Just like any build, it’s important to get the frame right. In many instances the Frame is the foundation for which everything else depends on for support.
When looking for Airframes there are a few things I needed for it to “fit the bill”
- It had to be simple to repair. In my experience these drones get beat up on landing. I’ve conducted well over 200 take off and landings, things wear out and I need to be able to repair it, preferably in the field, and with minimal tools.
- It has to protect the electronics. These are the most expensive parts of the build. While I hope that no single component will cost more then $400, I can’t be replacing $400 parts every other landing.
- The airframe needs to hold everything. Kind of a “Duh” requirement, but size matters, and we need something that will hold everything. This includes Auto Pilot, Battery, Camera, and Camera controller.
- It needs to be cheap. This kind of goes along with requirement one, but if we have to purchase $150 airframes to have on hand as a backup, that isn’t as ideal as having something that costs $50.
In many commercial drones the airframe is comprised of foam. This foam is similar to the foam you find in packing material. It is lightweight, and durable. The Ebee Drone that I am fond of, and think is a great little drone, just expensive, is completely made of with a few carbon fiber spars.
It makes sense to use foam for the construction of our DYI Drone, the down side is molding and shaping foam isn’t always practical. It depends on what type of foam you are using, but for the most part, unless you can extrude it into a mold to it’s final shape you are stuck with flat faces and airfoils. I know someone is going to tell me, “You can do XYZ or ZYX and get any shape you want.” They are probably correct, and you can chalk it up to my inexperience for not knowing such basic things.
In doing the research for this build I came across Flite Test. They specialize in making use of Foam Board to create all sorts of airframes. The construction looked to be simple, the materials are cheap and readily available, and it was something that was within my skill level to do. They offer the plans online for free, and you can purchase a laser cut kit, or download the plans.
Since foam board is cheap, and I can buy it at Walmart, it ticks off a few of the boxes. Furthermore watching the Flite Test Youtube Videos I can see that these purely foam board aircraft can take some abuse and keep flying again and again. I do not think that a foam board airframe alone is going to have the rigidity or the durability that I would like. However I do think it is a good starting point.
After reviewing the many different options for aircraft I decided their Spear 1041mm kit.
Based on their videos, the airframe can support an impressive amount of weight. They show it delivering a Chipotle Burrito with chips and dip. Check out their video on the build here. I don’t know if it was a video editing trick or if it was real, but this illustrated to me that the center fuselage had the room needed to fit all of my electronics. Given they often include First Person Camera’s (FPV), Radio Transmitters for video telemetry, along with the rest of the flight controls, on their builds, I felt fairly confident that this was a good place to start.
The second thing that I liked about this airframe was that it was a similar size as the Ebee drone that I was used to. This, I felt, was a plus. Larger drones can get cumbersome to launch in the field, as they are not easy to launch by hand.
As far as durability is concerned, I do not think that the Foamboard alone is going to get me there. If that is the case I plan on using expanding foam to fill the voids and give the foam board more structural support. This will add weight to the aircraft, which will increase the airspeed needed for it to maintain flight, but I feel the trade off will be worth it.
The nice thing about the Great Stuff Foam is that it’s very sticky. It will adhere to anything, and you’ll spend weeks picking it off your hands. I figure this will help hold things together.
Flite test offers both page size PDF’s that can be put together to create the templates, or they also offer large format PDF’s that can be printed on a plotter and used as templates. Since I have access to a plotter, the large format PDF’s were the way to go.
When I was at Walmart I purchased 3 foam boards that measured about 20in by 30in. Turns out this build requires 4.
As with most templates, I use spray on contact cement to glue the template to the material to be cut. I think a glue stick would have been less messy, and just as effective in this instance.
Cutting the foam board is easy, but I found that it best to take your time and work slow. The first cut cuts the top layer of paper, it is good to get this cut right, as the paper will guide you through your subsequent cuts. I also make the point to cut out the bare minimum each step, in favor of cutting holes as needed rather then trying to cut everything at once. I have found that doing to many things at once on a first time build can make it easier to make mistakes. One mistake in one part, isn’t bad, but the same mistake in many parts can ruin a project.
I am not going to go through the build step by step. First off it’s my first build, so I don feel I can give exact guidance, and secondly, I don’t want to steal any of the thunder from Flite Test who does a build video. That can be found here. I relied on their YouTube video to guide me through the process, and while I did make some mistakes, I made far fewer mistakes then I would have.
Much of the construction uses hot glue as the adhesive. I am not a fan of hot glue, I always burn myself. Then I don’t feel like it adheres well. However I put aside my misgivings and did it the recommended way. I got through the majority of the build without burning myself…except for that one time.
With most any glue, you want the adhesion to be stronger then the substrate. That way it is not the glue that fails but the material around it. This is one of my mistakes that I am sure will come back to bite me. I left the paper template in place and glued some parts directly to the paper template rather then the paper of the foamboard. Some of the contact adhesive was not as secure as I would have like. I found that out when the tension of the foam board began to pull up the paper template. I tried to remove as much of the template as I could after discovering this flaw.
Once I completed the airfoil the first thing I noticed was how stiff and rigid everything felt. I was quite surprised by this. I expected it to have some flex, and a soft feel to it. However this was sturdier than the eBee. The foam eBee has quite a bit of flex to it, this wing had comparatively less. It really built some confidence in this design, perhaps it wouldn’t require the expanding foam, and it may not benefit much from it’s application.
There was a fair amount of hand fitting on the parts for the fuselage. I blame myself, I am sure I am not the most precise builder out there, and given this is my first build I can be reasonably sure that I’ve made mistakes that required me to go back and custom fit some of the parts later on.
This is where things kind of went wrong. Putting on the skin for the fuselage really kicked my rear. I just couldn’t quite get everything lined up and in place. It came out looking less the pretty and frankly it’s a little embarrassing. However I decided for now to let it be. This airframe is going to get trashed, at least I’m expecting it to be. Figuring out the autopilot and getting it set up is likely not going to be soft process.
I had a roll of 3M Dual Lock which is a modern version of velcro. I have found it to be fairly strong. It has an adhesive backing that will stick to just about anything. I figured it would be a good choice to help place the electronics in the fuselage and to hold the top hatch close. You can see in the photos how I have this applied.
The last little bit to do was attach the control surfaces. Fairly straightforward and it only took me about 30 minutes to get everything lined and an glued down.
With the airframe completed I can do a little reflection on what went well and what didn’t go well. I think for the most part the plans and instruction provided from Flite Test were excellent. They included pretty much everything you need to get something build from the ground up. Foam board is cheap, easy to work with, and readily available. With that said, I think it is worth it to purchase a kit from Flite Test. If you look at the time it took me to cut out all the parts, a precut kit is definitely the way to go.
I had some issues with the assembly, mostly it is due to my inexperience and not due to the design or the materials. The final product is not exactly to plan, but I feel it is a good start to prove out the concept. I recognize that there will be weaknesses and issues that we will need to correct that come as a direct result of the construction methods and the materials, but I am confident that we’ll have a bird in the air before too long.
Flying usually isn’t the issue. For as much trouble as it gave the Wright Brothers, getting something to flight under its own power is a simple thing to do in today’s world. The landing bit, now that can be the real trick. A good landing is one where walk away from it, an excellent landing is one where you can re used the aircraft 🙂