PC Board Options (23 December 2008)

Completed a good, solid draft of this appendix.

Everything in the book has been drafted. The page count sits at 594. Missing illustrations account for three. The table of contents and index are budgeted for six and five, respectively. That will bring the total page count to 608.

I'm now editing for clarity, working on the missing illustrations, and verifying projects.

Joysticks Chapter (21 December 2008)

I expanded the coverage of control loading. There is now more background material on springs, hydraulic dampers, and gas springs.

Engine Controls Chapter (18 December 2008)

I've got a good draft of the Engine Controls chapter. It's missing one illustration, but otherwise complete. 

The chapter project uses slide potentiometers for position sensors. I've chosen Bourns PTE series pots. This is a "long-life" series with a rated lifetime of 100,000 full range movements. Standard life slide pots often have a rating of only 15,000 full range movements. A standard slide pot costs on the order of $2~3. The PTE series runs just under $7. Not too bad; for three time the cost you get six times the life.

Engine Controls Chapter (13 December 2008)

I'm continuing to work on the project write-up for the engine controls chapter. The project is a basic mechanism for a lever-style engine control. Here's the overview illustration:

The intent is to demonstrate solid, low-cost techniques that result in excellent performance.

This is the last project write-up needed to finish the draft manuscript. I'm very close to having a complete draft of the book, but a great deal of work remains. I'll be doing more prototyping. I "improved" some of the projects during the writing. These must be built again from the book descriptions to assure that the changes actually are improvements. Then there's editing for clarity, checking for holes in the overall scheme of the book, indexing, creating the cover artwork and copy, and so on.

Pedals and Throttles (9 December 2008)

I added a small section to the Pedals chapter. I hadn't realized it was missing. After uncountable read-throughs, I finally noticed. It's the section that addresses which characteristics to mimic when building a simulation of something. Of course, there is no one answer. It's both subjective and dependant on what resources can be drawn upon. The goal of the section is to suggest a methodology so you get the most bang per buck given your personal desires, resources and target aircraft. Anyway, that's done.

Currently, I'm attempting to finalize the project in the Engine Controls chapter. It's a modular lever throttle based on hardware store items (mostly). It uses a linear pot for the position sensor which it treats very gently to maximize its life. It uses a spring to take up any mechanical play in the linkage, and it has a friction adjustment for lever motion. Because it's modular, you can put as many units side-by-side as needed to build whatever throttle quad you want.

Panels Chapter Updates (4 December 2008)

I revised and completed the chapter on Panels. It was enough of a change that I'm sure a read through in a few weeks will result in some hopefully minor changes. But as it stands now, it's not looking too shabby. Not at all.

Scenery Display Chapter Updates (26 November 2008)

I revised the Scenery Display chapter. Half the revision work was just transcribing the red markups from the paper manuscript to the electronic document. The reminder was a re-write of the section about using a Fresnel lens in front of a monitor. When you don't have the room (or money) for a projection system, a Fresnel lens can add to the flight illusion. You get a little magnification, and the image is moved a bit away from the viewpoint. 

I didn't feel that my earlier version clearly described how the lens worked optically, or what the tradeoffs were. Three new drawings and a lot of revised text have improved the situation. 

This added two pages to the manuscript page count. It's now at 95% target size.

I/O Bus Adapter PC Board (21 November 2008)

The circuit board for one of the I/O Options chapter projects arrived yesterday. Digging for parts and assembling it took about an hour. This is a revision of the original I/O bus adapter project. The I/O bus is basically a full duplex RS-485 shared connection that allows multiple devices to share a single serial com port. 

The RS-485 standard limits the number of standard bus loads to 32 per bus segment. A bus load is an indication of the amount of signal power a data receiver pulls from the bus in order to reliably receive the data. Put too many hunger receivers on the same bus segment and none of them function properly.

