Rover Specs

[connorjak]

Rules & Info	SpaceTeamsROS	Q&A Discussions Category

Rover Dimensions

• Rover body frame: X-forward, Y-left, Z-up
• Camera location WRT the rover: (x, y, z) = (3.35, 0.14, 1.5) meters
  • Note that can oscillate on the order of ~5 centimeters out of position due to a minor bug in how Space Teams attaches objects.
• Camera rotation WRT the rover: quat(x, y, z, w) = (0, 0, 0, 1)
• Rover center of mass WRT its frame origin: (cx, cy, cz) = (0, 0, 1.2) meters
• Rover body dimensions WRT origin: ([x_min, x_max], [y_min, y_max], [z_min, z_max]) = ([-2.41, +3.03], [-1.88, +1.88], [0, +2.7]) meters

Note: rover dimensions change slightly as suspension springs compress and expand. Given values are for springs in the completely uncompressed position (i.e., not the rover's natural rest position).

Wheels

• Radius: 49 cm
• Mass: 20 kg
• Width: 20 cm

Rover Mass Properties

• Mass: 1500 kg

Rover Drivetrain

The rover electric drivetrain modeling is modified from an internal combustion dune buggy baseline. Based on the Accelerator and Reverse commands, the rover will accelerate and brake both in forward and reverse directions, with an automatic transmission.

• All-wheel drive, 50-50 front-rear split
• Transmission efficiency: 90%
  • Mechanical friction losses cause apparent loss of torque
• Motor Torque: 100 Nm, split between all wheels
  • Reduces with RPM according to torque curve

Gear ratios (24:1 forward and back)

Torque and motor dynamics per-wheel

Torque vs RPM curve

Steering

• Max Steering Angle (front wheels only): 40 degrees
• Output steering angle = (Input)^2 * 40 degrees

Max steering angle multiplier vs Speed (mph)

Suspension

• Max up/down travel from neutral: +-20 cm
• Spring rate 62 N/m
• Spring preload 100 N/m

Input change rate

These are how the actuators respond to instantaneous value changes in their commands. There will be a small extra latency from communicating the commands across programs.

• Commanded Accelerate (0 to +1) rises at 6 units/second and falls at 10 units/second
• Commanded Reverse (0 to +1) rises at 6 units/second and falls at 10 units/second
• Commanded Brake (Handbrake when > 0.5) rises at 6 units/second and falls at 10 units/second
• Commanded Steering (-1 to +1)
  • Input command tracking grows at 2.5 units/second and falls at up to 5 units/second
  • Output steering angle = (Input)^2 * 40 degrees
    • Squared input curve causes slow angle change near 0.0 input value

Camera Specs

• Pinhole camera model
  • Center of image pixels is the center of the focal axis
  • No additional warping / aberrations
  • Depth of field blur omitted
• FOV: 90 degrees
• Resolution width/height 512/512
• Exposure is user-settable from an Exposure Value of 20 (very dim) to 5 (brightest for night imaging). Defaults to 13.0

[shafinawake]

Would it be possible to provide us with the state and control equations for this rover?

[connorjak]

We don't have those on hand; you will need to make your own approximated model if you want to do that kind of control. We are happy to help fill in any missing info on the rover mass properties, structure geometry, steering control, etc if there's something we haven't documented yet.

[Salmon490]

Just want to make sure, what is the unit of depth values from the depth camera

[connorjak]

Centimeters