truck and trailer

Blitz3D Forums/Blitz3D Beginners Area/truck and trailer

Pete Carter (Posted 2006) [#1]

Just wondering how best to make the cab drive around and the trailer follow in the correct way? they are 2 different b3d models. the truck in question

jeffmorris (Posted 2006) [#2]

I think that you need JV-ODE add-on because there's a demo program with tractor-trailer.

b32 (Posted 2006) [#3]

You could try this: First, use pointentity to point the trailer to the cab. Then, move the entity with the distance between the trailer and the cab (EntityDistance)minus the allowed distance. .. edit: you should use a pivot on the connection point, parented to the cab instead of the cab itself. ie: pivot = CreatePivot(cab) moveentity pivot, 0, 0, 1

Pete Carter (Posted 2006) [#4]

thanks guys ive been playing with pointentity, but i want the trailer to pivot like a real trailer would in motion. i was hoping not to have to use any physics addons as the programs getting quite complex as it is. ill keep playing. if any one has any examples please post Pete

b32 (Posted 2006) [#5]

;setup graphics Graphics3D 800, 600, 0, 2 SetBuffer BackBuffer() CreateLight() camera = CreateCamera() PositionEntity camera, 0, 2, -8 ;create cab cab = CreateCube() ScaleEntity cab, 0.4, 0.4, 0.4 ;create pivot pivot = CreateSphere(8,cab) ScaleEntity pivot, 0.2, 0.2, 0.2 EntityColor pivot, 0, 255, 0 EntityOrder pivot, -1 ;pivot=CreatePivot(cab) PositionEntity pivot, 0, -1, 0 ;create trailer trailer = CreateCube() ScaleEntity trailer, 0.39, 0.4, 1 EntityColor trailer, 255, 0, 0 PositionEntity trailer, 0, -1.6, 0 ;main loop Repeat ;move cab If KeyDown(205) Then TurnEntity cab, 0, 0, -1 If KeyDown(203) Then TurnEntity cab, 0, 0, +1 If KeyDown(200) Then MoveEntity cab, 0, +0.1, 0 If KeyDown(208) Then MoveEntity cab, 0, -0.1, 0 ;align trailer to pivot PointEntity trailer, pivot MoveEntity trailer, 0, 0, EntityDistance(trailer, pivot) - 1 RenderWorld Flip Until KeyHit(1)

Beaker (Posted 2006) [#6]

Nice and simple demo, bram32.

Nathaniel (Posted 2006) [#7]

Hey, that's pretty fun :)

Pete Carter (Posted 2006) [#8]

thanks very much my code was almost the same apart from my align trailer to pivot bit didnt work right with the trailer snapping back to zero rotation. Hehe Pete

Pete Carter (Posted 2006) [#9]

oh sorry one more thing, in the code above how would you limit how far the cab can turn left and right? to stop the cab passing though the trailer and i want a large turning circle. Pete

Andy (Posted 2006) [#10]

>Ive been playing with pointentity, but i want the trailer >to pivot like a real trailer would in motion. i was hoping >not to have to use any physics addons as the programs >getting quite complex as it is. ill keep playing. if any >one has any examples please post Remember to set the centers of rotation between the back axles of both cab and trailer, that will make them seem more realistic without physics. Andy

Pete Carter (Posted 2006) [#11]

ive got it looking good with my model but with the code above whats the best way to limit the maximum turning angle of the cab?

b32 (Posted 2006) [#12]

For that, this example is better. The other one had the directions messed up a bit. "Yw#" is the difference in angles between the cab and the trailer. When the cab and trailer align, it is around zero: ;setup graphics Graphics3D 800, 600, 0, 2 SetBuffer BackBuffer() CreateLight() camera = CreateCamera() PositionEntity camera, 0, -8, 2 RotateEntity camera, -90, 0, 0 ;create cab cab = CreateCone() RotateMesh cab, -90, 180, 0 ScaleEntity cab, 0.4, 0.4, 0.4 ;create pivot pivot = CreateSphere(8,cab) ScaleEntity pivot, 0.2, 0.2, 0.2 EntityColor pivot, 0, 255, 0 EntityOrder pivot, -1 ;pivot=CreatePivot(cab) PositionEntity pivot, 0, 0, -1 ;create trailer trailer = CreateCone() RotateMesh trailer, 90, 0, 0 ScaleEntity trailer, 0.39, 0.4, 1 EntityColor trailer, 255, 0, 0 PositionEntity trailer, 0, 0, -2 ;main loop Repeat yw# = AngDist(EntityYaw(cab), EntityYaw(trailer)) ;move cab If KeyDown(203) Then TurnEntity cab, 0, -1, 0 If KeyDown(205) Then TurnEntity cab, 0, +1, 0 If KeyDown(200) Then MoveEntity cab, 0, 0, +0.1 If KeyDown(208) Then MoveEntity cab, 0, 0, -0.1 ;align trailer to pivot PointEntity trailer, pivot MoveEntity trailer, 0, 0, EntityDistance(trailer, pivot) - 1 RenderWorld Text 0, 0, yw Flip Until KeyHit(1) End ;----------------------------------------------------------------------------------------------------- ; AngDist() ;----------------------------------------------------------------------------------------------------- ;returns shortest difference between two angles Function AngDist#(ang1#, ang2#) Local c1# = (ang2 - ang1) Local c2# = (ang2 + 360 - ang1) Local c3# = (ang2 - 360 - ang1) If Abs(c3) < Abs(c1) Then c1 = c3 If Abs(c2) < Abs(c1) Then c1 = c2 Return c1 End Function

Pete Carter (Posted 2006) [#13]

nice example, but what ment was limiting the cabs turning angle so if you held down the left or right key the cab would stop turning before passing though the trialer. say at about 45 degrees

b32 (Posted 2006) [#14]

What I ment to say was, to achieve that, the difference between cab and trailer angle should be limited to -45..+45. Try this in the main loop: ;main loop Repeat ;align trailer to pivot PointEntity trailer, pivot MoveEntity trailer, 0, 0, EntityDistance(trailer, pivot) - 1 yw# = AngDist(EntityYaw(cab), EntityYaw(trailer)) If Abs(yw) > 45 Then TurnEntity trailer, 0, -(yw - (45 * Sgn(yw))), 0 PositionEntity trailer, EntityX(pivot, 1), EntityY(pivot, 1), EntityZ(pivot, 1) MoveEntity trailer, 0, 0, EntityDistance(trailer, pivot) - 1 End If ;move cab If KeyDown(203) Then TurnEntity cab, 0, -1, 0 If KeyDown(205) Then TurnEntity cab, 0, +1, 0 If KeyDown(200) Then MoveEntity cab, 0, 0, +0.1 If KeyDown(208) Then MoveEntity cab, 0, 0, -0.1 RenderWorld Text 0, 0, yw Flip Until KeyHit(1)

Pete Carter (Posted 2006) [#15]

thanks works great going forward reverse really screws it up, this is harder than i thought. ill keep playing with your code. thanks again bram32