why does the circle shape is in fact a 8 ?

[Mystic]

I've met an interesting bug this WE on a show with my pearl 2000 (upgraded to the latest 2004 software). When i playback the circle shape (the first one), the moving head do a 8 shape instead.

Detail : I had 6 MAC250 (in mode 2) patched ok, everything was fine (colors, gobos, etc..) and 2 starway elite servospot 250 (also ok). I made a brand new set of personnality disks last week also so i should be up to date for everything. But when i try to play back a circle shape (even at very low speed) it always end up in playing a 8 shape (double circle ?). This happens with both fixtures, even after a clean wipeall, load SG.dat, patch, apply shape.

Is this a known (or unknown) bug ? did I missed something in the configuration ? but the most important question is : how do i do a clean circle shape ?

thanks for your help.

[niclights]

That's a bit strange! Unless the shape or pattern has changed in the shape file I can only think it was to do with fixture orientation.

The shape is based on a Sin wave, with the P & T 90degrees out of phase.

Moving mirrors will always do the shape as expected, but heads might not.

eg. If you mount a head underneath a truss and set a circle revolving around a straight-out audience position the head will tilt up and down and spin left and right as per the sin wave, giving a circle.

If you mount a head on the front of a truss then things go wrong. To achieve a circle in this orientation the pan would need to be infinite, with a fixed tilt. When using the circle shape the unit will often find itself panning around a tilt of 50%, thus achieving no actual movement.


Apologies if I am stating the obvious!

[Mystic]

I think you're right, i've never noticed it but it is impossible for a moving head to do a clean circle if the point (50%,50%) is inside it... i nearly broke my ankle by trying to understand it visually but that must be it... ok next time i'll try it with that in mind (and i'll put more scans in my kit also).

Many thanks.

[niclights]

Took me a while to figure it out too. For all their benefits these movers have just as many annoyances (when they work!) I always 'under-hang' now and work everything else around.

Note that it is also, to my knowledge, impossible to to have movers on the deck and in the truss (ie inverted) move in the same direction with both P & T.

[jgubby]

A more mathematical look at it, there are two different co-ordinate systems at work in the different fixtures.

Moving mirror lamps use the standard X and Y coordinates, which means up and down. Yolk fixtures use R and theta, which is the distance from the middle, and the angle. The fixture has to do clever stuff to translate between these. But this means, if you think about it not all movements can be translated between the two!

Phew!

James

[Ed]

This is a problem we hear of quite frequently.

The fixture could also be hitting a flip point whilst it is playing back the shape. Move the head so that it isn't straight up or down and and try playing back the shape again.

Another thing to try would be to reduce the shape size and the shape time.

[thedj]

the answer i got from the good boys at AC is that it goes past a point 0,0 and doesn't know where to go from there.

ed

[jgubby]

Nope, because in order to cross the 0,0 point it would have needed to have decided to cross across the circle. i.e it wouldnt start the movement and not 'know' where to go.

[niclights]

It can be hard to understand, but it is simply (as already described) due to the way a moving yoke fixture works. A good example is to locate a fixture and then start a pan shape. The unit will revolve, but of course it makes no difference to the beam position which remains constant.

What we need is a unit with infinite pan. I wish someone would try developing this - ideally a very shallow base with all motors & control contained in the yoke. Power transmission through tracks (ballast could be remote if necessary) and wireless data. Introduces some control issues ie. you would need indexed as well as continuous rotate options, much like a gobo rotate, but surely this is worth a go?

[Vincent]

What we need is a unit with infinite pan. I wish someone would try developing this - ideally a very shallow base with all motors & control contained in the yoke. Power transmission through tracks (ballast could be remote if necessary) and wireless data. Introduces some control issues ie. you would need indexed as well as continuous rotate options, much like a gobo rotate, but surely this is worth a go?

It already exists, but is damn expensive, not so impressively well built and light output could be better. Plus, all the optics are in the base, not in the head. But still is an awesome effect: GLP Patend Light.

http://www.glp.de/en/Head_moved_Systems ... _1200.html

Speed of head: 7 rounds/second. Verrrry impressive!

[niclights]

Wow. Not something you see everyday! Tnx.