Cut Along...

The manufacture of the tube cutting jig, whilst progressing, is starting to grow arms and legs. I am eager to get on with the tube fabrication trials, and so I have decided to purchase a cutting jig for my angle grinder.

I had a comment on my last post from David, who suggested obtaining a small chop saw. Well David, you won, sort of. The Einhell jig I have ordered makes a standard 115mm angle grinder into a chop saw.

Here is a picture of the item in question:-

The idea is to bolt this unit to the bench and then cut the tube against a stop to give repeatable lengths.

Delivery is scheduled for tomorrow, so I will let you all know how I get on.

Tubes

As you know, in the middle of last week I ordered the metal that I intend to use as the basis for the tube bundle thrust chamber.

The 316L tube and hollow bar arrived today. The hollow bar came from Schoeller Bleckmann in Oldbury and the tube from Steel Express in Wolverhampton. I also ordered a piece of 316L plate. This didn't arrive today so I will have to chase it up tomorrow.

The hollow bar is 212mm OD x 170mm ID. Here is a photograph of it sitting in it's protective sack. It was too heavy to lift out...

This has to go in the lathe somehow. My current thinking is to drill and tap the piece and then bolt it directly to the faceplate.

Here is the 316L tube, it is 10mm OD x 2mm wall:-

These tubes will need to be cut into near enough identical lengths. I have decided to make a cutting jig based around an angle grinder to do this.

The jig will be composed of a section of aluminium angle welded to an aluminium plate. This angle will act as a sort of V block to hold the tube being cut. Sections of  drilled and tapped aluminium flat bar will be welded on to the angle to form a clamping feature. The angle grinder will then be mounted on a pivoted bracket, enabling repeatable cut off to be achieved.

Here is the base plate of the jig:-

This picture shows the angle with a piece of flat bar showing how this will be mounted to form a clamp:-

I milled the flat bar sections square - not strictly necessary but it made me feel better:-

Here is a final shot of the angle and plate trialled up with a scrap piece of angle to show the position of the angle grinder bracket:-

I will also have to make a tube bending jig, so there will be plenty of practical updates over the next few weeks. Once the jigs are made, I can trial the actual tube fabrication process.

Keep watching.

Step Off

Today has seen the completion of the stepper control box. The electronics and power supply are now mounted and wired in to the switches on the front panel.

The power supply was fitted using 6BA bolts. As mentioned in the last post, the mains lead enters the enclosure via a strain relief gland.

Here is a photograph showing the internal set up of the electronics and power supply:-

Here is another photograph showing a side view of the electronics installation:-

And finally, a shot of the completed system in it's entirety:-

The control box was connected to the stepper on the rotary table. A full functional test was successfully carried out.

With this tool now complete, attention can again be turned to the design and development of the tube bundle thrust chamber concept. It also means the end of step related punning post titles. I can almost hear your sighs of relief. 

Three Steps to Heaven...

Greetings, dear reader. I am back in Blighty again and ready to resume rocket engine related activities.

To that end, I have done some more work on the rotary table control system. I'm putting together the control box that will house the power supply, switches and electronics.

Here is a photograph of the front panel, showing the LCD display, menu scroll through paddle switches and menu select button:-

The rectangular holes for the LCD display and the paddle switches were created on the milling machine. The paddle switches snap into the holes and are held in position by integral spring clips. The LCD is bolted in place using the protruding 6BA bolts that hold the PCB stack together. Here is a photograph showing the arrangement of the electronics and switches on the rear of the panel:-

The power supply will be fitted in the space next to the switches. The mains lead will enter the enclosure through a strain relief gland. A socket will be fitted for the stepper motor drive pulses.

I'm looking forward to getting the control box finished. The automated rotary table will then be ready for use. Just in time, as I am now going to order the material to begin the construction of the tube bundle thrust chamber.

Look out for more updates over the next few days.

The 39 Steps...

Over the past few days I have been working on the rotary table control electronics. This has involved reducing the profile of some of the boards, to ensure they will fit snugly into the enclosure.

On the LCD/Keypad shield, I was able to move the contrast potentiometer from the front to the rear of the board. This allows the LCD to sit closer to the front panel. I also took the ICSP header off the shield; it will not be required in the finished device. Flying leads have been soldered to the buttons to enable these to be piggybacked with the panel controls.

The stepper drive board had it's screw terminals removed. I have soldered flying leads to the stepper output pads on the board which will be connected to the output socket. The capacitors on this board have had their leads extended and led out to the side.

