Posts Tagged ‘Design’

FreeCAD 3D design software

Our club has been (slowly) constructing a SatNOGS 3D printed satellite ground station. It uses a bunch of parts that have been designed on a platform called 3D CAD. This is a free (as the name suggests) 3D CAD solids modelling tool. For those not familiar with mechanical design here’s a very quick and simple run through.

The good old days gave you 2 dimensional CAD packages. One of the most famous was AutoCAD. There have been many releases and it still has a place today (you can even get a free version called Draft Sight).

Perfect for producing 2D drawings in the traditional was. Also ideal for those .dxf files for laser cutting front panels for example. These are simple tools to get your head round but ultimately very powerful. This technology has been used to deliver some pretty complex engineering so don’t underestimate its usefulness

3D CAD design can look like a complex business but as tools develop the proliferation of simple to use applications exist and as expected they use their own language. 2D drawings are no longer the standard and so 3D parametric CAD systems are available from a number of big players like AutoCAD and SolidWorks. They range from very expensive professional packages that have features that only the very keen would need (like finite element analysis, animation and computational fluid dynamics) through to offshoots that are particularly aimed at home users. In amongst these packages are offerings such as FreeCAD and SketchUp which are completely free and very well supported. There is only one preferred standard and that is for the .stl file type although there are key differences between types.

Solids modelling and Surface modelling. As the names suggest one type produces solid shapes which are determined through sketching a part in 2D then turning that into a 3D part by stretching or revolving it around and axis for instance. These are generally referred to parametric modelling tools and they produce solid shapes. Examples of these types are FreeCAD, AutoCAD inventor and Solidworks. SketchUp on the other hand produces hollow surfaces. An easy analogy is between a dice and a cardboard box. Both are cubes, one is hollow and the other is solid. 3D printers for example need to think in terms of solids. This doesn’t mean you can’t use a surface modelling tool to produce a part, it means there are some additional bits of computer based thinking that needs to be done.

FreeCAD falls squarely into the 3D parametric solids modelling camp (for the purists, yes it does do sheet and mesh work but stay with me on this). It is also nice and simple once you get your head round the basic premise. Sketch something in 2D then pad it to make a solid and perhaps put in a pocket for a bolt hole for example. I have been working my way through a few tutorials on YouTube and can recommend theses…..

Once you get into the workbench idea and the language used it is relatively straightforward producing designs. I think the issues are that the assembly workbench isn’t quite there yet and it isn’t as polished as commercial alternatives, but hey it doesn’t cost thousands.

There are also a number of developing online packages like 123D CAD and Onshape but I haven’t had a look at those in any detail. The premise is still the same. draw a 2D sketch, constrain it with dimensions, symmetry, equality etc and extrude, revolve, pocket to your hearts content. It is a really great step to see such powerful tools available for free.

It wouldn’t be fair to mention the extremely accessible surface modelling package that is SketchUp. A Once Google product that instead of producing solids models faces and uses clever tricks to make you thinks they are solids. This is a great tool and is good enough for 3D printing parts. Just beware of its limitations and well aware of the huge amount of models available in its warehouse.

Well worth considering for anything from shack layout to 3D parts design.

Hopefully I will get re-antiquated with this new tools as its been a while sine I behaved like a clanky (that is a mechanical engineer to you lot). There are some truly staggeringly clever products available that you only need invest a bit of time in learning.

 

KiCAD for clankies

If you fancy designing yourself a PCB for a project then you’ve got quite a few choices. For a long time Eagle has been the standard. It offers just about everything that the novice and expert needs to create a professional looking board that blurs the lines between hobby and business. It has been acquired by AutoDesk, the people behind the hugely impressive Inventor 3D CAD package. Loved by clankies like me.

But what about open source software? Well KiCAD is the ‘other’ standard, with a slightly different workflow it still roughly follows what must be normal. That is, design a schematic and then tackle laying out the PCB.

I’ve not designed anything in Eagle for a long time and so have largely forgotten how to do it. So, thought that now I’ve switched almost entirely to Linux that I’d give KiCAD a go. Download through your favourite method and take my advice, download and print off the ‘Getting Started’ pdf.

The plan was to copy an existing layout first and see if I could make the PCB. I can report that I have achieved what I set out what to do. So, without boring you to death about the in’s and out’s of the software, here’s what I learnt….

