Rotation Controller Installation

Controller Board

The controller card is shown below. Note that the Rotation Controller and the Shutter Controller boards are identical; a DIP switch is used to configure each board to rotation mode or shutter mode.

Dome Controller Circuit Card

The card should be mounted in a protected enclosure. For Sirius Observatories, it will slide into the slot intended for the original (non-automated) motor relay card. For other types of installations, you can use the four mounting holes, or if mounting on a non-conductive surface you can use stick-on Velcro buttons underneath the board. (Note: Velcro may not stick reliably if applied at low temperatures. Just use a small button of Velcro in each corner; otherwise you may need to apply a lot of force to remove the card, and you will run the risk of damaging it.)

WARNING: Use the supplied #4-40 screws, or other #4 or smaller hardware, when attaching the board. Do not force in screws that have threads larger than the hole. Using larger screws will damage the board and invalidate your warranty. Use appropriate spacers or standoffs to make sure the board electrical contacts do not touch metal.

WARNING: It is strongly recommended that a 10 amp in-line fuse be used for the battery connections, to prevent damage in the event that the wires are shorted or connected incorrectly.  A shorted battery can be a fire hazard.

Important: The card must be installed in a suitable box or otherwise protected against direct contact with moisture. Moisture accumulating on the card can corrode the electrical circuits and cause the board to fail. Damaged caused by improper installation is not covered by the warranty.

DIP Switch

The DIP switch is located just above the relays. Use the tip of a small precision screwdriver to set the switch positions. As shown in the picture below, OFF is to the LEFT, and ON is to the RIGHT.

The DIP switch must be set as follows:

Switch 1 (SHUTTER) must be set OFF for rotation controller operation.

Switch 2 (2 SHUTT) is not used for the rotation controller.

Switch 3 (AUTO CLS) is not used for the rotation controller.

Switch 4 (FACTORY) must be set OFF. It is only used when uploading new firmware and during factory test procedures.

Optical Rotation Sensor

The optical sensor detects the rotation of the dome by detecting white and black strips. A common way to do this is to paint the motor shaft half black and half white, as shown below. Sirius Observatories drive motors have shafts painted in this fashion.

If you need to do this yourself, the best approach is to use white and black spray paint. Apply the paint in two stages; first paint the whole shaft white and allow to dry.  Next apply masking tape to define the black area, and apply black spray paint. For both colors use two coats to ensure good coverage. Note: generally speaking black spray paint absorbs infrared light very well, but many other "black" coatings and materials (including most anodizing treatments) are actually highly reflective in the IR and as a result will not work. You can check the suitability of various materials by pointing the sensor at them and watching the ROT light.

Sensor Target

The sensor must be positioned viewing this target from the side, as shown below. The sensor must be mounted in a position where it can view the target, yet will not obstruct any of the mechanical components.

The next picture shows how the sensor board is positioned. You want the head of the sensor to be approximately 3/8” from the shaft. The sensor has to be at the correct distance or it will not reliably detect shaft rotation. Once you have determined the correct spacing, drill two holes in the plate for the mounting screws. For Sirius Observatories we strongly recommend that you mount the sensor to the metal plate on the gearbox, rather than the fibreglass case. That way the sensor moves with the motor and keeps a fixed distance from the shaft.

Tip: you can check whether the distance is correct using the ROT light on the Rotation Controller board. Once you connect the power to the shutter board, the light will illuminate whenever the reflective part of the shaft is facing the sensor.

Sensor Position

The sensor board is mounted upside-down; that is, with the connector and sensor underneath the board, facing the motor.  This is necessary to position the sensor at the correct height. Fasten it in place with two 1-1/4" 4-40 screws (it is best to use two screws to ensure that the sensor does not rotate).  Be very careful not to bridge any contact points on the circuit board. It is best to one screw hole in the center of the sensor, and one screw hole in the corner of the board (the second screw prevents the board from rotating if the cable is tugged).

Sensor Mounting Screw (1 of 2)

Although this is not recommended, some users prefer to mount the sensor module using Velcro, which is quick and allows easy adjustment of the sensor (to avoid any risk of injury due to unexpected motor operation, it is essential to disconnect the MaxDome II power supply before attempting to adjust the sensor). Make sure that all surfaces are clean and apply under "room temperature" conditions to ensure good adhesion. Be careful to tie off the cable so it cannot disturb the sensor position.

Once the sensor is mounted, connect the supplied cable to the phone jack, and route the cable over to the controller board.  Be careful to avoid pinch points that might damage the wiring during dome operation.

An alternative method is to paint white and black strips around the diameter of the dome, using masking tape and spray paint. The sensor will have to be mounted so that it maintains a constant distance from the dome; this may require a spring loaded idler wheel. It is recommended that the strips be painted so that there is a transition (from white to black or black to white) once every second as the dome is rotating. This provides a suitable signal for the Rotation Controller to process. Slower is okay, but it is not recommended to go much faster.

There are many other possibilities for sensor mounting; for unusual installations please consult the factory for recommendations.

Motors

MaxDome is designed to operate 12V DC motors. The maximum continuous current capacity for inductive loads is 5A.

It is possible to connect other types of motors, such as AC motors, using external relays. Please observe all electrical code regulations when installing AC powered motor drives.

The MaxDome II system does not provide motor ramping. We recommend using a modest rotation speed with the system, to avoid the need for ramping and to also ensure safe, reliable operation.

If motor ramping is necessary due to an extremely heavy dome, third party motor control modules can be added.

