RACECAR/J FlatNose Platform Part 2

In RACECAR/J FlatNose Platfrom Part I we built up the lower FlatNose platform. In an earlier article, we built a chassis. Now we attach them together. Looky here:

Introduction

Building even a simple robot like RACECAR/J usually means several assembly steps. Now that we’ve built the chassis and the platform decks, it’s time to hook up the wiring, install the base electronics, and attach the two together.

The RACECAR/J FlatNose is a more experimental version of the MIT RACECAR. Having more area on the platform allows for different sensor selection and placement. In the video above, we install some less expensive alternatives to the sensors on the MIT RACECAR. Of course, you could go the other way around too 😉

In the video, we install a Slamtec RPLidar A2M8 lidar and Logitech HD Pro C920 Webcam. This is an elementary alternative to the more sophisticated Hokuyo UST-10LX lidar and Stereolabs ZED camera on the MIT RACECAR configuration.

Tradeoffs? Yes. The Hokuyo UST-10LX provides a much higher scanning rate, better ranging, and denser measurement collection. The combination is mandatory when driving the vehicle at high speeds. On the other hand, the RPLidar A2 allows one to examine many of the same principles (using much the same software in ROS), assuming that the speeds of the vehicle are slower. And the RPLidar A2 is ~ $1300 USD less than the Hokuyo.

The sophisticated Stereolabs ZED camera provides 3D depth perception using 2 RGB cameras. The Logitech C290 is a simple webcam. While the difference is obvious, so is the price tag. The Logitech C920 is ~ $400 USD less expensive. If you are doing simple vision processing tasks, the webcam can provide a good starting point in your exploration. It might be fun to use the Intel RealSense D435 3D depth camera as an alternative to the Stereolabs ZED.

If you know your final build configuration, modify the steps to include the sensors, electronics and battery that you have chosen.

Tools and Parts

Full RACECAR/J Kits and parts are available in the RACECAR/J Store (United States only presently).

Electronics:

• NVIDIA Jetson Development Kit – Jetson TX2 shown in the video
• SparkFun SEN-14001 IMU

Here are a couple of screw types that we use:

• 1/4″ 4-40 machine screws – Attaches the IMU and Jetson Dev Kit to the Platform Deck via the 1/4″ standoffs
• 7/16″ 4-40 machine screws – Attaches the upper platform deck to the lower platform deck via 2″ standoffs
• M3x10mm machine screws – Attaches the lower Platform Deck to the Chassis via the body mount points

For wiring:

• USB 3.0 Cable. 6″ USB B Right Angle to USB A – Amazon Basics USB Hub to Jetson Dev Kit
• USB 2.0 Cable. 6″ USB micro B to USB A – SparkFun SEN-14001 IMU to USB Hub
• Right Angle Plug, 1.7mm ID, 4.755mm OD – Battery power to Amazon Basics USB Hub
• Right Angle Plug, 2.5mm ID, 5.5mm OD – Battery power to Jetson TX1/TX2
• XT-60 to Traxxas Male Converter – Attaches Traxxas battery to ESC

The wiring varies of course depending on which battery you choose to power the electronics.

Here’s the toolset in the video:

• iFixit Toolkit

For consumables, we use some electrical tape, 4″ and 8″ zip ties, and some 3M Dual Lock tape.

For this build, the wire routing is meant mostly to keep any wires from contact with the drive train during testing. Once the installation of the rest of the sensors and electronics is complete, that is a good time to go over the final wire routing and attachment.

Installation

Note that in the video we add a web cam, lidar, Jetson and battery. These are not included in the RACECAR/J kits.

First, attach the steering servo cable from the electronic speed controller to the steering servo. For extra security, wrap the connector in electrical tape.

For this particular electronic speed controller, we install a XT-60 to Traxxas Male converter cable.

Install the USB 3.0 Cable and power cable to the Amazon Basics USB Hub.

There are three motor wires which must be connected to the electronic speed controller.

Place the Platform Decks on the body mounting points. Install the IMU using 4 1/4″ 4-40 machine screws:

Then attach the Jetson Development Kit using 4 1/4″ 4-40 machine screws:

The next step is to connect the USB cable for the IMU, and then connect the USB Hub to the Jetson.

The Top Platform Deck is attached to the lower platform on 2″ standoffs using 7/16″ 4-40 machine screws. You can add a couple of strips of 3M Dual Lock to attach a battery.

Usually I wait to attach the Platform Deck until after initial testing in case I need to access the wiring. Attach the Lower Platform Deck to the chassis using 4 M3x10mm machine screws, and finish up the wire and cable management using zip ties.

At this point, you’re pretty much ready to go!

Conclusion

The base of the robot is now assembled, and we’re ready to start loading software on to the Jetson to control it. Now we are ready to install the ROS software and RACECAR packages! Please note that the software is currently for the MIT RACECAR configuration, and will need to be updated for your particular configuration. We are working on a more general purpose installer which does not include the Hokuyo or ZED camera packages.