The project goal is to experiment with video tracking systems to supplement precision tracking radars at low elevation angles.
To be honest the Meade Autostar is better suited for tracking slow moving deep space objects instead of that which is considered more “local.” At least I can only assume it to be true as likewise I have yet to have success with the unit in the former arena. However the hardware is there: two-axis motor control with positional-encoder feedback, all via UART. The problem is, however, that the hardware interface is via a UART to a controller that is well documented to have buffering issues which ultimately leads to processor hangs and motor runaway.
More problematic is that there are only a few speed settings available via the uart; FAST! slooow, stop, reverse time-travel. The video below shows attempt at putting aircraft in track via a simple PI loop. The tracker attempt to lock, overshoots the target then hangs. Subsequent attempts to bring the target back into track succeed temporarily and ultimately results in a runaway gimbal.
The next step is to open the Autostar, tap into the DC motor wiring, and provide a nice dynamic range of control speeds via the Amani GT and an H-Bridge PMOD. The UART connection will be maintained for positional encoder data.
It should be noted the control-loop bandwidth will then be limited by the Arduino/Nootripics assembly. While the video experimenter is a fantastic proof-of-concept tool, the design will eventually be migrated to an FPGA-based system where data can be collected and processed in real-time and passed to the host machine via ethernet. Moreover the control-loop itself will reside in the electronics package; the host PC will only provide a user control interface and data display.
Open Autostar picture courtesy of RobRoy.
The cheapest and fastest path-forward was to utilize the Video Experimenter Board from Nootropic Design.
The electronics package consists of the Nootropic shield interfaced with and Arduino. To control the telescope positioner, the electronics package must communicate with the Autostar via RS232. An Amani GT CPLD shield is used to bridge between the Arduino UART and a Digilent Pmod232.
The Amani is also being used to handle an issue I am having with the video shield/Arduino stopping the video tracking arbitrarily. Serving as a watchdog, the Amani looks for a heartbeat signal and resets the Arduino when loss of heartbeat is detected.
Of course this configuration is just a method of rapid prototyping, for proof-of-concept and experimentation. The VTE issue must be ironed out eventually, however to get the tracking algorithm development going the Amani-reset will serve as a patch in the short-term.
Progress thus far has involved sitting the unit in the window and observing the video tracker’s ability to resolve and track aircraft while I steer the gimbal manually. With minor code revisions to the sketch provided at Nootripic Design, I was able to develop an error vector, seen below, which will serve as the input error to the tracking loop.
Currently I am ironing out the Autostar commands I found online, some if not most of which do not seem to work. If anything I’ll need to sniff the comms between the Astrofinder software on the PC and the Autostar. It should be noted that the PC software is not involved in this project and is just used for troubleshooting and communications study. A PC will be included in this system to provide graphical data to the user as well as a general control interface. The biggest issue I have is not being able to control speed. If necessary I’ll open the gimbal itself, cut into the motor controllers, and take control via the electronics unit.
I do have feed back from the positioner in the form of encoder counts, which is vital for closing the tracking loop. Currently I use the building across the way for boresiting the unit and calibrating the encoders.
The Meade ETX-60AT itself is a beginner’s telescope, better suited for terrestrial viewing. As it is integrated into the controller base, I cannot remove it without compromising the internal optics, thus it serves as platform for the camera to piggy-back on. It does open possibilities of integrating the telescope into the system, for distant-object tracking.
Even more interesting, and a definite DO NOT ATTEMPT, would be to integrate a laser range-finding system into the telescope while the camera provides the video tracking. This solution would provide fully-integrated TSPI data for under $400.