The Arduino has had the power leads soldered directly to the board. All three of the PCB's have been stacked together using various 6BA screws and stand offs.

This view shows the stacked boards and the contrast potentiometer. The conductors for the stepper output, control signals and the button extensions can also be seen.

Here is another view of the stacked PCB's:-

This unit will be mounted to the panel by means of the 6BA bolts through the LCD shield. The intention is to secure these through the panel with acorn nuts.

I shall be back earning a living again soon, so no more practical updates. I'm hoping to use the time to get some more details of the tube bundle chamber design published. 

One Step Beyond...

I have just finished sheathing the stepper motor cables and wiring the end connector. I used 6mm diameter expanding braid sleeving to cover the stepper leads. I secured each end of this with adhesive impregnated heatshrink tubing. I'm not sure how long this will last, only time will tell.

The connector is a five way locking type, obviously the fifth pin is not used. The locking feature means that the stepper cannot be inadvertently disconnected whilst being driven. The pin assignments in the connector are as follows:-

1 = White

2 = Green

3 = Black

4 = Red

I realise that the above means nothing to any of you, but the more places I write it down, the less likely I am to forget it.

As mentioned earlier, the major mechanical part of this tool build is now complete. I will still have to make a hand wheel for the other end of the stepper shaft. This will allow manual operation of the table if required.

Here is a photograph of the (almost) complete motorised rotary table:-

And here is a view of the end connector:-

Tomorrow I will begin boxing up the electronics. Now, the bare minimum of front panel buttons would be five. These would be UP/DOWN LEFT/RIGHT and SELECT. Various trial button layouts on the front panel always looked cluttered, so I wanted to find a simpler solution.

You already know that I like a recycled component or two. Rummaging through my stock of useful parts, I found some small spring return to centre SPDT switches. So I can use one each of these for UP/DOWN LEFT/RIGHT and then one push button for SELECT.

Here is a view of one of these switches:-

More updates to follow.

Step-ford Wife

If only...

The four holes to mount the stepper have now been drilled in the square end plate, and the stepper and mounting have been successfully mated up to the rotary table.

I decided to use M5 nuts and bolts to attach the stepper, as I've never been too comfortable with the idea of threads tapped into aluminium. So the holes ended up being 5.1mm diameter.

Here is a photograph of the stepper motor and mounting connected to the table:-

I ran up the stepper and shifted the rotary table round under power; the system worked perfectly.

Here is a photograph looking along the inside of the mounting, showing two of the table attachment screws, as well as the coupling:-

That is the mechanical portion of this tool build completed, now it is over to the electronics - ruggedising the motor leads and fitting all the PCB's into a die cast box.

Quick Step...

I have just finished milling the coupling access slot. I milled it slightly off centre. This makes getting to the offset grubscrews in the coupling somewhat easier.

Here is the part showing the slot and slipped over the rotary table drive sleeve, but not bolted on. You can see the bellows coupling peeking through it's newly created "window":-

Hopefully sometime today I will get the stepper mounting holes drilled and tapped to M5. That will then be the part finished. It is a good job as I am rapidly running out of Step related punning post titles...

Step-toe and Son...

...pation.

The experiment in bonding seems to have worked. After almost 18 hours of cure time - not strictly required but entirely due to my paranoia - the mounting is solid. Will it last with the weight of the stepper motor on it, and with general handling? That remains to be seen. All seems well so far, at least.

Here is a photograph of the mounting to show the three 120 degree spaced holes. These are 5.1mm, to suit the M5 attachment screws:-

And here is the part fitted to the rotary table:-

The next task will be to drill the mounting holes for the stepper motor in the square portion, then mill the coupling access slot. After that it will be time to assemble the electronics in the die cast case. Keep watching.

Step on It...

I'm sitting writing this post having just returned from the workshop. This evening I drilled the three 120 degree spaced bolt holes that enable the motor mount to be fixed to the rotary table. I know what you are thinking...how do you drill three holes on a pitch circle without a rotary table (because your rotary table is in pieces...)? Well, it was a simple matter of removing the threaded portion on the table and using it as a drilling template. The work of a few minutes.

I said yesterday that I was moving away from using welding to join the components. An aluminium TIG weld bead is a broad thing at the best of times, and I feel that it would detract from the look of the part, as well as possibly being overkill.