If necessary, the system will tolerate a couple of seconds of "run-on" past the completion of a slew. If it continues for longer than that, the sensor "tics" will not be recorded and the dome position will be lost. Any minor run-on should be corrected on the next sidereal position update (e,g. the ASCOM Dome Control Panel issues these updates every 10 seconds).

Wiring

Referring back to the first picture above, you can see the terminal blocks (green), the rotation sensor jack, and the RS-232 serial port jack. The serial port jack should be connected to the PC COM port using the supplied cable. The motor sensor should be plugged into the sensor jack.

There are two green terminal blocks. Note that the terminal blocks can be unplugged from the board by gently pulling them out vertically.

The terminal blocks have the following connections, as shown from left to right in the picture above:

Large Terminal Block

Small Terminal Block

These connections are shown schematically below. Each connection will also be described in more detail.

Power Supply Wiring

The controller card nominally requires +12VDC for operation, but will operate between 8V and 14V. Both the charger and battery inputs have built-in 10 Amp fuses, which automatically reset once the overload is removed.

When idle, the board draws about 1 mA. When transmitting a magnetic induction message, it briefly draws about 10 mA. When the dome is rotating, the current draw is determined by the motor used.

The battery drain from the controller is minimal, so the battery should be sized to provide sufficient power for the motor during expected operation. A standard 12V, 6  or 12 Amp-hour gell cell battery is usually sufficient. Using a battery supply also ensures that the large inrush currents generated when the motor starts up will not cause the power supply to droop.

If a solar charger is used, it should be sized to fully recharge the battery during a single sunny day (30W is usually sufficient). Please note that high latitudes it may be necessary to use a larger solar cell. If AC power is available, a trickle charger will keep the battery topped up at all times.

If you do not wish to use a battery, connect the power supply directly to the BATT terminal. Note that the power supply will need enough capacity to handle the large inrush currents when the motor is activated. If the voltage droops too low during startup the microprocessor will reset and the dome will stop.

Magnetic Induction "Antenna"

If the shutter controller is also being installed, then you will need to connect the magnetic induction "antenna". This is simply a loop of wire that runs all the way around the observatory, and connects back to the controller. The wire generates a very low frequency (8 kHz) pulsating magnetic field, which induces a small voltage in the other controller's wire. The pulsations encode low bit-rate digital data, which is transferred back and forth every two seconds.

Note that only one wire needs to run the full diameter of the dome. Usually the base wire runs the full diameter, to ensure good communications in all dome positions. The upper wire usually only needs to extend about 3-4 feet to provide a reliable link. If this arrangement of the wire is used, return path of the wire must be kept at least one foot away from the other side of the loop, as shown in the diagram.

Magnetic Home Sensor Wiring

The Home Position sensor is a simple magnetic reed switch, commonly used in home burglar alarms. The switch is open when the magnet is not present, and closed when it is present ("Normally Closed" style).

The sensor should be wired between the HOME and GND terminals.

The magnet and sensor must be placed adjacent to each other, such that the magnet rotates with the dome, and the sensor remains stationary. The switch will close only when the dome is in a position where the magnet is directly adjacent to the sensor. This allows the Dome Controller to reposition the dome to a known position prior to operation, so that it knows the starting azimuth of the dome. From there it counts the position using the Optical Sensor.

The magnet is usually attached directly to the inside surface of the dome itself, and the sensor attached to the base where it will be close to the magnet at a particular dome position. For Sirius Observatories, the sensor is usually attached to the black wheel track cover, close to the dome itself. Be sure to position the wires so they will not touch any moving parts.

The azimuth of the dome at the Home position is not important, since this can be adjusted for in software. However, it may be useful to position the dome at an easily identifiable position, such as 180 degrees. This will make it easier to determine the correct number to enter. Also it is best to position the sensor in a position where it will be detected often during normal operation; for example, in the Northern Hemisphere, locating the Home position due South will cause it to be detected more often than locating it due North.

Motor Control Wiring

The MOT1+ and MOT1- wires connect to the rotation motor. The motor receives 12V DC, with the polarity determining the direction of rotation. Note that the +/- designation is arbitrary; if the motor rotates backwards, reverse the wires.

To test it, apply power and start the motor moving using the manual hand paddle. The dome should move right, as seen from inside, when the Right input terminal is connected to ground. If the motor rotates in the wrong direction, simply reverse the two motor wires.

As you rotate the dome, make sure the ROT light flashes on and off at a steady rate. If it does not, check the optical sensor. If the optical sensor does not operate properly, you will not be able to rotate the dome from the PC. You may need to adjust the spacing of the optical sensor for the best results.

When the dome is near the Home position, the HOME light should come on.  If not, check the home sensor wiring and the relative position of the magnet and sensor.

Auxiliary Inputs

The shutter may be commanded to close by an external device, by pulling either the AUX 1 or AUX 2 input to ground (GND pin). This is commonly connected to a Boltwood Cloud Sensor or some other type of rain or weather sensor. Before using the AUX inputs, you must install and test the Shutter Controller.

The AUX inputs should be left unconnected if they are not being used.

If the MaxDome system is configured to "Park Dome Before Operating Shutter" (configured in the PC driver setup), then it will also park the dome when an AUX input is detected, prior to closing the shutter. A couple of caveats: if rotation commands are received after the shutter is closed, then the dome will rotate out of Park to the commanded position. Also, because this configuration setting is made at the PC, it will not be remembered if the Rotation Controller loses all power. To restore the setting, you must reconnect connect the link to the PC.