We are going to make some brief technical articles in which we will approach concepts of general mechanics, which will help us define our movement system better and learn what details to observe in the commercial systems available to buy in the market..
The importance of the absence of backslash in motion simulation systems.
In this case we will focus on the mechanical backslash between the joints of the moving parts of our movement systems.
We will not enter into complex calculations, curves of wear and tear, strength of materials, etc … in order to avoid excessive density in this subject, there is certainly material to write several books about it, but I will try to make it educational, enjoyable and brief.
The mechanical backlash in motion systems is a deadly enemy of hardcore simulation, its effects are highly harmful to our systems and greatly diminish the quality of movement and the sensations we must perceive from the simulated environment.
First of all, it should be said that the mechanical play always exists between moving elements, although it is true that in a ball screw used in industrial machinery, its typical value can be around 0.003mm (3 thousandths); and in less demanding systems a typical value could be around 0.05mm (5 hundredths). Going beyond these 5 hundredths will cause an acceleration of the mechanical wear that will reduce our system of movement to a noisy, uncomfortable and useless “bone shaker” for its purpose.
If the mechanical play exceeds these minimums, we will find that the moving parts will “peal” between them as if it were a hammer and, since the working cycles in the motion simulation systems are around 95%, this hammer effect will cause the mechanical play between these elements grows exponentially with the use, until they become several millimeters. That would be deadly for the engines that generate the movement because they will suffer a high level of stress that will damage all their mechanics and in the worst case, its lifespan will finish, not to speak of the bad feelings that will transmit to us.
Imagine for a moment that you are driving a SEAT 124 of the year ’78, without power steering and with a play in the steering wheel of several “centimeters” … would it really be very difficult to drive in a straight line? This is what happens when we have an excessive game in the couplings.
While the system receives information from the PC about the vibration of a kerb in the circuit, what it transmits to us is an erratic “rattling” due to the delay caused by the excess travel generated by the mechanical play. We will be inside a blender and we will not have the sensation of being over a kerb, and this will happen with all the effects that will generate the telemetry of the simulator used.
For this reason, the most important elements in a motion simulator are the joints between the moving parts. We must use systems that guarantee the smallest play possible, that is to say, integrate universal joints, ball-and-socket joints, bearings and linear or angular couplings of the best possible quality.
We must avoid couplings with NOT calibrated axes which, even if they use ball screws, when coupled to a simple screw axis, will have a point of weakness in the assembly through which, sooner or later, it will become deteriorated and our system will fail to transmit the expected sensations… in addition to the money we will have to spend on repair.
At Logykal we have taken special care in avoiding the excessive play in our movement systems: we use elbows and joints of industrial quality, so that we never have to worry about losing sensation. We will always get a simulation of the highest quality.
If our body does not receive the expected sensations, we will find ourselves facing drowsiness and sickness and we will not know why. But this will be the subject for another article.
See you soon.
Juan Fco. (Trilogy) Sánchez