This is quite a departure for me, since I would normally look to my TIG welder before any other option. I have decided, in this instance, to use two part epoxy. I mixed some up and wet assembled the three parts with it. Here is a photograph of the unit clamped in the milling vice while the epoxy cures:-

I have to admit a certain level of anxiety about this experiment in bonding; will the epoxy have sufficient mechanical strength to do the job? I see you shiver with antici...

Step it Up...

I got the round portion of the motor mounting bracket finished today. This started life as a piece of 2 1/4 inch 6082 bar. I turned this down to 56mm in the four jaw, then bored a 21mm hole in the centre to suit the rotary table driveshaft outer sleeve. 

Once the central hole was complete, a 3mm deep recess was bored to suit the cylindrical portion described in the last post.

Here is a photograph of the round section showing the central hole and the locating recess:-

Here are the parts made so far:-

And here they are assembled:-

The next tasks will be to drill the mounting holes in the round section and then mill the coupling access slot in the tubular. When it comes to the final assembly, I am starting to edge towards joining the components together with Loctite rather than welding them. All that will be a job for tomorrow!

I did some more work on the design of the tubular chamber concept yesterday. I will post this in the next few days. 

A Step ahead...

I have just finished another portion of the motor mounting bracket destined for the indexer. A section of 2 inch x 10swg 6082 aluminium tube was set up in the four jaw and turned down to exactly suit the register in the square plate. Having turned the tube sides, I then faced the end to ensure it would be square with the sides.

The tube was then parted off. The length was decided by the amount of room required to mill an access slot to enable me to get at the bellows coupling grub screws, once everything is assembled. It ended up being near enough exactly 67mm.

Here is a photograph of the square plate and tube trial assembled:-

The next two pictures illustrate the fit up of the motor and the mounting hardware so far produced:-

I should get all the machining finished by tomorow, with any luck. Will I run out of step related titles for my posts? Stay tuned to find out.

Step to it...

This evening I started machining the parts for the stepper motor mounting bracket, to complete the indexing system.

The stepper will be mounted to a square plate fixed to a tube which transitions to a round plate screwed to the existing rotary table flange. My first action was to cut a piece of 6mm thick aluminium plate with a jigsaw. I keep promising myself a plasma cutter...it has to happen at some point! Next I squared this up to size on the milling machine. The plate is 56mm x 56mm, this being the standard NEMA 23 end face dimension.

Next I bored a 38mm hole through the plate in the four jaw. The idea is that this will act as a locating feature for the 38mm register on the front face of the motor. 

Still located in the four jaw, the plate was then counterbored to 48mm to a depth of 3mm. This was done to locate the tube that will join the square and round sections of the mounting. I will be welding the whole assembly together once the other parts are made.

Here is a photograph of the part thus far:-

I will hopefully get a chance to progress the mounting a bit further tomorrow. Keep checking for updates. 

Building this tool has taken me away from the actual design of the tube bundle chamber, so I intend devoting some time to that over the coming days.

Stepping Update

Today I got the stepper motor connected to the rotary table input shaft for a preliminary test. The mechanical link between the stepper shaft and table shaft was made with a bellows type aluminium coupling. The stepper drive shaft is 12mm diameter, whilst that of the motor is 6.35mm. i.e. 1/4 inch. I managed to find an off the shelf bellows coupling with these bore dimensions.

Due to the relatively high gear ratio of 90:1, I took the decision to dispense with micro-stepping of the motor, and I altered the appropriate line in the software to reflect this, as well as setting the dip switches on the driver circuit.

Here is a picture of the set up. As can be seen, the motor was supported by a machine table clamp during the test:-

The motor ran the table with no trouble at all. I ran the table in Step, Angle, Jog and Run modes. I am not sure if the motor will be able to drive the table for actual machining, as opposed to just positioning, but it certainly did not seem to lack torque.

I didn't attempt any accurate measurement of the angle the table turned through in this test. That said, going by the graduations on the side of the table, everything seemed to be in order.

The metal has now arrived to fabricate the mounting bracket, so look out for another update in the next few days.

Step by Step

I suspect that it will be abundantly clear to you, my astute reader, that the production of a tube bundle rocket thrust chamber will require the fabrication of a foundation element with a multitude of holes equally spaced on a PCD.

Of course this means indexing. The usual way to achieve this is to use a rotary table with dividing plates. This time honoured method, whilst working extremely well, is also rather tedious and is prone to human error - especially when I am doing it!

Therefore I decided that it would be worthwhile spending a little time motorising my Vertex 6 inch rotary table to automate the indexing process.

