THIRD PHASE, AUTOMATION OF THE DOORS
The automation of the rotation of the dome in such a way that it is a slave of the movement of the telescope is a great way to operate an observatory, it allows to program series of photographic shots without limit of duration and unconcerned because the opening of the dome is always in front of where I'm pointing the telescope.
A mechanically more complicated objective is the automation of the doors, the main one that slides, and the secondary or lower one that finish closing the dome in the lower part.
The slip was solved by means of a torque motor of 5 Nm and 7.2 rpm, to which two pieces of aluminum were attached, in which two cables are wound, so that when the motor turns in one direction, a cable pulls one end coiling and the other unrolling and when it rotates in the opposite direction, the process is the other way around. In this way, the motor opens or closes the upper door according to the direction of rotation. A limit switch establishes the end of the movement both in the opening and in the closing. After several tests, the best performance was with string instead of with steel wire, since the weight of the door is very light and the flexibility of the rope operated better.
The motor is fixed in the upper part of the dome and the strings are wound on the two pulley wheels each in the opposite direction of the other, so that when one is wound the other is unwound. The strings go through holes to the outside of the dome, one to be fixed on the front of the door and the other on the back. The effect is that the rotation of the motor pulls the string attached to the end of the door releasing the other string, and in opposite rotation pulls the other end, also releasing the other string. The entrance and exit holes of the string are under the door when the dome is closed so they do not cause water leaks.
To maintain the tension of the ropes and at the same time avoid sudden movement in the engine starts, the fixings of the ropes to the front and rear of the door are done with tension springs.
The lower door opens and closes with a linear actuator. Since it is very light, only the actuator has been placed on one of the sides. The door has been designed in two modules to reduce its length once opened, since I have space limitations with the distance of the dome to a terrace wall.
The automation is carried out with a second MaxDome II board, which is connected to a battery to be powered and a solar panel that recharges the battery.
The communication between the MaxDome II board of the rotation (installed in the fixed part of the dome) and the MaxDome II board responsible for the doors and installed in the mobile part of the dome is done by radiofrequency. Each plate has a ring-shaped antenna of the same diameter as the dome, so that the antenna of the mobile part rotates with respect to the fixed antenna, maintaining a separation of about 10 cm between them in any position. The MaxDome II board of the fixed part is the one that is connected by RS232 to the control computer, and from this plate the opening and closing orders are sent to the mobile plate by radiofrequency. The set is very stable and works perfectly.
When the dome is closed and in park position, which coincides with home position, the photovoltaic panel of 273x481cm is oriented to the south. The panel has dimensions lower than those recommended by the manufacturer of MaxDome II but in practice the system works without autonomy problems, even in winter. The panel recharges the battery that is exclusively responsible for the opening and closing of the doors, since the turn is controlled by a motor in the fixed part of the dome and powered by a 12VDC source.