How to design a quadcopter frame in AutoCAD
How to design a quadcopter frame in AutoCAD
This article is written by AirBladeUAV based on his experience designing micro drones for the past 4 years. Other designers may or may not follow the same process and workflow.
Are you a drone enthusiast who wants to fly your own creations? Are you an aspiring drone designer who wants to get started in the industry? If that's the case, you will find this tutorial a good starting point.
Before diving into this tutorial, I recommend getting familiar with AutoCAD design space, basic commands, controls and navigations. There are a lot of video tutorials on YouTube on these subjects. You can download a free version of AutoCAD through their education program. Basic commands that we will be using a lot for designing drone frames are: Line, Circle, Rectangle, Trim, Offset, Fillet, Move, PEdit, Group, Ungroup, Rotate, MeasureGeom etc
OK, so now that you're familiar with basic controls, and have set up your design space to your preference, LET'S DIVE IN.
Step 1: Determining the general geometry of your drone
Before getting into anything fancy, you need to first determine what type of frame you're designing because the type of frame will influence the general geometry of the frame. A few popular designs that you can explore is True X frame, H frame, stretched X, stretched H, deadcat style or reversed deadcat.
Step 2: Determining the max prop size your frame design supports
Next step is determining what maximum prop size your frame is going to support: 2 inch or 2.5 inch or 5 inch. Combining the decisions made after step 1 and step 2 will give you an idea of how big your frame is going to be. With experience, you will eventually have a rough idea of what sort of dimensions you can use as base line. These dimensions is what we will be using in step 3.
Step 3: Sketching the motor positions
Knowing the general geometry of the drone (step 1), and the prop size that this frame is for (step 2), you can take the very first step in designing your frame by drawing the motor position.
In our example here, we will be making basic H frame that can accommodate 2.5 inch propellers. So how do you determine where the motor positions are? It's really a blend of art and science here, and it also requires some experience to get it right, but I'll show you the thinking process that I applied.
So 2.5 inch prop is 63.5mm. That means at the very least, you need a square with dimensions of 63.5x63.5mm. This square will ensure that the prop tips are just touching. This is provided that the electronic stack and camera are already out of the prop line. In reality, you will make the square slightly bigger with dimensions of 63.5mm + X (where X is the extra buffer).
In our case here, I plan on having the camera on the same plane as the motor and positioned a little forward, therefore the width of the rectangle will have to be 63.5mm+ 20mm (width of camera) + X. And the length of the rectangle can be as little as 65mm. I've decided to go with 80mmx100mm.
Use command RECTANGLE to draw a rectangle with dimensions of 80mmx100mm.
Notice that I also draw 2 lines that go through horizontal and vertical midpoints. These lines are important for our Mirror command later. Because our frame is symmetrical, using the Mirror command will speed up the design process.
Step 4: Sketching the arm profile
Next step is sketching the arm profile. Use command 'Mirror' to duplicate it for all 4 different arms. Make sure you have the mirror lines sketched out as mentioned above.
Step 5: Test fitting your components
In this step, you want to make sure that your intended components will fit the frame. The full extend of the test depends on your design and what components you're using, but for the most basic test, you want to make sure that your props don't strike the stack or your camera.
So first you need to draw the prop line on all 4 corners. In this case, that would be a circle with diameter of 63.5mm. Use Mirror command to replicate the same circle to all 4 corners
Draw the intended stack configuration. In this frame, I want it to be able to take 16x16, 20x20 and 26x26 stack. Make sure you group all the different stack configuration into 1 object using command 'Group'.
Move the stack configuration to the intended mounting place and ensure that there is enough clearance from the prop line. Please note that the square drawn in this case is the mounting dimension, you need to make sure that the edge of the board (for example, 27x27 edge to edge for a standard 20x20 board) is also clear of the prop line
Step 6: Filling in details
Now that we know the frame fits your electronics and there is enough clearance for the props, you can start filing in the details: arm width, motor mount shape, body etc
Remember the line you drew for the arm shape? You can use command line 'Offset' to make the desired arm width. In this case, we want our frame to be fairly light and toothpick-like, so we will give the arms 6mm width.
Draw the motor mount and mounting holes for each motor. Use Mirror command line to replicate that for all 4 motors. Note: I forgot to add the c-clip hole in this picture, but you need to make a cutout for motor c-clip. Usually a circle of 5mm diameter.
For micro motors, most of them use 9mm spacing and M2 screws. So what you want to do is to draw 2 lines perpendicular with each other and then draw a circle with 9mm diameter. The 4 points where the circle intersects the lines are the mounting holes. Draw circles with 2mm diameter at those intersections.
Draw mounting holes for electronic stacks. I typically assume that they will use M3 hardware. It's simpler because M3 holes will always fit M2 hardware, but not the other way around. A trick here is that you need to draw circles with diameter just slightly larger than 3mm, so that the screws can go through effortlessly. I typically go with 3.1mm diameter.
Step 7: Adding your own personal touch
At this stage, you just need to add your own personal touch to the design. You decide how the general shape would look. You decide how the cutouts look, how the battery strap looks. You have all the tools at your disposal.
Use command line Fillet to soften all the corners
Final step: Cleaning up / Finalizing the design
The final step is simple, you just need to delete any objects that are not pat of the final design. Make sure to use fillet on corners.
Highlight all the object and group them together
Note: As mentioned above, I forgot to draw the c-clip holes for the motor mount. Usually those are circles of 5mm diameter.