NAME

nxtremote - Remote control NXT via PC joystick or USB game pad over USB or Bluetooth

SYNOPSIS

nxtremote [--btname name] <device> <max wheel power>
    <max implement power> <button|joystick>

DESCRIPTION

Nxtremote is a simple program which uses a USB game pad or analog joystick along with the roboctl library to control an NXT robot over a USB or bluetooth connection.

See legoctl(1) for instructions on establishing a bluetooth connection with your robot.

Communication with the control device is handled by libgamepad(1).

Nxtremote can control any robot with wheels connected to motor ports A and C, and a manipulator to port B. The primary game pad/joystick (i.e. axes x and y) controls the wheels. The manipulator can be controlled either by buttons 1 and 2 or, in the case of a game pad with more than one joystick, the z and rz axes.

COMMAND LINE ARGUMENTS

--btname name

Specifies the bluetooth device name as it appears in the bluetooth hosts database searched by bt_gethostbyname(3). This is not necessarily the same name configured in the NXT brick. If --btname is not used, the bluetooth device name defaults to NXT, which is the default in the NXT brick.

Device

This specifies the device to with the joystick or game port is attached. Under FreeBSD, nxtremote can utilize the analog game port and joy driver (/dev/joy*) to connect with a PC joystick, or the uhid driver and usbhid library (/dev/uhid*) to connect with a USB game pad. Other platforms and interfaces will become available as time permits.

Max wheel power

This is the maximum power setting for motor ports A and C, to which the wheel motors are presumably connected. Note that this is a percent scaling factor, not a cut-off value. All power settings are multiplied by max-wheel-power/100.

Max implement power

This is the maximum power setting for motor port B, to which the implement motor is presumably attached. Note that this is a percent scaling factor, not a cut-off value. All power settings are multiplied by max-wheel-power/100.

Implement control

This argument determines how the implement of the robot is controlled from the joystick or game pad, and must be one of the strings "button" or "joystick".

NOTES

To improve driving ease, joystick position is not mapped linearly to motor power. Instead, it is warped using the 4th root function, i.e.

power = maximum-power * (joystick_position ^ 0.25) / (100 ^ 0.25)

This is based on the experience that a motor power of around 60 is generally necessary to move the vehicle or implement. The root functions have a steeper slope than a straight line for small values, and shallower slope for large values. Hence, a smaller movement of the joystick from center position will more quickly cover the (useless) power values from 0 to 60. More of the joystick motion range is then utilized for the useful power values of 60 to 100. As a result, the vehicle will start moving with the joystick closer to center position and the joystick must be moved farther to effect a noticeable change in vehicle/implement speed, which makes the controls less touchy. (I.e., you're less likely to oversteer.) The 4th root was chosen based on experimentation. Higher roots tend to make the vehicle easier to operate than lower ones. The 5th root (y=x^0.2) is too high, however, since it produces a motor power of 64 for a joystick position of 1. Since most joysticks never center perfectly, the robot generally won't stop when you let go of the joystick.

Nxtremote is meant to be a sample program for the roboctl(3) library. While you can use it as is with a simple robot on supported platforms, it's probably more useful and more fun to experiment with other robot designs and customize the source code to match.

FILES

$HOME/.roboctl/bluetooth_address

EXAMPLES

nxtremote /dev/joy0 85 60 button
nxtremote /dev/uhid0 90 70 joystick

FILES

/etc/bluetooth/hosts

AUTHOR

Jason W. Bacon
http://acadix.biz