Mini Satellite-Antenna Rotator Mk1 - SARCNET

Reference

• SARCNET Rotator Mk1

Hardware Mk1b

Hardware Assembly

• The hardest part of the build was precision-marking and drilling the motor mounting holes. We recommend sticking adhesive paper labels to the diecast box, scribing construction lines on them using a digital vernier caliper, center-punching and drilling pilot holes first. A drawing of the motor mounting holes can be found in the motor datasheet here. Check three times - drill once.

• Countersink the motor shaft holes on the inside of the rotator case and slip 5mm o-rings over the motor shaft before assembly for ingress protection.

• Add two flat washers to the AZ motor mounting bolts on the side near the lid to counter the chamfer in the rotator case.

• Install a cable gland on the bottom of the rotator case for the PC/Battery and Sensor cables.

• Install the Motor Drivers to the case using countersunk bolts and stand-offs.

• Install the Arduino Pro Micro against the case wall using two layers of double-sided tape on its flat side.

• Prepare an Extra Heavy Duty Speaker Tripod. Try Altronics C0520A. Remove the speaker bracket if fitted.

• Attach a 6mm shaft-hub to the top of the tripod using a 25mm irrigation-pipe threaded plug, 3mm cheese-head bolts, flat washers, spring washers and nuts. Fix with self-tapping screws to the tripod. Replace the grub screws on the shaft hub with cheese-head bolts or cap screws to obtain additional torque.

• Attach the rotator's AZ motor shaft to the tripod and tighten the hub screws.

• Round the sharp edges of a lift arm made from 500x30x30x3mm aluminium angle.

• Make a counterweight from a 101x51x25mm diecast aluminium box: Altronics H0451, Hammond 1590G or similar. Filled with lead to a total weight of 860g/1.9lb.

• Attach the counterweight to one end of the lift arm with self-tapping metal screws.

• Attach the Arrow antenna to the lift arm using Velcro. This is for quick release of the antenna and hand-held operation, if required.

• Attach a 6mm shaft-hub to the lift arm close to the balance point. Ours was 140mm from the antenna end. A slight front-heavy balance offset will reduce backlash.

• Attach the lift arm to the rotator's EL motor shaft using the 6mm shaft-hub and tighten the hub screws.

• Enclose the sensor in 12mm double-wall heatshrink tube and crimp the front end. Mount the flat side of the sensor against the boom with a velcro strap around the boom. See: Sensor Orientation for details. Keep the sensor away from the VHF/UHF driven elements to avoid RF interference to the sensor. Don't use high power for satellites. Use ferrites on the I2C lines if necessary.

Sensor Orientation

• This project is using a LSM303DLHC sensor to measure Magnetic Fields and Gravity to determine sensor orientation. The diagrams show their correct orientation for the LSM303DLHC sensor.

• The sensor is attached to the antenna boom and is aligned with the antenna reference axes (X, Y and Z shown in red above) as follows: With the antenna horizontal and pointing North, X points due East, Y points due North, along the antenna boresight, and Z points up.

• Please disregard any axes printed on the PCB.

• Because the flat side of the sensor board is attached on the top of the antenna boom, with the long side of the sensor board parallel to the boom, the sensor axes (X', Y' and Z', as sometimes printed on the PCB) are not the same as the antenna reference axes (X, Y and Z) as used in our software and our original article. Instead, X = -Y', Y = X' and Z = Z'. Also, the gravity field vector G is the opposite of the device acceleration vector A.

• Therefore the following transformations of the Magnetic (M) and Gravity (G) vectors are applied by our software:

• MX = -MY', MY = MX', MZ = MZ', GX = AY', GY = -AX', GZ = -AZ'.

Electrical Assembly (Mk1b)

• Important: Bridge Jumper J1 on the Arduino Pro Micro.

• Connect Pro Micro SDA, SCL, GND and VCC to the Sensor SDA, SCL, GND and VIN pins via a long flexible cable. We use flat telephone cable.

• Connect Pro Micro pins 5, 6, 9 and 10 to the Motor Driver terminals (IN1, IN2, IN3 and IN4 respectively).

• Connect Pro Micro pins 16 (+) and 14 (-) to a Piezo Buzzer to assist with calibration.

• Connect Pro Micro GND to the Motor Driver GND terminal.

• Connect Motor Driver OUT1, OUT2 to the AZ Motor and OUT3, OUT4 to the EL Motor (be prepared to reverse these during testing as the motor pins are not polarised).

• Connect Motor Driver 12V and GND terminals to your 12V supply via a cutoff switch and fuse (Caution: Don't connect until safe: The motors may move)

• Connect Pro Micro USB port to the PC USB port. To fit the cable through the gland, cut a standard micro USB cable in half and re-terminate it. This port powers both the Pro Micro and Motor Driver electronics.

Testing the Arduino Pro Micro stand-alone

• Install the Arduino IDE from https://www.arduino.cc/en/Main/Software. Note: Give the drivers ample time to install.

• Connect the Arduino Pro Micro via a micro USB cable to the PC USB port.

• Open the Arduino IDE

• Select File | Examples | 01.Basics | Blink

• Select Sketch | Verify/Compile (Ctrl+R). You should see "Compiling sketch..." followed by "Done compiling"

• Select Tools|Board: Arduino Leonardo

• Select Tools|Port: COMnn (Arduino Leonardo)

• If you don't see COMnn (Arduino Leonardo) you may have to determine the virtual serial port used by the controller:

• On Linux start a terminal window and type: dmesg | grep "USB ACM device" Make a note of the tty device.

• On Windows start device manager and look under "Ports" for "USB Serial Device" or "Arduino". Make a note of the "COM" number.

• Select Tools | Port and the COM port number you noted earlier.

• Select Sketch | Upload (Ctrl+U). You should see "Uploading...". The Arduino Pro Micro LEDs will flash 3 times. Then "Done uploading".

• This indicates that you can successfully compile and upload an Arduino file.

• Note: The Blink sketch does not blink the Pro Micro LED unless you add "#define LED_BUILTIN 17" to the start of the program and accept the compiler warning

• If you can't upload. May we suggest: Closing the IDE. Disconnecting and re-connecting the controller. Starting the IDE again and repeating steps 4 onwards.