Fundamental Considerations For The Implementation Of Pedals In A Spacecraft Simulator Cockpit

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Any respectable flight simulator cockpit should have a set of pedals, even if it pretends to simulate a spacecraft, but how do you implement them?

Almost all aircraft have two pedals per pilot, and each one of those pedals has two modes of operation. This is a common format in all sorts of aerial, winged vehicles, from a Cessna 150 to a B747. Each set of pedals so configured allows for directional control using the front wheel in the case of tricycle planes, or the tailwheel in the case of taildraggers. The second mode of operation of these sets activates differential brakes on the landing gear axes both at the right and left sides of the machine. In some cases, this is a simple arrangement, while in others, especially in heavy aircraft, what the pedal brakes really do is to activate an array of brake pumps distributed among the applicable multiple wheels of the plane.

When you step over one of these pedals, it moves forward, sliding or rotating. This moves the rudder. If you step on the right pedal, the plane will turn to the right if it is on the ground, or yaw into that direction while in the air. By activating the brakes configured for the same pedal, you can turn more tightly.

Other planes, like my PA-11 use four pedals because mechanically speaking, the differential brakes and the rudder mechanism are separated. You will see such a design generally in older aircraft. But there are more, even stranger paradigms for rudder control: The Ercoupe is a nice little aeroplane that originally had no pedals at all. The rudder and the ailerons, necessary to turn while flying, are synchronised by means of the control wheel or stick. While taxiing you control a regular Ercoupe by moving the wheel just like in a car. Some Ercoupes where finally equipped with pedals due to the fact that some pilots find that odd.

In the case of spaceships there is no standard rule, although for me using pedals made a lot of sense since I am an aircraft a pilot in real life. Simply put: I am accustomed to using such pedals.

However, spacecraft have flight regimes that are only partially similar to those of aircraft; essentially, in the case of spacecraft designed to take off or land like aeroplanes, there will be three regimes, as opposed to two, and then there are some caveats, and there could be a fourth displacement regime, depending on the ship's design:

Taxiing: While standing on firm ground, such a spacecraft would move in a similar way as an aircraft, so a set of pedals would essentially operate in the same way as the pair of pedals of a standard plane.

Atmospheric or aerodynamical flight: Under this regime, the set of pedals in a spacecraft would also operate in a similar way to those of an aeroplane. However, if the spaceship is designed to enter different planetary atmospheres, with different gasses, temperatures, densities and gravitational pull, the effectiveness of the system would likely be different in each case.

Space flight: Since there is no atmosphere in space, a rudder system as we know it makes little sense. However, the pedal metaphor could be used to control the ship's rotation along its vertical axis, and translation along its lateral one. In other words, you can make your ship yaw or move sideways using your set of pedals.

Translation on the ground: Only few people know that some aircraft can move backwards on their own when they are standing on the ground, although it is usually not the wisest thing to do. However, in the case of a spaceship it could make sense for such a degree off movement. It would be required to modify the landing gear to allow it to move sideways by rotating the wheel's axes, like a supermarket cart. So,using such a system the spacecraft would move to port or starboard but keeping its longitudinal axis always parallel.

There is also an additional thing to take into account regarding displacement and taxiing by a spacecraft: Such a machine, if it is capable of atmospheric flight, space flight and non-atmospheric flight in any celestial body would need to take off and land conventionally as well as vertically. Such a machine is known as a VTOL ship and control systems should be designed for that.

A VTOL spaceship would eventually operate like a plane. In the Orbiter simulated world, the DG series of spaceships are able with more or less success to operate like true VTOL machines. This implies that any such spacecraft simulated or incorporated into a simpit should be able to taxi more or less like helicopters do on ground effect with no ground effect where there is no atmosphere, of course.

Heavy helicopters seldom do this and many times are equipped with wheeled landing gears, but light to medium helicopters are more often than not fitted with skids or floats in order to provide them with the capability to land in all sorts of terrain. These machines often operate from conventional airports but cannot taxi from the ramp to the runway in use by actually rolling. Instead, they take off and float just above the ground up to about seven metres by taking advantage of an aerodynamic trick called ground effect. So you will often see little helicopters just floating or hovering over the taxiways before reaching the runway or any really clear spot to go up and away. This is taxiing a-la helicopter.

Spacecraft using hover rockets do not take advantage of ground effect but it makes sense to have them operate in the simulated world much like helicopters. This means that pedals will have to rapidly shift from rotational to translational mode, and probably it would make more sense to place such a switch on the propulsion control subsystem (PCS). That is, on the same box as the power levers that will be used for moving forwards, backwards and upwards.

