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Multi-Robot Trigger Offset Calibration

[BOTH] When running two or more robots from a trigger cable, there is always a delay between the trigger signal leaving one system and the second system starting its move. This offset must be measured and compensated to ensure moves are in sync. This guide covers measuring the offset with bloop lights and trimming it in Flair.

Experienced operators only

Multi-robot operation carries significant safety risks. MRMC recommends this is only done by experienced and/or fully trained operators, with all safety implications fully risk assessed before attempting. Read the full safety section below before proceeding.

The Three Levels of Multi-Robot Safety

Level 1 — Simple trigger (independent e-stops)

Connect two robots using the Dual Robot Trigger cable (MRMC part 37W). If you have two trigger boxes, connect the output from one to the input of the other. The cable is symmetric — either end can be master or slave.

  • Programme Trigger 3 on the master to send the trigger output at the desired frame.
  • Programme Input 2 on the slave to start its move when triggered.

Separate e-stops

In this configuration each robot has its own independent e-stop. If the robots are within reach of each other or operated by a single operator, you should link the e-stop systems (see Level 2 or 3).

Level 2 — Master/Slave e-stop

Earlier generation Bolts and Bolt Jnrs can be wired so that pressing the master e-stop stops both robots. The slave retains its own e-stop, which only stops the slave (not the master).

Hardware modifications are required — contact MRMC for advice specific to your rig generation.

Level 3 — Universal e-stop (highest safety)

Recent Bolt family robots include the Universal e-stop system as standard. In this configuration:

  • Every robot is dual-channel and redundant.
  • All robots have mutual feedback — if any one robot stops for any reason, all others stop automatically.
  • This is the highest safety level and the best choice for multi-robot production.

Earlier systems can be upgraded to Universal e-stop — contact MRMC for cost and component requirements specific to your robot generation.

Measuring the Trigger Offset

A trigger cable introduces a constant delay — approximately 4–6 frames at 50 fps in typical setups. The delay must be measured on your specific system.

Procedure using bloop lights

  1. Attach a bloop light to each robot system (e.g. one bloop per Flair system).
  2. Programme each system to flash its bloop light at frame 0 of the move.
  3. Position the bloop lights next to each other so both are visible in the same camera frame or to a single observer simultaneously.
  4. Add a hold at the beginning of the move — this gives you time to stop all systems if they appear out of sync before the actual move starts.
  5. Run both systems.
  6. Observe the bloop lights: if they flash at different times, the difference in frames is your trigger offset.
  7. Adjust the trigger timing on the master (the frame at which it sends the trigger output) until both bloop lights flash simultaneously.

"I had roughly 4–6 frames at 50fps delay using the input trigger." — @julian

Use the hold time

Programming a hold at the start of the move gives you a safety window. If the bloop lights show they are out of sync, you can stop both rigs before the main move executes. Use this every time you set up multi-robot triggering on a new day or after any cable changes.

Trimming the Offset in Flair

Once you know the delay in frames, trim it by adjusting the trigger frame on the master:

  • If the slave starts N frames late, move the master's trigger output N frames earlier in the move.
  • Run again with bloop lights to verify.

For fine trimming, convert the frame offset to a timecode offset and adjust via TC calculation if your system uses timecode sync.

Network API Sync (Quad API / Multi Flair)

MRMC also provides a Multi Flair API utility (and Quad API controller) for running multiple Flair systems over a network. This is useful for browsing or single-frame control but:

  • It uses the network API, which is not under INtime real-time control.
  • It is not frame-accurate for continuous move synchronisation.
  • For frame-accurate triggering of continuous moves, always use hardware trigger cables.

Source: Connecting multiple robots — talk.mrmoco.com