Radio control

Some remotely-controlled devices are loosely called robots, but are more properly categorized as teleoperators since they do not operate autonomously, but only under control of a human operator. . Radio-controlled teleoperators are used for such purposes as inspections, and special vehicles for disarming of bombs. This lineage is made clear in Cutler's foreword to Inside Windows NT, quoted on Neil Rieck's "Windows-NT" is "VMS re-implemented" page. Today radio control is used in industry for such devices as overhead cranes and switchyard locomotives. Microsoft's Windows NT system is a distant descendent of RSX-11M but is more directly descended from an object-oriented operating system Cutler developed for a RISC processor (PRISM) which was never released. The most outstanding example of remote radio control of a vehicle are the Mars Exploration Rovers such as Sojourner. Principles first tried in RSX-11M later appeared in DEC's VMS.

Instead of a "turn left" signal that is applied until the aircraft is flying in the right direction, the system sends a single instruction that says "fly to this point".
Dave Cutler was the project leader for RSX-11M, which was an adaptation of the earlier RSX-11D for a smaller memory footprint. Remote control military applications are typically not radio control in the direct sense, directly operating flight control surfaces and propulsion power settings, but instead take the form of instructions sent to a completely autonomous, computerized automatic pilot. It existed in many versions:. Advantages include bit error checking capabilities of the data stream (good for signal integrity checking) and fail-safe options including motor (if the model has a motor) throttle down and similar automatic actions based on signal loss. RSX-11: A family of real-time operating systems mainly for PDP-11 computers created by Digital Equipment Corporation (DEC), common in the late 1970s and early 1980s, designed for and much used in process control, but also popular for program development. More recently, high-end hobby systems using "Digital Proportional" features have come on the market that provide a computerized digital bit-stream signal to the receiving device, instead of analog type pulse modulation. The IAS light pattern was a single bar of lights that swept leftwards.

The relative simplicity of this system allows receivers to be small and light, and has been widely used since the early 1970s. The RSX-11M light pattern was two sets of lights that swept outwards to the left and right from the center of the light display (or inwards if the IND indirect command file processor program was currently running). The pulse trains representing the whole set of channels is easily decoded into separate channels at the receiver using very simple circuits such as a Johnson counter. When run on certain PDP-11 processors, each version of RSX displayed a characteristic light pattern on the front of the processor any time the system was idle (and the processor was executing the PDP-11 WAIT instruction). The latter produces a voltage proportional to the output position which is then compared with the position commanded by the input pulse and the motor is driven until a match is obtained. Before DCL, the usual RSX prompt was ">" or "MCR>", standing for the "Monitor Console Routine". An electric motor and reduction gearbox is used to drive the output arm and a variable resistor or "potentiometer". For several years, the top item on the wishlist was "same day service".

Off-the-shelf servos respond directly to pulse trains of this type using integrated decoder circuits, and in response they actuate a rotating arm or lever on the top of the servo. Outside the office of the engineer in charge of ongoing maintenance of the taskbuilder was a whiteboard labeled "Taskbuilder wishlist". The pulse is repeated in a frame of between 14 and 20 milliseconds in length. If the overlay scheme was especially complex, taskbuilding could take a rather long time. In the type of system most commonly used today PWM is used, where transmitter controls change the width (duration) of the pulse for that channel between 920 µs and 2120 µs, 1520 µs being the center (neutral) position. In order to support large programs within the PDP-11's relatively small virtual address space of 64 KB, a sophisticated semi-automatic overlay system was used; for any given program, this overlay scheme was produced by RSX's taskbuilder program (called TKB). These R/C systems made 'proportional control' possible, where the position of the control surface in the model is proportional to the position of the control stick on the transmitter. The operating system and utilities were to run on the entire line of PDP-11 platforms, from the very small systems up through the PDP-11/70 which had memory-mapping hardware and supported up to 4 MB of memory." -- David Cutler, foreword to Inside Windows NT.

Typical radio control systems for radio-controlled models employ pulse width modulation (PWM) or pulse position modulation (PPM), and actuate the various control surfaces using servomechanisms. a multitasking operating system that would run in 32 KB of memory with a hierarchical file system, application swapping, real-time scheduling, and a set of development utilities. While early control systems might have two or three channels using amplitude modulation, modern systems include 20 or more using frequency modulation. .. The mechanical resonant systems using reed relays were replaced by similar electronic ones, and the continual miniaturization of electronics allowed more signals, referred to as control channels, to be packed into the same package. "My first operating system project was to build a real-time system called RSX-11M that ran on Digital's PDP-11 16-bit series of minicomputers. These systems were widely used until the 1960s, when the increasing use of solid state systems greatly simplified radio control. "RSX was a separate path at DEC and the progenitor more than anything of VMS that went to NT via Dave Cutler." -- Gordon Bell, Vice President, Research and Development, Digital Equipment Corporation.

These were typical on/off signals. OSRV and RSX driver interfaces are different & incompatible. The controller's radiotransmitter would play the different frequencies in response to the movements of a control stick. That happened because of better work by the RSX-11' re-coders, stability of patched RSX, and a faster update cycle for SM-RSX drivers & patches, made possible by the SM users community. The vibration would push on electrical contacts connected to the actuators of the control surfaces of the missile. (OSRVM is the next model of OSRV-SM for the SM-1425.) But RSX11M 'patched' for the SM's processor was used more often than rewritten OSRV. In front of the speaker were a number of small metal "fingers" with different resonant frequencies, each one tuned to vibrate when a particular tone was played in the speaker (a so called reed relay). But, there are differences between RSX and OSRV because of differences between SM and PDP' hardware and recognised by Soviet engineers bugs in RSX.

A small radio receiver was placed in the missile, the signal from the controller (transmitter) was "played" into a small speaker. Not surprisingly, the six-character string 'OSRVSM' fits nicely in the same 16-bit RADIX-50 word as 'RSX11M'. Radio control systems of this era were generally mechanical in nature. If read as Cyrillic, the name OSRV is an abbreviation for 'Operatsionnaya Sistema Realnogo(Razdelenija) Vremeni' -- Russian for 'Real Time(Time dividing) Operating System'. However none of these systems proved usable in practice, and the one major US effort, Project Aphrodite, proved to be far more dangerous to its users than to the target. According to other sources, RSX-11M source code might have been stolen by the KGB. Both the British and US also developed radio control systems for similar tasks, in order to avoid the huge anti-aircraft batteries set up around German targets. This system appeared to be an exact duplicate of RSX-11M save that the prompt was changed in the binary files.

The German development teams then turned to wire guidance once they realized what was going on, but these systems were not ready for deployment until the war had already moved to France. DOS/RV, OSRV-SM -- Two names for the clandestine clone of RSX-11M that was produced behind the Iron curtain. Jammers were then installed on British ships, and the weapons basically "stopped working". P/OS -- A version of RSX-11M-Plus that was targeted to DEC's PRO-325, PRO-350, and PRO-380 line of PDP-11-based personal computers. After initial overwhelming successes, the British launched a number of commando raids to collect the missile radio sets. Micro/RSX -- a stripped-down version implemented specifically for the Micro PDP-11, a low-cost multi-user system in a box, featuring ease of installation, no system generation, and a special documentation set. The effectiveness of the Luftwaffe systems was greatly reduced by British efforts to jam their radio signals. Derived from RSX-11S.

However by the end of the war the Luftwaffe was having similar problems attacking allied bombers, and developed a number of radio-controlled anti-aircraft missiles, none of which saw service. RSX-20F --11/40 front end processsor operating system for the DEC KL10 processor. Their main effort was the development of radio-controlled missiles and glide bombs for use against shipping, a target that is otherwise both difficult and dangerous to attack. The first version of RSX to include DCL (Digital Command Language). Radio control was further developed during World War II, primarily by the Germans who used it in a number of missile projects. RSX-11M-Plus -- a much extended version of RSX-11M, originally designed to support the multi-processor PDP-11/74, a computer that was never released, but also used widely as a standard operating system on the PDP-11/70. Nikola Tesla patented a radio-control scheme as early as 1899, and various radio-controlled ships were used for naval artillery target practice by the 1920s. RSX-11S -- a memory-resident version of RSX-11M used in embedded real-time applications.

The possibility of radio remote control was appreciated almost as soon as the first demonstrations of radio itself; the credit for the first to suggest radio control of aircraft may belong to Patrick Young Alexander as early as 1888. RSX-11M -- a multiuser version that was popular on all PDP-11s. . RSX-11/D -- evolved into IAS. The term is used frequently to refer to the control of model cars, boats, airplanes, and helicopters from a user-held control box (radio.) Industrial, military and scientific research all make use of radio-controlled vehicles as well. RSX-11/B programs used DEC DOS macros to perform disk I/O. Radio control is the use of radio signals to remotely control another device. To start up the system, first DEC DOS was booted, and then RSX-11/B was started.

RSX-11/B -- small real time executive based on RSX-11/C with support for disk I/O. RSX-11/A, C -- small paper tape real time executives.