# Unexpected output position readings

**URL:** <https://opensourceleg.discourse.group/t/unexpected-output-position-readings/222>\
**Category:** General\
**Created:** [June 10, 2026, 5:05pm UTC](https://opensourceleg.discourse.group/t/unexpected-output-position-readings/222 "2026-06-10T17:05:59Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![malizade](https://avatars.discourse-cdn.com/v4/letter/m/8baadc/32.png) [@malizade](https://opensourceleg.discourse.group/u/malizade)\
**Post date:** [June 10, 2026, 5:05pm UTC](https://opensourceleg.discourse.group/t/unexpected-output-position-readings/222/1 "2026-06-10T17:05:59Z")

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Hi.

During a recent experiment, despite homing the joints at the start, the reported ankle output position routinely exceeded its RoM (e.g., reported measurement of -45 degrees, while the limit is -30 degrees).

What could be the cause of this? This seemed like a drift in the encoder readings and/or some sort of miscalculation by the motor driver.

Note: I’m using the motor encoder readings (not the one at the joint output).

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**Author:** ![ldevillez](https://yyz2.discourse-cdn.com/flex036/user_avatar/opensourceleg.discourse.group/ldevillez/32/71_2.png) [@ldevillez](https://opensourceleg.discourse.group/u/ldevillez)\
**Post date:** [June 12, 2026, 7:59am UTC](https://opensourceleg.discourse.group/t/unexpected-output-position-readings/222/2 "2026-06-12T07:59:14Z")

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Hi @malizade

Did you check if the belt slipped ? Having also data from the joint output encoder would be great to fix the bug.

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<div class="post-metadata">

**Author:** ![malizade](https://avatars.discourse-cdn.com/v4/letter/m/8baadc/32.png) [@malizade](https://opensourceleg.discourse.group/u/malizade)\
**Post date:** [June 12, 2026, 6:26pm UTC](https://opensourceleg.discourse.group/t/unexpected-output-position-readings/222/3 "2026-06-12T18:26:22Z")

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I’m not sure how to detect that. In any case, I think the motor encoder readings are not affected by belt slippage (since it’s further down the drive train), right?

The output encoder is not used currently in the code.

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**Author:** ![ldevillez](https://yyz2.discourse-cdn.com/flex036/user_avatar/opensourceleg.discourse.group/ldevillez/32/71_2.png) [@ldevillez](https://opensourceleg.discourse.group/u/ldevillez)\
**Post date:** [June 12, 2026, 7:51pm UTC](https://opensourceleg.discourse.group/t/unexpected-output-position-readings/222/4 "2026-06-12T19:51:29Z")

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If the belt slips, your motor can travel further while avoiding the mechanical stop.

First, I would check the ROM at a slow speed and with no load. Then, while monitoring with the joint encoder, I would try to reproduce the shift of the ROM.