Control Systems Group
3Dwheel - Attitude Control of Satellites Using Magnetically Levitated Wheels
Jon Seddon - J.Seddon@surrey.ac.uk
Dr Alexandre Pechev - A.Pechev@surrey.ac.uk
The 3Dwheel provides the following benefits:
- 3-axis attitude control of a spacecraft from a single actuator
- a bandwidth 100 times greater than an actuator using conventional bearings
- an output torque up to 50 times greater than a similar sized conventional momentum wheel
- very low noise output
- no mechanical contact and so no lubrication required, and no friction, stiction or wear.
Download a video of the 3Dwheel (22 MBytes) (Quicktime is required to play the video and is available for download from Apple.)
Figure 1 - A rotation step response with the axis of rotation between the wheel's principle axes.
Figure 1 shows the response of the wheel to a step command for a rotation about an axis between the wheel's x and y principle axes. The electromagnets are aligned with the x and y principle axes. This plot demonstrates that it is possible to tilt the wheel about any axis on the plane normal to the wheel's spin axis and therefore to generate a torque about any axis on this plane. Experiments show that the translation loop is decoupled from the rotation loop by at least -46 dB up to the crossover frequency.
Figure 2 - The response to a 2.5 micrometre translation step command along the x-axis.
Figure 2 shows the wheel's response to the step command for a 2.5 micrometre translation along the positive x-axis at time 20.0 seconds. The data acquisition card used in the engineering model has a 12-bit resolution, with the least significant bit corresponding to a translation of 2.4 μm. The quantisation of the position is visible showing that the wheel can be controlled with a very high precision, with the engineering model's precision being limited by the resolution of the data acquisition card.
Figure 3 - The response to a 0.1 milliradian rotation step command about the x-axis.
Figure 3 shows the wheel's response to the step command for a 0.1 milliradian (0.0057°) rotation about the x-axis. Again the resolution of the 12-bit data acquisition card is defining the resolution that the wheel can be tilted with.
