This page contains answers to common questions regarding the Dynawiz
XSV packages.
- What kinds of satellite simulation can you do with Dynawiz?
- Can Dynawiz model control-structure interactions?
- Can Dynawiz XSV Packge be used to model robots?
- What practical use can you make of the prescribed motion?
- What practical use can you make of the inverse dynamics?
- How do I connect bodies ?
- How do I attach wheels ?
- How do you define a position marker?
- How do you define a directional marker ?
- How to enable/disable orbital effects?
- What are orbital computations done by Dynawiz in the XSV package?
It can simulate attitude acquisition, array and payload deployment, normal pointing
modes and sun-safemode. It can simulate spinners and the attendant attitude maneuvers. It
can simulate a single body vehicle just as well as a space station. It can model reaction
wheel and reaction jets based attitude control system. It can also accomodate CMG based
ACS. Furthermore, consider multiple payload deployment and precision pointing,
telerobotics, spacecraft-to-spacecraft docking, and the list goes on.
Yes, it can. Dynawiz can be programmed to model the flexible effects of member bodies.
The flexible structural property of member bodies are accounted for by the tuple {
freq(i), dm(*), grid(*), mass_integrals_list | i = 1, nof_modes} input to the simulation.
The elements of this tuple for each flexible body is explained in the User's Manual.
The system equations of motion include the deformation coordinates as states. The
response of the latter to control system activities can be extracted for plotting.
Yes, it can. This is because it models any tree configure system. That includes robots.
However, it does not have built-in constraints to handle grounding. That is constraining
any part of the robot to be fixed in the inertial coordinate frame. You can approximate
that constraint by imposing a constraining force based on a stiff spring and damper model
at the point of ground contact. In order to better treat this kind of problem, we have
developed the Dynawiz XMR package to handle grounding. (Please see XMR FAQ.)
Prescribed motion is generally applied to those "what if" situations where
you want to see the vehicle response to the motion of a joint that follows a particular
time function. The time function may be the result of a desired servo response or it could
be that of a failed servo response. This feature is thus helpful in both the design phase
of a mechanism and in an anomaly resolution situation.
Another way of using this feature is to see the amount of motion disturbance one
payload has on another. You can conduct this experiment by prescribing a series of
possible motions for one payload, while letting the other payload be under its own servo
control. By this set up, you can see the disturbance rejection performance of the second
payload control system.
One use of inverse dynamics is to compute the joint forces/torque that would be
required to produce a desired joint motion. The desired motion is defined by a time
function prescribed to the joint of interest. Thus, if you want a coordinated motion of
several joints, each with its desired time function, then this feature would compute the
desired torque needed at each of these joints. These computed torque can be used as the
command torque to the actual joint servos to effect the real coordinated motion.
Another application is to prescribe a range of possible motion at a joint to find out
the force/torque bounds that would be required of the joint servo.
It could also be used to compute the constraint torque/forces at the single
degree-of-freedom hinges to identify the cross axis torque and shear forces at those
hinges. These are useful for loads analyses.
Dynawiz recognizes connection between two bodies by the parent index of the two bodies.
Start with the reference body which is body 1 by default. Let's suppose you want body 4 be
connected to it. Then, you go to the body 4 menu via BuildX and set its parent index to 1.
Should you want body 2 be connected to body 4, you would then go to body 2 menu and set
its parent index to 4. And so forth... The order of indexing bodies is arbitrary other
than body 1. Its parent index is zero.
Let's suppose that you want to mount wheel #1 on body 2. Then go to the wheel #1 menu
via BuildX, and set its parent body to 2.
A Position Marker is a way for you to identify a point on a designated body. Once
marked, you can monitor its motion over a simulation run. Let's say you want to identify a
point on body 3 that's located at [1, 2, 3]' units of distance away fromt the origin of
body 3 frame. Then go to the Edit Marker Menu via BuildX, Select POS for position marker.
You should see POS Marker #1 menu. Set the name to PMKR1 or some name you like. Set its
parent to 3. Set its local (x, y, z) position to 1, 2, and 3. Type "d" for done.
A Directional Marker is a way for you to identify the orientation at a point on a
designated body. For example, if you need to know the direction that that line of sight of
a telescope is pointing in the inertial space, then you must define a Directional Marker
for that telescope. Let's suppose that the telescope is body 2, and the line of sight
vector in the body 2 frame is the local z axis. Then go to the Edit Marker Menu via
BuildX, Select LOS for directional marker. You should see LOS Marker #1 menu. Set the name
to LMKR1 or LOS1 (or choose your own). Set its parent to 2. Set the marker value (x, y, z)
to (0, 0, 1) [without the brackets]. Type "d" for done.
For the XSV package, you can enable the orbital effects by going to the Edit Timing
& Control Menu and request Ephemeris to set the Keplerian coordinates of the vehicle
motion. In the same menu, there is an Enable Orbit flag (EO) that can be toggled between 1
and 0. The former means that the orbit effects are invoked and that latter means the
opposite.
When the orbit effects are in force, the following computations are done:
- The initial position and velocity of the system center of mass is determined by the
ephemeris data supplied
- The initial attitude that you define for the reference body ( body 1 ) is the attitude
wrt the local vertical orbit attitude
- During the simulation, Dynawiz automatically calculates the following:
