Arm retraction issue

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1

Sometimes, after running robot code, the arm does not retract completely — it stops about 3–4 cm short of fully stowing. Even after running stretch_robot_home, the arm does not always go all the way in. This causes timeouts in my scripts.

When I try manually pushing the arm in, it moves smoothly at first but becomes noticeably stiff in the last few centimeters, requiring extra force. This makes me think the issue may be mechanical rather than software.

  • Has anyone experienced this kind of partial retraction?

  • Is there a recommended procedure to check or service the arm mechanism (e.g., cleaning, lubrication, partial disassembly)?

Thanks in advance for any advice.

2

Hey @seongwoncho, I’d recommend using the REx_calibrate_guarded_contact.py CLI described in Practical guide to guarded contacts

While it is possible to service the arm, it is easier to ensure the calibration for the arm motor is up to date.

3

Hi again and thanks for the quick reply earlier!

I ran the REx_calibrate_guarded_contact.py CLI as suggested (screenshots attached). The calibration completed but printed warnings that the contact thresholds are pegged at the limits:

Warning: Contact threshold of -90.000000 near minimum of -90.000000.
There may be a mechanical issue with the joint. Contact Hello Robot support.

Warning: Contact threshold of 90.000000 near maximum of 90.000000.
There may be a mechanical issue with the joint. Contact Hello Robot support.

Prior contact defaults were:
  Positive direction:  47.663993 (Effort)
  Negative direction: -42.573275 (Effort)

New contact defaults are:
  Positive direction:  90.000000 (Effort)
  Negative direction: -90.000000 (Effort)

It’s still usable, so before considering shipping the robot, is there any simple inspection/maintenance I can do myself?

(Screenshots + logs attached)

calibrate_guarded_contact_arm_neg_effort_pct_20250906235352
calibrate_guarded_contact_arm_neg_effort_pct_20250906235352640×480 19.5 KB

calibrate_guarded_contact_arm_pos_effort_pct_20250906235352
calibrate_guarded_contact_arm_pos_effort_pct_20250906235352640×480 17.7 KB

calibrate_guarded_contact_arm_results_20250906235352.log (34.2 KB)

4

Thanks @seongwoncho, you’re right, the arm mechanism is at the upper limit of what the arm motor can safely handle. Would you reach out to support@hello-robot.com so we can coordinate the repair?