©2014 Clearpath Robotics Inc. All Rights Reserved.
9
Vehicle Equations
As a starting point, Clearpath Robotics recommends using the following relationship between
wheel velocity and platform velocity:
𝑣 =
𝑣
𝑟
+ 𝑣
𝑙
2
, 𝜔 =
𝑣
𝑟
− 𝑣
𝑙
𝑤
v
represents the instantaneous translational speed of the platform and
ω
the instantaneous
rotational speed.
v
r
and
v
l
are the right and left wheel velocities, respectively.
w
is the effective
track of the vehicle (0.555 m).
Control Modes
Husky supports four distinct control modes:
Kinematic Control, the default, uses a speed control feedback loop, and allows specifying
the desired linear and angular speed of Husky. Access this mode by publishing a standard
ROS Twist message to the
/husky/cmd_vel
topic.
Torque Control may be used by switching the startup node in
base.launch
from
kinematic_node to torque_node. In this mode, a Twist message is used as well, but the
linear and angular values specified are multiplied by parameterized scaling factors and
used for a current control feedback loop.
Raw Control may be used by switching the startup node in
base.launch
from
kinematic_node to raw_node. Raw mode works similarly to torque control, but disables
feedback control altogether, instead using the scaling values to specify open-loop voltage
for the motor drivers. This mode may be useful for novel control algorithms on the PC, or
for debugging a suspected wheel encoder failure.
On included computers set up by Clearpath Robotics, the
base.launch
file may be found along
with other roslaunch files in the
/etc/ros/hydro/husky-core.d/
folder. This folder is owned
by root and sudo will be required to edit its contents, eg:
$ sudo nano /etc/ros/hydro/husky-core.d/base.launch