PrimaLuceLab ARCO 2" Robotic rotator

The ARCO 2" Rotator: Purpose and Audience

The ARCO 2" has two uses. On an equatorially mounted telescope, it rotates the camera without you touching the telescope.

On an alt-azimuth mount, without a wedge, it also works as a field de-rotator with PLAY software, so you can take long exposures. The manual lists the alt-az mounts tested so far: SkyWatcher AZ-EQ6 and AZ-EQ5 with a USB port on the mount head, and Panther TTS-160. ARCO is not a standalone unit: it must be connected to a PrimaLuceLab ESATTO focuser or SESTO SENSO 2/3 motor.

1 Arc Second Resolution

The ARCO 2" moves in steps of 1 arc second, so you can set the camera angle in very fine increments when framing a target or de-rotating the field.

You command the angle with a slider or a typed value in PLAY or the Virtual HandPad, or from ASCOM software, and the STOP button halts a rotation at any time.

Dual Functionality: Camera Rotation vs. Field De-Rotation

The ARCO 2" operates in two distinct modes depending on your mount type, both managed through the PLAY software. With an equatorial mount, it works as a camera rotator: in PLAY's CAPTURE section you use the slider or type an angle and press GO.

With a supported alt-azimuth mount selected in PLAY, field de-rotation starts automatically once the telescope reaches the target and the mount starts tracking. If you command a camera rotation meanwhile, de-rotation pauses and resumes when the rotation completes. The AZ-EQ6 and AZ-EQ5 must be set mechanically in alt-az mode and start pointed North at the horizon, with the counterweight bar pointing West.

50.9mm Aperture in a 20mm Profile with 4kg Capacity

The ARCO 2" body is 20mm thick (21mm with the ESATTO 2" adapter PL3600412), with a 50.9mm free aperture.

Its full aluminum case can rotate heavy cameras and accessories without flexure.

• Payload capacity: 4kg.
• Low Profile: 20mm body thickness.
• No Protruding Parts: All mechanical and electrical parts sit inside the case, so nothing touches the camera, accessories or telescope.

Connectivity: Telescope and Camera Thread Adapters

ARCO 2" is designed for flexible integration. On the telescope side, it connects through optional adapters held by three grub screws in the rotator body: PL3600412 for ESATTO 2", PL3600416 for ESATTO 3" and PL3600423 for ESATTO 4". On a focuser with a SESTO SENSO 2/3, use the PL3600413 2" nosepiece for a 2" visual back, or the PL3600424 M48x0.75 female adapter for an M48 male thread (for example a corrector already in the focuser).

On the camera side, the ARCO 2" has the same M56x1 male thread as the camera side of the ESATTO 2" draw tube, so it takes the optional M56 adapters with stop ring: PL3600218 (T2), PL3600216 (M48), PL3600225 (SC thread), PL3600242 (M54), PL3600227 (M57) and the PL8410001 2" visual back.

ESATTO & SESTO SENSO Integration: Single-Cable Power and Control

The rotator is powered and controlled through a single cable to the ARCO port of an ESATTO robotic focuser or a SESTO SENSO 2/3 robotic focusing motor, so it needs no USB or 12V cable of its own. The manual requires firmware 3.0 or later on the ESATTO or SESTO SENSO 2; update it with PLAY.

• ESATTO Integration: Use the optional adapter (e.g., PL3600412 for ESATTO 2") to mechanically couple the rotator. Connect the included 220mm rotator port cable.
• SESTO SENSO 2/3 Integration: Lock the optional nosepiece or thread adapter into ARCO first, then fit ARCO to your focuser. Use the longer 690mm cable, and check with the draw tube fully out that the cable still lets it move freely.

Software Ecosystem: Control via PLAY, WiFi, and ASCOM

You can control the ARCO 2" rotator through multiple methods. PrimaLuceLab's PLAY software (Windows 10 or 11) controls focus, camera rotation and the mount through its ASCOM driver. Installed on an EAGLE computer, PLAY adds more advanced features.

Without a computer, join the WiFi network of your ESATTO or SESTO SENSO, open 192.168.4.1 in the browser, turn on ARCO enable and use the Virtual HandPad to calibrate ARCO, rotate the camera and set a new zero position. Field de-rotation is not available from the Virtual HandPad, only from PLAY. For third-party software, the PLL ASCOM Focuser driver (version 3.0 or later, ASCOM platform 6.4 or later) adds a PLL ASCOM Rotator; the manual's example is Sequence Generator Pro, and any software that supports ASCOM rotators can be used.

System Setup: Calibration and Defining the Home Position

The ARCO 2" must be calibrated before use, from PLAY (Rotator section, ENABLE ROTATOR, then CALIBRATION) or from the Virtual HandPad, where it may take several minutes. ARCO makes a rotation during calibration, so first check that the camera and accessories after ARCO can turn a full 360° and arrange or disconnect their cables. In any rotation position, cables must not pull, or they may break or damage your devices.

Calibration is saved in the firmware, so it carries over between the Virtual HandPad and PLAY. Repeat it every time you enable or disable ARCO, and whenever you mechanically rotate ARCO relative to the focuser; once enabled and calibrated, you can leave it enabled. The Set ZERO position button makes the current position 0.

Power & Installation: Integrating ARCO into Your Telescope

The ARCO 2" receives its power from the ESATTO or SESTO SENSO 2/3 it is connected to. Power the ESATTO or SESTO SENSO with a 12V supply of at least 1A (5.5/2.5mm plug, center positive): a computer's USB alone may not provide enough power for both devices. On an ESATTO, thread the optional adapter onto the draw tube, fit ARCO onto it and tighten the three grub screws with the included 2mm Allen key. Do not over-tighten them, or you may ruin the thread or the inner adapter.

Two rotator port cables are included: 220mm for an ESATTO and 690mm for a SESTO SENSO, which may sit further from ARCO. Line up the connector pins and press the cable in gently; if it does not fit, do not force it, or the pins may break.

Maintenance & Limitations: Care and Operating Parameters

Do not disassemble ARCO, drop it, expose it to rain or use it below -20°C or above +60°C. It is not a standalone unit and requires an ESATTO or SESTO SENSO 2/3 (firmware 3.0 or later).

If the rotator does not move or you hear a clicking sound, first check the 12V supply of your ESATTO or SESTO SENSO. If power is correct, adjust the worm gear screw shown in the manual while the motor is moving, with small turns clockwise and counterclockwise until ARCO moves.

Unboxing: What's Included and Your First Steps

The box contains the ARCO 2" rotator unit, a 2mm Allen key for the locking grub screws, a short 220mm rotator port cable, a long 690mm rotator port cable, and a quick start guide.

Getting started on your first night is a clear process:

1. Securely install the ARCO 2" onto your focuser using the appropriate optional adapter.
2. Connect the rotator port cable from the ARCO to your ESATTO or SESTO SENSO 2/3.
3. Power on your ESATTO or SESTO SENSO 2/3 with a 12V power supply.
4. Connect the focuser/motor to your Windows computer or EAGLE via USB.
5. Download and install PLAY from the PrimaLuceLab website and update the focuser firmware if needed.
6. In PLAY's Rotator section, enable the rotator and run the calibration, with your camera cables free for a full turn.
7. You are now ready to control your camera's rotation and begin imaging.