3D Cad and 3D Printing for Radio

[Zeiss Ikon]

I've been a ham radio operator for a couple years; at present, the only working radio I have is in my car. This radio needs an antenna, of course, and since it's a quad-band radio, the antenna needs some joints and coils, rather than just being a length of stiff wire or rod stock. Since it mounts vertically on a car, either on the roof, edge of the trunk lid, or a fender, the one I bought also has provision to fold down as needed for parking under a low overhead -- though because I drive a small car (Ford Fiesta sedan), the clearance a large pickup truck with off-road setup needs for its roof is enough for my antenna without folding.

What's this got to do with 3D CAD and 3D printing?

The folding joint on the antenna is made to automatically "break" if you forget to fold the antenna before passing under a low clearance, to prevent actual breakage or bending the whip. Problem is, wind loads (those coils I mentioned are significantly fatter than the main whip) combined with vibration are enough to cause the antenna to spontaneously fold at highway speed -- which does nothing good for either reception or transmission of the radio signal (there's a huge loss if the transmitting antenna is perpendicular to the receiving one, and repeaters have vertical antennas).

My solution was to use FreeCAD to design a plastic sleeve to reinforce the folding joint on my antenna. In order to make it 3D printable on my Ender 3, I made it in four pieces (too tall and the wobble it gets from the movement of the bed causes a failed print). Each piece is a snug fit over one section of the stepped base of the antenna, and some of them have a notch (looks like a keyway) to clear a pair of setscrews that lock the whip into the folding joint. The sleeve makes the folding joint far stiffer than it was, but it still slides up and down on the antenna so I can fold it if I need to (for instance) park in a structure that has a low clearance (one of the advantages of a small car is easy parking, after all).

I'll link a couple photos of the item installed on my antenna, and I've attached the FreeCAD files for those who are interested. I used circular pads and pockets to join the tip and base to the two body parts, and hexagonal pads and sockets to ensure the two body parts stay aligned with the notches lined up so they can slip over the setscrews.

https://www.dropbox.com/s/veborgjgbrirs ... 9.jpg?dl=0
https://www.dropbox.com/s/wqaicxz6sk8qo ... 0.jpg?dl=0

[chrisb]

Hi and welcome to the forum!

In case you are interested in comments: You shouldn't use 0mm constraints, use geometric constraints instead, e.g. coincidence or point-on-object.

[Zeiss Ikon]

Thanks, @chrisb -- as I recall, I tried to use object and geometric constraints, and got an error when I did it, so (because I was trying to get this done in a weekend) I went the other way rather than try to chase down why I was getting an error about "you must select precisely" etc. Most likely the error was due to incorrect selections in the sketch, but the error messages in FreeCAD Sketcher suck a little.

FWIW, I was relearning FreeCAD as I went on this, having been three months since my first weekend learning it enough to create the https://www.thingiverse.com/thing:4744863 I have up on Thingiverse.

[chrisb]

If you have difficulties selecting things, you can increase in Preferences->Display->3DView PickRadius and MarkerSize.

[Zeiss Ikon]

That isn't the problem I was having. I'd previously used FreeCAD just long enough to design four parts of a single Thing, and then literally didn't open it for about three months. I hadn't used it enough for it to fully stick (I had to dig up YouTube videos to remember how to start creating an object), so I'd just forgotten what the rather cryptic error messages meant. Pointing accuracy isn't a problem, and I can see what's selected (changes color on my screen) -- I was just forgetting what to select.