The original bus adapter project supports 32 devices on a single bus segment. A device might be a simulated instrument like a VSI, a 16-switch interface module, or an LCD radio head. (These are all projects in the book. ) Thirty-two is a good number of devices for a small plane sim, but step up to a twin and 32 starts to look a little on the small side. It's easy enough to expand on this, so I thought, "Why not do it now?"

This revised version has two bus segments and will support 64 devices. It's easy to expand beyond this, but I had a board-size versus performance tradeoff to make. ExpressPCB has special pricing for boards which are exactly 2.5" by 3.8". I wanted to keep the price under control while still providing support for a large number of devices. I think getting an adapter which supports 64 devices for the special pricing is a "sweet spot".

Simulator Enclosures, Interfacing with MSFS & Sound Chapters (19 November 2008)

I just zipped through the chapters on simulator enclosures, interfacing w/MSFS, and sound, typing all the handwritten editing notes. I now have clean copy to add more handwritten notes.

I got email from ExpressPCB. They have shipped the serial com port to RS-485 boards. Delivery is scheduled for tomorrow

I/O Options Chapter (15 November 2008)

I've completed this pass through the chapter. I'll do a final artwork review of the revised adapter project, and order a PC board to verify the revisions.

I/O Options Chapter (12 November 2008)

I finished the intended chapter updates then noticed the descriptions of the chapter projects were rather lame, and also decided to update one of the projects. I'm using a duplex, serial RS-485 bus to connect all the projects to the simulation computer. The project is a serial com port adapter for this bus . (It could theoretically talk USB as well, but USB is a bit more complex.) I decided to expand the adapter to include two RS-485 connections. The change adds all of one chip and one connector. Plus, the whole thing fits on a cheap specially priced prototype PC board from ExpressPCB.

So... I need to keep working on the chapter, double check the artwork for the revised project, order the PC boards, build and test the project.  Then, maybe, just maybe, I'll be done with the chapter.

I/O Options Chapter (5 November 2008)

I'm well along in restructuring and renaming the Hardware I/O Options chapter. I've added a large section that presents an example I/O structure for a single engine sim. It's a much stronger chapter that better explains the key concepts.

Hardware I/O Options Chapter (2 November 2008)

Re-reading the Hardware I/O Options chapter didn't leave me feeling any warm fuzzies. So I'm revising it; adding more examples and illustrations.

Input Arbitration Module Tested (27 October 2008)

The arbitration module and the switch input module work well together. There were a few firmware errors in assigning pin numbers which were quickly resolved. The firmware listing in the manuscript was revised accordingly.

Input Arbitration Module PC Board (23 October 2008)

The circuit boards for the input arbitration module were delivered yesterday. These were made by ExpressPCB as were the 16-switch input modules. Nicely done, shipped on schedule, no complaints. 

Here's a picture of the assembled module. 

Tweaking the Switch Input Chapter (20 October 2008)

I revised the artwork for the DIY, single-sided version of the 16-switch input module, one of the chapter projects. The artwork is now very similar to the the layout used to make the double-sided board at ExpressPCB.

Input Arbitration Module (18 October 2008)

As a home simulator project grows, the number of switch inputs grows with it. The switch input module provides the means to add switches in a modular fashion. Need more switches? Add another module. The modules share an input port. Simply daisy-chain the cable through another module.

When there are only a few modules, software can poll the modules for changes in switch positions. As the number of modules grows, the delay between a switch being flipped and the simulation reacting to it starts to become objectionable. One solution is to enable a module to automatically send a message upon switch changes rather than wait to be polled. This is fine as long as only one module sends at a time. If messages overlap, both are corrupted.

There are a number of approaches to resolving this sort of situation. The approach I've taken is similar to that used in the early days on mini-computers. It's not the most elegant, but it's robust and easy to implement with inexpensive parts. It's an arbitration module that coordinates use of the input channel to the simulation computer. 

A switch input module, or any module that sends data to the simulation computer, asserts a request line to the arbitration module and waits until it receives a grant. The arbitration module will only issue one grant at a time, and will hold the grant asserted until the request is dropped. An arbitration module arbitrates among eight input modules.

