making wheels rotate for a vehicle

[RayRobert]

Hello all, I am fairly new to dcriptin and am modifying a vehicle script. The script doesnt make the wheels spin when moving forward or backward. Can anyone assist me in doing this? I know I need to use link message to communicate between prims but am not dure exactly how.

[steph Arnott]

Some reading.

http://wiki.secondlife.com/wiki/LlSetPrimitiveParams#llSetLinkPrimitiveParamsFast

http://wiki.secondlife.com/wiki/Link_Messages

BTW, A texture rotating maybe easier, but things have moved on since I did this stuff. 

[Freya Mokusei]

There'll be a separate script for you to put in each wheel. When the vehicle is linked, this link message will send to those child scripts.

Note that this is not the best way to achieve that functionality, you're probably using old (and obselete) scripts.

[Innula Zenovka]

Most older vehicle scripts use link messages to control script in the wheel prims, to turn llTargetOmega on and off.

Now you don't need to do that, since you can use llSetLinkPrimitiveParamsFast to control PRIM_OMEGA.

Note that you can control all four wheels in one call, by saying 

llSetLinkPrimitiveParamsFast(LINK_SET,[PRIM_LINK_TARGET,wheel_1, some params,PRIM_LINK_TARGET,wheel_2, some params...]);

 

[Madelaine McMasters]

---

Innula Zenovka wrote:

Most older vehicle scripts use link messages to control script in the wheel prims, to turn llTargetOmega on and off.

Now you don't need to do that, since you can use

llSetLinkPrimitiveParamsFast

to control

PRIM_OMEGA

.

Note that you can control all four wheels in one call, by saying 

llSetLinkPrimitiveParamsFast(LINK_SET,[PRIM_LINK_TARGET,wheel_1, some params,PRIM_LINK_TARGET,wheel_2, some params...]);

 

---

And I think (correct me if I'm wrong, Innula) that if your wheels are simple textured cylinders, Steph's suggestion to rotate the texture is best, as llTargetOmega's rotation vector must be changed if the vehicle's front wheels are steerable. Texture rotation doesn't care about prim orientation.

llSetTextureAnim(ANIM_ON | SMOOTH | ROTATE | LOOP, 0,1,1,0, rotation_rate, 1);

for example.

[Innula Zenovka]

Yes, you need to keep calling it to adjust the rotation according to the each wheel prim's local rotation, but I don't see that as a problem, since you're going to need to keep calling it anyway, when the car's speed changes, and it's no big deal to call it again in the control events when you change the car's direction. 

Something like this

 

integer i= -llGetListLength(wheels);		list params;		float speed = llVecMag((llGetVel()*llGetRot()));		do {			integer n = llList2Integer(wheels,i);			list l =llGetLinkPrimitiveParams(n,[PRIM_ROT_LOCAL,PRIM_SIZE]);			rotation r = llList2Rot(l,0);			vector size = llList2Vector(l,1);			float circumference = size.x*PI;			params += [PRIM_LINK_TARGET]+[n]+[PRIM_OMEGA]+[<0.0,0.0,(speed/circumference)>*r,TWO_PI,0.1];		}		while(++i);		llSetLinkPrimitiveParamsFast(LINK_SET,params);

 

[LepreKhaun]

---

Innula Zenovka wrote:

Yes, you need to keep calling it to adjust the rotation according to the each wheel prim's local rotation, but I don't see that as a problem, since you're going to need to keep calling it anyway, when the car's speed changes, and it's no big deal to call it again in the control events when you change the car's direction. 

Something like this

 

		integer -i=llGetListLength(wheels);		list params;		float speed = llVecMag((llGetVel()*llGetRot()));		do {			integer n = llList2Integer(wheels,i);			list l =llGetLinkPrimitiveParams(n,[PRIM_ROT_LOCAL,PRIM_SIZE]);			rotation r = llList2Rot(l,0);			vector size = llList2Vector(l,1);			float circumference = size.x*PI;			params += [PRIM_LINK_TARGET]+[n]+[PRIM_OMEGA]+<0.0,0.0,(speed/circumference)>*r,TWO_PI,0.1]);		}		while(++i);		llSetLinkPrimitiveParamsFast(LINK_SET,params);

 

---

Careful, that code won't compile.

// Syntax error for not following lhs/rhs rules.integer -i=llGetListLength(wheels); // Syntax error from poorly written list.params += [PRIM_LINK_TARGET]+[n]+[PRIM_OMEGA]+<0.0,0.0,(speed/circumference)>*r,TWO_PI,0.1]); 

 

[Innula Zenovka]

Oops.   Now fixed.  Sorry about that.

[Freya Mokusei]

---

Madelaine McMasters wrote:

llSetTextureAnim(ANIM_ON | SMOOTH | ROTATE | LOOP, 0,1,1,0, rotation_rate, 1);

---

This is (almost) what I would recommend using. More specifically:-

llSetLinkTextureAnim

Which removes the need for barely used child scripts.

If the OP goes the OMEGA route, disregard this post!

[steph Arnott]

All very clever, but I be amazed if anyone could tell whether the texture rotating matches the velocity. Just seems overkill and more math work than needed.

[LepreKhaun]

np, as Donald E. Knuth once said, "Beware of bugs in the above code; I have only proved it correct, not tried it."