After some internet research I discovered Gary Liming's excellent Step Index project. Gary writes for the US magazine "Digital Machinist". Gary also has a very good website with a build log for the project.

Step Index is an Arduino based system with the firmware currently at version 2.3. The system can work with fixtures with a variety of gear ratios. Initially it was designed for a 3:1 set up, but has since been re-written to cope with 40:1 and 90:1. Most rotary tables are 90:1, as is mine. The Arduino source code can be downloaded from the Digital Machinist site, as can a Read Me file explaining how to make modifications to the code to add more ratios or to make a specific value the default.

Gary gives a comprehensive explanation of the operation of his system on his site, so I will only briefly outline it here.

An Arduino Uno board is at the heart of the system. This is fitted with an LCD keypad shield. I got mine from Sain Smart, but there are many other sources for this part. The Arduino displays system modes and status via the LCD. A stepper driver board based on the Toshiba TB6960 IC is clocked by the Arduino, thereby driving the stepper motor. The motor I used is from Zapp Automation here in the UK, type SY57STH76. This is a NEMA 23 frame, 2A, 1.8 degree per step motor with a holding torque of 1.89Nm. I also obtained a 12V, 5A switch mode supply to run the lot.

The photograph below shows the system connected up for bench testing:-

The buttons on the LCD shield are used to scroll through and select menu items. I will piggyback larger, more user friendly ones when I fit the system into a die cast case. 

The menus are as follows:-

Ratio - Allows the user to select the ratio of the fixture being used. The software can be modified to include as many as are required, but 3:1, 40:1 and 90:1 are included as standard.

Temp - Facility to read motor and driver heatsink temperature, using two sensors connected to the Arduino's analogue inputs. I did not use this function.

Step - Enables user to specify a number of divisions. The motor is then incremented the correct number of steps for each division.

Angle - Similar to above except that the user inputs the angle the fixture is to be rotated through.

Run - The motor will run continuously with speed set by the user.

Jog - The motor can be nudged a preset number of steps.

The photographs below show the Arduino Uno board and LCD shield, the stepper drive board and the switch mode PSU.

The momentary push buttons can be seen here, as can the multi-turn potentiometer used to set the screen contrast.

Stepper driver board. DIP switches allow the setting of current characteristics and microstepping settings. The power IC and heatsink are on the underside.

The switch mode PSU. The preset potentiometer above the terminal strip allows the output voltage to be set exactly.

The next step is to prepare the rotary table. This unit is a Vertex HV6, and I've posted pictures of it on this blog before. It will need to be finessed somewhat before the motor can be fitted. I will also have to make the motor mounting hardware.

Once assembled the new improved rotary table will greatly facilitate the machining of the engine components.

Sound and Vision

More on telemetry...

It seems fairly obvious that a device as potentially fractious as a home built liquid fuelled rocket engine would be best viewed from a safe distance. Indeed, Krzycki suggests viewing the rocket exhaust plume by means of a conveniently positioned mirror.

Fortunately things have moved on since 1967. From the outset, a video system was always going to be a part of the telemetry set up I had in mind. Nowadays, small, reliable CCD cameras and USB digital video recording systems (DVR's) can be had for a modest outlay.

I purchased a four channel USB DVR and four miniature CCD cameras from Lightinthebox.com. The cameras are also equipped with a small microphone. Each camera has a flying lead terminated in three RCA type connectors. The colour coding used is as follows:-

Red = 9VDC power

Yellow = Video signal

White = Audio

The DVR features four video inputs through male BNC connectors, hence a BNC to RCA adaptor was required for each one. There is also one audio input. This is not a great worry as I do not anticipate hearing the engine being a problem.

Each camera measures ~ 20mm (0.75") square. They are thus small enough to fit into a tight space. 

Here is a photograph of the DVR unit with all four cameras connected:-

In and amongst this snake's wedding it is possible to see the four cameras, DVR and the RCA to BNC adaptors.

The DVR comes packaged with software to view and record the camera images. The images can be viewed in quad format, or each channel can be viewed separately. Motion detect record is also possible. Here is a screenshot of the software running, with some frankly resistable images of my kitchen:-

And here is a close up of one of the cameras, the lens through the lens, so to speak:-

When these cameras are spread around the test stand, they will greatly improve the safety of operation, as well as acting as a back up and cross reference to any data acquisition set up. Transducers may well tell the story, but a recording of a camera pointing at a bank of gauges is still hard to beat.

