OVERVIEW: The purpose of the Guide Telescope Motors is to rotate a pair of wedge prisms. This allows the optical axis of the guide telescope to be offset from that of the main telescope. The motors are nearly identical to the MDI Michelson Tuning Motors. The electronics are also nearly identical, the difference being that the TRACE electronics allow the motors to make single steps. PERFORMANCE: Rotation step size: 2 degrees +/- 5 arc min. Time (until AXIS goes low): To move 1 step, 35 ms. To move 180 degrees, 520 ms. To move 360 degrees, 1000 ms. To RESET, 350 ms. Wobble: 2-4 arc min p-p as the motor is rotated. WEIGHT: One Pair, 550g, no optics. With wedges installed, just prior to installation into GT: 581g. MOTOR: 3 Phase, 30 pole-pair brushless DC motor Step Size: 2 degrees Inertia: 1.5 oz in^2 Motor Constant: 16 oz in / W No-Load Speed: 8 rad/sec on 15V Terminal Resistance: 172 Ohms Viscous Damping: 0.17 oz-in / rad/sec Drag Torque: 2.8 oz-in Torque Constant: 213 oz-in / A The following commands can be sent: 0 Nothing 1 Move CW 2 Reset 3 Move CCW 4 Load Stopping Position 5 Read Encoder 6 Nothing 7 Nothing A CW move increases the encoder reading. The encoder counts 0 to 179. CONNECTOR: Pin # Function Backplane M1 M2 ------------------------------------ 1 Encoder RTN 24 34 2 Encoder A 25 35 3 Encoder B 26 36 4 Encoder C 27 37 5 IRED + 29 39 6 IRED - 28 38 7 Phase A 30 40 8 Phase C 32 42 9 Phase B 31 41 NOTES: 1. Based on our experience with the MDI MTM's it seems likely that the rotors (wedges included) will wobble about 2-4 arc min p-p as the motor is rotated. Bill Rosneberg calculated the following; 1 degree of wedge moves the image through a 1/2 degree 1/2 angle cone (1 degree p-p) as the wedge is rotated, and 1 degree of wobble moves the image .23 arc seconds p-p. 2. From bruner@sxt2 Tue Feb 27 09:51:18 1996: The duty cycle for the tuning motors will be much smaller, probably something more like once or twice per hour. Say 5 to 10 thousand cycles. 3. Single steps. The motor is adjusted so that it operates best making moves of a single step. When the motor is to be moved a single step clockwise (+) it should be given a stopping position that is 1 less than the desired position. If the move is to be 1 step counterclockwise (-) then the desired position should be loaded. Example: motor is at position 10, you want to go to 11, load 10 send CW. To move from 11 back to 10, load 10 send CCW. 4. Large moves. It is recommended that large moves (3 or more steps) be made in the CW (+) direction. To make a large CW move load a stopping position 2 less than the desired location. Large CCW (-) moves are possible but the results are not consistent; sometimes the motor will overshoot the stopping position by 1 step, sometimes by zero steps. 5. Wedge installation. When both motors are at position 0, the thick parts of the wedges are at the top of the Guide Telescope. When viewed from the sun WM_1 moves counterclockwise for positive moves, and WM_2 moves clockwise for positive moves: WM_1 WM_2 +Z ____|| ||____ ^ \ || || / /|\ Sun --> \ || || / | \_|| ||_/ | || || 6. Reset positions. When the motors are reset they go to one of the following positions; 0, 6, 12, 18, 24 etc, whatever position is closest at the time of the reset. After a reset but before a move the encoder will read 255. 7. Connector positions: ___________ View looking at motor |WM_1 WM_2| connectors (looking |P302 P301| toward sun) | | | | | | |___________| 8. From Roger Rehse: The low level flight software will take of part 3 using the MDI-inspired "finagle" operation. This will be applied consistantly, so the part 3 problem is handled. The test programmer or user doesn't need to know about the difference in moving CW versus CCW. Large moves as in part 4 are done for test or during the initial acquisition of the sun. The "finagle" will also be in effect for this class of motions. That means CCW moves are sent to the desired final position and CW moves are commanded to desired position -1. Until this is proven to be a bad approach, the software will not be modified. 9. From RR: The wedge reset causes the following functions: 1) reset sent to controller 2) position 0 CW queued in software 3) wait for non-busy status 4) finagle causes position to be 179 5) set position and data sent to controller 6) CW command sent to controller