very well balanced, which can be seen by simply balancing the center on a pencil (one side will likely be heavier than the other). As such, it is always good practice to balance your propellers before fixing them to the motors. It is very important that the propeller be balanced because if not, the vibrations caused by an unbalanced propeller often propagate to the flight controller , causing erratic flight. A propeller can be balanced many ways, but if you are building your own UAV, then an inexpensive prop balancer is ideal. A prop balancer simply allows you to easily see where there is a weight unbalance in the propeller. In order to adjust the weight, you can either sand down the heavier part (evenly sand the center part of the propeller only as opposed to leading or trailing edges, and DO NOT cut off part of the propeller), or add clear masking tape (which is very thin) to the lighter side (and keep adding lengths of tape evenly until it is balanced). Note that the farther away from the center you make the modification (sanding or adding tape) the more of an effect it will have based on the principle of torque.An ESC (acronym for " Electronic Speed Controller ") is what allows the flight controller (covered in the next lesson) to control the speed and direction of a motor. The ESC must be able to handle the maximum current which the motor might consume, and be able to provide it at the right voltage. Most ESCs used in the hobby industry only allow the motor to rotate in one direction, though with the right firmware, they can operate in both directions.An ESC might initially be confusing because it has several wires exiting on two sides.In certain instances, the manufacturer does not want to assume which connectors you are using, and leaves the wires for the motor connection and power input bare (they may provide bullet connectors in the packaging which you may or may not want/need and would have to solder onto the wires). The bullet connectors you received with the motors may also not match those of the ESC, so in this case, it's simply best to replace one or the other. Your next question is obviously given three bullet connectors, which one plugs into which on the motor? As far as the connector for the power, this is entirely up to you - ideally you would use connectors to make the ESC easily removable in case of failure, or if you want to use it on a different project, but be sure that the positive on the ESC goes to the positive on the battery, and same for negative. In order to reverse the direction of rotation, swap any of two of the three connectors between the ESC and the brushless motor.Most ESCs include what is called a "Battery Elimination Circuit" or BEC. This comes from the fact that historically, only one brushless motor was needed in a given RC vehicle, and rather than splitting hte battery, it would just need to be connected to the ESC, and the ESC would have an onboard voltage regulator to power the electronics.It is important to know the current which an ESC's BEC can provide, though it is normally in the range of 1A or above and is almost always 5V.

In a multi-rotor, you need to connect all ESCs to the flight controller, but only one BEC is needed, and having power coming from multiple sources all being fed to the same lines can potentially cause issues. Since there is normally no way to deactivate a BEC on an ESC, it is best to remove the red wire and wrap it with electrical tape for all but one ESC. It is still important to leave the black (ground) wire in place for “common ground”.

Firmware

ESCs are not all equally good for use with multi-rotors. It is important to understand that before multi-rotors were around, that brushelss hobby motors were used primarily for RC car drives, airplane propellers and as primary motors in model

Power Distribution

Since each ESC is powered from the main battery, the main battery's single connector must somehow be split amongst four ESCs. To do so, a power distribution board, or power distribution harness is used. This board (or cable) splits the main battery's positive and negative terminals into four. It is important to note the type of connectors used on the battery, ESC and power distribution board may not all be the same, and it is best, whenever possible, to choose a "standard" connector (such as Deans) which is used throughout. Many inexpensive boards require soldering, as they do not want to assume you are using any specific connector. A very simply power distributor could involve a two input terminal block or soldering all positive connections together, and then all negative connections together..

Chemistry

Batteries used in UAVs are now almost exclusively

Voltage

You should really only need to consider one battery pack for your UAV. This battery's voltage should correspond with the motors you chose. Almost all batteries used these days are lithium-based and incorporate a number of 3.7V cells, where 3.7V = 1S. Therefore a battery which is marked as 4S is likely 4 x 3.7V = 14.8V nominal. Providing the number of cells however will help you determine which charger to use. A single cell high capacity battery may physically look a lot like a low capacity multi-cell battery.

Capacity

A battery pack's capacity is measured in amp-hours (Ah). Small battery packs can be in the range of 0.1Ah (100mAh) though battery packs for medium sized

Discharge Rate

The discharge rate from a lithium battery is measured in C, where 1C is the capacity of the battery (normally in amp hours unless you're looking at a very

Safety

LiPo batteries are not entirely safe since they contain pressurized hydrogen gas and have a tendency to burn and/or explode when there is something wrong. As such, if you have any doubts about the battery pack you are holding, DO NOT plug it into the UAV or even the

Charging

Most

Mounting

The battery pack is the heaviest item on the UAV and as such, should be placed dead center to ensure the motors are subjected to the same load. A battery does not include any specific mounting (especially screws which could puncture the LiPo and cause a fire), so some mounting methods currently used involve Velcro straps, rubber, plastic compartment among others. Having the battery suspended below the frame using Velcro is quite popular because of accessibility.

