Tech terms: Step vs Proportional

[howartp]

Hi,

 

I'm reading the DMX spec for various lights to help determine which I might want to buy, and coming across the terms 'Step' and 'Proportional' control. Can someone explain the difference? Also, the Robe 575AT Zoom has a colour wheel channel which has various colour positions labelled 'continual positioning' with a single DMX value, then it repeats the same colours labelled 'positioning' but with a range of DMX values - could you explain how this works?

 

I've never used a DMX colour wheel before as the lights I've used have always been plain CMY mixing, but my logic is there's say 5 coloured circles in a wheel each of which needs one DMX value to select it? Why then two sets of values, one single and one ranged?

 

Cheers,

 

Peter

[GreatBigHippy]

Proportional - This will allow fine positioning of the wheel. Allowing you to see two of the colours at once or half of one colour. Imagine a circular disc with lots of circular gels around the edge. Proportion will allow you to rotate this to any position.

 

Step - This restricts the disc to only show one colour at a time. Once you get to the next range of DMX addresses the wheel will "snap" to the next colour.

 

This is very similar to many scrollers that allow you to set either continuous or step modes.

[JDLX]

Step/Proportional is referring to what will happen when you scroll along the colour channel from a desk. Step will just jump straight to the next colour, proportional will move the wheel relative to the percentage of the channel (so you can acheive split colours etc). On most fixtures across the colour channel you will have both at set values.

 

In my experience of Robe fixtures; the continual colours come first on the attribute and then the 'step' values after that.

 

Hope that makes sense.

[niclights]

Another way to look at it is if a fixed colour wheel has proportional (also sometimes called indexed) then it is possible to fade between adjacent colours. Stepped gives easy access straight to the colours without having to worry about getting the wheel positioned accurately but won't allow fade.

[howartp]

Thanks all - that makes sense.

 

Just one further question then; if proportional is aka indexed, are Gobo's the same? I believe gobo's are indexed, but I presumed they were essentially snapped/stepped to a specific gobo rather than using two halves of neighbouring gobos as you might with colours?

 

Peter

 

 

 

[timsabre]

Just one further question then; if proportional is aka indexed, are Gobo's the same? I believe gobo's are indexed, but I presumed they were essentially snapped/stepped to a specific gobo rather than using two halves of neighbouring gobos as you might with colours?

 

"Indexed" for gobos normally refers to rotation of gobos rather than selecting which gobo.

 

Gobo wheels normally snap to the gobo, then on the rotation control you can select either indexed mode, where you can rotate the gobo to any fixed position (for example to get a logo the right way up), or continuous rotation at variable speed.

[howartp]

Just one further question then; if proportional is aka indexed, are Gobo's the same? I believe gobo's are indexed, but I presumed they were essentially snapped/stepped to a specific gobo rather than using two halves of neighbouring gobos as you might with colours?

 

"Indexed" for gobos normally refers to rotation of gobos rather than selecting which gobo.

 

Gobo wheels normally snap to the gobo, then on the rotation control you can select either indexed mode, where you can rotate the gobo to any fixed position (for example to get a logo the right way up), or continuous rotation at variable speed.

 

Ah, that makes sense.

 

Thank you.

 

Peter

[Ynot]

Stepped MAY also mean that the motors being used rotate the wheels in hard steps instead of a smooth rotation.

That means that when moving a gobo or colour wheel, for example, you see a juddery movement rather than smooth scrolling.

[niclights]

Stepped MAY also mean that the motors being used rotate the wheels in hard steps instead of a smooth rotation.

That means that when moving a gobo or colour wheel, for example, you see a juddery movement rather than smooth scrolling.

I've read a lot of fixture manuals when writing personalities and I've never seen that. 'Stepped' and 'Proportional' are used by Martin and Robe (how all channel mappings should be written IMO).

[Ynot]

Usually used on budget fixtures (as they're very much cheaper) yes that is indeed what can happen with some stepper motors.

A stepper motor is a brushless, synchronous electric motor that converts digital pulses into mechanical shaft rotation. Every revolution of the stepper motor is divided into a discrete number of steps, in many cases 200 steps, and the motor must be sent a separate pulse for each step. The stepper motor can only take one step at a time and each step is the same size. Since each pulse causes the motor to rotate a precise angle, typically 1.8°, the motor's position can be controlled without any feedback mechanism. As the digital pulses increase in frequency, the step movement changes into continuous rotation, with the speed of rotation directly proportional to the frequency of the pulses. Step motors are used every day in both industrial and commercial applications because of their low cost, high reliability, high torque at low speeds and a simple, rugged construction that operates in almost any environment.

<quickly Googled source>

 

Decent kit using higher quality stepper motors (up to the micro-steppers mentioned on the link above) will of course not have the budget 'judder'.

 

E2A...

Having just re-read the OP, I think I see where the difference of opinion lies - I read it originally as referring to the types of motor in the fixtures, which on reflection is NOT what the OP is on about - so my apologies for the misleading veer slightly off topic...