Segway RMP System

The Segway RMP Vehicle
The Segway RMP is based on the commercial Segway Human Transport. It is dynamically stable, meaning that it actively balances to keep from falling over. The RMP has different firmware to accept software commands and issue state data on a dual channel CANbus rather than from a rider as on does the HT. The RMP is an inverted pendulum, and balances by moing forward and backward to keep itself under the center of mass above it. On the commercial HT model, the rider provides this mass. On the RMP, an aluminum superstructure and steel ballast plates provide the mass. The aluminum top plate also doubles as a mounting surface for sensors, computers, etc.

The RMP retains the handlebar for its key and display. Two E-stops are provided for emergency use. When either E-stop is pulled, the RMP's power is immediately shut off. However, this also stops the active balancing and the RMP will fall over. Some groups using RMPs have revised the E-stops and added outriggers or other devices to restrain the RMP when it must be powered off unexpectedly.

NRL Hardware Configuration
For computer control of the RMP, a dual channel Kvaser LAPcan PCMCIA CAN card is used in conjunction with two CAN cables to the connections on the RMP. The computer chosen for control is a Dell Inspiron 7000 laptop, which can accomodate two PCMCIA cards, one for the LAPcan and the other for a wireless ethernet card. The computer is held onboard in a special tray made at NRL. Although adding weight high up on the vehicle can normally improve operation, the computer is kept between the wheels both to reduce the risk from impact in a collision or fall, and to minimize the shock should the RMP fall over.

A Belkin Nostromo n45 USB game controller can be connected to the computer to directly control the robot (provided a suitable program is running on the computer).

With the wireless ethernet, stationary computers can be used for user terminals and processing, allowing the robot to move about untethered and keeping the amount of hardware at risk to a minimum.

A SICK scanning laser rangefinder is used for sensing the environment. It is attached to the RMP's top plate with an electrically insulated adapter plate and communicates with the onboard computer via a serial connection. The RMP carries two batteries of its own for balancing and movement, with a run time of several hours depending on use. The onboard computer is powered from its own twin batteries and also has a run time of several hours. The SICK laser rangefinder is powered by two additional 12V lead-acid batteries through a voltage converter and circuit breaker. These batteries are bolted onto the top plate and provide a run time of about 1 hour.