LiPo Battery

ESCs are not all equally good for use with multi-rotors. It is important to understand that before multi-rotors were around, that brushelss hobby motors were used primarily for RC car drives, airplane propellers and as primary motors in model helicopters . Most of these applications did not require very fast response time or rapid updating. An ESC equipped with SimonK or bheli firmware is able to react very fast (much higher frequency) to changes in input, which may mean the different between stable flight or a crash.Since each ESC is powered from the main battery, the main battery's single connector must somehow be split amongst four ESCs. To do so, a power distribution board, or power distribution harness is used. This board (or cable) splits the main battery's positive and negative terminals into four. It is important to note the type of connectors used on the battery, ESC and power distribution board may not all be the same, and it is best, whenever possible, to choose a "standard" connector (such as Deans) which is used throughout. Many inexpensive boards require soldering, as they do not want to assume you are using any specific connector. A very simply power distributor could involve a two input terminal block or soldering all positive connections together, and then all negative connections together..Batteries used in UAVs are now almost exclusively Lithium polymer (LiPo) , with some more exotic ones being Lithium-Manganese or other Lithium variations. Lead acid is simply not an option and NiMh / NiCd are still too heavy for their capacity and often cannot provide the high discharge rates needed. LiPo offer high capacity with low weight, and high discharge rates. The downsides are their comparatively higher cost and continued safety issues.You should really only need to consider one battery pack for your UAV. This battery's voltage should correspond with the motors you chose. Almost all batteries used these days are lithium-based and incorporate a number of 3.7V cells, where 3.7V = 1S. Therefore a battery which is marked as 4S is likely 4 x 3.7V = 14.8V nominal. Providing the number of cells however will help you determine which charger to use. A single cell high capacity battery may physically look a lot like a low capacity multi-cell battery.A battery pack's capacity is measured in amp-hours (Ah). Small battery packs can be in the range of 0.1Ah (100mAh) though battery packs for medium sized drones are 2-3Ah (2000mAh-3000mAh). The higher the capacity, the longer the flight time, but the heavier the pack will be. You can expect the flight time of a normal UAV to be in the order of 10-20 minutes, which might not seem like a long time, but you need to consider it's always fighting against gravity, and unlike an airplane, there are no surfaces to help with lift.The discharge rate from a lithium battery is measured in C, where 1C is the capacity of the battery (normally in amp hours unless you're looking at a very small drone the size of your hand). The discharge rate of most LiPo batteries is at least 5C (five times the capacity), but since most motors used in multirotors consume high current, the battery needs to be able to discharge at incredibly high current, which is often in the order of 30A or more.LiPo batteries are not entirely safe since they contain pressurized hydrogen gas and have a tendency to burn and/or explode when there is something wrong. As such, if you have any doubts about the battery pack you are holding, DO NOT plug it into the UAV or even the charger - consider it a "write off" and dispose of it properly. Telltale signs that something is wrong include dents or the battery is larger than it was when you first received it (i.e. leaking gas). When charging a LiPo battery, it is best to keep it in a LiPo safe bag. Storing the battery is also ideally done in a LiPo bag as well. In the event of a crash, the first thing you need to do is unplug and check the battery. Having the battery in a fully enclosed case may add to the weight, but can really help keep your battery safe in a crash. Certain battery manufacturers sell batteries with and without a hard case.Most LiPo batteries have two connectors: one is intended to be the main "discharge" wires which can handle high current, while the other, normally smaller and shorter one is the charging connector. This charging connector is almost always a white JST connector which has one ground pin following by the same number of cells used to create the pack. This is what you connect to the LiPo charger which then takes care of charging (and balancing) each internal cell. The charger should indicate when charging is complete and, given the safety issues with LiPo batteries, it is best to unplug the battery and charger when charging is complete.The battery pack is the heaviest item on the UAV and as such, should be placed dead center to ensure the motors are subjected to the same load. A battery does not include any specific mounting (especially screws which could puncture the LiPo and cause a fire), so some mounting methods currently used involve Velcro straps, rubber, plastic compartment among others. Having the battery suspended below the frame using Velcro is quite popular because of accessibility.

 

If you are looking for more details, kindly visit how to calculate thrust required for drone.

This is a companion discussion topic for the original entry at https://community.robotshop.com/tutorials/show/how-to-make-a-drone-uav-lesson-3-propulsion

Lookup Table: Motor & Prop Sizes, KV, Battery Cell Count ...