The arbitration module itself has a request output so that multiple arbitration modules can be linked together for simulators having more than eight input modules.

As I was pleased with the quality of the switch input module printed circuit board made by ExpressPCB, I've ordered arbitration PCBs from them as well. They should show up next week.

Switch Input Printed Circuit Board (10 October 2008)

The circuit boards for the 16 switch input module, ordered from ExpressPCB, arrived on schedule today. I'm very pleased with them.

The new board is the lower of the two in the picture. I included the original prototype for comparison (the upper board). It was made DIY style using the toner transfer method. 

Both the circuit and the layout have evolved. I simplified the circuit slightly and eliminated one chip. The layout is tighter. The switch inputs are now grouped together so that a flat cable can optionally be used. The voltage regulator is bolted to the heat sink and board to reduce flexing of the regulator leads.

I had four identical circuit boards made at a total cost of $105. Not counting my time, I could have made single-sided versions for less. But this is something of an apple to oranges comparison. The professionally made boards are double-sided, have no jumpers, and have plated through-holes. Also, I have far too much electronic junk in my garage, so my cost of materials approaches zero. When you start adding the costs of your time, materials, special tools, and mistakes, the professional boards hold their own. A big chunk of the cost is a $55 set up fee and the cost of shipping. Get a few friends together for a group order and the per board cost drops quickly.

Switch Input Printed Circuit Board (7 October 2008)

I prototyped the original switch input module back in March 2007.  I developed basic artwork for a single-sided printed circuit board, added it to the Switch Inputs chapter and moved on to other things. I'm now revisiting the project and investigating professional approaches to having the PC boards made. I redesigned the board artwork and ordered a few boards from ExpressPCB. The process is perhaps not the cheapest, but the PC layout software is easy to use, and ordering is a snap. I should have the new boards by the end of the week. I'll let you know how it works out.

Project Printed Circuit Boards (30 September 2008)

The book presents several projects that involve electronics. Each project is documented with a complete schematic and circuit board artwork. The board designs allow for single-side construction. Most of the traces are on one side. The few remaining conductors can be added as jumpers. So, if you wanted to make the boards at home using the toner transfer method, you certainly could. In fact, the projects were prototyped using that very approach.

There is also nothing to prevent you from have boards made professionally. There are a number of PC board houses that will make small quantities for a reasonable price. Given the convenience, I suspect this approach will be the preferred one. So, I'm giving it a try myself.

This is a screen grab of the free board layout software from ExpressPCB. The project is the 16 switch input module from the Switch Inputs chapter. 

Switch Inputs Chapter Edited (27 September 2008)

I've finished the edits to the Switch Inputs Chapter. It now has a few more illustrations and two more pages. The result is that the firmware is better explained. I need to read through the whole chapter to make sure it hangs together well, but just the thought of looking at makes me cross-eyed. Time to put it aside for a while.

Warning & Status Lights, and Switch Inputs Chapters (24 September 2008)

Wrapped up the edits to the Warning & Status Lights chapter, at least as much as these things are ever finished. I've completed the changes I had intended to make, but I fully expect that I'll find something else when I review it several weeks from now.

The Switch Inputs chapter is next. The firmware overview needs some help.

The manuscript page count is at 560. The book's missing a project, an appendix or two, a few dozen illustrations, a table of contents and an index. Looks like it'll come in close to the projected 608 pages. I have a lot of project building to do. Designs get "improved" during the writing. Building verifies that these evolutionary steps really are better.

Warning & Status Lights Chapter (20 September 2008)

The Warning & Status Lights chapter is one of the oldest. It may even be the first I wrote. It's been extensively revised, but during a recent re-read it was apparent there's room for still more revision. I've added a firmware flowchart, made some tweaks to the firmware, and am expanding the description of firmware functionality.

DIY Instruments Chapter (16 September 2008)

I'm filling in holes. 

