# Rotator The rotator is an AlfaSpid BIG RAS. The datasheet is located here: http://alfaradio.ca:81/downloads/Rotators_Controllers/Manuals/Rotators/AlfaSpid_RAS_15SEP2022%20.pdf The rotator is supported by a galvanized steel rod it is bolted to. Rotation of the unit about this axis is azimuthal rotation. A fiberglass grounding rod is bolted into the rotator at a right angle to the support rod. Rotation of the grounding rod about this axis is elevational rotation. The antenna is attached to the grounding rod at a right angle, causing this rotation to adjust the elevation of the antenna. The YouTube video at [_this hyperlink_](https://www.youtube.com/watch?v=4z9RnTd4_vw) from Bob Darlington demonstrates the action of the rotator. The rotator comprises two DC motors which power rotation about the azimuth and elevation axes. Each DC motor turns a worm which drives a gear in a worm drive mechanism. The gear then actually moves the rotator and antenna. ## Important Information from Datasheet The datasheet tells how the wires are meant to be connected. ``` Pin 1 -- Gray -- Motor Drive Pin 2 -- Black -- Motor Drive Pin 3 -- Brown -- Impulse Sense Pin 4 -- Yellow-Green -- Impulse Sense ``` It also describes a troubleshooting procedure including expected ohmmeter measurements between the four wires. It says there should be 2-4 ohms between the motor drive terminals and 600-1200 ohms or an open circuit between the impulse sense wires depending on the motor position. Looking at rotator with the wiring housing facing you, the Azimuth terminals are on the left. The elevation terminals are on the left. ## Our Own Deductions We measure either 150-200 ohms or open circuit on the motor drive pins, seemingly randomly from day to day. It probably has to do with the alignment of the planets. Neither of these are what the datasheet says we should expect. Nonetheless, we found that when we apply 12V (10A max) directly from a PSU between the motor drive terminals for azimuth, the rotator moves as expected. And the same for elevation. So we assume this is not a problem. The rotator uses a worm drive to avoid needing brakes and provide high torque. In addition to the two four-wire bundles coming into the wiring box, there is another two-wire bundle that comes in with a blue wire and a black wire. ### Elevation Limit Switches There are limit switches in the housing around the elevation shaft that are connected to the blue and brown wires coming into the wiring area. The circuit looks like this: ``` Blue Wire -------- SW1 ---- SW2 --------- Brown Wire \ / \ / -- D1 -- -- D2 -- ``` The total range of motion of the elevation axis is 180 degrees. At one positional limit, SW1 is depressed and D1 is put in the circuit pointing from Blue to Brown. At the other positional limit, SW2 is depressed and D2 is put in the circuit from Brown to Blue. When the blue wire is soldered to the black motor drive wire, this causes the motor drive current to be blocked when the rotator reaches a positional limit. When the position limit in one direction is reached, a diode is placed in the circuit in reverse bias, blocking current. Now current can only be applied in the reverse direction, moving the motor away from the position limit. The circuit works in both directions. ### "Impulse Sense Mechanism" The "impulse sense mechanism" is poorly named. There is no current or voltage impulse produced on the impulse sense lines. Instead, a resistor is periodically connected and disconnected between the lines as the motor moves. The mechanism is variously called the reed switch, reed sense, and sometimes misspelled as "read switch" on the datasheet. It is technically an incremental encoder. To clarify that point that a resistor is periodically connected and disconnected, consider this example: Say that the electrical connection between the azimuth impulse sense pins initially looks like an open circuit. As the motor rotates, the connection will change so it looks like a resistor. Then again like an open circuit, then a resistor. The actual impulse sense mechanisms are contained, along the with the worm drives, beneath the circular plastic caps on either side of the rotator secured with five screws. The driver is meant to read the "impulse" by applying a voltage on the impulse sense line and measuring how much current is drawn. ## Other Notes As we took the rotator apart, one of the screws holding the case around the elevation shaft broke. We lost another. # (Broken) MD-02 Driver The driver has two simple jobs: - Apply a voltage on the motor driver lines to move the motor according the the user's commands - Count "impulses" on the impulse sense lines to keep track of the relative position of the motor The driver does not seem to be capably of applying the drive voltage, although the position tracking mechanism via pulse counting seems to be working. The datasheet is here: https://www.wimo.com/media/akeneo_connector/media_files/2/5/25089.MD02_Manual_MD_02_EN_11b7.pdf ## Operation Basically, you use the arrows on the front of the unit to command changes in azimuth and elevation. So we would expect that when you press the right arrow, adjusting the azimuth, you observe that a voltage is applied on the motor drive pins and the unit begins counting "impulses" on the impulse sense lines and adjusting the displayed position accordingly. ## Wiring ### Power 1 ``` 3 - 15V (3A max) 2 - GND ``` ### Power 2 ``` 1 - 12V (10A max) 2 - GND ``` ### Azimuth ``` 1 - Oscilloscope probe + 2 - Oscilloscope probe - ``` ## Configuration ### MOTOR CONFIGURATION ``` TEMPLATE: 1:AZ, 2:NC SHOW AZIMUTH: NORMAL SHORT WAY: OFF START: IMMEDIATELY STOP: IMMEDIATELY MOUSE CONTROL: OFF CONTROL A1: NONE PROT. A1: NONE DISP. RESOL.: 0.05 ``` ### SET MOTOR 1 ``` STATE: ON TYPE: DIGITAL KIND: AZIMUTH INPUT: ELECTRONIC GEAR: 0.023438 MIN ANGLE: -180.0 MAX ANGLE: 540.0 MAX POWER: 100% MIN POWER: 100% PULSE TIMEOUT: 6s REVERSE ENCODER: OFF REVERSE MOTOR: OFF ``` ## Voltage Measurements When we press the right arrow to adjust azimuth, we observe on the probes a choppy sine wave with amplitude 400 mV and period 20 ms. We are expecing 12 volts DC. That's not right! ## Successful Position Tracking Test If with our hands we rapidly connect and disconnect the impulse sense line to the ground line via a resistor, while holding the azimuth adjust button, we see the displayed position increase or decrease depending on whether the left or right button is being held. So this system is actually working! ## Other notes The datasheet for the MD-02 says pin 4 should be connected to ground, while the rotator datasheet says it should not be connected to ground. Since the "signal" is just a resistor being connected and disconnected, we concluded that this discrepancy does not matter. # Conclusion Unless some hail mary troubleshooting succeeds, Jack is going to e-mail the dean requesting that the MD-02 be returned for a refund. At which point we can purchase an Rt-21 Az/El from Green Heron Engineering. Hopefully his product (it's just a dude named Jeff) is better than the SPID MD-02 control box. He seems to provide good support and he answers the phone during US business hours, unlike the German WiMo who sold us the MD-02.