You’ve built the car and set up the software, now here’s how to administer the Liberty Car. Also, here is some help troubleshooting common problems.

By now, you should have your very own working Liberty Car that you can operate from a mobile phone. If you need help with administering the car, or if the car’s driving is a bit, um ropey, this is the article for you. If you have any other problems, let us know. We can’t promise to be able to help but we’ll do our best.

Administering the Liberty Car

The admin page (<IP of Pi>:9080/Liberty Car/admin) is where you can control the maximum speed of the car and who is in control of the car:

Car admin page

  • Car max speed is a range from 0 to 200, where 0 is no speed and 200 is maximum speed. This will not change the frequency range that is set in the config page (<Ip of Pi>:9080/Liberty Car/config) but will limit people to a smaller range than the maximum (effectively setting a different top speed).
  • User ID length sets how many characters long a user’s ID is. The ID is basically the IP address of a user; if you’re running on a local network then setting it to one, two, or three characters works fine. If you put the car on to the internet, you’ll want to set it to a much larger range (like 15 characters) to make sure only one computer can control it. Setting the value to 0 will set it to match the length of the IP address and setting it to -1 will let anyone control it.
  • User ID in control takes the ID as it appears above the remote control page’s control pad and needs to match it exactly.
  • The Throttle and Steering check boxes control what parameters the user whose ID is in User ID in control gets control over. Throttle is speed control and Steering is steering control.
  • The Remove control from dropdown lets you remove control from someone who has control; choose the ID to remove and it will immediately prevent them from controlling any part of the car.
  • Clicking Submit applies all of the settings on the page, so you can change everything at once if you like (although you can only remove control from one person at a time). To remove everyone’s control at once, set the user ID length to a different value and all of the users’ IDs will no longer be valid.
  • Car is currently on lap: 0 is not implemented in the version of the car you have just built. In a later article, we will explain a new addition to the car that you can make to enable this functionality. Keep an eye on for details of some of the cool new features we are adding!


There are a few issues with the car that we’ve found over the past year:

  • Car control is stuttering a lot when doing anything (forward, reverse, steering).
    This happens if you have more than one person in control of the same part of the car at the same time, or if you have the same person with two browser tabs to the controls open at once. This is basically where both pages are fighting each other by sending conflicting orders at once. To fix it make sure only one person has control and that they only have one browser tab open on the control page.
  • Car is driving forwards slowly and not responding.
    This often happens when the battery in the car gets very low. When this occurs the first devices to lose power are the Pi and the WiFi. Unfortunately the PWM controller board will remain powered and it will send whatever signal it was last sent from the Pi; if it was driving forwards or backwards, it will continue to do that until the battery dies or you turn the motors off.
  • Reverse is “jittery” or stutters but forwards and steering is fine.
    This happens sometimes and usually happens the first time you reverse. I’m not entirely sure what the cause is in the software (it is a software issue). The fix is to go forwards and reverse again; this tends to fix it and stop it happening again.
  • Car is moving forwards when I am not telling it to.
    This will be because your “neutral” PWM setting on the config page is not correct. Fix it by going to the config page and finding the correct frequency for neutral.
  • I am seeing “COMMUNICATION ERROR” above the control pad.
    This is due to an error on the application on the car. Log into the Pi from another machine and go to <wlp install location>/usr/servers/car/logs and read the messages.log and any FFDC messages to see what the error may be. It could be a Liberty configuration error or a problem in the code and shouldn’t happen if you are using the default code download from us.
  • When I rotate my phone/tablet the car won’t respond correctly.
    This is because we have found that the majority of smartphones’ web browsers stop listening for new touch inputs while rotating so during the rotation they use the touch locations that were used immediately before rotating. Once the rotation has finished you should have control again. There’s no fix for this; we tend to disable screen rotation while driving the car due to this.
  • My phone can’t control the car – I have control but the wheel below the page doesn’t turn when I move my finder across the touch pad.
    This can be because of the browser on your device not working with the Javascript correctly; we have found Windows Phones suffer from this. There’s no real fix other than someone rewriting the Javascript to work with whatever your device’s browser supports.
  • The steering servo is making a buzzing noise and gets quite warm.
    This is either because the PWM frequency you are sending to the servo is not correct and it is overheating, or the servo is trying to turn to a position it can’t reach (maybe because the wheels are on full lock already). Check and make sure that the steering PWM settings do not make it buzz when on max left, max right, and neutral; if it buzzes then either the frequency is wrong or the servo is trying to move but can’t.

Look out for future articles here on about some of the different things you can add to your Liberty Car to make it even more awesome!

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