![]() ![]() After a short pause the car accelerates again (around 2400, or about 48 seconds later). The same data from the accelerometer, inverted to show correct polarity, and with only the Y (up/down) data shown since the other two are irrelevant in this case.Īfter loading into the ride vehicle, the car ascends at around sample 1200 (the first bump on the graph) – the ride car accelerates upwards, then decelerates to a stop. ![]() The graph is actually inverted so that a negative value for acceleration represents a upward force (obvious from the fact that when the car is not moving, the nominal g-force value is around -345 … it would be expected that this would be a positive value). As expected, the X and Z axis hover around zero while the Y axis (in violet here) shows the up/down acceleration of the ride vehicle. The horizontal axis of the graph represents sample number (at 25 samples per second), while the vertical axis represents acceleration as a signed number from the chip. You’ll notice as well that all three columns show a noise figure in which the signal varies randomly even with the device sitting still – some of this noise is generated by the shaking of the ride vehicle and some is electrical in nature.ĭata from the Twilight Zone Tower of Terror ride, graphed. The third column shows an acceleration of approximately -560 or -1.6g but since the unit is actually inverted, the real force is +1.6g (the upwards force of the elevator on the passengers as it rises rapidly. There is a small offset error from the device itself which could have been eliminated by using the self-calibration feature of the ADXL chip (but was not used in this case so small errors must be corrected during analysis). Inversion of the axis (so that, for example, it reads “+1g” when stationary and not “-1g”) is accomplished in the spreadsheet quite easily. There are not many flat surfaces in a ride to mount this device (nor time to look around) so the device was attached to the first steel post found. ![]() In this example, the unit was oriented such that the Y axis is in the vertical (up/down) direction and so the X (column two) and Z (column four) readings hover around zero as expected. The actual force is in the forward direction and is, in fact, the force of the vehicle pushing on the passenger. Regardless of definition, acceleration is often measured in units of “g’s” with one “g” defined as an acceleration of 9.8 m/s 2.Ī similar situation exists in an accelerating vehicle in which the user feels pushed back into the seat. So, we often speak of gravity as a “force” but it is really an acceleration – what we feel as gravity is the force that the earth exerts upwards to keep object from entering a free-fall. The scale upon which Mickey is standing would read zero and an accelerometer in the elevator would read also zero. Since nothing pushes upwards on the observer (here, Mickey) feels weightless. Now, in a free-fall gravity acts on a mass to accelerate it towards the earth. A stationary accelerometer will hence read “+1g”. While Mickey might “feel” the “pull” of gravity, the real force is exerted upwards by the elevator. Consider Mickey in an elevator (as depicted on the left). #The tower of terror freeWe often say that an accelerometer measures “g-force” but this is actually not a force at all – rather what is felt is the force of the earth pushing upwards on the observer preventing them from entering a free fall. An accelerometer measures “proper acceleration”, which is the physical acceleration an object experiences resulting from either motion or from gravity. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |