¶ Main Board Options
The OAT supports multiple boards and platforms as the MCU.
Currently the following is supported:
- MKS Gen L (Recommended)
- RAMPS
- ESP32 Dev Board (Not recommended, as it does not support all features due to limited pins available)
¶ Steppers Motors
NEMA steppers, use a significant amount of power, enough to potentially destroy your hardware. This is why you need to double check that you have wired them correctly before first powering them up.
You must NEVER disconnect the steppers or drivers while the OAT is powered on! This will likely destroy your drivers. Likewise you have to make sure that the stepper connections are secure and do not disconnect by themselves during operation.
You should always power up the OAT, then connect the USB.
¶ Motor Types
The OAT uses bi-polar stepper motors. Refer to the OAT Firmware Configurator for the available stepper types for each axis.
- NEMA 17 motors (recommended)
- Modified 28BYJ steppers
¶ Modified 28BYJ Steppers
To modify a 28BYJ stepper to be bi-polar, a guide can be found here. The 5-pin JST terminal must also be replaced with a 4-pin JST or 4-pin dupont to connect to the OAT control board. Like this:
¶ RA Motor
The RA motor/driver connects to the X-axis position on your board.
¶ DEC Motor
The DEC motor/driver connects to the Y-axis position on your board.
¶ Alt/Az Motors (AutoPA addon for OAT / Built-in for OAM)
The Az motor/driver connects to the Z-axis position on your board.
The Alt motor/driver connects to the E0 position on your board.
¶ Focuser Motor (Addon)
The focuser motor/driver connects to the E1 position on your board.
¶ Stepper Control Wiring
Refer to the appropriate board pages linked above for control wiring instructions for each stepper type. For custom boards using the ESP32 look at the boards/ESP32_ESP32DEV folder for the pins file which you can either follow or customize.
¶ Stepper wires
The pins or wires on the NEMA are usually arranged COIL 1 - COIL 1 - COIL 2 - COIL 2 but can also be COIL 1 - COIL 2 - COIL 1 - COIL 2. You should check the layout before making any cables to connect the steppers. If you find that your steppers just vibrate or twitch, this is a likely cause of the problem.
Sometimes, NEMAs don't get shipped with connectors, so you’ll have to do that yourself. You can either solder or crimp. The best method is to solder or crimp a 4 pin JST connector to the wires, but Duponts are ok too. They just don't hold as well.
The order in which to connect the wires is as following:
BLACK - GREEN - RED - BLUE
The order isn't important, if you do blue red green black the motor will simply have its direction reversed. If you wired everything up and find your stepper turning in the wrong direction, simply reverse it in the code with: INVERT_RA_DIR or INVERT_DEC_DIR
If your stepper has other colors, take a look at its datasheet. It’s usually sent with the stepper or you can find it online. You’ll have to align the wires as following:
COIL 1 - COIL 1 - COIL 2 - COIL 2
Coils are sometimes also referred to as COIL A and COIL B. It doesn't matter if you switch the wires within the Coils, so within COIL 1 or COIL 2, but you should never put a wire from COIL 2 together with a wire from COIL 1. E.g. Coil1 - Coil2 - Coil1 - Coil2. Do not do this!
¶ Power Supply
The OAT is powered via a DC power supply:
| Board | Voltage |
|---|---|
| RAMPS | 12 V |
| MKS | 12-24 V |
If supplying power from a USB battery bank, a 5V-to-12V boost converter can be used.
Alternatively, if the USB battery bank supports USB-C PD (Power Delivery), a USB-C PD receiver module can be used to directly provide up to 20V of power over USB-C.
Do not plug/unplug drivers or steppers while the board is energized. Disconnect power prior to connecting any motors during setup. Failure to do so may fry the board.
¶ Display (Optional)
We currently support two types of displays:
¶ LCD Display Shield with integrated buttons
This is a 16x2 character LCD display with 5 buttons.
For how to wire the LCD, see here.
The LCD menus are documented here.
Advanced users only: Some I2C displays are compatible (see code for details).
¶ Informational Displays
Currently we support a I2C 128x64 pixel display based on the SSD1306 chipset. See here for details.
¶ Troubleshooting
¶ Stepper just vibrating but not moving
Check your STEP wire. Also test your UART connection as described below.
Check the sequence of the wires from the breakout board to the stepper. The default shown in these diagrams is Coil1 Coil1 Coil2 Coil2 but can be Coil1 Coil2 Coil1 Coil2.
¶ Testing UART Connections
Ensure your configuration specifies that your motors use a UART driver type:
DRIVER_TYPE_TMC2209_UART
If you change any microstepping and you have adjusted the RA or DEC steps at any point, you need to run the EEPROM_clear sketch in File > Examples > EEPROM! You can also do this in OATControl by going to Settings -> Factory Reset.
¶ There are two methods of verifying UART connectivity depending on your hardware:
The difference is whether only a TX wire is connected, or both TX and RX.
¶ By default:
- The MKS Gen L v2.0 and v2.1 have both TX and RX connected, provided the UART jumpers have been installed. Make sure that at the V2.1 board a jumper is set at "Drive IC Power 5V".
- A RAMPS shield and the MKS Gen L v1.0 do not have any integrated UART wiring.
¶ To test:
- If you have both UART TX and RX connected:
- Add
#define UART_CONNECTION_TEST_TXRX 1to yourConfiguration_local.hppfile to enable testing TX/RX functionality. If a stable UART connection is not detected (no reply from the driver), the motors will automatically be disabled.- Note: this option is enabled by default for the MKS Gen L v2.0 and v2.1.
- Add
- If you only connect UART TX and not RX:
- Add
#define UART_CONNECTION_TEST_TX 1to yourConfiguration_local.hppfile to enable texting just TX functionality. This will send commands to both the RA/DEC drivers at boot to move the steppers slightly. If you do not see the motors move, you likely have a connectivity error with UART (or potentially a power issue to the driver/motor)
- Add
¶ If UART is not working:
- Double check your wiring
- Check your wiring again
- You may connected to the wrong UART pin on the driver. Try the other one. There are two, and some manufacturers have only one of them enabled
¶ Stepper getting really hot
It is normal and even desired that the steppers get warm during operation. If they however get very hot very fast the current is too high. Depending on the driver being used, there are different methods to adjust current.
If using UART control, reduce your motor current operating percentage in your configuration and to be save also reduce the max current over the drivers potentiometer.
If using a generic driver or TMC2209 in standlone mode, you need to adjust the potentiometer until the reference voltage is lower. Search "stepper driver current adjustment" online to look for guides applicable to your driver type.