DIPLECS RC Car

History
As part of the EU Project DIPLECS, one of our demonstration platforms is a small RC car/mobile platform. We had previous used an RC car (in COSPAL) as a mobile platform mounted with a small wireless camera. Images were transmitted back to a central computer which processed the images and controlled the car via a USB connection to the buddy port on the RC transmitter. This was achieved using an interface from Tom’s RC, original developed for interfacing RC transmitters to flight simulators. This system had many problems:

  • The various components and associated power requirements (i.e. batteries).
  • The terrible video feed quality (low power transmitter makes it prone to interference and occlusion).
  • RC controller inoperable during buddy mode meaning control was via keyboard mouse or joystick.

To make things easier we used a gaming style ‘steering wheel’ to generate the control signals to send to the transmitter. This made control easier but the system was difficult to capture data with and had very little mobility, meaning, out door use was not feasible.

Shortly afterwards, we started the SEP project and a small team of undergraduates built two mobile platforms based on a 4WD3 low end robotics platform from Lynxmotion that carried a laptop. The platform carried a custom frame on which was mounted a camera, ultrasound detectors and a motor controller all connected via a PIC microcontroller to the USB port of the laptop. Having reasonable processing on board was a huge advantage for autonomous control. The ability to connect seamlessly with a network of additional processors using wireless meant that processing could be deployed over various machines. This was facilitated using a generic peer-to-peer networking API. However, the platform was quite slow (2-4 miles per hour), cannot carry much weight and has no direct interface other than via the onboard keyboard or laptop via the network.  

The New Platform
For the DIPLECS demonstrator car we have combined the best of both worlds. The DIPLECS car is based upon an TRAXXAS E-MAX RC car. The advantages being:

  • Low cost consumer electronics (£250).
  • Four wheel drive.
  • Powerful and very fast (30+mph).
  • Configurable gearing and suspension.

The E-Max is a 1/10 scale, 4 wheel drive, electric RC monster truck with dual 14V 550 electric motors, 4 inches of ground clearance, 8 oil filled shock absorbers and can achieve 30+mph.

The stripped E-MAX carries an aluminum platform on which a laptop can be strapped and a box that contains the interface.

The interface box contains a 40MHz receiver which connects directly to a MFTech USB-Interface II  which allows the PWM signals to be read directly on the computer where they can be logged. A 2nd USB interface from Pololu, capable of controlling up to 16 servos, then reproduces the PWM signal when instructed. This connects directly to the servos and motor controller. The box of electronics contains a small USB hub, the MFTech and Pololu interfaces, RC receiver/arial, Bluetooth adapter and GPS receiver. The control box connects to the laptop is via single USB cable and connects to the servos and motor controller via standard . During normal driving the onboard laptop simply reads the incoming PWM signal and reproduces this directly on the output allowing the platform to be controlled via a standard RC transmitter. However, while this is done it can be logged to memory or stored to disk along with any sensors or camera data that is required.  During autonomous operation the onboard laptop can directly generate PWM signals to control the platform, however, it can continue to monitor the input channels from the receiver providing a wireless "dead man's" switch allowing the operator to terminate or take over control of the platform at any time.  

Adam, a very able Nuffield student, came back to do some work on the car for us and wrote the software library to handle the communication with the interfaces.

Shocks have been upgraded to cope with the additional weight of onboard electronics and both electronics and laptop are mounted on a custom aluminum platform that attaches directly to the E-MAX chassis. The ludicrous foam at the front and rear was a direct result of our first test run which resulted in a high speed crash into a brick wall damaging the rear shock absorbers when the control box was driven into them. This is an interim measure and we expect the appearance to change considerable over time as we add new components and change the onboard processing. The "successful" 2nd test 2 days later when the shocks had been replaced can be seen here.

Richard Bowden
CVSSP, EPS
University of Surrey
Guildford, Surrey
GU2 7XH , UK
+44(0)1483 689838
r.bowden@surrey.ac.uk