And finally...on the subject of telemetry, National Instruments have just released a home version of their industry leading LabVIEW software, aimed at the Maker Movement. It boasts elements compatible with Arduino, and is being offered at a bargain price. Google "NI LabVIEW Home bundle" and you will see what I mean.

More to come, keep watching.

Tubes: A Way Forward?

I've been thinking about chamber and nozzle design a good deal recently. My motivation was to try to come up with a different method of fabricating a thrust chamber. A method that doesn't involve machining the chamber and nozzle from solid, which I've always thought was wasteful. That said, it certainly works. A superlative example is Anders Johansson's long running thread at the Jet and Turbine Owners Forum:-

 http://jetandturbineowners.proboards.com/thread/49/n2o-ethanol-bipropellant-rocket-engine?page=1

So I just wanted to try something different, to see what was possible. You'll remember from my post on cooling that I posited a notional tube bundle chamber for my calculations. What if it wasn't purely notional? I decided to see what it would take to build a tube bundle thrust chamber.

My initial thoughts were based around bending the tubes to shape and stacking them together around a circular manifold, possibly using some sort of temporary centralising mandrel or jig. The idea was to braze the tubes, but my attempts at brazing did not go very well. I had much more luck TIG welding them. After a few false starts to get the TIG parameters right I produced a reasonable weld:-

I didn't use any backing gas here and got away with it; in a production unit I would have to set up an internal argon shielding flow in the tubes. However, cheered by this result I next looked at methods of manifolding the tubes and anchoring them to a manifold. Using 10mm dia. 2mm thick wall metric hydraulic tubing meant it was possible to turn down a portion of the tube to 8mm:-

I used a collet to hold the tube, as seen. Next I envisaged the manifold ring to have a series of holes on a PCD, into which the tubes would be welded. I decided to make a rough mock up of such an arrangement using just two tubes, to see how they sat together and generally get a feel for the problem.

I took a square block of mild steel and cleaned it up in the 4 jaw chuck. I then drilled two holes in it of the correct size and pitch for the tubes. I countersunk one end of these holes. This would mate with the chamfer on the tubes so they'd sit flush to the block/manifold. The four pictures below show cleaning up the block faces, drilling the holes, the countersunk portions and the tube/block fit up.

Centre drills are very rigid and are great for starting drilled holes (as well as for creating centres!):-

The countersunk ends of the holes:-

And the tube to block fit up:-

Ideally the hole for the tube on the right should have been countersunk fractionally deeper, but you get the idea. The number of required holes and the PCD they'd need to be on for the diameter of the projected chamber would put them closer together than shown here. The gap between the tubes in this mock up is about 0.25mm. The number of tubes and the PCD required for the chamber I have in mind would put this gap at just over 0.05mm. I might need to play with the diameter a little to get an adequate gap for the welding. This would also feed into the tube bending calculations to ensure that the throat diameter was correct.

Here is a close up of the machined end of one of the tubes. The chamfer is 45 degrees and this then mates nicely into the 90 degree countersink:-

The dimension from the start of the chamfer to the tube end is 20mm. Finally, here is a photograph of the opposite side of the block showing the tube exits. In the design under consideration this is where the fuel/coolant would exit and cross over to go down the next tube. I machined the block thickness to 20mm so that the ends of the tube would be flush with it. The holes would need to have a countersink to correspond with a chamfer on the tube end to get a nice weld. I tried to do this by hand on one of the holes and made a pig's ear of it; why is it always the last operation that wrecks your part?! Anyway, it isn't too much of a worry and I think you can see what I'm trying to achieve.

I'm back at work now so there will be no more practical updates for a few weeks. You might be lucky though and get a lot of meandering nonsense with some highly suspect calculations thrown in. I bet you can't wait.

Telemetry

In between calculations and doing development work on the engine itself, I have been looking at what will be required for the power and telemetry set up on the test bed.

I've built a few data acquisition and control systems, mostly centred on either the Basic Stamp or PIC type microcontrollers. Over the years I have formulated a set of guidelines to assist rapid system prototyping. These are as follows:-

Accretion

Each part of the design problem is broken down into manageable portions. The sub-assemblies produced are then combined to form a coherent whole.

Recycling

In 2002 the DEER report stated that due to rapid advances in component design, leading to rapid obsolescence, component recycling will be necessary in the future for repair of in service equipment.

Indeed, nowadays most electronic equipment is simply thrown away when it reaches the end of its useful life, containing hundreds of perfectly serviceable, usable components. These components can and should be re-used when possible.