In this way, the pilot will use his or her feet to control movement on two axes in different flight regimes; with one hand he will have control over all the exhausts and propulsion system, while with the remaining hand, he will hold a joystick to control the rest of the steering system.

Dumb Peripherals And DB25 Connections

The construction of dumb peripherals and input devices such as the pedals, throttle controls and so on allows for significant savings in the construction of a simulator.

A joystick is a common type of peripheral that sends input to a computer. Within the context of a simulation or computer game this is used as the main input device, more often than not. Inside a joystick there are some potentiometers, buttons and so on associated to a processing card that also has some sort of input/output connector used to connect it to a computer. These days, such connections are almost in all cases of the USB type.

This would make most people think that you will need one USB connection per peripheral such as pedal box, throttles, etc. and indeed, most commercial cockpit modules available today for sim enthusiasts follow such paradigm: Whether you purchase a whole top panel or a radio module, you have a USB cable somewhere that needs to be attached to the computer.

USB connections area dream when you compare them to past options. Building a cockpit before the USB era was far more complicated, but having such an interface, and despite the fact that USB connectors are inexpensive, end up costing a lot of money: Mass-produced joysticks cost very little, but try to build your own and you will find out that it will cost you far more, and the reason is that USB cards for such purposes cost generally more than the whole joystick put together.

Nevertheless, there are a few alternatives in the market that make sense because they allow to build or emulate joysticks with home-made devices for a reasonable cost. You just have to think a little bit before committing.

Consider that a regular joystick available at any computer shop normally offers three analog axes plus between four and twelve buttons. And you get all this for about fifteen euros. Meanwhile, some cards like the USBAxes made by Opencockpits.com provide five analog axis plus twenty four buttons. These numbers equal two joysticks, so by using one of these cards you can actually have two joysticks or pseudo-joysticks for about the same price than the commercial ones, plus the fact that instead of relying or having to do with something designed by someone else that seldom looks like a true cockpit joystick or control, you can build something that is more functional and realistic, according to what you intend to reproduce or simulate.

This implies a change in the internal topology of the peripherals because instead of relying on a USB connection per peripheral, a single card would grant this interface, while each peripheral would need to communicate with this card in the simplest of electrical terms instead of requiring any protocol or modulation. This means that for each actuator, servo, button, switch or potenciometer, just a couple of standard wires would do. Such peripherals would be dumb or blind, with no capacity on their own to process anything. They would send and receive signals that would be processed by just one card, located elsewhere.

Since I had a number of DB9 and DB25 connectors in my garage, I decided to connect the peripherals to the joystick-emulation card using them. I finally favoured the DB25 connectors because they could eventually be used to expand the number of connections without any structural change. A DB9 connector is indeed more limited. Thus, things like the pedal box in this home cockpit will just have some mechanical components, the electrical input devices such as vuttons or potentiometers, and a couple of cables going in and out via a DB25 connector.

Designs For Pedal Construction

As I commented before, pedals for a space sim cockpit should work in a similar fashion to those found in most conventional aeroplanes, and there are some very good designs for making them at home.

Of course, if you plan to build your own set of sim pedals you should already be knowledgeable in the handling and uses of tools, and have some experience reading schematics and thinking over such stuff as to implement the modifications that you might desire in a sensible way. If you don't feel confident about this, you shouldn't attempt to build your pedals, but then, perhaps you should also consider whether you want to risk a lot of money in attempting to construct a simpit with reduced chances of success.

At this moment I have already finished Nerkabtu's pedals. The total cost for them was between one fourth and one fifth of the price of the nearest-priced commercial competitor, plus my pedals are made with a degree of sturdiness similar to sets costing much more. I already know how aeronautical-degree pedals should be made, and how pilots tend to crush pedals in simpits. So, I have simply over engineered mine. In the various tests that I have already performed, these pedals worked flawlessly as well.

The basic design is not mine: I found several, very interesting articles on this issue at www.flightsim.com, and the one that made more sense for me was the design described in a tutorial called How To...Build Rudder Pedals, and written by Bruce May. As a very handy bonus, the author added a PDF file containing the schematics of his pedals.

Recycling Old VAX Components For Your Flight Sim Cockpit

The tenth commandment for C programmers, as written by Henry Spencer, says "Thou shalt foreswear, renounce, and abjure the vile heresy which claimeth that 'All the world's a VAX', and have no commerce with the benighted heathens who cling to this barbarous belief, that the days of thy program may be long even though the days of thy current machine be short."

