Stopping rotating gobos the right way up

[pscandrett]

Hi

 

I was thinking about this the other day and I can't come up with a solution... wondered if anyone else had any tips? It relates specifically to a Mac 250+ (and the control console I have in mind is a Pearl, but I don't think it's actually relevant as the issues arise from the way the Mac works and is controlled, I think).

 

Imagine the scenario... you have a custom gobo in one of the gobo, er, locations. This is normally projected the right way up, say onto a cyc. The way the macs have their DMX assigned is that the 'gobo' channel goes through the gobos in sequence in 'orientation' mode and then through them in sequence again in 'constant rotate' mode (and then in 'bounce' mode but that's irrelevant here). The gobo rotate channel therefore is interpreted differently according to which gobo setting it's in - if it's in 'orientation' mode then the gobo rotate channel is interpreted as the absolute position of the gobo (to get it the right way up) and in the 'constant rotate' mode it defines the direction and speed of rotation.

 

So, back to our scenario; the logo is projected the right way up on a cyc or something. If one wants to rotate that gobo from a standing start that's not too much of a problem; you set your desk to snap the gobo channel to the 'rotate' mode/version of your gobo and then the gobo rotate channel to the speed/direction in which you want it to rotate - and voila, a rotating gobo from the still version.

 

However... if you want to stop it, the right way up... doing this in reverse doesn't work. That is, setting the gobo channel back to its 'orientation' mode and the gobo rotate channel to the right place for the up-the-right-way orientation gets it back to the right place but in a really messy way - it rotates the gobo at high speed (whilst the mac works out which way is 'up' for the gobo in question by waiting for the magnet to go past, I guess) and then spins it into the desired position.

 

A far better effect from the viewers' point of view would be for the rotating gobo to either a) keep going until it's the right way up and then stop or b) for the rotating gobo to slow down and stop the right way up (presumably this involves more desk programming over a period of time - say, a second or two.) However, with regards to a) in particular, I can't think of a way of getting this to happen - mainly because the desk doesn't know which way up the gobo is at any point in time, so just snapping the gobo to the appropriate settings will result in the travesty of visual loveliness as described above as the mac spins it round to the right place. If the desk somehow knew when the gobo was the right way up (and then therefore that /that/ was the moment to send its new DMX control signals to stop it) then that'd work but there's no feedback from the mac.

 

Can anyone think of a way of achieving this? Or, if I wanted to do something like this, would the most elegant way be to fade out the rotating gobo, snap the gobo to where it should be and fade up again? Am I missing something here and there's an easy way of doing it?

 

(This is partly hypothetical but also the sort of thing I might want to do at some point! :-)

 

Thanks in advance...

[jfitzpat]

In general, I think that the behavior is unavoidable. In addition to variations of the approach you mentioned (go out of focus for the switch, use a prism change to cover it, etc.), I have also simulated rotation with the index mode.

 

That is, I fade the position up and down to get a back and forth rotation look. Then I can finish the fade to a desired position. I did this for a corporate event where the 'logo' was broken into pieced on multiple fixtures and I needed them to all stop moving and line up smoothly on the down beat.

 

-jjf

[soundo26]

the stop point can be set up in the Pearl when programming, but beware of the gobos slipping round within the holder.

 

 

:P - Completely unnecessary quote of entire lengthy OP removed. Please read this and this.

[gareth]

the stop point can be set up in the Pearl when programming

Read pscandrett's post again, and you'll see that he already knows that - his question concerns how to get to that 'stop point' from a continuous rotation in an elegant way.

[johnhuson]

Instead of changing from indexing to rotating and rotating the gobo the way, it might work if you create a chase of indexed positions, so for example first step 1 @ 0 degrees, next @ 10 degrees and so on that might work, providing you have a nice smooth fade between each step, obviously the more steps there are in the chase the smoother it will be.

 

I've used this method when moving a gobo from one position to the other, but keeping the gobo the same way up as it moves.

[Tomo]

The problem is endemic to the way many moving lights are controlled, so it applies to every desk you might wish to control them with!

 

There are two ways I've found to do this, depending on how the fixture handles gobo angular position control:

 

A) If the gobo angular position always moves 'shortest-path', then don't use the continuously rotating gobo feature at all - create a sawtooth effect that fades 0-255 then snaps back to 0 etc on the rotation ANGLE channel.

 

This will then fade nicely into any desired end position.

 

However the smoothness of the jump 'over the top' depends on the algorithm used in the fixture, and you can't spin the gobo at anywhere near maximum speed.

 

While you can use a chase instead of an effect, it's not as controllable and will tend to be very jerky.

 

B) The rotating gobo doesn't move shortest-path, then there isn't an elegant way to do it - the only way I've found to do this is to time the rotation speed and create an automated cue sequence that begins rotation, rotates for a fixed time and then exits rotation with the gobo/litho just ahead of the position it finished up at, and then fades into the desired position.

It's a evil hack, takes ages to get right, and can't be easily changed.

 

It's very easy to test if the rotating gobos move shortest-path - rotate them to 255, then snap to zero.

It should just move on a short distance. If it spins all the way back, then you're pretty much stuffed!

 

If you want to use maximum spin speed and then gradually slow it down to a chosen standstill, then you'll have to use a combination of the two techniques and fiddle until the transition from speed to position control looks ok.

[peter]

Following on from Tomos reply, I believe there is a menu option in Macs to turn Shortcuts on or off. This, I believe, changes whether or not the wheels take the shortest route, or the full channel values.

[TommyToad]

Following on from Tomos reply, I believe there is a menu option in Macs to turn Shortcuts on or off. This, I believe, changes whether or not the wheels take the shortest route, or the full channel values.

 

That is only for the color wheel, the gobos are on a wheel also but the rortation is done with a rubber band (actually two) around the gobos. So it does not work that way.