This page contains answers to common questions regarding the Dynawiz
XMR.
- What kinds of mechanism simulation can you do with Dynawiz in
the XMR package?
- How is XMR package different from XSV package?
- Can Dynawiz model control-structure interactions?
- Can Dynawiz in the XMR Packge be used to model satellites?
- 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 ?
It can simulate the dynamics of any system of interconnected bodies. This could be an
automobile engine, the engine power train, the steering system, the differential gear
mechanism, the tire suspension system. It could also be an airplane landing gear system or
a robotic lift system. It will simulate any system as long as the connectivity and the
constraints can be defined based on Dynawiz.
The main difference is in the choice of the states of the the system's equations of
motion. XMR has the the relative coordinates and the relative rates as the states, whereas
XSV has the relative coordinates and the generalized momenta as the states. Another
important difference is that XMR has the inertial displacement of the origin of the
coordinate frame fixed on the reference body as a state whereas XSV has the inertial
displacement of the center of mass of the whole system as a state. These differences makes
it easier for XMR to handle ground contact constraints.
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
satellites. However, it does not have the built-in geocentral gravitational force
calculations as in the XSV package. This part of the force calculation would have to be
supplied by the user.
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.
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