Heterogeneous Architecture

This approach to control system design was first enunciated by Whitcomb and Yoerger, of Woods Hole Oceanographic Institute, in their 1993 paper on the Jason MK2 ROV. They argue that most control systems can be split into at least two computational subsystems, namely user interface and control.

The heterogeneous approach attempts to speed up system development by using standard, off the shelf hardware and software for generic system functions: -

“A better alternative for medium and large-scale fast-track development is to embrace heterogeneous architecture at the outset. Use general purpose machines for commonplace tasks such as user-interface and logging, use dedicated real-time machines for control.”

The case is made for the use of commercially available machines and software wherever possible. Whitcomb and Yoerger conclude that: -

“The metric of success in fast-track development is not the uniformity of design, but its rapid and successful implementation.”

Dr. AM Turing

Dr. Turing’s paper "Intelligent Machines" (King's College, Cambridge, 1947) is now widely regarded to have been the first introduction of the software control concept. Turing argued that software based control could produce an extremely flexible system in which very few hardware alterations would be required. Rewriting software would accommodate any problem that arose, or changes in operating parameters.

The basic design of the test bed control and data acquisition system will be guided by these principles. Use will be made of as many standard, readily available components, communication protocols and sub-systems as possible.

With the above in mind I decided to go with a laptop running a GUI that would then interface with a microcontroller based I/O card at the test bed end. Rather than build my own microcontroller board, I went for a kit solution in the form of the Velleman K8061 USB I/O card. The specification of this card is as follows:-

8 analogue 10 bit resolution inputs: 0…5 or 10VDC / 20kohm

8 analogue 8 bit resolution outputs: 0…5V or 10VDC / 47ohm

8 digital inputs: open collector compatible (connection to GND=0) with on board LED indication

8 digital open collector outputs (max. 50V/100mA) with on board LED indication

One 10 bit PWM output: 0 to 100% open collector output (max 100mA / 40V) with on board LED indication.

General response time: 4ms per command

USB Port: 2.0 and 1.1 compatible (USB cable included)

Further details may be found at www.velleman.eu

As can be seen the K8061 card has a fairly impressive analogue and digital I/O capacity. It took me an afternoon to build and test, using Velleman's own free diagnostic software. This was significantly quicker than had I programmed and debugged my own PIC based board. Here is a photograph of the completed board:-

The long narrow IC to the left of centre at the top of the board is the pre-programmed PIC that handles the USB communication to the laptop. The long wide IC below this is the second pre-programmed PIC that deals with all of the analogue and digital I/O.

The communication routines for the K8061 are contained in a DLL which the user is given access to. This enables custom control applications to be written in a variety of languages. That said, one of my chief reasons for wanting to use the K8061 was my choice of Profilab to develop the GUI on the laptop.

Profilab is a graphical programming language for the development of control systems. It is somewhat similar to NI LabVIEW. In the Profilab hardware library there is a module for communicating with and controlling the K8061. You can read more about this software at www.abacom-online.de/uk

My first step was to attempt to interface one of my K type thermocouples to the K8061 and obtain a temperature readout in Profilab. Initially I was going to design and build my own thermocouple pre-amplifier, based on the AD8495 IC. Whilst researching this I found another excellent kit designed and produced by Dr. Matthew Little of re-innovation, here in the United Kingdom. More can be found at www.re-innovation.co.uk The construction was straightforward, although I had to solder the tiny SMD AD8495's to the PCB by hand, something I'd never attempted before. Fortunately I quickly got the hang of "drag soldering".

I got four of these boards, here is a photograph of a completed one:-

You can see where this is going; any electronics design and construction I would do myself would be restricted to signal conditioning and driver circuitry. This is where the recycling aspect would come in as I have literally thousands of components in my workshop to use up!

I had to connect the thermocouple and AD8495 board to the K8061 via an op-amp buffer due to the relatively low input impedance of the K8061. I used an LM324. It has the great advantage of not requiring a split supply.

Here is a photograph of the test set up. The K type thermocouple is connected to the AD8495 board and thence through the LM324 buffer on the breadboard to the K8061:-

And here is a screenshot of Profilab displaying the temperature in my electronics lab (which my wife continues to refer to as the dining room):-

Now, you are all probably thinking, quite rightly, that a safe distance ought to be maintained between an untested homebuilt rocket motor and it's tester. And you'd be right. Of course, USB only has a range of 3-5 metres....but as Baldrick used to say "I have a cunning plan...." All will be revealed. That is, if I can do it...