Lab: RACECAR Hardware IntroWelcome to the RACECAR
(Rapid Autonomous Complex-Environment Competing Ackermann-steering Robot)!
Turning on the Car
Use Blocko Friendo
Set the car on a block on your table, such that the wheels aren't touching the table. Unless you're actually testing your code on the ground, leave the car on this block.
Plug in the Electronics Battery
Unplug the battery charger.
Troubleshooting Tip: if something isn't receivng power, check to make sure that the blue and green ports inside the Energizer aren't broken apart. Each should have a center pin.
Boot it Up
Turn on the car using the power button on the TX2. The lights should turn green.
Plug in the Traxxas Battery
This battery can supply ample amperage to the VESC (Vedder Electronic Speed Controller) which controls the drive and steering motor.
ssh command allows you to use a remote computer's (i.e. a racecar's) terminal on your host machine.
To ssh, make sure you are connected to the same wifi network as your car.
Then run in your terminal:
The RACECAR's password is racecar@mit.
Make sure everyone on your team is able to do this before moving on!
scp command allows you to copy files back and forth from a remote machine.
From local to remote (i.e. upload to car):
scp <LOCAL_FILE_PATH> <REMOTE_USERNAME>@<IP>:<REMOTE_FILE_PATH>
From remote to local (i.e. download from car):
scp <REMOTE_USERNAME>@<IP>:<REMOTE_FILE_PATH> <LOCAL_FILE_PATH>
For example, if you wanted to move a file on your Mac desktop called "drive.py" to the "racecar_ws" folder of car 101, you would run:
scp ~/Desktop/drive.py firstname.lastname@example.org:/home/racecar/racecar_ws/
Troubleshooting Tip: You should run
scp outside of the racecar (i.e. not in an ssh'd terminal). Otherwise, you'd be flipped around and need your computer's hostname and IP.
Controlling the car
Once you've successfully ssh'd in, type
teleop. This will allow us to actually drive the car. If there is an error about it being unable to connect to the joystick, end the program (ctrl-C) and try again. If there is still an error, as a TA for help.
Now you can drive the car using the controller! The cars have a Dead Man's Switch for safety; this means that to use the controller to drive, you have to hold down LB at the same time. If the Mode light is turned on, press Mode. The controller must also be in the X mode (this is changed by a switch in between the bumpers). Try driving around! The left joystick controls speed, and the right joystick turns.
Keep in mind that these are expensive (i.e. several kilodollars!) piece of equipment; always be aware of your/the car's surroudings when driving, and communicate with other teams that are also driving their cars to avoid damaging them.
If your car doesn't drive with the controller...
teleopfor any errors. There should be a "force feedback" error for the joystick, but everything else should run fine.
- If there is a VESC error, quit
teleop, wait a minute or two and try again. This often happens if you try to run teleop immediately after turning on the car or pluggin in the Traxxas battery, since it takes a minute for the VESC to boot up.
- If you get individual errors for the Hokuyo or IMU, check that these are properly plugged in.
The IMU should be plugged into the USB hub, and its micro USB port should not be ripped off. It should light a blue LED when it's powered on. For the Hokuyo, check that its Ethernet cable is plugged into the USB and that it's power cable is plugged into the power harness. You'll know the Hokuyo is receiving power if you can hear it whirring.
- If you get multiple errors for the VESC and IMU, there might be a problem with your USB hub. Try power-cycling the car (turning it off and on). If that doesn't fix it, check that the USB hub is connected to the TX2 board and is getting power from the electronics battery through the power harness.
Alternatively, you may also get a similar whopping load of errors if more than one person tries running
teleopat the same time. Power cycle the car and try it again with only one person ssh-ed in (or just use the monitor and keyboard).
- If your controller was on D and then you switched it to X, try power-cycling the car.
When you think you have a good feel of the car, move on to the next section.
Intro to autonomous driving
First, let's just program the racecar to drive forwards on its own. Open
controller.py. Change the car's velocity in the function
drive_callback. You can change the speed with the variable
self.cmd.drive.speed. Start off with small values like 0.5 so you don't accidently crash!
When you want to run your code on the car, press the right bumper on the controller after
teleop and your code are running.
Next, try having the car drive in a circle. You can change the wheel angle with the variable
self.cmd.drive.steering_angle (the car uses radians). Explore the range of values that might work best for your car (speed, turning angle, etc).