Too much motor and servo latency P1

[billmania]

The delay between moving the joystick, both from 0 to non-zero and from non-zero back to 0, and the drive motors responding is too great. The delay between the sliders and the servos is also too great.

See roboquest_ui Issue 67

[billmania]

To pass a joystick position from the joystick to the drive motors, the following happens:

in the browser

• create a joystick event by clicking the joystick knob
• assemble a cmd_vel payload object
• stringify the object and emit it as a cmd_vel event

• in the NodeJS server

• capture the cmd_vel event
• use the payload to assemble a ROS TwistStamped message
• publish that message onto the /cmd_vel topic

• at the backend ROS base node

• subscribe that message from the /cmd_vel topic via RQManage._motor_cb()
• extract the twist.linear.x and twist.angular.z attribute values
• verify and scale the two values
• call the RQMotors.set_motors_velocity()

[billmania]

Reduced the severity of this issue by setting the subscription queue to 1 for both /cmd_vel and /servos in the base node.