SatNOGS Rotator Controller

SatNOGS Rotator Controller
SatNOGS Rotator Controller
Information
Type:	Rotator Controller for SatNOGS rotator.
Cost:	?
Release Information
Status:	Working
Latest Release:	[v2 v2]
Repository:	SatNOGS Rotator Controller
Documentation:	SatNOGS wiki

Intro

SatNOGS Rotator Controller refers to the set of electronics designed to operate a SatNOGS Rotator. There have been multiple iterations of the rotator controller design, but the modularity of the approach enables operations between different versions of the controller and the rotator. Since the start of 2016, the rotator controller design is able to facilitate a DC-motors or stepper-motors rotator design. We intend to keep this modularity for the electronics and firmware design to facilitate the variety of build by our community.

Rotator Controller v2

The PCB are tested in this ground station.

Features

It is designed to fit the entire electronics needed to control rotator in Euroboard 80x50 mm.
Main micro-controller is Arduino pro-mini dev-board with ATmega328p.
The modular design includes plug-in either DRV8825/A4988 or DC motor drivers (MC33926).
The power supply in embed in the same board in contrast with previous version.
Filter in power supply of micro controller.
It has an I2C multiplexer to connect I2C encoders AS5601 (same ID) to get position feedback for each axis.
A temperature sensor TC-74 monitoring the temperature inside the controller box in order to protect them from over-~~temperature~~heating.
More dev-pins to connect other peripherals like IMU, LCD display.
Pins with RC-Low Pass filter for end-stops.
Default communication interface is RS-485 (WIP) but it can be also be used as a UART.
Avoid connection with GNDD directly with motor GND use keep out area.
Electrolytic capacitor and TVS-diode in PSU input

Build sequence

Make sure you have a mechanical assembly of the rotator constructed and ready
Buy the PCB. OshPark(Board) or DirtyPCBs.com have been used in the past with good results.
Assemble the PCB, by soldering the components
Burn the firmware
Using the wiring diagram, connect the controller to the Rotator
You are ready! Proceed with testing

Micro controller

Microcontroller

Microcontroller Orientation

I2C pull-up resistors

Motor Specification

Maximum specification

rotation speed: ~1200(200RPM) deg/s (after 1.8*30 = 54 gear reduction ~20deg/s and we want 5deg/s according to v3 rotator specification
stall torque: 1.2Nm (after 1.8*30 = 54 gear reduction 64.5Nm)

Minimum specification

rotation speed: ~360(60RPM) deg/s (after 1.8*30 = 54 gear reduction ~6.5deg/s and we want 5deg/s according to v3 rotator specification
stall torque: 0.48Nm (after 1.8*30 = 54 gear reduction 25.92Nm)

You can design an adapter, to mount any motor to motor mount, like dc motor flange. This is the motor mount.

The DC motor that we use is 50:1 Metal Gearmotor 37Dx54L mm,

Size: 37D x 54L mm
Weight: 195 g
Shaft diameter: 6 mm
Free-run speed @ 12V: 200 rpm
Free-run current @ 12V: 300 mA
Stall current @ 12V: 5000 mA
Stall torque @ 12V: 1.2Nm

The stepper motor that we use is Nema 17 Bipolar 59Ncm,

Size: ▱42 x 48 mm
Weight: 390 g
Shaft diameter: 5 mm
Step Angle: 1.8 deg
Nominal speed @ 12V: 720deg/s
Rated Current/phase: 2.0A
Stall torque @ 12V: 0.59Nm

Motor Drivers

Stepper motor driver

Jumpers

Orientation

For the stepper motor driver 2 options are tested, DRV8825 and A4988. For both options it is necessary to solder:

2 electrolytic capacitors C3, C4 100uF
4 single 0.1" male connectors for U3, U4
2 fixed terminal blocks, Phoenix 1985467
6 jumpers to adjust the micro-step, default option is Full Step
Not solder 2 resistors 100k, R4, R7

Be careful:

adjust the current (current limiting) for stepper motors
add a heat-sink.
plug the stepper motor drivers

JP3/JP6	JP2/JP5	JP1/JP4	Microstep Resolution
Low	Low	Low	Full step
High	Low	Low	Half step
Low	High	Low	1/4 step
High	High	Low	1/8 step
Low	Low	High	1/16 step
High	Low	High	1/32 step
Low	High	High	1/32 step
High	High	High	1/32 step

DC motor driver

The DC motor controller is Dual MC33926 Motor Driver Carrier

Motor driver: MC33926
Motor channels: 2
Minimum operating voltage: 5V
Maximum operating voltage: 28V
Operating voltage: 12V
Continuous output current per channel: 2.5A
Current sense: 0.525 V/A
Maximum PWM frequency: 20 kHz
Operating PWM frequency: 3921.5Hz (~4kHz)
Minimum logic voltage: 2.5V
Operating logic voltage: 5V
Maximum logic voltage: 5.5V

Communication

UART

UART Jumpers

Pin Header

To use UART:

solder JP7 and JP8
solder pin header 0.1" female connector
not solder C1, U2, R18, R9, R8, R1, D3
A is TX and B is RX

RS-485

WIP

Power Supply

Recommended power supply for rotator controller is: 48V @ 1A DC. A good choice is MEAN WELL LRS-50-48

The switching power supply could get as input voltage, 19-60V DC. In different input voltages, must be change the components like D4 and F1.

Endstops

Mechanical Endstops

Endstop

Encoders

For stepper motor setup is optional (AS5601 encoder).

WIP

Wiring

Temporary wiring

Rotator Controller enclosure - Placement

WIP

Firmware and Pin Assignments

Firmware

More info in gitlab repository For DC motors

Pins Configuration

M1IN1 6, Step or PWM1
M1IN2 5, Direction or PWM2
M1SF 7, Status flag
M1FB A1, Load measurment

M2IN1 11, Step or PWM1
M2IN2 3, Direction or PWM2
M2SF 10, Status flag
M2FB A0, Load measurment

MOTOR_EN 8, Enable/Disable motors

SW1 9, Endstop for axis 1
SW2 4, Endstop for axis 2

RS485_DIR 2, RS485 Half Duplex direction pin

SDA_PIN 3, Data I2C pin
SCL_PIN 4, Clock I2C pin

PIN12 12, Digital output pin
PIN13 13, Digital output pin
A2 A2, Analog input pin
A3 A3, Analog input pin

Pre-Flight Check

Need to add testing procedure here.

How do you align the rotator?