Scratch

Rotation Velocity. Gimme a sec, I'll type up a script.

I would recommend this script.  Normal direction means that 0 corresponds to pointing right, 90 to pointing up, 180 to pointing left, etc.  This allows you to perform trigonometric functions accurately.  Adjust the starting values for Friction, Velocity.Max, and Speed, as you like.  They control how fast the object accelerates, how quickly it slows down, and how fast it can go.  Make sure that friction is a positive number less than 1 (if you want it to slow down).  Numbers closer to 0 will cause it to slow down more quickly. 

when gf clicked
set [Friction v] to [0.8] // 0 < Friction < 1, in general.  
set [CurrentDirection v] to [0] // "Normal" direction, not Scratch direction.
set [Velocity.R v] to [0] // Rotational velocity.
set [Velocity.Max v] to [15] // Maximum velocity.
set [Acceleration.R v] to [0] // Rotational acceleration.
set [Speed v] to [0.5] // Rotational speed. 
forever
set [Acceleration.R v] to [0]
if <key [right arrow v] pressed?>
change [Acceleration.R v] by ((-1) * (Speed))
end
if <key [left arrow v] pressed?>
change [Acceleration.R v] by ((1) * (Speed))
end
if <not<<key [right arrow v] pressed?> or <key [left arrow v] pressed?>>>
set [Velocity.R v] to ((Friction) * (Velocity.R))
end
change [Velocity.R v] by (Acceleration.R)
if < ([abs v] of (Velocity.R)) > (Velocity.Max) >
set [Velocity.R v] to ((Velocity.Max) * (([abs v] of (Velocity.R)) / (Velocity.R)))
end
change [CurrentDirection v] by (Velocity.R)
set [CurrentDirection v] to ((CurrentDirection) mod (360))
point in direction ((90) - (CurrentDirection))
end

I know nothing about trig, mainly due to my year 9 knownloedge xD

sanjayraj wrote:

Is this what you need?

when gf clicked
forever
turn (15) degrees

That's a rotation script...

Hhehe sanjayraj, thanks, but I am looking for a script like the one above ^^ xD thanks anyway!

daniel_j wrote:

amcerbu wrote:

I would recommend this script.  Normal direction means that 0 corresponds to pointing right, 90 to pointing up, 180 to pointing left, etc.  This allows you to perform trigonometric functions accurately.  Adjust the starting values for Friction, Velocity.Max, and Speed, as you like.  They control how fast the object accelerates, how quickly it slows down, and how fast it can go.  Make sure that friction is a positive number less than 1 (if you want it to slow down).  Numbers closer to 0 will cause it to slow down more quickly. 

when gf clicked
set [Friction v] to [0.8] // 0 < Friction < 1, in general.  
set [CurrentDirection v] to [0] // "Normal" direction, not Scratch direction.
set [Velocity.R v] to [0] // Rotational velocity.
set [Velocity.Max v] to [15] // Maximum velocity.
set [Acceleration.R v] to [0] // Rotational acceleration.
set [Speed v] to [0.5] // Rotational speed. 
forever
set [Acceleration.R v] to [0]
if <key [right arrow v] pressed?>
change [Acceleration.R v] by ((-1) * (Speed))
end
if <key [left arrow v] pressed?>
change [Acceleration.R v] by ((1) * (Speed))
end
if <not<<key [right arrow v] pressed?> or <key [left arrow v] pressed?>>>
set [Velocity.R v] to ((Friction) * (Velocity.R))
end
change [Velocity.R v] by (Acceleration.R)
if < ([abs v] of (Velocity.R)) > (Velocity.Max) >
set [Velocity.R v] to ((Velocity.Max) * (([abs v] of (Velocity.R)) / (Velocity.R)))
end
change [CurrentDirection v] by (Velocity.R)
set [CurrentDirection v] to ((CurrentDirection) mod (360))
point in direction ((90) - (CurrentDirection))
end

Agghhhh, I followed your script exactly, and it is awesome, but it does not slow down, it just instantly stops...? I followed your instructions as best as I could..... any ideas?
Thanks
Dan Jones

Did you try mine?

http://www.scratch.mit.edu/projects/daniel_j/2636046
^^ that is the test Amcerbu 

Here you go.

I simplified it a ton, amercbu, your script is overly complicated. Remember, not every user is as math-oriented as you. ;D

Anyways, dan, here is a very basic rotation script. You can change the (.94) in the script. A smaller fraction will make it slower, a larger fraction will make it very fast.

