====== Re-zeroing A Servo ======

<note>
Please only do this if you've been asked to do so by Robotical, or if you know what you're doing!
</note>

If Marty receives a large knock, it is possible that the servo arm will skip around the servo spline. This will result in Marty not being able to move a joint to the full range of movement

===== Remove the link from the affected servo =====
Using a screwdriver, unscrew and remove the blue link. Be careful not to lose the nut!

{{ :martyv2:support_faqs:hardware:martyleglinkunscrewed.jpg?direct&600 |}}

===== Remove the Servo Horn =====

Remove the small screw from the black servo horn as well, and then remove it from the servo. It will be stiff but will pull off - you can lever it with the end of the screwdriver if you need to

{{ :martyv2:support_faqs:hardware:martylegservohornremoved.jpg?direct&600 |}}

===== Zero the Servo =====

Go to https://updates.robotical.io/zero-servo/ , connect Marty by USB cable to the computer, and click the "Connect" button. Select the option that appears as "USB Serial"

{{ :martyv2:support_faqs:hardware:servozeroapp.png?nolink&600 |}}

Once connected, click the button to zero the affected servo. 

In the case shown in these photos that is the Left Knee

The servo will rotate to its true zero position. You can then re-assemble the joint

===== Reassemble the Robot =====

{{ :martyv2:support_faqs:hardware:martylegservohornreplacement.jpg?direct&600 |}}

Reinstall the servo horn, being careful to align it with the position it would be in if Marty were standing straight. It will likely have to be a few degrees off to fit on the spline, that's fine and will be taken care of by the calibration step

{{ :martyv2:support_faqs:hardware:martylegassembled.jpg?direct&600 |}}

Reassemble the leg

===== Calibrate the legs =====

{{ :martyv2:support_faqs:hardware:martyappconfiguration.png?nolink&600 |}}

Calibrate the legs in the app. 

Go to https://codemarty.com, connect to your Marty, click "Configure Marty", then "Calibrate", then "Leg Calibration", and follow the onscreen instructions. You will need to manually move Marty into a standing position before saving the calibration and testing the walk

===== Any issues? Contact Robotical =====

If you have any issues, or if there is damage to the servo horn and you need a replacement, please contact support@robotical.io and we'll get it sorted asap