24.7K

Choosing the right motor size and KV for your FPV drone can be challenging, especially when considering prop size and LiPo voltage. While there isn’t a one-size-fits-all answer, this guide provides a range of options based on my years of experience of various builds.

Some of the links on this page are affiliate links. I receive a commission (at no extra cost to you) if you make a purchase after clicking on one of these affiliate links. This helps support the free content for the community on this website. Please read our Affiliate Link Policy for more information.

Looking to learn how to build an FPV drone from scratch? Check out my comprehensive tutorial here: https://oscarliang.com/how-to-build-fpv-drone/

FPV Drone Components Table

This lookup table is designed to help those building a new FPV drone who may be unsure about the ideal motor and propeller combinations. It’s important to note that this isn’t an exhaustive list, but rather a collection of popular and successful examples for different prop sizes and LiPo cell counts.

I’ve tried to include as many examples as possible, new motor and propeller combinations are regularly being updated, but if you find something missing, please share in the comments below. Your feedback is invaluable in making this resource even better for fellow FPV drone enthusiasts.

Prop SizeClassCell CountMotor SizeMotor KVLiPo Battery mAhDry Weight 31mm TribladeTinywhoop1S0603, 0702, 0802, 080318000-25000300-45020-30g Tinywhoop2S08021200030020-30g 31mm TwobladeTinywhoop1S08021900030020-30g Tinywhoop2S0802300 40mm (1.6") TribladeTinywhoop1S0802, 1002, 110215000-2000045025-35g Tinywhoop2S0802, 0806, 1002, 1102, 110310000-16000300-45030-60g Tinywhoop3S1102, 11038000-11000300-45040-70g 40mm (1.6") TwobladeTinywhoop1S0802, 1002, 11022000045025-35g Tinywhoop2S0802, 0806, 1002, 1102, 110310000300-45030-60g 2" Triblade1S1002, 1003, 110215000-2000045030-40g 2S1103, 1105, 11066000-11000300-45060-80g 3S1104, 1105, 11065500-7500300-45060-100g 4S1105, 11065000-6000450-65070-130g 2.5" Triblade2S11045000-600030055-70g 3S11064500650120-140g 4S1304, 14044500-5000450-850140-180g 2.5" Two-Blade (65mm)Ultralight1S11021350030025-35g Ultralight2S1103, 1104, 11067000-10000450-65040-60g Ultralight3S1104, 1105, 1106, 1203, 12046000-8000300-55045-65g Ultralight4S1104, 1105, 1106, 1203, 12044000-450045055-90g 3" TribladeFreestyle2S14044500-5000 Freestyle3S1407, 1408, 15073500-4500550-850120-200g Freestyle4S1306, 1407, 1408, 1506, 1507, 16063000-4200450-850140-260g Freestyle6S1408, 1506, 1507, 16062800-3000550-650140-260g 3" Two-BladeLong Range1S1103, 120211000Li-Ion 2500-3000mAh Ultralight1S1103, 1202, 1202.511000-14000450 Ultralight2S1105, 1106, 1203, 1204, 13036000-800045040-60g Ultralight3S1105, 1106, 1108, 1203, 1204, 1207, 1303, 1304, 14044500-6500300-45055-75g Ultralight4S1105, 1106, 1108, 1203, 1204, 1207, 1303, 1304, 14043500-5000450-55060-80g 3" Cinewhoop4S1404, 1408, 1507, 2004, 2203, 22043800-4600850-1300180-350g 6S1507, 2203, 22042800850180-350g 4" TribladeFreestyle3S Freestyle4S1407, 1507, 16063000-4000850-1000120-200g Freestyle6S16062000-3000600-850120-180g 4" Two-BladeUltralight3S1306, 1404, 1406, 1408, 1504, 15053500-4500650-850110-130g Ultralight4S1306, 1404, 1406, 1408, 1504, 15052500-3000450-650110-130g Long Range3S14043500-4000Li-Ion 2500-3000mAh130-180g Long Range4S14042500-3000Li-Ion 2500-3000mAh130-180g 5" TribladeFreestyle4S2306, 2207, 2207.5, 2306.5, 2207.5, 2208, 23082300 - 27001300-1600250-450g Freestyle6S2306, 2207, 2207.5, 2306.5, 2207.5, 2208, 23081700 - 20001000-1400250-450g Racing4S2306, 2207, 2207.5, 2306.5, 2207.5, 2208, 23082500-27001300-1600250-300g Racing6S2306, 2207, 2207.5, 2306.5, 2207.5, 2208, 23081800-21001000-1400250-300g 5" Two-BladeUltralight4S1606, 1806, 2004, 2204, 22052300-3000750-1000150-250g Ultralight6S1606, 1806, 2004, 2204, 22051600-2300450-700150-250g 6"Freestyle4S2207, 2207.5, 2208, 2405, 2407, 24082100 - 25001300-1800250-450g Freestyle6S2207, 2207.5, 2208, 2405, 2407, 24081500-18001000-1500250-450g 7"Freestyle6S2510, 2806, 2806.5, 2808, 3106.51000-14002200-3000350-500g Long Range4S2408, 2507, 2508, 2806, 2806.5, 28081600-1900Li-ion 2500-4000mAh350-500g Long Range6S2408, 2507, 2508, 2806, 2806.5, 2808980-1300Li-ion 2500-4000mAh350-500g

Dry weight refers to the total weight of the drone without the battery. Here are the definitions of the terms used in the lookup table.

