What are some of the reason that people in the simulation industry hate motion platforms? Let’s explore…
How long has the manufacturer been in business? This might be a no brainer, but it is critical. Motion platform manufacturers come and go… the good ones stay in business. Over 30 years in business might be a good thing… they have seen and built most everything. How long have the engineers supporting that business been in the industry?
Does the manufacturer actually do the engineering? Ask the sales person and then ask for someone in engineering… email is really preferred as you can keep track of what you have asked and their responses. If they are reselling systems, ask who makes them!! Can you contact them directly and talk to an actual engineer? What is their turn around time for answering your questions? These should be taken into account. Depending on the question, they should either answer directly or get back to you in a day or two.
What does the motion platform use for the moving axis? Electric is the typical way to move a motion platform axis until the system requires a large payload. This is because of the inertia of the motors required for electric systems. If the inertia is too high in the motor, it might not be able to maintain a constant speed that is required to move the payload. Hydraulic typically used for very large applications, but they have limitations such as turn-around bumps and speed. Pneumatics are hard to control and soft (low velocity). If the system is using linear actuation, does the actuator have built in stops? Does it have a braking system? What is the life expectancy of the actuator (MTBF)? These should be answered with a yes, yes, and a mean time between failure. If the company that you are asking these question of cannot answer them, move on. If the system is using a non-linear actuation, i.e. a crank and pushrod, can the crank move freely around the shaft (360˚ of rotation) without interference to other parts of the motion platform? Does it have a braking system? What is the life expectancy of the actuator? These should be answered with a yes, yes, and a mean time between failure. If it cannot, move on. The designer of the motion platform has not done the design work necessary to build the system properly. The crank should be able to rotate freely.
Use of the proper materials is critical for all motion platform applications. Steel is commonly used. Stressproof and ETD150 for critical parts maybe used. Framework for supporting the motion platform and the payload should be engineered properly for the application. Typically, if it doesn’t look strong enough, it isn’t. Always ask if a stress analysis has been done for the system that you are inquiring about. You might have to pay for it, but it is better than wondering if some part of the steel might fail. Grade 8 or better hardware for mounting and installation of essential/critical parts.
Most electric motion platforms require the use of an amplifier to drive the motor for the axis. Use of the proper amplifier for the electric motor is crucial for proper operation of the system. The better the resolution of the amplifier, the better the motion platform will feel. This does not apply to hydraulic systems which are typically analog in nature. For electric systems, 16-bit resolution on the amplifier is the best. The amplifier should have enough amperage on the output for the motor that it is controlling.
The feedback device is an essential part of the motion platform. It allows the user to know where the motion platform axis is. It is either an encoder, a feedback potentiometer or angle displacement transducer. If an encoder is used (for velocity control only and not in a closed servo loop system), it should have a large amount of resolution (1024 or better). If a feedback potentiometer is used, it should be of high quality with a sealed ball bearing for longevity. If it is an angle displacement transducer, it should be properly matched to the system. If the manufacturer is using something other than these, ask what it is. Do some research on the part and its application to see if it is a good fit for you. If the system that you are inquiring about does not use a feedback (servo) system, then what are they using? Can they explain the different between the system that they are using and a typical servo system? They should be able to explain this concisely.
Motion Platform Software… this is an issue. What do you want the motion platform to do? Do you need a sea state generator? Do you need it to run via a joystick? Do you need it to sync to a playback video? Do you need it to follow a real aircraft or other vehicle? Do you just want a SDK and take control for yourself? Can the manufacturer provide you with all the information that you might require in regards to software? In a non-linear system, can the software accommodate the non-linearity? All of these issues should be addressed by the manufacturer. Ask questions.
What exactly is included? Does it include a top and can that top be customized? Does it include a controller and what exactly is in the controller? Does it include installation? Does it include a warranty and, if so, is an extended warranty available? Does it include technical support and how long does that support last? You should get a year warranty at the least.
