Balsacopter: The Project.
We’ve had fun building our £20 quadcopter but we’re also keen to see what other ways there are to put a cheap quad into the air. To this end I’ve been working on a design for a frame using balsa wood to which I’ll add some basic quadcopter componentry. Welcome to Balsacopter!
Quadcopters are pretty basic in design but two things which are essential are (relative) light weight and robustness. Balsa certainly meets the first criteria but it remains to be seen whether it will have the strength to withstand our amateurish piloting. I’m expecting to to go through a number of iterations before arriving at a satisfactory design.
For decent performance I’m trying to get as close as possible to the weight of Hubsan’s X4 quad. All in, this fantastic little machine weighs just 35g which will be pretty tough to beat. We’ll see how it goes.
I’ll be using off the shelf motors, props and FCB (flight controller board) together with a 3.7V Li-Po battery. Hopefully we’ll get 5-10 minutes of flight time with each charge with this set-up if I can meet our weight target.
I decided pretty early on to create two main interlocking members to form a cruciform frame. I think this will give better strength than the alternative of a central hub with separate legs attached. Of course, this is the advantage of designing something from scratch rather than making do with off the shelf components as with our £20 quadcopter.
The next challenge is how to attach the motors to the frame. This is further complicated by the desire to use just one material thickness throughout so all parts can be cut from one sheet of balsa. After some thought, I ended up with an interlocking section mounted at 90° to the main cross member, drilled out for our 7mm diameter motors.
I haven’t quite worked out how best to attach the FSB to the frame. It’s awkward because of the electronic componentry gubbins on the underside so it can’t be just screwed down directly to the balsa. I clearly need some spacers of some kind.
Using 3D CAD for such a relatively simple project is probably overkill but it does at least mean the 2D geometry is available for creating cutting templates. It also helps to get a feel for the proportions of the vehicle. FreeCad was used to create the 3D model, which although not in the same league as a professional CAD package is pretty decent for basic stuff and it is, as the name suggests, free. Incidentally, I couldn’t find a way to print 2D geometry directly so exported DXF files into LibreCAD before printing. If anyone knows how to do this without an intermediate step, please get in touch!
So far we’ve cut out the parts from 1/4″ balsa sheet and bonded them with balsa cement. The motors and FCB are in place but not permanently attached. As pictured it weighs 31g so we’re under target but to be honest in the flesh it doesn’t look terribly robust so there’s probably some more work to be done. Also, it would have been sensible to include somewhere to stow the battery. I’ll work those improvements into the MkII version.
Next step is to wire it up and see how it flies. Stay tuned for the next exciting episode!