Continued from June 2008 CTI Newsletter
RDM: What It Is, How It Works, and How You Will Use It.
By Martin Chisnall
What on
earth is RDM?
It’s
possible you’ve never heard of it, or maybe you have heard of it, but
aren’t too sure what it is. RDM stands for Remote Device
Management. It is a new ‘extension’ to DMX, that ubiquitous system
we all use to connect our lighting consoles to our dimmers, moving lights
and other varied lighting (and sometimes not-so lighting) equipment.
Since the
inception of DMX back in 1986, and through a couple of later revisions, it
has always been a ‘one way’ control system. Data only ever flows in one
direction, from the lighting controller outwards to whatever it may be
connected to. And the controller has no idea what it is connected to,
or even if what it thinks it’s connected to is working,
switched on, or even there at all!
RDM
changes all that. For the first time, equipment can answer back!
An RDM
enabled moving light, for example, can tell you many useful things about its
operation: The
DMX address it is set to, the operating mode it is in, whether its pan or
tilt is inverted, and how many hours since
the bulb was last changed, all without ever having to get out the
ladder. RDM
enabled fog machines can tell you how much fluid they have left in
them,
But RDM
can do more than that. It isn’t limited to just reporting back, it can
change things as well. As its name suggests, it can remotely manage your
device. So if your fixture is set to the wrong DMX address, you can
change it. If your widget is in the wrong mode, you can change it, and if
your moving light pans left when all the others pan right, you can change
it.
RDM allows
you to assign friendly names to fixtures. No more looking up DMX numbers in
pages of hook-up paper work. That moving wash light behind the door can
finally be called ‘door back light’, and the scroller at
the end of Electrics 2 can shrug off its former title of DMX2.435,
and rejoice in its new name, #2
SL Pipe End Scroller.
So how
does it work, and what do you need?
The really
clever bit is that RDM has been designed to work over your existing DMX
network. It interleaves its messages with the regular DMX signal, over the
same wires. There is no need to change your cable, but because the RDM
messages now go in two directions, any in-line DMX processing you have will
need to be changed for new RDM hardware. This will most commonly mean that
DMX splitters and buffers will need to be upgraded for RDM ready devices.
You will
also need some kind of RDM controller. Presently these are devices that plug
in to the DMX line and talk the RDM language. They put the messages on to
the DMX line, and listen for any replies, and display the results via an
attached computer. In the future it is probable that lighting consoles and
other lighting controllers will become available with RDM controllers built
in. And then of course, you need some RDM ready equipment to connect
to.
The RDM standard was officially released in 2006, but to this date, take up has been relatively slow. This is probably for a number of reasons, not least of which is that there are few RDM enabled products currently available. But this is slowly changing, initially led by the smaller ‘niche’ lighting control companies, but it may not be long before the big players start to add RDM to their existing product range. One available RDM application is City Theatrical's own SHoW DMX wireless DMX system. Here are some of the things it can do via RDM:
Additionally,
take up in the major hire companies will involve some significant investment
in new equipment. This may be hard to justify when their existing equipment
stock works perfectly well, and perhaps we will only see RDM equipment
becoming available for hire when it is bought to replace equipment which has
reached the end of its life.
Everybody
uses equipment in different ways, and some of the features RDM can offer may
be of little apparent use to some people, whilst to others they may be the
ideal solution to a long standing problem.
Take, for example, the ability to remotely set DMX addresses via RDM. For a production electrician fitting up a
RDM also
has the ability to read and report operating statistics and error conditions
from any enabled equipment that supports it. This opens up the possibility
of remotely monitoring the condition of your lighting rig and getting notice
of failed equipment, or even advanced notice of things that may be cause for
concern. For example, a moving light that reports a very high bulkhead
temperature may be suffering from a failed fan or clogged filter, or a
scroller that reports a high motor current may have a jammed scroll.
What does the future hold?
In the
future it may be possible to remotely monitor a lighting rig over the
internet, enabling off site hire and production companies to know the health
of the rig, and if something fails, what spare parts to turn up with to
effect a speedy and efficient repair.
But in the
future, RDM may lead to the development of a host of new devices that
don’t even exist at the moment. Devices that, in themselves, provide no
visual effect on stage, but will exist purely because they can talk back and
tell you something useful about your production, over the existing DMX
cabling.
For
example, how about a three phase power meter which clamps on to your
incoming mains supply to your dimmer racks, and can report the line voltage
and power consumption back to the lighting operator using RDM. No more
guessing how much further you can push those fuses!
The possibilities are huge, and I suspect RDM will find applications that we cannot even imagine at the moment.
Martin
Chisnall (mchisnall@citytheatrical.com)
is City Theatrical's European Operations Manager, and runs City
Theatrical's London Office. Prior to joining CTI, he worked as a
freelance theatrical production electrician, working in
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