I have a quadcopter drone, is there an advantage say of having a octocopter instead of a quadcopter. Will it improve performance?
Performance is unlikely to be improved, in terms of speed or agility, or even load-bearing capacity, as they are heavier, slightly less efficient aerodynamically, and more expensive.
What you do get is a degree of fault-tolerance.
With a quadcopter, losing one rotor means your drone will fall out of the sky. With an octocopter (or hexacopter, but an octocopter can lose more motors and still be able to fly) losing one rotor is not fatal - it will still fly, however, it will have a reduced control authority.
This makes them very desirable for carrying expensive loads - such as a £50,000 camera - you really don't want to drop that out of the sky if you have a fault.
There are a number of factors that change with more propellers. Some of these are trade-offs (e.g. you lose the redundancy benefit if your weight needs all the motors to fly). The pros and cons, and their relative size, will depend on your specific use case.
In general, an octocopter (compared to a quadcopter) can have:
- Increased redundancy - more motors and propellers can allow for at least one failure while still being able to control and land the aircraft.
- Increased payload weight - the extra thrust from the additional motors allows for a heavier aircraft and payloads.
- Increased stability and control - with 8 motors, you have 8 points/4 axes on which you can change the attitude of the aircraft. By increasing lift through more propellers rather than larger propellers, they can change speed and react faster as they have less inertia.
- Increased power consumption - by running more motors and ESCs, the power demands increase. Even when the motors are doing less work, they are generating a base level of wasted energy (heat, noise, etc.)
- Increased 'dry' weight - Not only the extra motors, but more airframe is needed to hold them and more batteries are needed to achieve similar flight times.
- Increased size - the aircraft is, in most cases, going to be larger to keep the propellers apart which could affect use cases (e.g. doesn't fit indoors, but can be seen further outdoors.)
- Cost - the need for more parts (or more specialised parts) increases the price of the system. However, in some areas, the use of more small parts could be cheaper than fewer large parts.