I've had a sudden burst of motivation this morning, possibly due to a nice model flying day finally turning up (maybe the second this year!). I thought I'd use this to make a post since I've not updated in a while. I have a bunch of projects on the go, but they're all moving rather slowly.

For months now I've been building another R/C model, a Speed Twin ST2. The full size is a nifty looking and rather rare (2 prototypes made, one sold to someone in the US) twin prop aerobatic plane. It's somewhat of a departure for me as, with the exception of the HiFly, it's a lot larger than any of the models I've previously built. The plane was built from free plans in RCM&E Magazine, designed by Tim Hooper. I'm cheating a bit by using a CNC cut short kit they offer. Once I find some time I'll hopefully make a series of posts on the construction process.

Speed Twin ST2

Speed Twin Progress

Work on the Speed Twin has mostly stalled for the past few months. This was due to a holiday immediately followed by the arrival of my eShapeOko CNC machine, which stole a large chunk of my working space. In the short term, I'm planning on using the machine to experiment with mechanical PCB etching. The controller for the machine is currently built on a breadboard. If all goes to plan it'll be used to build itself a more permanent controller, and a nice housing for it too.

ShapeOko parts

Breadboarded CNC controller

The controller is based on an Arduino running GRBL and four EasyDriver stepper controller boards. The DIY Arduino (made during a workshop at Nottingham Hackspace) doesn't include a USB to serial adapter, so I've hacked one together using a Minimus USB microcontroller board.


Unfortunately, I'm waiting on some PCB milling bits to be delivered, along with a few other parts, before I can use it in anger. Experiments with it acting as a pencil plotter are promising, and the accuracy seems more than sufficient for the job.

PCB plotting test

I'll hopefully write a few posts about some of the mods I've done to the machine shortly, and about building the final version of the controller once the parts arrive.

Last but not least, I've resumed work on the Unholy Chalupa, my own design model aircraft. The original Chalupa is a 22" span low wing trainer I designed in early 2012 and built over the Easter bank holiday weekend that year. It was designed in CAD but the parts were hand cut.

Original Chalupa

The original model flew well but the wing was overly delicate and became quite twisted after a few repairs. After shelving the model for a few months I redrew the wing with laser cutting in mind. I borrowed a lot of ideas from the style of Dave Thacker's micro scale models, which I'm rather fond of.

Laser cut MKII wing

The new laser cut wing flew nicely initially, but was lightly built for this model. This wing broke during a crash caused by the motor working its way loose from the mount in flight. The wing was repaired, but due to one piece construction it was never really straight after that, making the plane less fun to fly.

The new design has a simplified two part wing that will plug into the sides of the fuselage. This will limit any damage taken to a single wing panel. Since this design change will require a new fuselage, I took the opportunity to redesign that too. The new design will be a lot less boxy.

MKIII Chalupa Parts

I have the parts cut for the new design now, I'll post more about it once I get around to putting it together.