Hydraulic units can either use standard hydraulic oil, or food grade oils when necessary. Note: food grade oil has been used in food processing applications for nearly one hundred years with no adverse effects. In fact, food grade oil, if boiled to kill any bacteria, can be consumed with no adverse effects (not recommended) other than lubrication of your intestinal track. Hence, the “fear” of oil and leaks are no longer of major concern.
Unfortunately, and in most cases erroneously, the promoters of electrical systems point to oil as one of the major reason for selecting electrical systems due to some questionable set of theoretical environmental constraints. This is a misconception of the systems involved. Motion platforms and their hydraulic components are “NOT” to be equated with a typical industrial or farming hydraulic applications. Motion platform hydraulics employ only the highest quality components, fittings, materials, oils and control systems. The cost of an industrial hydraulic cylinder, for example; might be $60.00; a comparable servo -system actuator would be $1000.00 for the same payload capability. Similarly, the fittings and connections for servo quality systems commonly utilize JIC and SAE connections which virtually protect against leakage. Industrial and farming systems commonly use “pipe” fitting connections, which are at best poor. Pipe fittings are poor, not only for hydraulic systems but for “home” applications as well. Hydraulic systems, when designed and installed properly do not leak and are not of major concern, and, can be installed in a very compact package.
Depending on the design concept, hydraulic systems are inherently safe, particularly when E-Stop conditions are encountered. Hydraulic systems can be very easily designed to either lock-in-place, or, soft settle during E-Stop conditions and power outages. This is accomplished by either stopping the command to the servo-valve, or providing either a control voltage to the servo-valve or using a separate abort valve. Different manufactures use differing schemes.
Electrical systems, on the other hand, are typically designed to “lock” in position when an E-Stop command is initiated. Also via use of more expensive and complex battery backup schemes for providing power during E-Stop, “slow settle” requirements can be achieved. All of this is at additional cost and complexity of the control system logic. These systems are “critical” to electrical systems which if not addressed properly for all potential failure cases, can result in an immediate retraction collapse of the actuators due to the higher efficiency mechanical designs.
Hydraulic Motion vs Electric Motion – Closing Thoughts
The intent of this analysis has been to show that there are several advantages of hydraulic systems in lieu of electrical systems. Advantages range from simplicity, durability and versatility to safety. The author’s twenty five years of experience in building both hydraulic and electric motion platforms is the culmination obtained, which is the basis of this comparison and analysis.
It is critically important that when considering the purchase of a custom motion platform, to listen very carefully to what is being offered by all manufacturers; consider the application in detail and do not dismiss hydraulic systems out-of-hand because of misleading statements. Ask the offering party to demonstrate each system for your review. Only then, can the advantages of each and every system be evaluated. Learn more at FluidPower World and download their handbook.
The original PDF Version of this Hydraulic Motion vs Electric Motion whitepaper entitled, Flight Simulator Motion Bases – Hydraulic Motion vs Electric Motion, is available for immediate download.
By J.F. Samicola and G.P. Kokalis