Friday, 24 May 2019

Hackspace Magazine! Keeping track of my articles.

It's been a privilege to write for the Raspberry Pi foundations Hackspace Magazine since last October and I have been meaning to create a post about various articles I have written but never got around to it. So I thought I might create this post with links to all the issues I have article in and a little description of the articles and keep adding to it as (hopefully) the articles keep getting commissioned and published!



Issue 12, Where it all began! I had a "design your own rocket" tutorial in here using the amazing opensource Openrocket design and simulation package.

Issue 14,  An article on Manual Milling machines and beginning machining.

Issue 15, An article on Lathes and their use and a review of a Neke Laser Engraver.

Issue 16, An article on Making a multi headed screwdriver using the lathe and mill and a review of the Eleksmaker Eleksdraw pen plotter.

Issue 17,  Part one of a two part introduction to laying out PCB's for professional fabrication with Kicad.


Issue 18, Big issue for me this one! I had the feature article on Space, featuring lots of maker/amateur satellites, a focus on Libre Space Foundation and a tutorial on setting up a SatNOGS ground station. Also had a tutorial on making a "Slim Jim" antenna and also the second part of the Kicad two part tutorial.

Issue 19, Tutorial on Marking out and Centre punching accurately for metal work and I also wrote the space of the month article on the fabulous Prishtina Hackspace.

Wednesday, 8 May 2019

DIY Screw Switches for Rocketry




In high power rocketry its good practice to have some kind of keyed switch or remove before flight system that isolates the avionics from power. Important as often these systems are connected to small wells filled with explosives that are fired at points in the flight to split airframe sections and deploy recovery parachutes etc. Isolating the system (killing the power) enables the flyer to handle, carry and prepare other aspects of the rocket and only arm the system when necessary.

I've used small 3.5mm stereo jacks and sockets and when the stereo jack is removed 2 pins are connected under a spring steel load to which I have soldered a power cable. I have also experimented with rotary key switches. I have never flown key switches and recently read about some failures using rotary key switches and I've always wondered at what force/speed would it be possible that my clamping stereo jack socket might separate in flight and and kill power?

I then came across the idea of screw switches. A screw switch essentially is a system where a circuit only becomes connected when a screw is tightened. They are often made by hand by epoxying a nut onto a metal bar which is insulated and another metal piece added on top which will be connected when the screw/bolt is tightened. I wanted to try and make one that was accurately repeatable so I could make a multiples but also smaller, tougher and neater.



So I quickly decided on using double sided copper clad fr4 and a PEM nut press fitted to one side. I CNC routed the boards with a hole to receive the PEM nut and 2 holes for M2 mounting bolts. As the M2 mounting bolts would connect the 2 sides of the FR4 I routed a clearance area which generously clears the head of the M2. I fitted a PEM nut (press fit using a 1.5 ton arbour press) to the first prototype and continuity checked that the two sides of the board where still electrically isolated. To make the switching screw I have epoxied another PEM nut onto an M2 bolt and when fully tightened it connects the 2 sides of the board. On the other end of the M2 bolt I made a small punch mark to disrupt the last couple of threads on the bolt which means it cannot be fully unscrewed.

As the device is copper clad I routed the board to have a tab on one end  (at the top of the picture below) onto which power wires can be soldered either side. Therefore when the M2 bolt is fully tightened it connects the wires and allows current to flow.



It then just needs to be mounted in a position inside the rockets electronics bay where its possible to have a small hole in the airframe allowing a small screwdriver to be inserted to open and close the switch. As a mockup I made a small 29mm bulkhead and added a standoff to mount the switch too.
Finally one of the great benefits of a CNC is repeatability, I have now knocked up a few of these and they sit awaiting deployment in upcoming rocket builds.


EDIT!! So some people where asking questions and struggling to see how this worked so I've done a little video explanation and demo! 

DIY Rocketry Screw Switch from concretedog on Vimeo.

