CNC cut control horns

I was at a loose end during today's bank holiday so I decided to do a mini-project (with bonus recycling features) and make a set of control horns for my radio controlled SpeedTwin ST-2.

Control horns in DraftSight

After deciding on a sensible size for the control horns I drew them up in DraftSight. These ended up being 25mm tall and 12.5mm wide at the base. I designed them on a sprue so that when I come to etch the remaining copper off they don't get lost in the etching tank. The horns are shaped so that the holes for the linkage can lie on the hinge line with plenty of material around them for strength.

The DraftSight file for the parts can be found on GitHub in my rc-parts repository, which also contains drawings of various bits of radio control hardware that I've designed parts around. Please feel free to use any of it or to contribute drawings of parts.

The victim

The PCB material I used comes from a nice FR4 board onto which was otherwise unusable due to a design mistake. The board was intended to be used as a 2 player version of Charlie's 'Minigun' miniature SuperGun project. Unfortunately after etching I noticed I had messed up the pinout of the JAMMA connector when transcribing the design from Eagle to KiCad. Rather than throwing it away this project is allowing me to reuse the material for something useful. My 2 player 'MiniGun' will eventually get finished and written up too.


As a quick aside, the SpeedTwin has made some progress since I last posted about it. The fuselage is nearly finished, except for sanding the canopy to shape and some more work on shaping the nose cone. The wing is also coming along, with the top half of the engine nacelles planked and mostly sanded to shape. The remaining work on the wing is to install the tips and build the bottom half of the nacelles, which will be removable for access to the landing gear.

Once the control horn design was ready I used CamBam to convert it to G-Code. Unfortunately some manual editing was required on the output to get Grbl to accept it happily. The main problem was a G17 code, intended to signal that arcs should occur on the XY plane, which caused Grbl to error after any subsequent G3 (arc) code. This setting was default anyway so the line was removed with no adverse effects. I also tend to remove comments from any code that is passed to Grbl - the parser can choke on lines over 50 characters so comments at the end of lines are best removed. If I find an open source CAM program that will provide Grbl compatible G-Code out of the box I will probably switch to it, I just need to put in the time to find one. :)

Cutting the parts

This is the first time using my eShapeOko since I rebuilt the controller so I had to spend some time setting up again. Once I'd calculated the appropriate steps/mm settings for each axis everything went fairly smoothly and after a few 'air cut' test runs I cut the parts. Since this part is all made in one cut I simplified things slightly by removing all of the Z axis movement from the program. I manually plunged the bit into the work from GrblController and then set the program going.

I decided not to drill the holes on the CNC to save setup time and because I don't have a suitable drill bit that fits my eShapeOko's rotary tool. They will be quick and easy to drill accurately on the drill press at NottingHack at a later date.

Mostly finished parts

All that remains is to etch the remaining copper off (and sadly lose the current futuristic look), drill the holes and cut off the sprue.