ECE5320 Mechatronics Assignment#01: Literature Survey Actuators Topic: Torque Coils/Rods and Reaction Wheels

1. ECE5320 MechatronicsAssignment#01: Literature Survey Actuators Topic: Torque Coils/Rods and Reaction Wheels Prepared by: Brandon Thurgood Dept. of Electrical and Computer Engineering Utah State University E: bkthurgood@cc.usu.edu ; T: (435)797-7577; F: (435)797-3054 (ECE Dept.) 3/10/2006

2. Outline • Reference list • To explore further • Operational interface • Attitude Control • Major Application • Reaction Wheels • Torque Rods • Torque Coils • Buy/Cost ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

3. Reference list • http://einstein.stanford.edu/highlights/hl_102805.html • http://www.sti.nasa.gov/tto/spinoff1997/t3.html • http://www.vfct.com/satellites/wheels/wheels2.html • http://scienceworld.wolfram.com/physics/ReactionWheel.html • http://www.thetech.org/exhibits_events/online/hubble/whichway.html • http://www.nasa.gov/centers/ames/research/technology-onepagers/advanced_min_wheel.html • http://www.vectronic-aerospace.com/html/reaction_wheel.html • http://www.thetech.org/exhibits_events/online/hubble/direction.html • http://fuse.pha.jhu.edu/educ/RW_FAQ.html • http://cubesat.ece.uiuc.edu/Teams/Attitude_Control.html • http://www.plus2physics.com/ecurrent_and_mgfield/study_material.asp?chapter=3 • http://global.mitsubishielectric.com/bu/space/news/articles/image/86tr6.pdf ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

4. To explore further • http://staff.ee.sun.ac.za/whsteyn/Papers/Magsat.pdf • http://ocw.mit.edu/NR/rdonlyres/Aeronautics-and-Astronautics/16-358JSystem-SafetySpring2003/B169A368-9DCC-4916-8897-12B0DE4DC855/ 0/hete.pdf • http://www.sti.nasa.gov/tto/spinoff1997/t3.html • http://www.nasa.gov/centers/ames/research/technology-onepagers/advanced_min_wheel.html ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

5. Operational Interface From ECE 5320 class slides ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

6. Attitude Control • Attitude Control determines and monitors the direction of a spacecraft. Small mistakes could lead the spacecraft miles off course. Thus, it is important to have accurate sensors and actuators on board the spacecraft. Spacecraft attitude systems usually consist of two components: Spacecraft orientation sensors: magnetometers, gyroscopes, etc…; and Control actuators: e.g. reaction wheels, torque rods, etc… ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

7. Attitude Control Attitude Controll parameters Figure from mitsubishielectric Table thanks to Goodrich ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

8. Major Application An example of spacecraft control. The answer is using a system called the Pointing Control System. The main components of the pointing control system are reactions wheels. The reactions wheels can be moved to change the orientation of a body. The reactions wheels spin quickly in one directions and the satellite rotates the other way to conserve angular momentum. “The Hubble is the size of a large bus, travels at 17,500 miles per hour and is 370 miles above the Earth's surface. How do you point it at a tiny speck in the universe millions of light-years away and hold it steady, sometimes for hours at a time, so it can take a picture? (Hubble direction)” Figures are from hypertech ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

9. Reactions Wheels In order to keep the satellite steady or pointed in the right direction reaction wheels, or momentum wheels are used. Reactions wheels exert torque forces on the satellite to control its direction. The spinning flywheel is placed on the body of the aircraft and with a variable rate of rotation from an electric motor the spacecraft can be re-aligned. Momentum Storage (h): h = TD*(Orbital Period/4)*(0.707) Slew Torque: Θ/2 = (1/2)*(T/I)*(t/2)2 Angular momentum: 0.4 to 400 Nms @ 1200 to 1500 rpm Weight: 2 to 25kg Power: 8 to 150W Picture from NASA spin-off ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

10. Reaction Wheels Table is from Valley Forge Composite Technologies ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

11. Reaction Wheels in Space The axis of rotation for each reaction wheel is fixed. Do to this fact three reaction wheels are needed for each spacecraft. One for the x, y, and z components as illustrated in the figure bellow. Usually a fourth wheel is also added to relate the three other wheels. NASA Ames’ Project Development Division has produced two generations of small advanced reaction wheels for use in robotic astronaut assistants and small spacecraft. The small reaction wheels are energy efficient. They are able to assist astronauts both inside and outside of manned space vehicles. Figure from NASA Figure is from CubeSat at UofI ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

12. Location of Reaction Wheels Figure is from hypertech Figure is from Harvard ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

13. Torque Coils vs. Rods • Coils • Easier to implement • Linear response makes control requirements simpler • Lower cost to manufacture • Create stray magnetic fields • Rods • More efficient • Implement is simplified • Core material is rare ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

14. Torque Rods Torque rods are in essence electromagnets. The rods are mounted on the body of the spacecraft and while interacting with the magnetic field of the Earth place a controlled force, or torque, on the spacecraft changing its orientation. Like the reaction wheels there are three torque rods, each in a corresponding to one of the spacecraft's three axes (X, Y, or Z) Torque Rods from Goodrich ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

15. Torque Rods in Space Figure and Charts are from Einstien The diagrams above shows the Earth and its magnetic field lines and a chart created by the ATC team for the Gravity Probe B vehicle . The two plots in the chart to the right show the magnitude of the average pitch-yaw (X-Y) (top) and roll phase (Z-Axis) (bottom) pointing error over a period of 45 orbits as a function of the spacecraft's position. The green vertical lines are the two best pointing positions in each orbit, and the orange vertical lines are the two worst pointing positions. This occurs due to the location of the spacecraft in the Earths magnetic field. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

16. Torque Coils • Torque coils carrying a current that are placed in an external magnetic field experiences a force according to its orientation with respect to the magnetic field lines. • Example to the right: There is a rectangle coil of length l and width b with N turns and current I. The could is placed in a uniform magnetic field of flux density B. Figure from plus2physics ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

17. Torque Coils Torque Coils: Custom design:      4 layers,      30 loops each, of      0.0007in wire      Traced on a PCB boardTotal resistance      96.3 OhmsMax Current      114 mA Figure from plus2physics τ= B I l N x b cos θτ= B IlN x b sin ατ= BINA sin α α is the angle between the normal to the coil and the magnetic field , A (= l x b) is the area of the coil. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

18. Torque Coil Controller Figure from CySat ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

19. Torque Controller Magnetometer and gyros send information to the microcontroller. The microcontroller then creates the current to the torque coils. This causes the spacecraft to move in the desired direction. With the know direction of the Earth’s magnetic field a current will be pushed through each of the three different torque coils (x, y, and z) in the desired direction over a period of time to create the movement. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

20. Places to buy/Cost Reaction Wheels • Bendix • Honeywell • Cost approx. $5000.00 Torque Coils • Lockheed • Hughes • McDonnell Douglas • Cost approx. $1500.00 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators