You are currently not logged in! Enter your authentication credentials below to log in. You need to have cookies enabled to log in.
This shows you the differences between two versions of the page.
|
functions:llapplyrotationalimpulse [2015-01-09 16:48 SLT] sei created |
functions:llapplyrotationalimpulse [2016-11-03 18:18 SLT] (current) sei speed -> velocity |
||
|---|---|---|---|
| Line 6: | Line 6: | ||
| </code> | </code> | ||
| - | Apply an instant change to the angular momentum of a physical object. It has no effect on non-physical objects. | + | Apply an instant change to the angular momentum of a physical object. It has no effect on non-physical objects or on attachments. |
| ===== Parameters ===== | ===== Parameters ===== | ||
| === impulse === | === impulse === | ||
| - | A [[types/vector]] specifying the impulse to apply, which will add to the object's current [[http://en.wikipedia.org/wiki/Angular_momentum|angular momentum]]. The vector indicates the impulse's axis and magnitude. The units of the angular impulse vector seem to be [[lsl/lindograms]]·m²/s. Like in the real world, the effect on the angular velocity depends not only on the mass of the object, but also on its shape, as it's the product of [[http://en.wikipedia.org/wiki/Moment_of_inertia|moment of inertia]] (which itself depends on the [[http://en.wikipedia.org/wiki/List_of_moments_of_inertia|shape of the object]]) and angular velocity. | + | A $lty[vector] specifying the impulse to apply, which will add to the object's current [[http://en.wikipedia.org/wiki/Angular_momentum|angular momentum]]. The vector's direction indicates the impulse's axis and its length indicates the magnitude. The units of the angular impulse vector seem to be $lart[lindogram|lindograms]·m²/s. Like in the real world, the effect on the angular velocity depends not only on the mass of the object, but also on its shape, as it's the product of [[http://en.wikipedia.org/wiki/Moment_of_inertia|moment of inertia]] (which itself depends on the [[http://en.wikipedia.org/wiki/List_of_moments_of_inertia|shape of the object]]) and angular velocity. |
| === local === | === local === | ||
| - | [[types/Boolean]] value indicating whether the **impulse** axis' coordinates are local to the root prim (if [[constants/TRUE]]) or in sim coordinates (if [[constants/FALSE]]). | + | $lty[Boolean] value indicating whether the $prm[impulse] axis' coordinates are local to the root prim (if $lct[TRUE]) or in sim coordinates (if $lct[FALSE]). |
| - | When **TRUE**, the **impulse** axis' coordinates are local to the root prim. For example, if **impulse** is `<1, 0, 0> and the X axis of the root prim is looking northwest, then the impulse will have its axis oriented in the northwest direction, aligned with the root prim's X axis. | + | When $ct[TRUE], the $prm[impulse] axis' coordinates are local to the root prim. For example, if $prm[impulse] is `<1, 0, 0> and the X axis of the root prim is looking northwest, then the impulse will have its axis oriented in the northwest direction, aligned with the root prim's X axis. |
| - | When **FALSE**, the vector specifies sim coordinates, where positive X is east, positive Y is north, positive Z is up, and vice versa for negative; for example, if **impulse** is `<-1, 0, 0>, the rotational impulse will have its axis pointing west, no matter how the root prim is oriented. | + | When $ct[FALSE], the vector specifies sim coordinates, where positive X is east, positive Y is north, positive Z is up, and vice versa for negative; for example, if $prm[impulse] is `<-1, 0, 0>, the rotational impulse will have its axis pointing west, no matter how the root prim is oriented. |
| + | |||
| + | ===== Notes ===== | ||
| + | |||
| + | * The maximum angular velocity of an object seems to be about 127 rad/s (about 1212 rpm). Note, however, that $lfn[llGetOmega] will not return a value with a magnitude greater than 62.8 rad/s (about 599.7 rpm). | ||
| ===== Short examples ===== | ===== Short examples ===== | ||
| Line 28: | Line 32: | ||
| llApplyRotationalImpulse(<0, 0, 1>, TRUE); | llApplyRotationalImpulse(<0, 0, 1>, TRUE); | ||
| // 0.6 rad/s is derived from the moment of inertia of a cube spinning over its | // 0.6 rad/s is derived from the moment of inertia of a cube spinning over its | ||
