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What should one look for when purchasing a Motion Platform… Here’s a short list.
- How long has the manufacturer been in business?
- Does the manufacturer actually do their own in-house engineering or are they reselling the system (this matters)?
- What does the motion platform use for moving the axis? Is it hydraulic, electric, pneumatic or something else...
- What materials are used to construct the motion platform? Are the correct materials used? Where are the critical parts of the system?
- What is required to drive the motion platform axis? What is the resolution?
- What is being used for feedback and position location?
- How does the software move the motion base?
- Does the motion base accurately model what is being simulated?
- What is included? What warranty/technical support is provided?
- Has the motion platform manufacturer taken into consideration the CG of your payload, the payload weight, the overhung load, the velocity, the accelerations and angularity required for your specification?
- What fails first?
- Is it easy to set up and maintain?
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 company selling the motion base 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 the actual manufacturer 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.
How does the motion platform move the axes? 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 regulate. 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 bearings in the actuator? 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.
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 parts. Is the motion platform system as a whole structurally strong and rigid so that it doesn't affect the bandwidth of the system?
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 fidelity the motion platform will have. 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, it should have a large amount of resolution (4096 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 is that top 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. 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 and then the seals due to dirt. 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 installation. The bottom part of the motion platform should be designed in such a way as to spread out the weight of the system across the floor. 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. 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.