Building a welded Ronja from thick iron pipes

We decided to build a couple of Ronja links for the CZFree.Net community network in Prague. We did not quite like the design of Ronja's mechanics being based on thin wobbly tin pipes. We re-designed the mechanics using thick iron pipes that allow welding. Some of the Ideas come from a brainstorm session with Clock and Deu dating a couple of years ago. This is an attempt to document the building process for the benefit of other builders in the Ronja community who would like to try an alternate design.

This is not an idiot-proof step-by-step building guide, and can in no way compare to Clock's official guides. There are no exact dimensions, formulas, and procedures in this document. It is intended to provide ideas to brave builders who like to think on their own. Having to invent parts of the construction yorself, instead of blindly following a polished guide, may be very exciting and the results more rewarding.

Due to lack of time, after almost two years since buying the first parts, we only just finished the first link. it operates between the "Bakulak" and "AVP Spojka" nodes. The other three links still need painting and a little more metalwork before they will be finished.

Overview

The key features of this design are

• As much drilling and screws as possible replaced by welding
• A sturdy and durable construction
• As little holes to be sealed as possible

This is a picture of an assembled Ronja to give you an overview of the overall layout before you start reading throught the details

The main pipes

We used a 133mm outer diameter pipe, 4mm thick. We bought it at Ferona in Malesice, Prague. I must say we were very lucky that they cut it for us - although they charged as much as cca EUR 2 per one cut, it saved us a lot of hassle.

The pipes needed to be lathed a little on the front side. This allows the lens to be nicely snapped in the lathed space and glued. This is probably the only thing you can not really do by hand in an average home workshop. We had this done by someone's friend and it cost us around EUR 35 for the 16 pipes.

Then we welded on the standard Ronja quoin... note that none of us had any experience in welding. The joints are not nice, but at least we (almost) learned something new

The lid at the back of the pipe will be tightened by four screws sticking backwards from the pipe. To weld them on relatively straight, we made this template from an aircrete building block.

The electronics (rx/tx) box is held in place by three 4mm thin threaded rods that are bent and welded on the inside of the pipes. Again, we made a arcrete template with the three holes drilled in it to ensure the positioning of the rods would be (relatively) accurate.

The modified RX/TX layout

As you have seen, the electronics boxes are placed in the pipes in a different way than in the original Ronja design. I can only see two disadvantages of this layout:

• The TX PCB will probably be difficult to use (we used airwire, because we started before the TX PCB was released)
• The two more populated RX compartments are really crammed, while the relatively empty one wastes a lot of space. It is more difficult to solder, but it's doable.

You can download my RX/TX box drilling template and the drilling template for the tin triangle holding the box.

Assembly

This has shown to be a weak point of the construction of the first prototype. The RX/TX boxes are placed on the threaded rods inside the pipes. Then nuts are screwed on the rods to hold the electronics boxes focused. Don't repeat the mistake I did -- wrap the threaded rods with something before painting. We had a really hard time screwing the nuts down the rods, as the thread was full of paint. Also, I should have made the holes in the tin triangle screwed to the electronics boxes slightly larger. I made them just large enough for the threaded rods to go through, and the modules turned out to be very difficult to move and focus, as the friction of the not-perfectly-straight threaded rods was significant.

Originally I planned the electonics module to be pushed against the nuts using three metal springs from the inside of the pipe. I could not get the springs, however, so I replaced them with ruber bands holding the modules against the nuts from the outside. The bands are hooked on the ends of the threaded rods. To prevent the threaded rods from puncturing the rubber bands, I put small rubber blocks with a hole in in them on the ends of the rods. The rubber bands are made of an old bicycle innertube. I hope they will not be torn by the tin holding the rx/tx modules, but I fear they will eventually. The springs would have been much better.

The lens are glued into the pipes with Epoxy and so are the heating resistors to the lens.

I already used this simplified Ronja holder (with the two pipes attached to a single metal part) on my previous Ronja. It just works and is much simpler to make. It is not so versatile, but has always been versatile enough for my needs.

The lids are straightforward. Make them thick enough so they don't bend when tightened. Ours are something like 5mm (??) thick. There is a piece of rubber between the lid and the pipe used as a waterproof seal.

Contact/questions