Drone Frame Design Basics – Part 2: Designing the Frame Be sure you have gone over
Drone Frame Design Basics – Part 1: Stacks and Motor Mounting Constraints before diving into this part. Now that we have our stack mounting and motor mounting templates ready, we can design the bottom plate and arms around those constraints.
First, I like to make sure I have about 1.5mm of minimum clearance around each screw hole to any edge of the design. So I’ll draw circles with a radius of 2.5mm around any M2 screw hole that will be near an edge or corner. Using the Circle tool (click Shapes then select Circle or just press C), draw circles around the M2 holes for the 20x20 template since these holes will be closest to the edge of the frame.
Copy and paste the entire object further below and leaving some room this time so we can start making the outlines of the bottom plate around the stack template. From the duplicated objected, draw lines that extend from the middle of the outer top and bottom sides extending out 15mm. Recall that these lines will be colored red as you draw them indicating they are parallel to the red axis.
By now, you should be familiar enough with the Line tool to complete the object as in the following image:
By now, you should also be familiar enough with the Circle tool to replicate the M2 screw holes (2.1mm diameter / 1.05mm radius) and buffer area (5mm diameter / 2.5mm radius) to create those one ach of the four outer corners of the object. These will be for M2 standoffs. Note that the 5mm diameter of clearance is suitable for M2 knurled aluminum standoffs which typically have 4mm of outer diameter.
Activate the Tape Measure tool by clicking the icon or hitting T. With the Tape Measure pointer active, click on the upper side of the object to measure the distance between the standoffs as 15mm.
This frame is compatible with 14mm nano cameras using a TPU mount on the front standoffs to secure the camera and make up for the 1mm difference (0.5mm on each side). Generally, it is good practice to leave some small buffer rather than measuring your camera clearance to precisely 14mm (nano) or 19mm (micro).
Note also that this is yet another constraint: camera compatibility. It just so happens this design is compatible with a nano with little to no modification. However, if we wanted to make this compatible with 19mm micro cameras, we would then be subject to the constraint of needing those front standoffs to be about 19mm apart rather than the 15mm they are now. We got lucky lol.
Now let’s work on the arms.
Go back to the motor mounting template, make a copy, and Explode the grouped object so we can work with it.
(Note that you can “work” with a grouped object by double clicking on it. This will bring you “inside” the group container allowing you to work with the object as if it was not grouped. Exit the “container” by clicking anywhere outside of the object.)
Make your screw hole buffers by drawing out circles with a 2.5mm radius as you did with the stack mounting template. This will show us how far the edges need to be from the holes. You can use a larger radius if you think you need more material around the holes.
Select the Circle tool and draw a circle out from the center of the object to the outer edge of any of the screw hole buffers. This form the outline of the arm ends ensuring that no edge is too close to any of the screw holes.
Draw vertical lines from the center of the object to the outer edge ensuring that the line is green indicating it is parallel to the green axis.
Draw lines along the left and right sides as shown in the image below:
Use the Eraser tool to remove the sides past the lines you just drew as shown in the image below:
From the center of the object draw 4mm lines out to both sides. This will place markers along that line that are 4mm from the center.
We are going to use these markers to draw arms that extend out 8mm in width. Using the line tool, draw lines extending out 100mm from these markers and connect the ends to box it off as shown in the image below:
I know. Not the prettiest arm. But it is an arm complete with precise 12mm motor mounting lol. Select the entire object then group it.
Now let’s make some props!
Well not really props. But big ass circles to double as props so we make sure we aren’t slicing up standoffs or adjacent props. Since this will be a 4 inch, draw a line that is 101.6mm long (4 inches) then draw a circle from the center of that line. (Yes, I am moving faster along since you should be familiar with how to do this by now.)
Divide the circle into quarters to provide a reference for the exact midpoint. Select the entire object and group it so it can be moved from the midpoint. Voila, you have a 4” propeller! Lol
Copy and paste the grouped bottom plate object and place it somewhere with a lot a space below. Draw a line from the center out 75mm to the left of the object. Copy and paste 2 of your 4” props nearby (don’t forget to group it before copying). Now using the Move tool, click on the bottom edge of a prop and position it along the line. Do the same for the other prop. Now position the props taking advantage of how the move tool snaps to nearby locations so they are exactly aligned. Make sure to position both props so there is sufficient clearance between them as well as to the front and rear corner standoffs. In this image, there is 3mm clearance between the props and standoffs.
