Focus Motor Trips — Limit Set Too Close to Mechanical Hard Stop¶
Summary¶
A focus motor trips repeatedly during a move — or when manually jogging focus — because the soft limit in Lens Setup is set at or beyond the mechanical hard stop of the lens. The motor overcurrents when it hits the physical stop. Fix: back the soft limit off by a small amount away from the hard stop.
Symptoms¶
- Focus axis trips (overcurrent) when moving toward the close-focus or infinity end of the lens
- Motor appears to work normally at first but then trips at or near the limit
- After a trip, the lens gear may have jumped teeth, putting calibration out
- Focus motor trips when moving Focus Independent, not only on programmed moves
Root Cause¶
The focus limit defined in Lens Setup is set at the same position as (or past) the physical hard stop on the lens barrel. When the motor drives the lens to this position, it hits the mechanical stop and draws excess current, triggering an overcurrent trip.
Some lenses have the close-focus mark very close to the hard stop — particularly lenses where the focus ring has very little travel in the macro range.
Gear jump
If the motor hits the hard stop with enough force, it can jump gear teeth on the lens gear or follow focus gear. After a hard stop trip, always verify that the gear is still meshed correctly and re-run the lens calibration before shooting. A gear jump will silently put your focus calibration out.
Solution¶
- Open Setups -> Lens Setup for the affected lens.
- Locate the minimum limit (close focus) or maximum limit (infinity) that is causing the trip.
- Back the limit value off slightly — move it away from the hard stop by a small amount (typically 1–5 axis units, depending on motor gearing).
- Test by jogging the focus motor slowly to the limit and verify it stops cleanly before the mechanical hard stop.
- If the calibration was disrupted by a gear jump, redo the full lens calibration.
Identifying the hard stop vs the soft limit
Remove the motor from the lens ring and physically rotate the lens focus ring by hand. Feel for the hard stop (the physical end of travel). Your Flair limit should stop the motor before this point — allow at least a small margin of travel.
Related Scenario — Focus Moves Only in One Direction¶
A separate but related symptom: after a trip while switching cartesian modes, the focus motor will only move in one direction. This is caused by the axis value having fallen into negative numbers — the system is trying to return to positive values and so will only move one direction.
Fix: Check the focus axis current value in Numeric View. If it shows a very large negative or unexpected number, the axis has drifted off-zero. Reload an older known-good job, or re-run the focus calibration from scratch in Setups -> Lens Setup. Backing the hard stop limit off before calibrating will prevent recurrence.
Prevention¶
- When setting up a new lens, physically feel for both hard stops, then set Flair's limits to stop motor travel well before each physical end-of-travel.
- After mounting the motor and meshing the gear, run the focus from end to end slowly at low speed before running any programmed move, to verify clean travel.
- The soft focus limits in Lens Setup are there specifically to protect the lens — always verify them when setting up a new lens.
References¶
- MRMC Forum — Lens Calibration
- Flair Operator Manual — Lens Setup / Focus Limits (Flair Classic — Ch.5 Setups: Lens Setup — p.54 · Flair 7 — Ch.5 Setups: Lens Setup — p.39)
Official Documentation¶
WhatsApp Excerpts¶
- 2022-07-06 20:40 - ~ Chavez.Camera: Yes this sounds exactly right. I don’t know why the motor keeps hitting the hard stop. I have the limit set in the lens setup.
- 2022-07-06 22:02 - ~ Peter Constan-Tatos: Is the limit on the hard stop itself? Try backing off a little and set the limit there.
- 2022-07-06 22:03 - ~ Chavez.Camera: Yes, the close focus mark is very near to the hard stop on the lens. I’ve backed off the maximum limit and all seems to be well.
- 2022-07-06 22:11 - Gordon Eschke: 🚨🚨🚨 Bolt X on Track power - Update https://talk.mrmoco.com/t/bolt-x-on-track-location-power-requirements-warning/996/2