I wrote the DIY Instruments chapter and built the chapter projects quite some time ago. As subsequent chapters came into being, my descriptive approach evolved. In particular, I found that flowcharts help explain firmware. I may be over explaining things, but I don't think so. Firmware is confusing because of its size. The little micro controllers have a limited repertoire of instructions. You can only cram so much processor on a tiny bit of silicon, but what you get is cheap and fast. On the down side, you end up with a lot of code, and that can be a bit off-putting.

The code listings have a lot of comments. Even so, I think starting with an overview supported by a flowchart is a good thing.

So, I'm now going through early chapters and updating the firmware descriptions.

Motion & Force Cueing Chapter (12 September 2008)

I have a strong draft completed, (and already see where I can improve it).

I now have at least some version of every chapter. There are a number of holes, some major. 

It's beginning to look like a book.

Motion & Force Cueing Chapter (9 September 2008)

I'm about two thirds through creating a decent draft of the chapter on Motion & Force Cueing. I had pages of notes from longer ago than I care to admit. Since making those notes, many of the motion system companies have vanished, either being bought or just leaving the business. Another important change is a small but important growth in DIY motion systems. As I've pulled the draft together I've made sure to reflect the changes in both areas. 

This is an advanced topic, right on the edge for an introductory book with broad coverage. It will be a short chapter, but full of information.

Position Sensors Chapter Revisions (3 September 2008)

I keep a hard copy of the manuscript in a three-ring binder, and make notes on it as I have flashes of brilliance. 

Well, not really. What really happens is I make notes when I read through the manuscript and have flashes of despair, thinking "Did I actually write that?"  

Periodically, I have to go through the manuscript along with its collection of red scrawling notes and bring it up to date, which I just did with the chapter, "Position Sensors". I also added new material to further cover the topic a Hall Effect sensors. Here's an illustration from that new section.

Originally, I just covered the Hall Effect theory and pointed to commercial products for those interested in position sensing with Hall devices. This is a bit expensive. The new material explains how to use the $1~2 Hall Effect field sensor along with a simple magnet structure to make a nicely linear rotary position sensor.

Hardware I/O Options Chapter (1 September 2008)

I've got a solid draft. I'm sure it'll be covered with red marks before too much longer, but it's much closer to finished than it had been a week ago.

I've now bumped the draft page count up to 90%. I am officially "90% done". That means I can start working on the second 90%.

Beating on the Hardware I/O Options Chapter (27 August 2008)

After reading through the Hardware I/O Options chapter draft, I decided it dipped too deeply into techie details about I/O possibilities. It really needs to discuss the specific I/O requirements of a simulator. So, I'm hacking on the draft, removing extraneous detail and adding requirements discussion. This looks to tie in much better with projects in other chapters. It leads to a better understanding of why certain I/O choices were made and how they all work together.

Computer Drawn Instruments Chapter (26 August 2008)

I finished a revision of the chapter on Computer Drawn Instruments so that it now reflects FSX rather than FS9. Probably need to add a few illustrations.

Computer Drawn Instruments Chapter (24 August 2008)

I've been working through some of the Panels & Gauges documentation for FSX. I've succeeded in producing a demo panel on a second screen. All the gauges are stock MS gauges. Note that the background is black and the gauges are round. I consider the roundness quite an achievement. FSX tries hard to make full use of all screen real estate. It scales things to fit. It's a nice feature until you don't want it and don't understand how it's working its magic. I can't claim to understand all of it, but I think I've got a grasp of this little bit.

The knowledge behind this will be condensed into a few paragraphs in the Computer Drawn Instruments chapter. This is how to produce a custom panel layout that will allow you to place the instrument monitor behind a nice looking instrument panel facade. The scenery can be displayed out in front on an impressively large monitor or projection screen.