Well, as a C++ programmer myself I have to say that I have committed hardware heresy, albeit the great inquisitor just might spare my soul for three things:

I am programming this simulator in C++, not C, and while they are similar, they are not exactly the same.

Mr. Spencer was referring to software heresies, while mine was a hardware one.

I saved quite a bit of money.

Indeed: Thinking about some components for the sim this weekend, I came across a treasure chest of very old to old computer components that I stored in my garage about twenty years ago, after a friend of mine brought the stuff from the trash can right outside his company's building. The were trashing away old computers, including a VAX, and I got some cards as well as buttons, keys and other stuff.

The issue with old computer hardware is not incompatibility with newer machines, but quality: Old keyboards, switches and so on, especially those coming from mainframes and minicomputers are of excellent quality, mechanically speaking. In fact, I have been using the same 360-dollar IBM keyboard since 1992; it is the on with which I am typing this blog post and I would not change it for anything else. I have programmed literally hundreds of thousands of code lines with it and so far not even a single key has ever failed. You can literally hammer it and nothing will happen plus, it is far more pleasant to write with than most modern types and the better quality of its mechanical components produces less typos. It was truly expensive at the time, but worth every bit. So, when I get a new computer, I just set the keyboard that comes with it aside or just purchase the machine without it.

Considering this, my weekend project this time was to recycle some VAX components, and I did. I got as a result nearly two dozen switches of the highest quality for nothing. Similar ones cost between two and six euros each, so go figure the amount of money saved. Moreover: The better quality of these components will surely mean less downtime with the simulator in the future.

With thins not only I saved a considerable amount of money, but also made a little contribution to our environment plus for my future satisfaction: My past experience with simulators is that the kind of malfunctions that switches and hardware gadgets produce are of that sort that result I a double amount of exasperation, for they require you to disassemble things and get dirty under the hood just in those occasions in which you feel more eager to go flying.

Redundancy?

A simple concept, although not generally an inexpensive one is redundancy: You can apply it to construct a more reliable sim cockpit in the fashion of the true aeronautical and aerospace industry.

Redundancy consists simply in having duplicate components; the idea is that such redundant parts will supply results at the moment in which the main components fail. However, there is a big difference between having spare parts and redundant ones: A spare is just something kept in a shelf for relatively quick access in the event of maintenance work, while a redundant one is installed and actually in place, working in parallel with similar components. If the system is well designed, redundancy will provide a far higher degree of reliability. It will not avoid failures completely but will make them far less noticeable to the user simply because what would normally cause a serious disruption in the case of redundancy will be bypassed.

A UPS is a device designed to provide electrical energy in the event of a blackout or failure of the main electrical network. If the lights go off and you have a UPS installed in your sim, it will at least provide you with enough time to finish what you are doing and shut off the system in a proper way. Needless to say, it would be good to have one of such devices connected to a sim cockpit but if you are planning a move in that direction, consider that you will need one capable of providing you with at leas1 KW, a fact that will place you on the medium to higher end price range.

Another example of redundancy applied to a flight sim is that of switches: Where there is one switch you can place two working in parallel. This will make a mess of cables and increase your costs and construction problems in most cases, but there might be a few occasions in which going redundant might be advisable: Landing gear levers, toe brakes and some other devices generally make use of some sort of switches that are very frequently used, making wear and tear a potentially serious enemy. Pedals, especially toe brakes, are among the list of components that will aggravatingly fail first than any other, just in the middle of a nice flight session. So, if you build your own pedals, you could consider either using some sort of expensive industrial-strength switches made for heavy duty abuse or go parallel in circuitry, so that if one switch fails after you have been stomping on your toe brakes for a while, the other will keep working, increasing the time span between maintenance sessions that require dismantling your pedals.

If you plan on letting other people use your home cockpit, based on my experience, I would advice you to use redundant circuits in the case of toe brakes, your landing gear and flaps levers, at least. Keep in mind that while it is obvious that you will handle properly what you have designed and built with your own hands, other users might not think about that and will not know the structural limits of those components, or maybe, they will just prove to be sloppy or uncaring in general terms.

Thus, while installing redundant components may look expensive in the first place, in some cases it might prove to have the contrary effect in your pockets: Less critical failures that interrupt your flights will mean less frustrating and unexpected maintenance sessions.



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