Mecanum wheels assembly instructions

Note

The mecanum add-on package is a standard catalogue item for the Origin One. However, please note that an Origin One with mecanum wheels should not be operated in autonomous mode, which means you should either drive it manually or send velocity commands directly (see the documentation or code examples).

Although we reccommend to stop the autopilot of the Origin One while operating it with mecanum wheels, by running docker stop autopilot information_manager in an ssh session with the robot, you may still decide to run the autopilot on the background as it will not sent any commands as long as no task or behavior is sent to the robot. You may even exploit the localization on a 2D map on your Origin One with mecanum wheels as that is (still) available in the autopilot's ROS2 network on \autopilot\estimated_pose (be it with less accuracy).

Note

Driving of the Origin One with mecanum wheels is not as steady as the Origin One with pneumatic tires, as the mecanum wheels are much more firm compared to tires. Therefore, read the section on driving surfaces.

The manual here presents the instructions for using the mecanum wheel add-on with the Origin One platform and addresses:

• Hardware reconfiguration guide
• Software reconfiguration guide
• Mecanumdrive operation guide

Hardware reconfiguration guide

Preparations

Info

The tools that you will need for this assembly are the following:

• Loctite 248
• Torque wrench that can be set at 2.5 Nm
• Torque wrench that can be set at 8 Nm (may be same as one above)
• Long Torx 20 bit to fit in torque wrench
• Hex 5 bit
• Box / block to support Origin (about 500mm wide, 100mm tall and about 650-500mm long)

Step 1: Unpack the wheels

Collect the additional package with the mecanum wheels. The parts are ordered in a specific manner.

Step 2: Get the Origin One

Take the Origin One and press the E-stop or turn it off. Then, put the Origin One on a setup, such as a crate, by which it is lifted from the ground so that all wheels are off the ground.

Warning

Make sure frame parts are supported. The bottom plate can’t be used for support (marked with a red cross). Use the orange highlighted parts to support the weight of the robot.

Step 3: Envision the end goal

The image below presents an overview of the Origin One with mecanum wheels after assembly. Pay attention to the direction of the rollers of the wheels, which form a “cross” in the middle of the Origin.

Assembly

Step 1: Remove pneumatic tires (incl. wheel hubs)

When elevated, the M4x20 bolts (6x) can be loosened using a TX 20 screwdriver or wrench. After loosening the M4 bolts the wheel incl. the wheel hub can be removed. Do this for all 4 tires..

Keep the bolts and washer safe because you will need them when installing the Mecanum wheels.

Note

When re-installing pneumatic tires incl. wheel hubs, tighten with 2.5 Nm torque and according to star pattern shown in the following Step 2.

Step 2: Install mecanum wheel hub

Using the M4x20 bolt and washers you have put aside when removing the pneumatic tires, mount the Mecanum wheel hubs supplied in package 2. Also (re)apply Loctite 248 to the bolts. Do this for all four motors

Warning

It is recommended to exchange used M4x20 screws after every two times tightening the screws. This is to prevent damage to the screws.

Replacement screws: ISO 14580 – M4x20 A2 (stainless steel)

Step 3: Install mecanum wheel

Use the Mecanum wheel position overview to mount the Mecanum wheel (A & B) on the correct positions. Use the bolts supplied in package 2.

Please adaopt the following assembly sequence: Mecanum wheel –> (1) DIN 125A_M6 –> (2) DIN 127B_M6 –> (3) DIN 912_M6x16.

Software reconfiguration guide

Before you reconfigure the software on the Origin One you should first start an ssh session with the robot, see the section on how to connect to the Origin Access Point: Step 4.

Once the ssh session is established, then the next steps will guide you through the reconfiguration.