  1. KiCAD has moved on. A lot – It is a simple and quick way to produce a hobby project. I understand as well that a big update is on the way.
  2. Workflow is different to Eagle – Schematic – Netlist – PCB rather that Schematic – PCB. This additional step is actually beneficial as it lets you make sure that the component can be sized separately from determining its functionality.
  3. AutoDesk still has a fantastic set of suite of applications and no doubt it will produce a superb link between electrical and mechanical that will be hard to beat. Commercially this will be hard to beat. The hobbyist will reap the benefits in time.
  4. KiCAD is fundamentally fit for purpose and definitely is not second best. What is clear is that the two suites follow different paths. There are a bunch of other pieces of software that fit the bill but most hobbyists have heard of both of these.
  5. RTM – Did I say Read The Manual? I’m going to say it again, read up. This isn’t a 5 minute investment and planning will pay off.
  6. If you’re keen on open source software then crack on. No need look elsewhere.

I’m going to continue with this project and no doubt learn new stuff. Today I learnt that importing .dxf files for the creation of PCB shapes is simple. A really quick way of getting the Altoids tin shaped PCB I need.

 

Two biography books for engineers

The F-117 Nighthawk, designed by the Lockheed ‘Skunkworks’. (Image in public domain from Wikimedia Commons)

I have just finished reading ‘Skunkworks’ by Ben Rich and Leo Janos and it should be one of those books that engineers, students of engineering and those that like technology should read. The book details the secret Lockheed Martin aircraft design branch, set up and run by Kelly Johnson, which became known as the ‘Skunkworks’. Out of this special projects group came the F-104 Starfighter, the U-2 spy plane, the SR-71 Blackbird and the F-117 Nighthawk (also called the stealth fighter), amongst other aircraft.  The book starts out with the development of the Nighthawk which was developed by a team led by Ben Rich, who replaced Kelly Johnson as the head of the Skunkworks.  After telling that story of the stealth fighter development over the first few chapters it goes back in time to when Ben Rich first joined the special projects unit and how he became involved in the development of some of the most advanced military aircraft of the 20th Century. The book is an exciting insight in to how advanced engineering projects can be run.  ’Skunkworks’ was allowed to be free from the usual corporate bureaucracy and therefore it could move quickly in development. There was also a philosophy of using off-the-shelf parts as much as possible, including engines, so reducing delays from manufacturing new parts that would then need to be continued to be produced.  Although this philosophy was challenged with the development of the Blackbird which was designed to achieve Mach 3 speeds and so needed to be constructed with large amounts of titanium.

Combining details of how the planes were developed, the challenges and uses of the planes, as well as some insight into management styles and how to obtain multimillion dollar contracts make the book extremely interesting. When you read about the uses of the U-2 in the Cuban Missile Crisis, the shooting down of Gary Powers, and the use of the F-117 in Iraq you can see these aircraft had influencial and important roles in the the Cold War period and beyond. It was also interesting to read about the irony of how a relatively obscure Russian paper on electromagnetic theory  lead a young mathematician at the Skunkworks to propose how they could devise an aircraft that was almost invisible to radar.

Check out your library or bookstore to find a copy of ‘Skunkworks’ and read about engineering at its best.  To illustrate the performance of the U-2 here is a video from the BBC where presenter James May gets a flight in the two seater version of the U-2.  You can see how the U-2 could fly so high it was out of range of fighter jets and missiles (although there is a report of an English Electric Lightning F3 intercepting one at 88,000ft during a NATO excercise in 1984).

Onto the second engineering biography book to read.  This is ‘iWoz’ by Steve Wozniak and Gina Smith, which I read a year or two ago and should have written about sooner.  This is the story of Steve Wozniak, co-founder of Apple and the real technical brains behind the development of the first Apple computers, including the massively successful Apple II.  This is a very personal account, and more like a traditional autobiography than ‘Skunkworks’, but there are some interesting insight into how ‘the Woz’ come come up with the design for computers that effectively started the microcomputer revolution. It is fascinating to read how in high school he collected minicomputer manuals and with the help of catalogues and datasheets of newer components he would redesign the circuitry of those computers to use fewer components. Also interesting is his interest in using components in more than one way on the same board.  Here you can see the real engineering genius coming through. Below is a short clip of Wozniak talking about the ‘economy’ of the design of the Apple II at book signing event for ‘iWoz’.

Summer is not far away so chase down one or both of these books for your Summer vacation.  Lots of engineering inspiration is contained within the both books.


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