| - | // axis (m*l*l/6, where l is the length of the side) and the impulse applied. | + | // axis (m*l^2/6, where l is the length of the side) and the impulse applied. |
| // The mass of such a cube is 10 lindograms. Measurement with llGetOmega | // The mass of such a cube is 10 lindograms. Measurement with llGetOmega | ||
| - | // indicates that it works this way (to the 3rd decimal place). | + | // indicates that it works this way. |
| </code> | </code> | ||
| - | ===== See also ===== | + | ===== Complete examples ===== |
| - | * [[llApplyImpulse]] is similar but for [[http://en.wikipedia.org/wiki/Momentum|linear momentum]] instead of angular. | + | This example verifies the physical accuracy of $fn[llApplyRotationalImpulse] on an undeformed box of any dimensions. Moment of inertia varies with shape, so most deformations affect the results. |
| - | * [[llSetAngularVelocity]] applies the rotational impulse necessary to set the given angular velocity for an object. | + | |
| - | * [[llGetOmega]] obtains the current angular velocity of the object. | + | <code lsl2 llApplyRotationalImpulse-test.lsl> |
| - | * [[llSetTorque]] applies an angular force (a torque) to an object continuously | + | float IMPULSE = 1.31; // change this value to any value to test |
| - | * [[llSetForce]] is the linear equivalent to **llSetTorque**. | + | |
| - | * [[llSetForceAndTorque]] sets both force and torque at the same time. | + | default |
| - | * [[llSetVelocity]] and [[llGetVel]] are the linear equivalents of **llSetAngularVelocity/llGetOmega**. | + | { |
| - | * [[llGetMass]] returns the mass in Lindograms of an object. | + | touch_start(integer n) |
| - | * [[llGetMassMKS]] returns the mass in kilograms of an object. Most LSL functions use Lindograms, so this function is of limited use in physics calculations. | + | { |
| + | // Disable gravity, enable physics, wait for the setting to take effect | ||
| + | llSetPhysicsMaterial(GRAVITY_MULTIPLIER, 0, 0, 0, 0); | ||
| + | llSetStatus(STATUS_PHYSICS, TRUE); | ||
| + | llSleep(0.5); | ||
| + | |||
| + | // Begin the test | ||
| + | llApplyRotationalImpulse(<0, 0, IMPULSE>, TRUE); | ||
| + | llSleep(0.03); // let a simulator frame pass | ||
| + | |||
| + | // NOTE: Rotational friction is applied almost instantly, meaning the | ||
| + | // returned value will be less than the theoretical one most of the | ||
| + | // times. Sometimes we're lucky and get the actual value. | ||
| + | vector omega = llGetOmega(); | ||
| + | |||
| + | // Disable physics again, return to zero rotation. | ||
| + | llSetStatus(STATUS_PHYSICS, FALSE); | ||
| + | llSetRot(<0, 0, 0, 1>); | ||
| + | |||
| + | // Calculate and report results. | ||
| + | vector size = llGetScale(); | ||
| + | // Predicted omega is impulse divided by moment of inertia. | ||
| + | // Moment of inertia of a box rotating on its z axis is m*(size.x²+size.y²)/12. | ||
| + | float predicted = IMPULSE/(llGetMass()*(size.x*size.x+size.y*size.y)/12); | ||
| + | llSay(0, "Theoretical omega: " + (string)predicted | ||
| + | + ", actual omega: " + (string)omega.z | ||
| + | + ", difference:" + (string)(predicted - omega.z) | ||
| + | ); | ||
| + | } | ||
| + | } | ||
| + | </code> | ||
| + | |||
| + | ===== See also ===== | ||
| + | * $lfn[llApplyImpulse] is similar but for [[http://en.wikipedia.org/wiki/Momentum|linear momentum]] instead of angular. | ||
| + | * $lfn[llSetAngularVelocity] applies the rotational impulse necessary to set the given angular velocity for an object. | ||
| + | * $lfn[llGetOmega] obtains the current angular velocity of the object. | ||
| + | * $lfn[llTargetOmega] tries to keep a constant angular velocity. | ||
| + | * $lfn[llSetTorque] applies an angular force (a torque) to an object continuously | ||
| + | * $lfn[llSetForce] is the linear equivalent to $fn[llSetTorque]. | ||
| + | * $lfn[llSetForceAndTorque] sets both force and torque at the same time. | ||
| + | * $lfn[llSetVelocity] and $lfn[llGetVel] are the linear equivalents of $fn[llSetAngularVelocity]/$fn[llGetOmega]. | ||
| + | * $lfn[llGetMass] returns the mass in $lart[lindogram|Lindograms] of an object. | ||
| + | * $lfn[llGetMassMKS] returns the mass in kilograms of an object. Most LSL functions use $art[Lindograms], so this function is of limited use in physics calculations. | ||
| + | * $lfn[llVecNorm] to obtain a unit vector from a given one. | ||