FSX Panel and Gauge Tutorials (22 August 2008)

The brown square and its contents are the result of the working with the building XML gauges tutorial in the FSX SDK. The SDK also includes an XML editing tool ("ACE Tool") which is helpful but temperamental. Sometimes the preview function works, and sometimes it doesn't. At least it seems to produce cleanly formatted XML. 

In any case, the left portion of the image is a 1440X900 chunk of scenery while the right portion with the black background is the tutorial test gauge set. It's straightforward to build a panel of floating gauges that you could display on a monitor positioned behind an instrument panel facade.

Computer Drawn Instruments Chapter (21 August 2008)

Been working through some of the tutorials on building gauges and panels to refresh my memory and make sure I keep the FS9 -> FSX differences in mind. This chapter isn't big enough to cover the details of panel and gauge building, but it can show the direction to what's possible. 

And there's actually quite a lot you can do without much difficulty. Just moving the instrument panel to a separate monitor can boost the sense of immersion. If the instruments are on one display, the outside view can be moved farther away, perhaps even projected if the budget's there. With the instruments and the scenery at different eye focal points, there's a subtle subconscious cue that distinguishes between inside the airplane and the outside world of the scenery. The flight illusion gets a bit better.

Computer Drawn Instruments Chapter , MS ESP (20 August 2008)

I wrote this chapter quite a while ago. In fact, it was before FSX came out, and things have changed. So, in addition to the normal editing cleanup, I've got some updating to do as well.

ESP is the commercial simulation offering from Microsoft. FSX is built on the ESP technology. Because ESP is a commercial product, there is now extensive online support in the form of the MSDN ESP Developer Center. This is a good thing. All the documentation that was in the SDK that shipped with FSX Deluxe is online, plus they've added videos, blogs and a forum. If you're interested in the highly technical details, this is a great resource.

Sound Chapter (18 August 2008)

Completely rewrote the chapter on sound in your simulator. Decided there is no great value in a chapter project. DIY doesn't save any money here.

Removed some of the appendix material, good stuff, but a little off the mark for the book target.

Stepping Motor Instrument Movements (16 August 2008)

While air-core movements swing the pointers in a great many automotive and marine gauges, they don't swing them all. Stepping motors are used in some. 

The stepping-motor movements contain a very simple 2-phase stepping motor followed by a 1::180 reduction gear train. Even though the stepping motor has a large step size, the gearing results in a 1/3 degree step size on the output shaft. These aren't real power houses, but they do have adequate torque to swing a pointer at up to 600 degrees per second. They're compact enough to fit into a standard 2" diameter A/C instrument shell, and the current required to drive them is a maximum of 20 milliamps, something within reach of a micro controller. (Download specs in PDF format here.)

This particular model (the only model available through the vendors on Ebay) has an internal stop and is limited to 315 degrees. 

The internal stop removes the need to use some sort of indexing sensor to determine where the needle is positioned on power up. You simply write the initialization firmware to rotate the needle 315 degrees counter-clockwise. The needle turns until the internal stop stalls the motor. From then on it's just a matter of keeping track of how many (up - down) steps the micro controller has sent the movement.

The 315 degree limit somewhat restricts what you can do with this. No compasses, DGs, or sensitive altimeters, but airspeed, EGT, flap position, oil pressure, fuel quantity, and so on look to be slam dunks. 

These movements are made by Micro Components SA, a member of the Swatch Group. They have been on my radar screen for awhile, though at a low priority. Recently I noticed that they were available retail from two different vendors on Ebay, so I had to buy a couple. They showed up today giving me something else to toy with instead of writing.

Actually, I have managed to get some writing done. I made an editing pass through the Interfacing with MSFSX chapter, correcting a number of smaller issues while noting that I have more there to do. The section on setting up a programming development environment was originally written with Microsoft Visual Studio 2005 in mind. VS2005 did not incorporate the Win32 platform SDK by default. I had to add instructions on how to do so. Well, it looks like VS2008 does default to having the platform SDK. So, I've got to update that part.

Chapter 4: Engine Controls (13 August 2008)

Back to engine controls. 

