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Physics of Drone Payloads

Updated: Feb 16, 2022

Contributed by Abhimanyu Vijayraghavan


Drone Payloads


Drones are capable of carrying a diverse range of storage in the form of payload, making them suitable for a variety of roles. The most common payload/ purpose intended in recent times includes delivery and rightfully enough, copters are able to produce an unparalleled amount of autonomy, precision and convenience as compared to any other modes of conventional delivery. They have also been documented to carry medicines, essential supplies, mail, fertilizers/ pesticides among other goods.


The maximum allowable payload that a drone can carry along with the weight of the drone itself should remain within the bounds of manufacturer-specified MTOW (maximum take-off weight). That figure hinges directly on the maximum thrust of the motors in case of a copter and the maximum lift generated at cruising speed for a fixed wing plane. This variation is due to the difference in method of lift produced between the two.


Commonly used terms:

  • MTOW (Maximum Take-Off Weight): The maximum physically permissible weight of the drone with which it is capable of flying within expected flight parameters. Exceeding this limit can severely impact the handling characteristics and range while possibly accumulating structural damage.

  • Empty weight/ Dry weight: Weight of the drone with all its systems and motors but without batteries and any payload (The weight that gets loaded and unloaded after every flight)

  • Effective payload weight: MTOW - Empty weight. This is the carry-on weight that can be added safely


In the case of an off-the-shelf, ready to fly product, the payload includes all the auxiliary components that are aftermarket add-ons. This may apply to various sensors for data collection, LIDAR, Thermal or infrared cameras, additional cameras and so on which are not a part of the default frame provided by the manufacturer.


The payload may also be droppable mid air, post which the drone may continue operating. Such an additional feature may require actuation whose mechanism further adds to the mass of the drone as compared to a manually open and shut hatch where payload is retrieved after landing.


Not all thrust produced is the same. High pitch, low diameter propellers paired with high kV rated motors are best suited for racing drones or any applications requiring quick response and nimbleness while on the other hand, low pitch large diameter propellers are stable, and provide more torque. However the higher the rpm demand of the motor, the increased battery discharge - essentially shortening mission time


In all, a heavy lifting drone would be capable of shorter flying time whereas a near zero payload capacity would be ideal for flying only. Finding an optimal trade-off between the two characteristics is vital to carrying out a successful drone mission.



Note:

Please ensure the following at all times:


  • In case of a custom build, the payload, batteries and empty weight should not be greater than 50% of the thrust produced for an effective thrust to weight ratio of 2:1, at least for the first flight

  • Do not disproportionately add any attachments to an part of the product since it may disrupt center of gravity and its roll/pitch/yaw characteristics

  • Ensure the payload is firmly constrained or fixed onto a rigid support. A flimsy support could add vibration or harmonics to the frame and also possibly interfere with the flight control system and various mounted sensors

  • Payloads dropped from a drone will encounter heavy wind influence (particularly if a parachute is employed during drop) causing it to sway from desired drop point. Take maximum precaution

  • Abide by maximum rpm specification for propellers if any, since centrifugal forces acting on them increase with square of rpm



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