Foto Master

Robot Stops Mid-Drawing

Updated 5 days ago · 4 min read

A DexArm that stops partway through a sketch -- or appears to lose connection to the Mac mid-event -- typically traces back to one of three causes: the Mac going to sleep, a flaky USB cable, or the powered hub losing power. This article walks through the diagnostics in priority order.

Quick Diagnostics

  1. Was the Mac touched recently? If the screensaver was active and you just nudged the trackpad to wake it, the bot may have lost serial communication during sleep.
  2. Are you using the powered USB hub Foto Master supplied -- and is it plugged into a wall socket?
  3. Are you running multiple bots from one Mac? USB power and bandwidth limits matter more with each additional arm.
  4. Did the bot stop completely, or pause and resume on its own? A pause-and-resume points to a brief connection drop. A full stop points to a hard disconnect.

Common Issues

The Critical Issue: Mac Screensaver and Sleep Mode

Problem: The robot is drawing fine. The Mac display goes dark (screensaver activates or display sleeps). The robot freezes in the middle of the sketch.

Cause: When macOS sleeps the display or activates the screensaver, the system can interrupt USB power and serial communication to the DexArm. The drawing job halts because the bot stops receiving instructions.

Solution:

  1. Disable the screensaver during events. Open System Settings > Lock Screen and set Start Screen Saver when inactive to Never.
  2. Disable display sleep. Open System Settings > Displays > Advanced (or Battery > Options on MacBook). Set Turn display off after to Never.
  3. Disable system sleep. System Settings > Energy Saver (or Battery > Options). Set Turn off display after to Never and disable Put hard disks to sleep when possible.
  4. Disable Automatic graphics switching if your MacBook offers it.
  5. Confirm the Mac is plugged into power. Battery mode applies more aggressive power saving.

Tip: Run caffeinate -d from the Terminal during long events to keep the display awake without changing settings. Press Ctrl+C in the Terminal window when the event ends.

Random Disconnections With Multiple Bots

Problem: With two or three robots running, one will randomly stop. It is not always the same arm.

Cause: This was Rick Taylor's exact ticket in March 2026 -- "The DMB will randomly lose connection to the Mac. It's not just one or two, I had it happen to each one at different times." The cause is almost always USB power instability or a flaky cable.

Solution:

  1. Confirm the powered USB hub is plugged into a wall socket for external power. The Mac alone cannot deliver enough sustained power for three bots through a hub.
  2. Use the powered hub Foto Master supplied rather than a third-party hub.
  3. Swap cables to find the bad one. If a specific bot drops more than the others, move its cable to a known-working bot. If the issue follows the cable, the cable is bad.
  4. Avoid daisy-chaining hubs. One powered hub directly to the Mac is the cleanest setup.
  5. Disable Mac energy-saver settings (see the screensaver fix above).

Drawing Pauses vs. Drawing Stops

These look similar but mean different things:

  • Drawing pauses: The arm holds position for a few seconds, then continues. Usually a brief USB hiccup or a full processing buffer. Action: No intervention needed. If pauses are frequent, check the cable.
  • Drawing stops: The arm stops moving and never resumes. The robot may show as "not connected" in DrawMeBot's port list. Action: Stop the job, recover the bot, restart the drawing.

Robot Recovery and Resume Procedure

When a robot stops mid-drawing and you need to recover during a live event:

  1. In DrawMeBot, stop the current job for the affected bot. Do not unplug it yet.
  2. Lift the pen carefully off the paper so it doesn't drag when the arm moves.
  3. Replace the paper -- do not try to resume on a half-drawn sketch. The arm cannot align precisely enough to a partial drawing for a clean continuation.
  4. Confirm the bot is still listed in the port list. If it dropped, follow Draw Me Bot Not Connecting.
  5. Re-queue the same photo for the affected guest and start a fresh drawing.
  6. Apologize to the guest and explain it will take another 2-3 minutes. Most guests are understanding when handled gracefully.

Tip: For paid events, keep one printed "we apologize" card or a small giveaway behind the booth. A small gesture turns a robot stoppage from a complaint into a positive memory.

Connectivity Logger for Diagnostics

If disconnections persist after the fixes above, enable the connectivity logger so support can review what is happening:

  1. In DrawMeBot, open Settings > Diagnostics and enable Connectivity Logging.
  2. Run a normal event session.
  3. After a disconnect occurs, export the log file and email it to support@fotomaster.com with your Mac model, macOS version, DrawMeBot version, hub model, and which bot dropped.

Related Articles

Was this helpful?

Related articles