1. Navigate to the Avular Docker compose files with the following command: avular compose config.
2. Open the "config.env" file with the “nano” in-terminal text editor with the following command: nano config.env.
3. Inside this config file you need to modify the drive configuration environment variable. Set the variable to corresponding desired mode: DRIVE_CONFIGURATION=1 for skid-steer drive mode with pneumatic tires, DRIVE_CONFIGURATION=2 for mecanum drive mode with mecanum wheels.
4. Save your changes using ctrl + o and press enter to acknowledge the changes. Exit the file using ctrl + x.

Warning

The next step will remove any changes made inside the Avular containers. It is strongly recommended not to make changes to the Avular Docker containers and to not develop inside these containers.

1. To make your changes take in effect you must recreate the Avular containers with the following command: avular compose up.

   In the background the Origin re-boots the Avular containers and the changes are directly implemented.

You've now successfully changed the drive configuration of the Origin robot. From skid-steer drive to mecanum or vice-versa

To inspect in which drive mode the robot is right now. Enter the pioneers-prod container using the following command in the terminal: avular compose enter origin-bringup, after which you can inspect the environment variable used by the Origin One drive controller software using the command: echo $DRIVE_CONFIGURATION. The output will be either 1 or 2.

No harm is done when accidently the wrong software drive configuration setting is applied when not matching wheel setup hardware. Yet, this can result in unexpected behavior and could result in abnormal wear on the wheels.

Mecanumdrive operation guide

Specifications

The mecanum drive setup uses smaller diameter wheels (203 mm) than the skid-steer drive setup, resulting in an overall lower maximum achievable driving speed. In the mecanum drive mode the Origin can drive laterally with a lower lateral max speed than longitudinal speed because the motion efficiency of mecanum wheels when driving laterally is not 100%.

• Longitudinal max velocity: 1.18 m/s
• Lateral max velocity: 0.98 m/s
• Rotational velocity: 1.5 rad/s
• Wheel diameter: 203 mm
• Track width: 475 mm
• Wheelbase: 410 mm
• Ground clearance: 46 mm

Control options

When in MANUAL control mode, velocity inputs of the robot are accepted from the PlayStation 4 Bluetooth controller

• Lateral velocity limited to 0.3 m/s (0.6 m/s boost mode) to enhance manual controllability.
• Other settings remain equal to skid-steer drive

When in USERcontrol mode, velocity inputs of the robot are accepted from ROS2 API

• Velocities & acceleration are not limited in this mode, it’s up to the user to provide sufficient limits for their use-case.

Playstation control

The Origin One with mecanum wheel add-on is controllable using longitudinal, lateral and angular velocities in both manual as user control modes. In the manual control mode using the PlayStation 4 remote, see Remote Controller documentation, the user can choose between two modes of operation. Two-stick (default) and one-stick control mode. The mode switch is performed by pressing down on the left joystick.

Furthermore, in manual control mode there are two speed modes: non-boost (default) and boost. The boost mode is activated by holding down the L1 action button.

Two-stick control mode

In this mode the left joystick controls the translation motion (longitudinal and lateral). Here, the left to right motion on the stick controls the lateral motion. The right joystick control the angular motion.

One-stick control mode

In this mode the left joystick controls the longitudinal and rotational motion. The left to right motion on the stick controls the angular motion. In this mode the lateral velocity cannot be controlled.

Driving surfaces (MUST READ)

Origin One with mecanum wheels is to be used on smooth and flat indoor surfaces. Any imperfections in the flatness of the floor can and will result in slight deviations of the expected motion output. This is because not all four wheels contact the surface at all time due to the Origin frame to be very stiff and the mecanum wheels to be rigidly mounted without suspension.

For lateral and diagonal motions, the combined velocity vectors or each individual wheel contributes the resulting body velocity vector of the robot. Therefore, any non-contacting wheel can result in a different resulting body velocity vector.

Even on “flat” hard poured floors like concrete the Origin can have trouble moving perfectly sideways/diagonal motion trajectories. The user is to proceed with caution and needs to assess the driving surfaces with a manual drive to determine the drive quality of the Origin One with mecanum wheels.