Payload specifications are always a problem and should be handled on an individual basis. The manufacturer should ask what the payload is, how much it weights, what its dimensions are and if the CG of the payload is available. Overhung loads should be calculated to make sure that the motion platform can handle the load. If they do not ask these questions, move on. They should ask you for the specification that you require. These are critical to the manufacturer as it determines how the motion base needs to be built. Most of the time, standard motion base designs that are on the market meet the requirements for the consumer, but they should be checked by the manufacturer. The manufacturer should want to know this information to make sure that the system you are purchasing is correct for your application.
What fails first… if they cannot answer you properly, they might not know. In linear electric systems, it is usually the bearings in the linear actuator. In hydraulic systems, the seals and valves fail first. In non-linear systems, the computer usually fails first if properly designed. In pneumatics, the air pump fails first. Sometime the feedback device fails if improperly installed.
Is the system easy to set up and maintain? What is required to install the system? What is the maintenance for the system? The manufacturer should be able to supply the consumer a manual for the system. They should be able to inform you as to what type of flooring is required for proper loading. They should be able to tell you the power requirements or be able to change the input power to the consumer’s specification. Maintenance and parts replacement on the system should be easy, straightforward and explained in detail in the manual. The manufacturer should be able to supply a generic manual for inspection as long as the consumer realizes that this is just a sample of what their actual final manual will be.
Once you are armed with these answers, it should not be difficult to make an informed decision as to who to ask to bid on your motion platform requirement. Some may be more expensive than others, but if they have really put in the effort to design the system, the actual upfront cost of the system will pay itself back in the low cost of ownership of the system.
 The bump felt when reversing the direction of the hydraulic ram
 Within the limits of the amplifiers used
This was written by Mr. E Bruce Baker back in 1999. It was in response to customers questions about the use of motion for a aircraft trainer. Mr. Baker has over 50 years in the simulation industry and has integrated more than 300 systems in that time. He founded Servos & Simulation in 1981. This experience drives all of our designs for our customers.
Over the last several decades, there has been much discussion about the need for motion bases for aircraft simulators. Several times, an attempt has been made to prove or disprove the need for a motion base, and indeed, the need has been both proved an disproved. From all these studies and from personal experience, a few fundamental truths have emerged:
This is a copy of a letter that was sent by Mr. Bruce Baker of Servos & Simulation to Mr. Edward Boothe at the National Simulator Evaluation Program Flight in Atlanta, GA. It is in regards to a simulator upgrade for a CH-46 at MCAS Tustin. The main problem was that the motion base was not following the visual cues and made it hard for the pilots to train on (simulator sickness). The problem was resolved...
Why is frequency response of a servo critial to motion base design? Why is it even required? The fact is, the better the frequency response of the servo, the better performance of the motion base platform.
In the simpliest terms, the motion base must follow the input properly. So if the motion base is to follow the commands from a Host computer in a full-flight simulator, and the pilot response is about 2Hz or less, the motion base needs to have >5˚ at 2Hz of phase shift so that the motion base accurately tracks the signal from the Host Computer flight model. It is required as the phase loss of the motion base affects the stability of the pilot's control loop.
The Engineering Team at Servos & Simulation, Inc., analyzed the performance of one of our motion base designs. The plots for the performance show the maximum position as a function of frequency, the maximum velocities as a function of frequency, and the maximum accelerations as a function of frequency. The servo has an inner rate loop using the encoder on the motor for feedback allowing the servo to have a bandwidth of more than 40 Hz. The outer loop is a position loop with a bandwidth of 4 Hz. The position loop gain is limited by the gain available in the drive amplifier (power amplifier that drives the motor). Servos’ engineers add electronics to the servos and increase the gain by at least a factor of 4 which increases the position loop bandwidth to 16 Hz.
Since pioneering the first all electric digital control loader in 1990, Servos & Simulation has been there at every turn to deliver reliable products and services to its customers.