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Autonomous Mobile Observatory Stations – Development in Progress Bill Hanna IOTA North American Annual Meeting July 29, 2016 Stillwater, OK Issues With Multi-Station Deployments • There is a lot of “stuff” to deal with • It takes time to align to the pre-point target – Reduces the number of stations that can be set up prior to the event, especially if it occurs shortly after sundown – There are workarounds for this, but at the expense of visiting the observing sites multiple times over more than one day Concepts Being Examined • Self-contained unit – No (or almost no) fiddling with “stuff” on site – Requires only an initial coarse manual alignment • Able to steer the optical axis as necessary – To the pre-point target – Track thereafter? • “Inexpensive” – Commercial mounts can align themselves autonomously, but at significant expense Self-Contained Unit • A single housing to integrate all of the components – – – – – – – – – – – Telescope Camera Battery / Power Controller / (Solar Cells?) Executive Computer Recorder GPS / Time Inserter Dew-Suppression Heaters Cables Optical Axis-Steering Assembly and Controller Rain Sensor? Security Sensors? All of the Physical Components Are Available • The amateur robotics community is an excellent source for the mechanical components – Rotational and Linear Servos • Analog and Digital – Stepper Motors – Gears, Belts, Pulleys, etc. • Wide selection of executive computer platforms – – – – Raspberry Pi Arduino Micromite Single-Board Computers Initial Manual Coarse Alignment • Want to point the default optical axis to the nominal EL@AZ from Occult Watcher • Manual coarse alignment, possible even in daylight, based on three components – Level – Elevation – Azimuth • Referenced to a celestial body – Sun – Moon – Bright star • Referenced to a ground target – Mountain peak – Transmission tower – Building / Structure • Should easily get the default axis within 5°, perhaps within 2° Freely-Available Information • The easiest way to do something is to get someone else to do it for you – Sun AZ and Moon AZ from the USN Observatory – Star positions from C2A or similar – Ground targets from Google Earth • Will require a “pre-processor” to collect (and compress?) the necessary information for a given event – Shared among multiple deployed units Optical Axis Steering • Pan/Tilt Mirror Control – Two rotational servos – Worm gears • X/Y Mirror Control – Two galvanometers • Housing Alignment Control – Two (or three?) linear servos changing the lengths of the legs Pan/Tilt With Two Analog Servos • The cheapest option, but is it suitably accurate and repeatable? • Lynxmotion SSC-32U USB Servo Controller – 32 servo channels, in two banks of 16 each • Provision for separate voltages on the two banks – Accepts ASCII text commands via USB or RS-232 serial – Controls 500µs to 2500µs pulsewidths in 1µs increments – Additional functions using minimal external components • Hitec HS-422 analog servos – Speed and torque are not significant factors – Want a small deadband Pan/Tilt Test Rig • Pan/Tilt assembly mounted over an Orion 80mm Short Tube OTA • First-surface mirror to minimize false images – Edmund Scientific • Astrovid StellaCam3 (Peltier-cooled Watec-120N+) • Pinnacle Dazzle to VirtualDub on a Lenovo laptop • SSC-32U commanded via USB to a virtual COM port using Tera Term – 2000 1µs counts = 180 degrees = 10800 arc-minutes – 1 1µs count = 5.4 arc-minutes Pan/Tilt Mirror w/ Analog Servo Evaluation Rig Pan/Tilt Assembly Close-Up Pan/Tilt Target Ruler Results • Arbitrarily chose 30 arc-minutes (the apparent diameter of the moon) as a repeatability goal • Reasonably accurate and repeatable, to within ~16 arcminutes (3 1µs counts) but only after making a large (≥ ~5-degree) slew • Small moves (such as those necessary for tracking) were essentially impossible due to the typical ~5µs to ~8µs deadband of a standard analog servo • Good position holding after removing power to the servo – The mirror assembly has an extremely small mass • Overall assessment: good, but not good enough Next Test Will Use Digital Servos • More expensive • Need to be programmed individually prior to use – Only need one programmer • Higher power consumption • The deadband can be programmed to zero at the expense of continuous “hunting” – This will have a minimal impact on the servo lifetimes because the powered use will be relatively intermittent • Significant parameters to be evaluated – Position hold after power removal – Small motion (i.e., tracking) performance • In particular, the effect of any resulting vibration on image stability Software Issues • If using an analog camera, need a reliable driver for the various available video digitizers (e.g., eMPIA Technology em28xx chips) for various small platforms (e.g., Raspberry Pi) – Able to capture a single frame • Plate-solving routines Looking Forward • Design for the future – Internet of Things (IoT) – 3D Printing • The number of different cameras currently (and projected to be) in use may mean that it will be simpler to have a separate (and standardized) camera for the alignment process – Also means that only a single version of plate-solving software will be necessary I Invite Questions and Comments • Best to contact me at: [email protected]