How To control a Segway RMP with Player

Credits

The original segwayrmp driver was written by John Sweeney, and overhauled by Brian P. Gerkey, with help from Andrew Howard.

This document was written by Brian P. Gerkey

Examples

Overview

This document describes how to get your Segway RMP (Robotic Mobility Platform) under control with the Player robot device server. Be warned that the driver that allows this control (segwayrmp) is brand new, is experimental, and will likely be in a state of flux for some time to come.

1. Get CAN equipment
2. Build and install LAPcan drivers and CANLIB
3. Connect CAN equipment
4. Download CVS snapshot of Player
5. Build Player with Segway RMP support
6. Start Segway RMP
7. Start Player
8. Play!

The steps

1. Get CAN equipment

   The control interface to the Segway RMP is CAN (Controller Area Network), an industrial bus standard for which you need a special card. For redundancy and safety, the RMP uses 2 CAN channels, and you are required to talk to both of them simultaneously. Thus, you need a 2-channel CAN card. The transceivers for these 2 channels must be opto-isolated.

   Currently, Player's segwayrmp driver only works with Kvaser, Inc's CANLIB, which is a Linux interface library to Kvaser's CAN cards. CANLIB should work with any of Kvaser's CAN cards, but we've only tried it so far with the LAPcan II, which is a 2-channel PCMCIA card. If you do buy the LAPcan II, you'll also need 2 of the DRVcan DNopto transceiver dongles. For DARPA MARS participants, the (discounted) cost for the LAPcan II and 2 DNopto dongles together is about US$1000.

   The underlying CAN I/O subsystem in Player's segwayrmp driver is modular, to allow for the use of other CAN cards and/or interface libraries. If you're interested in adding support for a non-Kvaser card, take a look in the Player source tree at server/drivers/mixed/rmp/canio.h, which defines the interface that you must implement. Check server/drivers/mixed/rmp/canio_kvaser.h and server/drivers/mixed/rmp/canio_kvaser.cc for an example of how to implement the interface. Post questions and comments to the developers' list.

2. Build and install LAPcan drivers and CANLIB

   If you're using a non-Kvaser CAN card, then you'll have to do something different (but functionally equivalent) here.

   Download the Linux support package from Kvaser. Build and install canlib (as root):
   # make canlib_install
   Build and install the LAPcan kernel modules (as root):
   # make lapcan_install
   Beware that the install script for the LAPcan modules (installscript_lapcan.sh) is written in a Redhat-specific manner, and may require some tweaking to run properly on your system. In particular, if you're running Gentoo, try this modified script instead.

3. Connect CAN equipment

   Insert your CAN card. If you're not using hotplug (which autoloads modules for PCMCIA and USB devices), then you may have to first load the appropriate module manually. For the LAPcan II, you need to load lapcan_cs.o.

   Connect the transceiver dongles to the card and to the 2 DB9 ports on the underside of the black control box on the Segway RMP.

   You'll need to somehow attach your computer to the Segway. We've had some success with putting the laptop in a laptop bag in the footspace of the RMP and using the bag's shoulder strap to secure it to the robot. You should put some thought into this step, because when (not if) the robot falls over, you don't want your laptop to be destroyed.

4. Download CVS snapshot of Player

   There is not yet an official release of Player with the segwayrmp driver. For now, get the latest CVS snapshot from our snapshots page.

5. Build Player with Segway RMP support

   Note that you need to build and run Player on the computer that is connected to the Segway's CAN bus (i.e., the laptop that you've physically attached to the robot)

   Support for the Segway RMP is disabled by default. To enable it, run Player's configure script like so:
   $ ./configure --enable-segwayrmp --with-canlib=/usr
   You might also pass other options (like --prefix or --with-rtk); see the FAQ for more info. To see all available options, do:
   $ ./configure --help
   Now build and install Player:
   $ make
   $ make install
   

6. Start Segway RMP

   To start your Segway, hold any one of the keys (they're all the same for the RMP) in the ignition slot until it beeps. We've found the keys somewhat unreliable, so try all of them, and hold each one in the slot for several seconds in order to find one that works.

   The RMP starts out in "tractor mode", wherein it does not autobalance. You can control the RMP from software in tractor mode, but you need to attach some kind of trailer/caster assembly. To put it in "balance mode", hold the RMP upright and push the red button on the handlebars once. It should beep, turn the handlebar display green with a happy face and balance itself.

7. Start Player

   Start Player with the supplied configuration file. For example, if you installed Player in /usr/local (which is the default), then do the following:
   $ /usr/local/bin/player /usr/local/share/player/config/segwayrmp.cfg
   

   The segwayrmp driver supports both the standard 2-D position interface and the new 3-D position3d interface. You should use the position3d interface if you want access to pitch and roll information from the RMP.

   There are examples of how to load the driver for each interface in segwayrmp.cfg. You should only pick one interface; comment out the other one. The position3d interface is brand new and not widely used or supported. At the moment, it is only supported in the C++ client library; use Position3DProxy. To see the 3-D info, try playerjoy with the -3d and -v flags.

8. Play!

   Now it's time to play with your robot. I highly recommend that you first try it under manual joystick control. Included with Player is a Linux-specific utility called playerjoy (it's installed alongside player in bin), which is a Player client that reads from a joystick and sends appropriate speed commands to a Player server. It should work with pretty much any basic joystick, although I've only tested it with analog USB joysticks.

   Note that because of Player's network-centric design, you can run playerjoy off-board, for example on a joystick-equipped desktop machine and point it at Player running on the laptop that's attached your robot (presumably over a wireless network). Then you can happily control the Segway while not being physically near it. For example, if the laptop on your RMP is called foo, then run playerjoy like so:
   $ /usr/local/bin/playerjoy -c foo:6665
   You'll need the -c to cause playerjoy to continuously send commands (instead of only sending them when the joystick moves). For safety, the segwayrmp driver will stop the robot if no new commands have been received in the last 400ms or so.

   Your next task is to get the RMP going under autonomous control (after all, this is robotics research). Look here for movies of some of our early successes in autonomous control for wall-following and obstacle traversal.