# Stretch Body release 0.4. and new contact model units **URL:** \ **Category:** Announce\ **Created:** [September 6, 2022, 9:14pm UTC](https://forum.hello-robot.com/t/stretch-body-release-0-4-and-new-contact-model-units/476 "2022-09-06T21:14:34Z")\ **Posts on this page:** 1\ **Showing post:** 1
**Author:** ![aedsinger](https://yyz2.discourse-cdn.com/flex030/user_avatar/forum.hello-robot.com/aedsinger/32/6_2.png) [@aedsinger](https://forum.hello-robot.com/u/aedsinger)\ **Post date:** [September 6, 2022, 9:14pm UTC](https://forum.hello-robot.com/t/stretch-body-release-0-4-and-new-contact-model-units/476/1 "2022-09-06T21:14:34Z")
Hello Stretch users! **TLDR** : If you upgrade to Stretch Body v0.4 you will be required to run tool RE1\_migrate\_contacts.py before Stretch Body will operate * * * We have recently released a new version of Stretch Body. In addition to a number of small bug fixes, this release introduces a new approach to guarded contact values. When Stretch moves its arm, lift, or base it does so with contact parameters that tell it at what force to stop motion. Typically these parameters are pulled from the robot’s YAML parameter file. In some cases you may have existing code that directly passes in these contact parameters. Prior to Stretch Body 0.4.0 the units of the contact model were very approximate Newtons (using the `*_N` suffix). We found that these units were confusing to users. With Stretch Body 0.4.0 we are moving to more intuitive units of `effort_pct`. Effort Pct is simply a percentage of the maximum allowable winding current for the motor. Its values are bounded between -100 and 100. More information on contact parameters is available [via this tutorial](https://docs.hello-robot.com/0.2/stretch-tutorials/stretch_body/tutorial_contact_models/). Starting with v0.4.0, Stretch Body will automatically check if you must first migrate your contact parameters and code to the new format. For example: ```auto >>$ stretch_robot_home.py Please run tool RE1_migrate_contacts.py before continuing. ... ``` Fortunately, this migration is straightforward. Simply run: ```auto >>$ RE1_migrate_contacts.py ############## Migrating stretch-re1-1021 ############### Checking parameters at: /home/hello-robot/stretch_user/stretch-re1-1021 ------------------------------------- Attempting migration of contact data for robot stretch-re1-1021. Proceed? [y/N]: y ... Converted [-60.000000, 80.000000] to [-33.542039, 44.722719] for homing_force_N of arm Converted [-62.621646, 65.061853] to [-35.007629, 36.371787] for contact_thresh_N of arm Converted [-70.000000, 80.000000] to [-29.166667, 33.333333] for homing_force_N of lift Converted [-56.140879, 79.694501] to [-23.392033, 33.206042] for contact_thresh_N of lift Updated stretch_configuration_params.yaml. Robot stretch-re1-1021 now configured to use effort_pct contact parameters ``` This tool migrates your existing robot contact parameters to the new units. It also stores a backup of your original data In some cases you may have existing code that directly sets the contact values. For example: ```auto robot.arm.move_to(x_m=0.2, contact_thresh_pos_N=30.0, contact_thresh_pos_N=-30.0) ``` Running this code will now exit as it is using the deprecate API variables `contact_thresh_pos_N` and `contact_thresh_neg_N`. You will now need to port your code by: ```auto import stretch_body.hello_utils as hu p=hu.pseudo_N_to_effort_pct('arm', 30.0) n=hu.pseudo_N_to_effort_pct('arm', -30.0) robot.arm.move_to(x_m=0.2, contact_thresh_pos=p, contact_thresh_neg=n) ``` The helper function `pseudo_N_to_effort_pct` automatically converts the contact settings for you. As always, feel free to email us at [support@hello-robot.com](mailto:support@hello-robot.com) or post here if you have any questions or issues. Best, Aaron --- _[View the full topic](https://forum.hello-robot.com/t/stretch-body-release-0-4-and-new-contact-model-units/476)._