What’s a Tinywhoop?

Whoops or Tiny Whoops are small palm sized FPV drone with propeller guards or ducts, typically weighing around 20-40 grams. It’s known for its compact, enclosed propeller design, making it safe and suitable for indoor flying. Tiny Whoops are equipped with tiny, brushed or brushless motors and a small camera and video transmitter, providing a live video feed to the pilot’s goggles. They are popular for racing in tight, indoor spaces and for FPV beginners due to their durability, ease of control, and relatively low cost. Their small size and maneuverability make them ideal for navigating challenging courses or small, cluttered environments.

What’s a Freestyle FPV Drone?

A freestyle drone is a type of FPV drone optimized for agility, maneuverability, and creative flight. Unlike racing drones, which are built for speed and precision on a track, freestyle drones are designed for performing aerial acrobatics, flips, and complex maneuvers in open environments. They often have powerful motors and responsive controls to execute intricate flight patterns and tricks. Freestyle drones typically carry action cameras such as GoPro to capture dynamic, often acrobatic footage from the pilot’s perspective. Durability is also a key feature, as these drones frequently undergo rough landings and crashes during stunts. Freestyle flying emphasizes personal style, fluidity, and the art of aerobatic flight.

What’s a Long Range FPV Drone?

A long range FPV drone is designed for extended flight distances, often exceeding several kilometers. These drones prioritize efficient power consumption, stable flight characteristics, and reliable communication systems over speed or agility. Equipped with large Li-ion battery packs and efficient propulsion systems, it’s possible to get 20 minutes, 30 minutes or even longer flight time. With advanced GPS capabilities, long-range drones can cover vast areas, making them ideal for exploration or aerial photography. They often feature robust radio equipment to maintain a strong connection over long distances and may incorporate fail-safe mechanisms like return-to-home functions to ensure safe recovery. The focus is on endurance and reliability, rather than speed or acrobatic capability.

What’s a Racing FPV drone?

A racing FPV drone is designed for high-speed competition, emphasizing agility, speed, and responsive control. Unlike freestyle drones, which are built for acrobatics and aerial stunts, racing drones prioritize compact, streamlined frames and lightweight construction for maximum velocity and maneuverability in races. Differing from long-range drones, which are optimized for distance and endurance, racing drones focus on short, intense bursts of speed in confined courses. Unlike cinewhoop-style drones, known for stable, smooth footage in cinematic productions, racing drones lack heavy camera gear, trading off filming capabilities for swift, agile flight dynamics essential in competitive racing scenarios.

What’s a Cinewhoop?

A Cinewhoop is a type of quadcopter specially designed for capturing cinematic footage. Characterized by its compact size and unique ducted propeller design, a cinewhoop offers stable, smooth flight, making it ideal for navigating tight spaces and intricate environments. Unlike traditional racing or freestyle drones, which prioritize speed and agility, cinewhoops focus on steady, controlled movements to produce high-quality video. They often come equipped with HD cameras like GoPro. Their ducted fans not only provide safety by shielding the propellers but also enhance flight stability, making cinewhoops popular for indoor filming and close-up shots in complex settings.

What’s an Ultralight FPV Drone?

An ultralight FPV drone, commonly known as a “toothpicks“, is a class of extremely lightweight and compact drones designed for agility and speed. Typically weighing less than 250 grams, these drones bypass certain regulatory constraints. Toothpicks are characterized by their minimalist frame design, small brushless motors, and simplified electronic components. Despite their small size, they offer a powerful flight experience with responsive controls, making them ideal for freestyle flying in intricate environment and popular among experienced pilots for fun, acrobatic flying.

Conclusion

I hope this lookup table has provided valuable guidance in selecting the appropriate motor size, propeller size, KV, and LiPo cell count for your next drone build. Remember that these are merely suggestions, and there’s always room for experimentation to find the perfect combination for your specific applications and flying style. Happy building and flying!

Edit History

  • Mar 2021 – Table created
  • Apr 2023 – Article revised
  • Jan 2024 – Added more motor sizes/KV to the table

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