The Making of bbQ v1.0
Let’s build a multi-rotor from scratch. Not from exotic materials like carbon-fiber or G10, whatever that is (and what happened to G9? And is there a G11?). No, we need something cheap, say one US dollar for a large sheet of the stuff. How large? How about 20x30 inches? (that’s 451 millimeters for you non-US folks.)
Lucky for us, the free enterprise system has produced just such a thing: Dollar Tree Foam Board. It is paper-covered foam about 3/8 inch thick (that’s .680 meters in non-standard).
It is light, cheap, and easy to work with. Given a razor-blade and some hot-glue, you are on your way.
So using foamboard…
with these parts…
we will build this:
Our goal is to make a multi-rotor that kind-of, sort-of looks a wee bit like the current generation of racers. Perhaps a QAV 250, or HMB 235, or even a VersaCopter. (Using black foamboard helps!) The features of our multi-rotor include replaceable arms, a body with FPV and flight-recording cameras, and a frame size of about 250. “250” is the distance between motors and is measured in tiny, tiny meters, called minimeters. (millimeters for you non-standard folks).
The current trend on youtube is to refer these “250” sized machines as “twenty-fives”, because that saves the environment by using one less number than “250.” (Not true. Not even in Texas).
The goal is not to make the simplest possible multi-rotor that can fly, but to try our hand at overcoming the constraints inherent in foam-board to build something visually similar to the current crop of FPV racers.
Although rare, a multi-rotor runs into things besides air. This usually results in broken propellers. But it often also requires a bit of rebuilding. The industry has adjusted by using stronger materials for the arms. We will adjust by making many arms and sacrificing them to the trees-that-wave-in-the-wind. This requires removable/replaceable arms and the style chosen here uses Flitetest Powerpod skewer technique, seen below.
Besides removable arms, the other major design commitment is to a vertical stack with several layers. Current FPV racers tend to have 2 layers separated by nylon or aluminum standoffs. Foamboard can’t handle the concentrated stress a standoff would make, so we spread out the load by building around the arms and then adding a layer for good measure.
The bottom layer accepts the battery. The Middle layer is used for power distribution. The top layer holds the flight control board. For simplicity of configuration, I chose the KK2, a great board for multi-rotors like this. In other words, multi-rotors suitable for running around a bit and having fun, not winning the grand prix.
Use packing tape on the bottom layer for strength. You should use a strap around the battery to keep it mostly attached to the frame and tape helps the foamboard hold up better.
Foamboard doesn’t handle wet weather very well. Two tips help: 1. a coat of polyurethane 2. sealing the exposed edges with a thin layer of hot glue.
Heads up when you are gluing the doublers on the bottom layer to receive the arms: be sure the arms are spaced according to the sides. Our current build videos show both arm doublers being glued, then sides being attached. This has caused some grief when the cutouts in the sides don’t match exactly where the arms are attached to the bottom layers. It might be a good idea build the rear arm-holder, attach a side, then build the front arm holder. That way the arms are guaranteed to fit the sides well.
If you have ever built Flitetest powerpods, you know they are fastened to the fuselage with barbeque skewers. To keep the skewers from working their way out during flight, we use bits of fuel tubing on the ends. I used this techique to keep the arms in place. The center of the body has a circular cut-out that allows us to recess the ends of the skewers.
bbQ motor mounts are cut out of aircraft plywood. These were produced on a laser cutter, but plywood motor mounts are not tricky to cut by hand. They extend a bit so we can tape them on to the arms. Tape turns out to be strong enough.
Don’t forget blue thread-lock on the motor-mount screws.
Motor mount attached to arm.
The camera tray up front is sized to hold a Mobius. The FPV camera is taped to a piece of foam that has a cutout for the lens. The foam is then hot-glued to the top level at the angle of your choice.
The video transmitter (VTX) is attached to the rear bumper with double-sided tape. Although video transmitters can get quite hot, so far it has stayed attached.
A few questions to wrap this up:
1. Multi-rotors have a rich tradition and heritage of naming-ness. How did you pick such a fantastic name, the bbQ?
- Good designers sometimes prefix their names with two letters, perhaps FT, or NN.
- This is Texas.
- My middle name starts with N.
- Therefore… “bbQ”
2. Who in the world deserves credit for this?
- ACU Maker Lab fellowship.
- Special thanks to Nil, Chad, Adam, Korbin, Austin, Hao Zhe, and Shawn for beta testing. Sorry about the burns, but in my defense it is called hot glue.
3. Where are the plans?
- Here: bbQ_v20_20x30.pdf
4. Where are the build videos?