Copy the arm and paste it nearby. Using the Move tool from the center of the motor mount, move the arm to position the motor mount exactly center on the front prop.
Click on the Protractor tool and position the Protractor in the middle of the motor mounts / prop. Click once, then move down the center line of the arm a third of the way down or so (exactly is not important). Click a second time and now as you move left or right, the arm will rotate around the center of the motor mounts (where you clicked first). Position the pointer to the exact center of the stack mounting template. (I told you those lines would come in handy.) Click one last time to set the rotation.
The arm is now angled perfectly to the center of the bottom plate with sufficient clearance for a 4 inch prop to the front standoffs adjacent prop. Repeat this process for the bottom prop.
Since frames are typically symmetric, I personally like to work on just one side only. When I’m done, I’ll delete the other side, copy the working side, flip it, and connect the two. This serves to ensure that both sides are precisely identical. Well, that and I’m lazy. Copy the entire thing you have so far and paste it further down. Delete the props and the 75mm line you drew as a guide.
Double click on the grouped upper arm to “enter” its container. Now draw a line along the edge of the frame that intersects the arm. Note the tooltip that indicates “Intersection Outside Active” ensuring you are precisely at that line intersection outside of the group.
Delete the portion of the arm that extends into the frame. Do this by erasing the 3 lines highlighted in blue in the picture below. Once delted, you’ll notice that the group “container” shrinks to reflect the shorter length of the arm. “Exit” the container by clicking anywhere outside of the arm.
Do the same for the lower arm.
Select all three grouped objects (the 2 arms and the bottom plate), right click over any of them and then select “Explode” in the drop-down menu. This will ungroup the objects and connect them as once single object where they intersect.
Select the entire right side of the bottom plate by dragging the pointer. Be sure that absolutely nothing on the left half is selected. Then delete the selection.
Copy the remaining left side and paste it to the right. Make sure it is a decent distance away from the original left side. Then right click over the copied side and select “Flip along” and “Green direction” in the drop-down menu.
Using the Move tool, anchor to the uppermost left corner and move the entire right side so it aligns perfectly with the original left side.
Notice that if you double click on either side of frame, only that side is highlighted suggesting that this is not a single object which is what we need it to be.
This is one of the quirks of Sketchup. In Fusion360, the program would likely correct this error without you noticing. But in Sketchup, the geometry got tweaked ever so slightly (in the 0.0000001mm’s) that the center line is technically not overlapping. You can fix these types of situations by simply re-drawing the center line that runs the entire model.
And now when you double click anywhere, the entire model is selected confirming that is all once connected, single objected. Take that, Sketchup!! lol
This part sucks. You now need to delete any and all lines that do not serve as a physical border to the frame. You will want to leave the screw hole circles but everything else needs to be deleted using either the Erase tool or by clicking on the line segment (circles and curves are nothing more than many line segments) and deleting them. You will also want to zoom in as some areas that appear to be clean …
… are actually not once you zoom in.
In the end your frame should look like this.
Last but certainly not least, we need a top plate. I’ve found it’s best to model your top plate from the very same model used for the bottom plate. This ensures precise alignment of the standoffs. Make a copy of the bottom plate and draw lines down to complete the sides as shown in this image.
Delete the arms and stack mounting holes leaving only the front and rear standoff holes. Voila, top plate! lol
Copy and paste your amazing creation and delete the screw holes by clicking on the area inside the hole and presing delete.
Congratulations on making a frame!! Sure, it aint the most pretty but perfectly functional as a quadcopter frame with precisely measured components. At this point, you can literally use the steps outlined at the end of the first section,
3D Programs to export DXF files for the bottom and top frame and send it off to get cut!!
But … you may want to test it first.
When I first got into this thing, one of the draws was having a 3d printer. I figured what better way to prototype designs and not have to deal with the cost and time of getting actual carbon prototypes cut. Yea, not so much. I don’t care how precisely tuned your 3d printer is, the tolerances suck. Period. No way you will be able to ensure the best fit for more complicated geometry like those for perpendicular joins using a frigging 3d printer. I got to understand that pretty fast. But lose hope not, young grasshopper. For it turns out the very tool you used to design this stuff has for me served as the best tool to test the very stuff I used to design it!! That didn’t sound as Yoda as I hoped. Anyway, in the next and last part to this epic trilogy of a segment, I’ll show you how I check my models using … wait for it … the modeling program lol. All this in
Part 3: Testing the Design.
And this is what your dilly should look like by now …