In the early days of human factors in aviation, aviation controls were given standardized characteristics. Throttle knobs are rounded and black, mixture knobs are red and have raised ridges, and prop controls have recessed grooves and are blue. The fourth knob with radial ridges is a supercharger control.

Then along came HOTAS... 

Chapter 17: Simulator Enclosures (12 August 2008)

An enclosure is another simulator element that adds to the flight illusion. It deepens the feeling of immersion by actively contributing components that say "airplane!", by isolating you from distracting sights and sounds of the real world, and by tying all the disparate controls, annunciators, instruments, and scenery displays into a connected whole. 

I've just completed a draft of this chapter.

Chapter 4: Engine Controls (10 August 2008)

Random vernier push-pull engine mixture control.

Chapter 4: Engine Controls (9 August 2008)

Random push-pull throttle with friction lock.

Hey, gotta cover the basic stuff too!

Chapter 4: Engine Controls (8 August 2008)

So here I am, working on the Engine Controls chapter. (Yes, I know. I do tend to hop around.) I drafted this chapter some time ago. I had placeholder pictures for the illustrations, so I'm now producing the line drawings that will go in the book. This particular group of illustrations go in the section that overviews the range of engine controls in real aircraft. 

The main thread in the book is how to create a flight sim experience, ranging from okay to awesome. If your preferences lean toward the awesome end of the scale, you quite likely need to implement the same controls in your sim as a pilot uses in a real plane. And if you're exploring simulator options, it can be really helpful to have an idea of what's important and how complex different amounts of awesome might be. 

That's the goal of this section, at least with regard to engine controls. There will be illustrations of simple push-pull GA throttles, of multi-engine throttle quads, of helicopter collectives, and of the F-16 HOTAS throttle grip pictured below. The goal is to communicate an idea of what's important in producing a quality flight sim experience, and what your options might be in pursuing it.

Chapter 0: Recreational Flight Simulators (2 August 2008)

Okay. I have officially (or maybe officiously, I'll see on re-reading) completed the first draft of the introductory chapter, "Recreational Flight Simulators". This brings the total of currently drafted material to 533 pages. 

I'm probably going to cut some material. I'm in danger of running over. I figure 608 pages is a reasonable total. That's an even 19 signatures of 32 pages each. I hadn't planned on quite as much intro material, but I'm liking it now. So something's got to go. I've got some appendix material that's a bit too much detail for the book... hmmm, a page here, a page there...

Chapter 0: Recreational Flight Simulators (27 July 2008)

This is the introductory chapter. I had originally intended to put this material in the Introduction. No one reads book introductions though. So I figured I'd try writing it as a separate chapter and see if there's enough material to justify itself. I've bounced back and forth on this. Intro-chapter-intro-chapter-sigh. I'm leaning toward chapter at this point.

The book is supposed to be an advanced introduction to the home-built sim hobby. So, in theory, a lot of people at ground zero (experience-wise) will buy it. (What I'm hoping is that these people will post to forums asking all kinds of newbie questions, and all the answers will be 'Welcome to the mad house, now go buy Mike Powell's book'.) That kind of means I can't just dive into the details. I need to be up front with these new guys and explain that once you start, there's no way out, kind of like trying to eat just one potato chip. Sticking something really important like this in an Introduction that nobody reads just doesn't seem right. The material just has to have its own chapter.

So, anyway, that's what I'm doing, and I'm about halfway through the first draft.

Editing the Joystick Chapter (27 June 2008)

I've created a number of new illustrations for the Joystick chapter to cover the change from potentiometers as position sensors to Hall sensors. There are at least two or three more drawing to do, and a great deal of re-writing. Then I get to build the project to check for errors.

Here's a picture that won't be in the book, though something similar will be. This is the way the hall sensor will be supported: stuffed into a brass tube and held by RTV.

