Analysis of Alternation Solutions:
Hexacopter vs. Quadcopter
The two main solutions presented for the frame were a quadcopter and hexacopter. A hexacopter would give us the ability to lift greater amounts, and more reliability as the drone would still be able to safely land if one motor or propeller broke. A disadvantage of this design is that overall it would be expensive and while it could provide a lot of thrust, it is not necessarily needed for this competition. One advantage of a quadcopter is that it can have larger propellers and
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a smaller frame as the arms can be closer together since there only needs to fit 4 propellers rather than 6. It also decreases the motors, ESC’s and batteries needed compared to a hexacopter. The final decisions was to go with a quadcopter for the above advantages and in order to provide enough lift focused on finding motors that were suitably efficient
Discuss:
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Motor, Propeller and Battery Selection
In previous competitions, WARG has used motors powered by 14.8V batteries. These were initially considered as they are more commonly available and the batteries to power them are much lighter. However, when looking into the max payload, these motors could not support the drone weight along with a 2kg payload.
In order to carry the proper weight, the decision was made to switch to larger motors. After choosing a supplier, in this case T-Motors, and a couple of the potential motors, they were compared to find the one most suitable. A custom excel sheet was used to calculate the lift and flight time for different combinations of motors, propellers and batteries. Using this data, the final decision was to go with T-Motor Antigravity 5008 motors and 18” propellers
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. These will be powered by two 5000mAh Turnigy batteries. This combination was the best option as it allowed to flight time to be over 16 minutes with the maximum payload of 2kg while maintaining a 50% throttle which helps the drone be more efficient. During the second challenge when there is no payload, the drone can fly for over 28 minutes ensuring it has time to complete the task.
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Frame Shape
Early on, the frame was designed to have 2 levels. This allows there to be lots of space for electronics, computer vision equipment and batteries. It also lets the arms be securely mounted between two plates while still ensuring that they are easily removable. It was key to make the arms easily removable so that if the drone is to crash during testing, an arm can easily be replaced and testing can resume. Currently, the frame has lots of holes to ziptie electronics on for testing however in the final design, there will be mounting holes for each part to ensure that everything is secured well.
The following image is a CAD model of the frame and batteries. The light blue parts are 3D printed as they need to be a custom size. For the prototype, the frame itself will be laser cut out of wood however in the final drone it will be waterjet with carbon fiber so that it can be lighter.
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The following picture is of the frame fully assembled.
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Landing Gear (I can add if we want to include it but I don’t think it’s really important for the report)
Landing Gear Megan Spee can talk about new 3d printed parts?
To add:
Pictures of frame cad
Motor Flight Calculations