Controlling Moving Heads, Foggers and Effects Over DMX
Moving heads, fog machines and effect units are DMX’s most spectacular application. They are also the side that eats the most channels, runs the hottest and needs the most maintenance. Controlling them takes a different way of thinking from dimming a par.
In short
- Moving heads divide into spot, wash, beam and hybrid, each with a different beam character.
- Pan and tilt are almost always 16-bit; the speed channel governs smoothness.
- Lock the control/reset channel or the fixture will reset mid-show.
- Write focus positions into palettes, never straight into cues.
- Use haze, not fog, to reveal beams — and clear fire detection in advance.
- The usual cause of lost output is not a fault but dirty lenses and filters.
Types of moving head
| Type | Beam character | Typical use |
|---|---|---|
| Spot | Hard edged, takes gobos and focus | Projecting patterns, sharp accents on stage |
| Wash | Soft and wide | Washing an area, filling colour |
| Beam | Very narrow, visible shaft in the air | Aerial effects, concerts |
| Hybrid | Does all three, compromising on each | Touring rigs limited by budget and truck space |
Typical channel structure
A moving head’s channel list is far longer than a par’s. Common channels:
- Pan / tilt — almost always 16-bit: pan coarse, pan fine, tilt coarse, tilt fine.
- Pan/tilt speed — governs smoothness. Set too fast and movement looks jerky.
- Dimmer and shutter — separate channels; the shutter does mechanical blackout and strobe.
- Colour — a colour wheel (discrete) or CMY/RGB mixing (continuous).
- Gobo wheel and gobo rotation — where discrete and continuous channels sit side by side.
- Focus, zoom, iris, prism, frost — shaping the beam.
- Control / reset channel — restarts the fixture at certain values. It needs care so it is never triggered by accident.
Watch the control channel
On most moving heads a specific range of values resets the fixture or douses the lamp. Apply an effect engine to that channel by mistake and every head resets mid-show. Before you start programming, find those ranges in the manual and park or lock that channel on the console.
Rigging and first setup
- Homing. The fixture drives all motors to a reference position on power-up. Make sure the movement envelope is clear while it does.
- Pan/tilt invert and swap. Heads hung inverted have reversed pan or tilt; correct it in the fixture menu. Set every head in a group the same way or your effects will fall apart.
- Position palettes. Write focus positions into palettes, not directly into cues.
- Safety bond. Always fit a steel safety wire in addition to the clamp; vibration from movement can loosen a clamp.
- Cable slack. Leave enough for 540° of pan without snagging.
Fog and haze machines
What makes a beam visible in the air is atmosphere. Two different devices exist and should not be confused:
- Fog machine — produces a dense, visible cloud. It is an effect in itself and disperses quickly.
- Hazer — produces a fine, even mist that hangs for a long time. This is what you actually use to reveal beams.
DMX control is usually two channels: output level and fan speed. Things to watch:
- The unit has a warm-up time; switch it on well before the show.
- Output stops while the heater recycles; allow for that if you need continuous haze.
- Fire detection systems can mistake haze for smoke. Speak to the venue in advance; in many buildings isolating detectors is a formal procedure. This is a safety matter, not a formality to skip.
- Ventilation clears haze quickly; plan the HVAC settings around the show.
Heat, dust and maintenance
Moving heads generate heat continuously and their fans pull in dust. Over time:
- Dust builds on lenses and gobos and light output drops noticeably.
- Fan filters clog, the fixture overheats and drops into protection mode.
- Motor belts loosen, positions drift and heads take the same palette to different places.
- Colour wheels develop positioning errors.
A regular maintenance plan removes most “fault” reports: lens cleaning, filter servicing and calibration checks at the start of each season. Reading the fixture’s running hours from its menu and logging them takes the guesswork out of service intervals.
Common problems
| Symptom | Likely cause |
|---|---|
| Heads take the same palette to different places | Calibration drift, or inconsistent pan/tilt invert settings |
| Jerky movement | Pan/tilt speed set too fast, or a low refresh rate |
| Fixture resets mid-show | Values reaching the control channel by accident |
| Output has dropped over time | Dirty lenses and gobos; lamp life |
| Fixture shuts down after a while | Overheating; clogged filter or poor ventilation |
| Beams not visible in the air | Insufficient haze, or ventilation clearing it |
Related articles
Project and product support
Stuck somewhere in your installation, or unsure which product fits? Drop us a line for project consultancy and product support.