Control Yoke Chapter Progress and Hall Sensors (20 June 2008)

The Control Yokes chapter is now a 32 page draft. It's far enough that I've printed out a hardcopy for further editing. I think more explanation about real control yoke linkages would help, but overall the chapter is coming together nicely. As time permits I'll build the chapter project following the chapter directions as a check on completeness.

I'll be heavily revising the Joysticks chapter to use Hall sensors in place of potentiometers. Pots get good coverage in the Control Yokes and Pedals chapters. The joystick project is a floor-mounted stick with small angular motion. This makes it a good candidate for using a linear output Hall sensor. 

By "Hall sensor" I'm referring to the $1.30 Allegro A1301 magnetic field sensor rather than the $35~50 Honeywell/Clairostat rotary Hall position sensor.

If you rotate a Hall sensor in a uniform magnetic field, the sensor output varies as the cosine of the angle of rotation. The cosine (or sine, if you prefer) is not particularly linear. In fact it's pretty darn wavy. However, If you zoom in on a small portion of the cosine (or sine) curve, that changes. If you look at the regions around cosine(90 degrees), sine(0 degrees), cosine(270 degrees), and sine(180 degrees), the curve flattens out. For about 45 degrees the curve is flat within about 2%, and that is pretty darn good.

To use this approach you need a uniform field strong enough to produce full output from the sensor at 70 degrees and 110 degrees. The field should be uniform over a large enough volume that minor lateral movements of the sensor don't produce noticeable errors. Finally, the magnet structure shouldn't generate stray fields that influence other, nearby sensors.

This picture shows a rudimentary magnet structure that meets those goals. The magnets are 3/4" diameter ceramic disks. (I could have used neodymium, but would have had to order them. Ceramic magnets are available locally.) They are large enough to provide a comfortable volume of uniform flux  in the gap between the two. The steel brackets and stack of steel washers provide the magnetic back circuit so there is little flux outside the gap. Finally, by changing the number of washers, the gap size can be varied and this adjusts the magnetic field strength in the gap.

Bottom line: This works, and it's cheap.

I'll be using  this approach (with a more robust magnet structure) for the revisions of the joystick project.

Plodding Continues (10 June 2008)

Text for the Control Yoke chapter project has been drafted. I'm back working on the drawings.

Hall Sensors (2 June 2008)

It occurred to me that I have used potentiometers as position sensors in too many book 2 projects.  It's not that potentiometers are bad sensors, in fact, some models are very, very good. It's that book 2 is supposed to demonstrate, through their use in projects, various techniques and items for use in DIY sims. Showcasing rotary pots in every project shortchanges the reader. What about other approaches, like Hall-effect sensors?

One could argue that the Honeywell HRS100 Hall-effect rotary position sensor is mechanically a drop-in replacement for a rotary pot, so why bother? One could, except that there are less expensive approaches than the HRS100. The best price I've seen lately is on the order of $35 each. For about $1.30 you can buy a linear output Hall-effect sensor, the Allegro A1301. It's not a position sensor, it's a magnetic field sensor. When you buy the HRS100, you're getting the magnetic field sensor imbedded in a magnetic circuit that linearly varies the strength of a magnetic field applied to the sensor as you turn the shaft. There's no secret regarding how to do that, but it does usually entail the use of special materials to avoid inaccuracies due to magnetic hysteresis . So you really do get something for your money when you buy an HRS100.

But what if you don't need a full 90 degrees of rotation sensing? What if you have something like toe brakes or a floor mounted joystick that only moves 40 or 50 degrees? Then the design parameters change. 

Some simple bench tests show that an Allegro A1301 Hall-effect sensor, a pair of cheap ceramic hobby/craft magnets, and a few bits of steel can produce a rotary position sensor with better than 2% linearity over a 40 degree measurement range.

So... It looks like the best place to showcase rotary potentiometers is the control yoke chapter. The joystick chapter, with its floor mounted joystick project, seems a natural for showcasing DIY rotary Hall-effect position sensors. Sadly, the joystick chapter had been "complete". 

