Historic

The inertial position indicator has been conceived in year '99 for updating the old elevators (french market, small residential buildings 4 to 6 floors) without any facilities for connection of regular position indicator and also in response to a defiance. If we are able to know the position of an jet fighter moving at hight speed in a large 3D space just by computation of data from his navigation inertial system and his take-off point, we are certainly able to find the car elevator position inside a 20 meters 1D trajectory at 80 cm/s ! (also an application in maintenance for localisation of zones of vibrations and theirs magnitudes has been anticipated)
This apparatus has no more utility today but it can be interesting for the hobbyist to think about the possibilities of a component like the integrated accelerometer in single axis or double axes now very affordable.

An accelerometer ADXL105 from Analog Devices is interfaced with Microchip's PIC16C715 clocked at 8 MHz, a set of coded rotary switches preseted at the building data values, a main 7 segments for to display the floor level, two small 7 segments displays for service purpose, giving :

The car position is computed from acceleration data, time and building charateristics programmed on coded switches, after that the only thing to do for complete the installation is to fix the box on the elevator wall and connect an ac/dc adaptor to permanent line source on the top of the car.
The major difficulties are the identification of real events and the management of conditions leading the lost of synchronisation between the actual car position and the value displayed for to resynchronize both quickly. The entire space memory is utilized.

The purpose of this very imperfect assembling is to show the comportment of gyro trapped in a single or double axes gimbals, more precisely the precession phenomena. Don't throw away your old discontinued hard discs, there is a lot of obsolete h.d. but with very fine and accurate mechanic inside, specialy the spindle motor, the ball bearings used in mobile head assembly, the molded frame, the screws ! This modest setup is built from few old Western Digital Caviar 2100, 22500 (1Go to 2.5 Go). This last allows to stack 7 plates on each spindle, as you can see on the picture, the whole gyro is made by the assembly of two units head to head.
Hard disc plates are not very efficient as gyro drum but sufficient for this demo.

The double gimbals is mainly made from aluminium 3/4" (16 mm) U and 1/2"x3/4" (13x19 mm) L, ball bearing (molded in mobile head assy), screws are recovered from several hard discs, all this stuff can be used for make the gimbals assembly.The ball bearings are interesting because the center is a threaded hole in one side and threaded stud on the other side, this configuration allows to feed the 12V power to the h.d. through the centers of rotation of the gimbals. Brass screws (4-40) in ball bearing fill the function of sliding contact perfectly centered (but the number of rotation in the same direction is limited). On each h.d. printed circuit board a 5V regulator is added, reducing at 2 the number of feeding wires.

The continous rotation of spindle motor is done simply on this experiment by the insertion of a relay in the 12V power source (contacts NClose), the relays coil is connected to a function generator set in square mode, frequency approximately between 1/20Hz and 1/30Hz, this setup creates a short pulse just enough to reinitialize periodically the processor in is starting programme keeping the three phases generation running. Ok this is not very bright but it's only for demo purpose.

For to get correct results the following criteria must be kept in view :

• the gimbals axes and the gyro spinning axis must intersect in the center of gravity and this is not easy,


• mechanically the gimbals geometry must be clean as we can in any direction (right angles equal to 90°), this also is not easy without the help from a machine shop but as mentioned at the beginning the purpose of this setup is not to find the North...


• gyro not powered: any movement around the two gimbals axes must be free, without hard point, the gyro must be motionless whatever his orientation (as best we can...). This setup as described gives a real and positive demo of precession, visible and "perceptible" by several people simultaneously.

A set of pins and sockets contacts connected to pcb tracks feeding the spindle allows the phases inversion, selecting the rotation direction of both gyroscopes (one side inverted for to get precession), also, a mechanical lock located on the gimbals allows to immobilise the gyro in the first gimbals axe and so on cancel the precession.

Both h.d. form together one gyroscope, this mobile assembly around his axis (here horizontal) is inserted inside frame witch have is axis, here, vertical. If the counterpoising is correct, gyro and gimbals are stable on theirs axes independently of main frame sitting

One can see the counterweight mounted on aluminium angle fixed on hard disc, same thing on the other disc.
Two EMI ferrites for flat cable are used as counterweight, few 1/2'' round ceramic magnets are used on each side for to achieve fine counterbalancing.

The 2 ball bearings supporting the gyroscope in the first frame are mounted on 2 pieces of copper clads enclosed in each side by 1/2"x3/4" (13x19 mm) L. This allows the gyro to be balanced around this first freedom axis.

We can see a brass screw feeding the mobile frame through the ball bearing axis itself insulated from the ground by plastic sheet.
This sliding contact gimmicks used for demo can be easily improved.

This experiment applies the physical behaviour of gyroscopes as done from long time in marine equipment. The peoples not involved in those fields, have low chance to meet those technologies. Several internet sites around the words "gyroscope", "gyrocompas", "gyrocompass" are good sources for to know more about theorical and practical aspects of those technologies.
This experiment is based on the two fondamentals gyroscopes properties: rigidity and precession, combined to the gravity and the earth's rotation.
Suspended as a pendulum, the gyro's rim in cw rotation (view of the South side) on his horizontal axis oriented W-E, so at right angle of the meridian, free to rotate around his vertical axis and to draw a cone of revolution (6° max) limited by the inner diameter of primary coil rotary transformer, the gyro's rigidity in space combined with the planet rotation in W-E direction bring the gravity force outside the pendulum axis in the East direction, this creates a torque on horizontal axis at right angle of the plane of rotation, thus starting the precession of the gyro to the West, passing the neutral zone of meridian this torque will be first decreased then reversed (balance of potential energy stored in pendulum), the neutral zone is a "minimum", in other words a zone of stability... at the equator, but at latitude 45°? Supposing the [weakly] damped oscillation completed, the gyro now rigids in space and without disturbance seems to drift to Est, due to earth's rotation and the angle formed by the intersection of gyro's N-S axis (horizontal) and earth's rotation axis. Plenty of astuteness is necessary for to fixe this problem and many others for to install this gyroscope inside a ship moving at variable speed, in bad sea, at any bearing, northern or southern latitudes and a demand for ± 0.5° max. error from the true North.