Success with Flight Simulators

Contemporary Controls' CANISA Card is the Hidden Gem in the Flight Simulator's Control Loading System

Ever since the Wright brothers took to the sky in 1903, aircraft simulators have been employed to train indivduals to operate an airplane. These simulators enable individuals to experience a wide range of flight situations without running the risks associated with actually flying a helicopter, a commercial jet airplane, or a military aircraft.

The control loading system is an important element of a flight simulator. The system is comprised of a model of the aircraft and a command stick that is driven by an electric motor. It provides the force-feel characteristics of aircraft controls such as centersticks, pedals, and throttles within a simulator to provide realistic forces for the pilot. The end-result is a simulation that has the appearance and feel of the aircraft during all phases of operation.

As aircraft simulators and training devices became more sophisticated, companies like WITTENSTEIN aerospace & simulation Inc. of Bartlett, Illinois entered the business to design and construct control loading systems for simulators. Part of WITTENSTEIN AG, recognized as a world leader offering solutions for flightworthy applications, WITTENSTEIN aerospace & simulation Inc. has built a a reputation for the reliability of its equipment. The company employs CAN technology as this is the standard bus used with their control electronics. Among other things, CAN technology is characterized as being efficient and robust.

From a design perspective the key to the control loading system’s functionality is a network interface module (NIM). When the former ISA CAN card in the system became obsolete from a company in the UK, WITTENSTEIN’s engineers did their research and found a suitable replacement from Contemporary Controls, a Downers Grove, Illinois-based manufacturer. Contemporary Controls is able to meet all automation market needs for its customers across the continents.

The Story

Conventional flight simulators apply a controlled load on a target, such as a control stick and associated linkage, by using force sensors located between an actuator (electric motor) of the simulator and the target. The first force sensor detects the external force exerted on the load target and is coupled to the mechanical linkages which transmit the forces from the actuator to the load target. The torque and, therefore force, is controlled by the control electronics to ensure precise and accurate representation/simulation of forces to the pilot. At the same time, a pilot is also applying a force to the target.

WITTENSTEIN aerospace & simulation's drop-in assembly control loading systems

Visual image of WITTENSTEIN's drop-in systems on the frame of a simulator

To put together a sound simulator control loading system in place, WITTENSTEIN’s engineers realized that they required an industrial PC CAN card to interface with the actuators in order to provide a robust control bus. ”It allowed us to network a number of axes on a single CAN bus,” said Senior Systems Engineer Scott Metcalfe. “The CANISA-DN module from Contemporary Controls provided a simple method to set-up and install a card which could communicate with a number of our control electronics. The CAN card was used to communicate on the CAN bus to the actuators with messages that control the torque and speed of these devices in order to vary the force-feel characteristics. These actuators are modular in form, so the individual can select the servo, gear ratio, and the system control module configuration to suit the application.” Mr. Metcalfe said implementation was the result of everyone on the team in agreement on all phases of the project from startup to testing to proper training.

Metcalfe said the decision to use the CANISA-DN was made easier because the card is COTS which required no design effort, and is ISA which meant it could be assembled into an industrial PC.

Contemporary Controls’ product supports 8-bit transfers and benefits from the additional interrupts on the expanded AT bus.

It incorporates the Philips SJA1000 CAN stand-alone controller chip. The CANISA is backward compatible with its predecessor, the 82C200, but has more advanced features. The SJA1000 operates in either BasicCAN (11-bit identifiers) or the new mode called PeliCAN which supports the CAN 2.0B specification (29-bit identifiers). It is equipped with a 16 MHz clock frequency, larger receive buffer and better acceptance-filtering?including the ability to extend the acceptance mask to the data field.

This product measures 4.20" x 6.50" (106 mm x 165 mm) with data rates up to 1 Mbps. Power requirements for ISA bus are: +5 V, 80 mA and for CANbus are: +24 V, 80 mA.

Mr. Metcalfe explained that one or two CAN cards are located in a System Control Module (SCM) which runs the proprietary software, the Aktiv8® Software. This software controls the actuators over the CAN bus to provide the appropriate force-feel for the aircraft controls in the simulation. It is stored on a compact flash card which acts as the hard drive for the SCM. The SCM is connected to a host which runs the simulation and provides inputs to the control loading system and receives position and force data over an Ethernet TCP/IP connection. Cables are built to specification which connect all the actuators on one bus to the SCM. “We can construct CAN cables from standard 24AWG cable and 9-pin D-sub connectors,” said Mr. Metcalfe. “The lengths change dependent on the number of nodes and to where they are located in the simulator.”

Visual image of WITTENSTEIN's drop-in systems on the frame of a simulator

WITTENSTEIN aerospace & simulation's drop-in assembly control loading systems
are ideal for the distributed mission trainer (DMT) market
because of their compactness, modularity and easy installation.

He added that although the CANISA has no on-board microprocessor as other more expensive CAN cards, this did not pose any issues. “This card was a relatively simple card to integrate into our software.”

For this application, WITTENSTEIN engineers did not write their own driver for the CANISA nor did they use an off-the-shelf type such as Linux open-source CAN driver. Mr. Metcalfe said his team selected one from Contemporary Controls. Contemporary Controls' drivers support Windows® 98/ME/2000/XP, Linux and DOS.

Operating systems are a matter of choice. Therefore, WITTENSTEIN used the Real Time OS called RTOS32 from OnTime GmbH. On Time’s royalty-free hard real-time embedded operating system for 32/64-bit x86 CPUs implements a Windows subset kernel in only 16k of memory. It provides about 290 Win32 API functions and can load Windows DLLs. It also fully integrates with MicroSoft® Visual Studio and other Compilers.

The high performance and programmability of the control loading systems make them equally suitable for the complete range of applications, from PC-based trainers to level-D simulators.