Smoker

A few weeks ago I made a smoker out of an exhaust pipe and two old party-balloon helium cylinders. Since then I have smoked many a brisket! Check out the pics.

The Chuffer

I just completed my second ever air engine: The Chuffer. With this project I decided that I’d go for complexity, rather than the simplistic approach I took when I built The Wobbler earlier this year.

The Chuffer is a twin-cylinder double acting engine – which means each of its two cylinders both push and pull the piston. This means it operates much more smoothly and can self-start as there’s always a piston on a power stroke, regardless of where the flywheel is.

Unlike its predecessor, the Chuffer has fixed cylinders and airflow is controlled by two spool valves, operated by eccentrics next to the flywheel via some pushrods and a hopelessly over-engineered lever mechanism.

And of course everything was made by yours truly, in the garage, from chunks of brass, steel and aluminium bar and flat stock I bought on eBay. Needless to say, I have learned a lot since I started the project this February!

What’s next? Well, maybe a Watt Governor or a little generator

The Wobbler

I made a Wobbler! A single acting, oscillating air engine, to be precise. I was inspired by the amazing Tubalcain, who’s YouTube channel has been the source of many top tips and the cause of many late nights. Though the design of the wobbler wasn’t new to me, the old Mamod steam engine I had when I was a kid used the same principle.

The wobbler is probably the simplest engine design there is. I tried to to a nice job of this one, though didn’t go overboard with the look of the thing – I don’t see the point of pretending it’s not made from some bits and bobs I has knocking about in the garage! Here are some photos:

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Fixing the gear stick

For the last couple of weeks, gear changes in The Duke have been very hard work. The tiny pin which stops the stick spinning sheared off, adding a new element of drama to my commute.

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The original pin had sheared and was stuck in the channel in the ball at the base of the stick.

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So I had to strip the whole thing down.

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The pin and the thread on the hole were totally ruined, so I had to think if something new.

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I drilled out the hole

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Then tapped it with an M8 thread. Much bigger and stronger than the old one.

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Then turned down a set screw on the lathe

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And heat treated it with case hardening compound, which will hopefully stop it getting squashed and bent.

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I doubt there are many Land Rovers on the road with the original rubber blob on the base of the great stick. It’s meant to prevent vibrations but was totally worn away.

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So I turned a replacement out of nylon and hammered it on.

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At 19.3mm diameter is a snug fit on my spare gearbox and should help prevent rattles and make gears a bit easier to find.

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All in all I’m very happy with my evening’s work. Just need the sun to come up so I can put it all back together again!

Build Status Traffic Lights

Recently I got the time to knock up a set of build status traffic lights for the office. It’s likely that I am the world’s greatest fan of Continuous Integration. I’m not going to bang on about why it’s a good idea here, suffice it to say that anyone who isn’t rabidly devoted to the greenness of the build will surely pay the price in time.

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The lights themselves are from eBay. They were 24v and fitted with huge great bulbs which left no room inside for anything else. I swapped these out for some 12v LED brake light bulbs, which are fitted into some DIY holders made of nylon bar and odds and sods. Looking back, I’d have just soldered a load of LEDs to a circle of stripboard, but I went with what I had at the time.

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The lights are switched by two of these great little relay boards. Each one comes assembled and ready to go – they just need connections for 5v, ground and signal. If I’d have gone with the DIY LEDs-on-stripboard design I guess I could have used a transistor circuit but I do love the loud mechanical clunk that the relays make when the lights change. It adds to the antique feel of the project. I did use stripboard to make a “shield” to connect the relay cables to an old Arduino I had knocking about.

It’s worth noting that you can get an Arduino relay shield (and I do in fact have one in the garage) but it seemed like overkill to use such an expensive board, with twice as many relays as I needed.

Power for the lamps is supplied by a 12v wall adaptor I got from Maplins. Again, a custom LED solution would have allowed me to use the 5v USB supply… but hindsight is richer than I am. I installed a line socket for the power, so when the PAT testing man comes round the office he won’t test the lights, just the wall supply.