SciTecCf wrote:

daniel_j wrote:

amcerbu wrote:

I would recommend this script.  Normal direction means that 0 corresponds to pointing right, 90 to pointing up, 180 to pointing left, etc.  This allows you to perform trigonometric functions accurately.  Adjust the starting values for Friction, Velocity.Max, and Speed, as you like.  They control how fast the object accelerates, how quickly it slows down, and how fast it can go.  Make sure that friction is a positive number less than 1 (if you want it to slow down).  Numbers closer to 0 will cause it to slow down more quickly. 

when gf clicked
set [Friction v] to [0.8] // 0 < Friction < 1, in general.  
set [CurrentDirection v] to [0] // "Normal" direction, not Scratch direction.
set [Velocity.R v] to [0] // Rotational velocity.
set [Velocity.Max v] to [15] // Maximum velocity.
set [Acceleration.R v] to [0] // Rotational acceleration.
set [Speed v] to [0.5] // Rotational speed. 
forever
set [Acceleration.R v] to [0]
if <key [right arrow v] pressed?>
change [Acceleration.R v] by ((-1) * (Speed))
end
if <key [left arrow v] pressed?>
change [Acceleration.R v] by ((1) * (Speed))
end
if <not<<key [right arrow v] pressed?> or <key [left arrow v] pressed?>>>
set [Velocity.R v] to ((Friction) * (Velocity.R))
end
change [Velocity.R v] by (Acceleration.R)
if < ([abs v] of (Velocity.R)) > (Velocity.Max) >
set [Velocity.R v] to ((Velocity.Max) * (([abs v] of (Velocity.R)) / (Velocity.R)))
end
change [CurrentDirection v] by (Velocity.R)
set [CurrentDirection v] to ((CurrentDirection) mod (360))
point in direction ((90) - (CurrentDirection))
end

Agghhhh, I followed your script exactly, and it is awesome, but it does not slow down, it just instantly stops...? I followed your instructions as best as I could..... any ideas?
Thanks
Dan Jones

Did you try mine?

I did    very good thankyou!

Yes, amcerbu has gone a bit overboard with the coding. 

Simple rotation velocity like the one posted by SciTecCf is probably enough. 

Last edited by fg123 (2012-06-26 16:05:59)

Wes64 wrote:

Here you go.
I simplified it a ton, amercbu, your script is overly complicated. Remember, not every user is as math-oriented as you. ;D

Yeah, sorry about that daniel_j.  Math is my favorite subject, and I tend to get carried away a bit...

About the script not working:

I think you made a small mistake copying it into Scratch.  That's why it would stop immediately after the keys were released. 

Your program says:

if <not<<key [right arrow v] pressed?> or <key [left arrow v] pressed?>>>
set [Velocity.R v] to ((Friction) * (Acceleration.R)) // Caught you, bug!
end

Because of previous statements that set Acceleration.R to 0 (and ensure it remains at 0 if no keys are pressed), the object will stop immediately when you let go of the arrows, as Velocity.R will equal 0. 

Here's the fixed version:

if <not<<key [right arrow v] pressed?> or <key [left arrow v] pressed?>>>
set [Velocity.R v] to ((Friction) * (Velocity.R))
end

If you want, I can upload a version to my test account (although it looks like Wes64 got there first). 

Wes64 is right about the friction variable.  A value fairly close to 1 is often the best (the closer you are, the slower it slows down).  To apply friction, the program sets the velocity to itself multiplied by the friction variable.  A value closer to 1 results in a new velocity closer to the original value.  I would recommend between 0.9 and 0.99 for this, although you should play around with different values to find what you like. 

Hope that helps.


MAJOR EDIT (please read):  Actually, now that I look at it again, I would get rid of the if statement checking to see whether no keys are pressed, and simply apply friction regardless.  That'll look smoother.

So, just

set [Velocity.R v] to ((Friction) * (Velocity.R))

...not...

if <not<<key [right arrow v] pressed?> or <key [left arrow v] pressed?>>>
set [Velocity.R v] to ((Friction) * (Velocity.R))
end

Last edited by amcerbu (2012-06-26 17:48:30)

^^ The only problem with that script is that if both keys are pressed, the program will see a right keypress and continue accelerating right, rather than slowing down.  It turns out to work more smoothly if friction is applied constantly, without waiting until the arrow keys aren't pressed.

pipercubjl wrote:

You ALL are going overboard.

(Look below for proof)


var rot = 0
if right arrow key down
     var rot +1 
     if (var rot)> 0
            var rot -0.25

if right arrow key down
     var rot -1 
     if (var rot)< 0
            var rot +0.25
rotate (var rot) degrees


This is the basic velocity script I always use.
Thanks 

Hope I helped.