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LTC Timecode Freezes When Robot Motors Engage

CONFIRMED RESOLVED ALL RIGS BOTH

Summary

LTC timecode reads correctly in Flair while the robot is disengaged, but freezes (stops ticking) the moment the robot is engaged. When the robot is disengaged again, timecode resumes from the correct current time. Caused by EMI from the robot servo system or a ground imbalance between the LTC source and the robot power.

Symptoms

  • Timecode ticking normally in the bottom-right of the Flair main window
  • Engage the robot → timecode display freezes at a specific value
  • Disengage the robot → timecode immediately jumps forward to the correct current time
  • Timecode cable being unplugged and re-plugged does not help while robot is engaged

Root Cause

Electrical interference from the robot servo system corrupting the LTC audio signal. Confirmed causes:

  1. SDI cable routed through the Bolt arm — carrying the SDI video feed from the camera through the robot arm introduces ground loops between the camera, the arm, and the Flair system. The servo EMI couples into the LTC signal.
  2. Ground imbalance between LTC source and robot power — Flair PC and LTC source (e.g. AJA I/O) powered from different distribution points; different ground reference corrupts the signal under load.

Solutions

Solution A — Remove SDI from Arm (Confirmed fix)

If you are routing an SDI cable from the camera through the Bolt arm to an external recorder/QTAKE:

  1. Remove the SDI cable from the arm run.
  2. Instead, run the SDI direct from the camera to the external device (bypassing the arm entirely).
  3. Reconnect and test — timecode should remain stable when the robot engages.

Solution B — Common Ground / Common Power Strip

  1. Plug the Flair PC and the LTC source device (AJA I/O, Tentacle Sync, etc.) into the same power strip / distribution point.
  2. This ensures a common ground reference between the LTC source and the Flair system.
  3. Test by engaging the robot — timecode should remain stable.

Solution C — Wireless Audio for LTC

If the source cannot be moved to the same power or the SDI issue cannot be resolved:

  1. Use a wireless audio transmitter (Comtec or similar) between the LTC source and the RT14 LTC input.
  2. Wireless provides full electrical isolation between the LTC source and the Flair system.
  3. An additional benefit: wireless units have a volume control, allowing you to set the LTC signal level precisely — LTC is sensitive to signal level (too loud or too quiet both cause read failures).

Solution D — Phone or Laptop as LTC Source

A mobile phone or laptop playing an LTC .wav file is electrically isolated from the robot system:

  • Phone headphone output → RT14 3.5mm LTC input (stereo-to-mono adapter may be needed)
  • LTC WAV files: elteesee.pehrhovey.net

Notes

  • Simon Wakley (2020): "Timecode into RT units is not robust. Splitting the signal, ground imbalance, too loud, too quiet — all cause issues."
  • This problem is unrelated to the Flair serial/TCP configuration — that's for triggering mode, not signal stability.
  • Ground issues are more common on location when power distribution is not properly set up by the gaffer.

References

Official Documentation

RT-14 Quick Start Guide — p.26: LTC In (3.5mm TRS) Wiring

RT-14 Quick Start Guide — p.11–12: Troubleshooting

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Media Text / Description

  • Media 1: 2020-09-24 20:12 - ~ Tran Quang Duy

WhatsApp Excerpts

  • 2020-09-24 20:11 - ~ Tran Quang Duy: Hi guys. We try to trigger the move by using timecode and it ok for 2 days ago. Today we try with another fbx file and this bug come up. When we do not engage the robot the timecode is sync and running. But when we engage the robot the timecode is freeze. Anyone know how to fix this?
  • 2020-09-24 20:12 - ~ Tran Quang Duy:
  • 2020-09-24 20:24 - Tom D: That is a curious one - and I would be keen to see how the issue is solved. If you unplug and then plug back in the timecode cable after engaging does the TC remain frozen?
  • 2020-09-24 20:28 - ~ Tran Quang Duy: Yes it still freeze. But when i disengage the timecode immediately update. Like freeze at 00:05 and disengage the number will automatic update to now like 00:16
  • 2020-09-24 20:40 - ~ joel.spezeski: It seems to be electrical interference. We found that if we disconnected the SDI feed from the camera, Flair continued to receive the timecode (from QTAKE playback). Then we tried running the SDI cable direct from the camera to QTAKE instead of passing through the Bolt arm. This resolved the issue.
  • 2020-09-24 23:46 - ~ Simon Wakley: Timecode into RT units is not robust. Splitting the signal, ground imbalance too loud too quiet all cause issues. You can try going wirelessly and using a comtec or similar wireless audio and this has the advantage of having a volume control. Good luck!
YouTube 11 - Camera Triggering and Synchronisation Flair Classic

▶ 05:15 — Film and video sync: enabling LTC lock in Flair