Plodding along  (29 May 2008)

I've made one pass through the Control Yoke chapter roughing out the illustrations. I'm now expanding the text. This, of course, has resulted in reordering a few of the sections which means the detail in the illustrations must change. So, once this wordsmithing pass is complete, it's on to pass two on the artwork. Usually this process converges. At some point I decide the chapter draft is pretty much there and move on to building the project as described in the chapter. This is the "proof in the pudding" step which leads to more revision. I did say this converges, didn't I?

HUD Book Overviewed, Looking at Yoke Options (23 May 2008)

I added an overview of Head-Up Displays, Designing the Way Ahead to the HUD page.

I've also been exploring different approaches to making control wheels. I'm not trying to build a perfect replica of any given yoke, rather the goal is to demonstrate technique. I want to communicate skills for using commonly available materials to create flight controls of arbitrary shape, how to mount a yoke to a control shaft, how to embed wiring, and so on. 

As usual, what I thought had been nailed down a long time ago continued to evolve while I had my back turned. I need projects that stay pinned down long enough for me to write them down and move on to others. Unfortunately, when I start working on the drawings new ideas keep popping up. 

HUD Book (18 May 2008)

I finally managed to borrow a copy of Head-Up Displays, Designing the Way Ahead by Richard L. Newman. This is an extensive survey work covering aviation HUDs. It focuses on design criteria rather than technology. There is a great deal of what a HUD should accomplish, but very little of how to do so. Nonetheless, it's interesting, and I'll be writing more about it on the "Head Up Displays" page over the next several days.

Book 2 Milestone (16 May 2008)

Okay, maybe it's just an inch-pebble, but it's still progress. The manuscript for Recreational Flight Simulators hit 500 pages today. I'm estimating 608 pages total which includes table of contents, index, and so on.

 Why 608? It's an even 19 signatures. A signature is a group of pages which are printed together. The printer I will probably use puts 32 pages in a signature. The sheet fed press prints a four by four array of pages on each side of a large sheet of paper. After folding and trimming it results in 32 pages in the book. 

In any case, I'm busily churning out illustrations that show how the Control Yokes chapter project goes together. Tossing in a few words, too, but mostly it's drawing time.

Tiny Stepping Motors part 4 (15 May 2008)

Just thinking out loud. If variable reluctance won't cooperate, perhaps permanent magnets will.

Control Yoke Chapter Project Drawings (13 May 2008)

The construction drawings for the Control Yokes chapter project are starting to come together. The project is a general aviation style yoke based on drawer slides and industrial mounted bearings. I tried to stick to materials available from home building stores, but there was just no substitute for the industrial bearings that came close in performance. The yoke has springs for control loading. High end potentiometers play their parts as position sensors. These are the same Bourns model 6639S potentiometers I have written about before. The mechanical design minimizes backlash for smooth, precise handling.

This is in general what it looks like, though I'm still tweaking.

Tiny Stepping Motors part 3 (11 May 2008)

It works. Grudgingly, but it does work. Unfortunately, it doesn't work well enough. The biggest issue is that it's right at the limit of my fabrication ability. I'm using telescoping brass tubing for the bearings, and I've got too much play. This sets a minimum possible gap between the rotor and the stator poles. The motor produces more torque with a smaller gap, but if the gaps is too small the bearing wobble lets the rotor hit the stator. There are a few other issues, but this is the most troublesome.

I chose the telescoping tubing approach because the hollow center can be used as a wiring channel. 

 Well, there are other approaches for the future. For the time being I'll table this and move on to more pressing issues. I have a few more things to do on the updated air-core movements, and there is a growing box of parts for the Yokes chapter project.

Tiny Stepping Motors part 2 (10 May 2008)

I'm simply not getting the performance from my first version stator. I'm going to the more standard three phase stator. It's easier to build. Because the poles are farther apart it should relax the dimensional demands on the stator to rotor gap.

Update: New version stator is much better.

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