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The arduino inside the lights implements a very simple serial protocol. It listens for commands “red”, “green” and “off”, terminated with a newline. There’s a USB connection to the old laptop which drives our Information Radiator TV; the idea with the traffic lights was to keep all the intelligence on the PC end to make upgrades and changes easier. Here’s the arduino code. Told you it was simple!

const int redPin = 2;
const int greenPin = 3;
int redState = LOW;
int greenState = LOW;
long interval = 1000;
String inputString = "";
boolean stringComplete = false;

void setup() {
  inputString.reserve(200);  
  
  pinMode(redPin, OUTPUT);      
  pinMode(greenPin, OUTPUT);    

  Serial.begin(9600);
}

void loop()
{
  if(stringComplete) {
    stringComplete = false;

    if (inputString.equalsIgnoreCase("off")) {
      redState = LOW;
      greenState = LOW;
    }
    else if (inputString.equalsIgnoreCase("red")) {
      redState = HIGH;
      greenState = LOW;
    }
    else if(inputString.equalsIgnoreCase("green")) {
      redState = LOW;
      greenState = HIGH;
    }

    inputString = "";
  }

  digitalWrite(redPin, redState);
  digitalWrite(greenPin, greenState);
}

void serialEvent() {
  while (Serial.available()) {
    char inChar = (char)Serial.read();

    if (inChar == '\n') {
      stringComplete = true;
    }
    else if(inChar != '\r') {
      inputString += inChar;
    }
  }
}

The code on the PC end is a little more complex, but all the heavy lifting is done by Team City Sharp which connects to our Team City server and get the status of our multitude of builds. The only other complicated thing it does is open a serial port and dump the commands “red” and “green” to show the build status. It also sends “off” at 7 o’clock in the evening… just in case a red light shining from an office window at midnight were to attract the attention of the local constabulary.

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Over Engineering the Barbecue

Our trusty old barbecue is getting old.  I think it’s about five or six years old now and it’s lived all that time outside in the garden, summer and winter, sun and (usually) rain.  It might make financial sense to blow £50 on a new one, but I really like ours.  Much better to refurbish it using scrap bits and bobs and the tools in the garage.

The lid and bowl are fine, but most of the ironwork is made of poor quality pressed steel, less than a millimetre thick.  I have already replaced the hinges with some rock-solid 3mm steel ones, born of a sheet of scrap and my own blood sweat and tears.  This weekend I decided to replace the vent jobbie in the lid.

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I used some aluminium salvaged from an old computer case and the rotary table on the mill. The vast majority of the time was spent setting things up. After that I got the job done in an hour or so. The hardest job was to centre the rotary table on the mill. In the end I made a tool to do it. I turned a steel rod down to 16mm on one end to fit into the hole in the middle of the rotary table and 19mm at the other end to fit the largest collet I have.

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I slackened the bolts holding the rotary to the mill table, bunged my new tool in the mill and into the rotary table, got it all centred and tightened the bolts. After that the rest was easy!

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For next time, the formula for making these things is as follows, using a 3mm end mill:

From centre, with rotary set at 0 degrees
Wind X out to 15mm
Tool down
X out to 40mm
Rotate 20 degrees clockwise
X in to 15mm
Rotate 20 degrees anticlockwise
Tool up (and clean off all the crap!)
Rotate 60 degrees clockwise
Start again!

EZSnap Motor Mounts

I really liked my old motor mounts for the Quadrotor. I made them on the lathe out of “Engineering Nylon” which costs very little, is easy to machine and can be found on eBay (search for “nylon round bar”). The motor snuggly fits into a 9mm hole and is fixed with two 3mm hex head set screws from either side. Another 3mm set screw goes through the bottom and bolts the mount onto the frame. To stop the torque from the motor spinning the mount I milled a 10mm wide slot into the bottom which fits over the aluminium frame.

I liked them because they are light, look nice and form an integral part of the frame (so no extra cable ties and fixings, just one bolt to do everything). The big problem made itself very apparent when I had a crash on the airbase; the motor hit the ground first and because there was no “give” in the motor mount I bent the arm and broke the motor (detaching one of the magnets).

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This would never have happened in the old days – when the factory motor mount was attached to the frame with cable ties. It might have been ugly, but the cable ties would snap long before any other damage could be done.

So, how could I improve my nice looking “purpose built” motor mounts to add a weak point? The answer is in the next picture:

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Basically it’s exactly the same design, but with an added cable tie! This time I made the mounts in two parts: a base part which bolts securely to the frame and a motor part which sits on the base and is held down by a cable tie. There’s a little knob on the motor part which sit in the 5.5mm hole in the base part (at the bottom of which the hex-head of the set screw goes). This keeps the two parts locked together as long as the cable tie is in place.

In a crash the cable tie will snap and the motor part will detach – hopefully protecting the motor from damage and protecting the frame in the event of a “motor-first” crash.

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Have I tested them yet? Well, no. I’m not going to crash on purpose!