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With the completion of the full 50 m primary reflector surface of the Large Millimeter Telescope/Gran Telescopio Milimetrico (LMT/GTM), the project also upgraded the primary surface actuators. These actuators were custom-designed by ADS International in Valmadrera, Italy to meet the accuracy, load, and physical size requirements necessary for robust operation. Specifically, the actuators had to provide precise and repeatable positioning, support both operational and survival loading conditions for even the largest surface segments, and still fit within the geometric constraints imposed by interior angles of the backup structure truss members. Factory and laboratory testing confirmed that the actuators should meet the requirements. As reported in earlier papers, the LMT/GTM site poses particular challenges for electromechanical devices. As expected for a mountaintop site (4,600 m), the low atmospheric density reduces cooling effectiveness for motors and drives. To add to the challenge, the ambient temperature hovers near freezing and there is significant precipitation during the summer. This results in frequent freeze/thaw cycles. The constant formation and either sublimation or melting of ice has been an operational challenge for many devices at the LMT/GTM. Because of the large number of primary surface actuators (720 in total), it is particularly important that these units, their drive control boxes, and their cable connections be able to meet all specifications even under the site conditions. To confirm the suitability of the actuators, the LMT/GTM procured an initial set of sixteen actuators for testing at the site. After laboratory testing, the actuators were installed into the outer two rings of the telescope and cycled from February 2016 through January 2017. This extended testing provided direct operational experience over a wide variety of weather conditions. The program was long enough to provide confidence in the actuator design. With the first article testing complete, the project ordered a production run of the actuators. The installation of these actuators met the telescope completion plan requirement of bringing the LMT/GTM to a 50 m active surface telescope for the 2017-18 scientific observing season. This paper presents the final report on the first article testing program, as well as a summary of the characterized performance of the production actuators prior to installation.
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