Saturday, 23 February 2019

DIY mini vacuum former



I've been meaning to make one of these for years and in amongst everything else I found a bit of time to do it the other week. It's a simple build of a box with a very holey lid - it's ace owning a small CNC as this is precisely the kind of job it's worth its weight in gold for. A quick measure of my cheap shop vacuum nozzle diameter (an Argos special that has lasted years despite abuse) and the CNC cut the side sections to match. I'm experimenting with recycling milk bottles at the moment and using a hand held heat gun. It works well and pulls a strong seal around objects. I fancy trying to make some lightweight small nosecones next to see how they compare in weight to the very thin walled 3d printed ones I have made. 

Tuesday, 12 February 2019

FOSDEM 2019

A snowy welcome on the saturday!



 The huuuge keynote by mad dog. Amazing sight!

I was incredibly lucky to go out to FOSDEM as part of the Libre Space Foundation (LSF) team the other week and despite lots of snow and travel disruption had a great time hanging out and working over in Brussels. It was my first time at FOSDEM and I was blown away by the worlds largest conference. It was fabulous to be able to move around and see and meet the teams behind some of the most prevalent open source software, debian, opensuse, grafana, gitlab, nextcloud and so many more. As currently I am freelancing mainly as a writer I made sure to have a little chat and express my thanks to the Libre Office team, whilst it might not be the most exciting platform in the world it does provide me with the basic tooling to earn my living!


Above, the Gitlab team who have been great supporters of LSF. 

LSF/SatNOGS contributors meet the Grafana team (and inform them of an Influx db bug they found!!)

Going out early the LSF set up camp in a large apartment (The Mansion) and LSF contributors poured in from all over europe staying a while to have meetings, hack on code and discuss development face to face. Its astonishing, humbling and exciting to see these volunteers pour their considerable skills into LSF project. As a more mechanical guy it was hard to follow much of the development but everyone was incredibly kind and patient and willing to teach others. Very affirming. (Although there was some discussion around rocketry hardware which funnily made me boot my tiny laptop to show how my ematch ignitor circuit works!)

Team... looking tired on the Saturday night!



Flying Ryan air means taking the worlds tiniest laptop!


A busy booth


FOSDEM was incredibly busy and I spent some time each day helping on the LSF booth, speaking to a constant flow of people from all over the planet about our missions to democratise space and provide open hardware and software to enable people to get involved. Hopefully it results in more people supporting what we do but also I feel sure that certainly a few more people are interested in moving towards setting up their own SatNOGS groundstations on the global network.

General picture dump..


Loved this!



So many LSF people! All in to see Alex Csete talk about our SDR makerspace project




Wednesday, 23 January 2019

Project Roundup!



Been a while since I posted here so thought I might get the ball rolling again with a little round up of current projects I am tinkering on. Above is a picture of a planned level two rocket build I am starting to work on as it would be great if I could get my L2 certification flight and exam done this year and also pass my RSO (Range Safety Officer) as well. That would mean that it could be possible for me to officiate over other people HPR flights but could also look into the possibility of running a launch event more locally?



I've also on an off since before Xmas been tinkering with some odd parachute designs, first playing with plastic and tape and now moving to making a ripstop nylon version. These hexagonal annular parachutes fly quite well, have low side loading and seem very strong due to the way the shroud lines continue over the canopy. I'm slowly developing more skills and knowledge around recovery/chute making and have a few other projects I want to explore.



I've also been tinkering on and off with a simple GPS tracker design using a NEO6 gps board and  HC12 radios. My current off the shelf GPS tracker (works on mobile network) is too large for a 29mm rocket airframe I am considering and therefore this route gives more options in terms of getting it to fit. The tracker currently spits whole NMEA sentences which are received by another HC12 hooked up to the one note mini laptop and the whole thing acts as a wireless serial bridge. 


Finally been making, machining and tinkering with various things to write some more articles for Hackspace Magazine, I'm really enjoying the writing and hopefully the articles are being well received! I'll post a roundup of articles out so far after the next issue with some of my work is published.