This article marks the start of the prototype RACECAR/J build. RACECAR/J is an 1/10 scale autonomous vehicle. First up, preparing the chassis. Looky here:
This is the third hardware prototype of the RACECAR on JetsonHacks. The prototype base is the MIT RACECAR, an “open-source powerful platform for robotics research and education”.
The platform houses state-of-the-art sensors and computing hardware, placed on top of a powerful 1/10-scale mini race car.
Over time, a couple of different parts have become obsolete since we our first prototype. This includes the Sparkfun IMU, and the TRAXXAS car that we originally built upon. This is not unusual, but still requires some changes to the deck/platform for attachment.
We can break the hardware down into different sections:
- Chassis – This version is based on a TRAXXAS Platinum Slash Truck.
- Computing – NVIDIA Jetson Development Kit.
- Sensors – The robot can use different types of sensors including LIDAR, stereo camera, RGBD cameras, and IMUs.
- Electrical – Batteries, Wiring and Interfaces
- Mechanical – The “nuts and bolts” that form the backbone of the mechanical structure of the car. This includes the decks.
TRAXXAS Platinum Slash Truck
In this prototype, we build on the TRAXXAS Platinum Slash Truck. In earlier prototypes we used the TRAXXAS Rally which has since been discontinued. However, both the Rally and Slash are similar vehicles built on the same chassis platform. In fact, the Slash meets the demands of our application even better because many of the various suspension bits have been upgraded from plastic to aluminum. This includes the C-hubs, steering blocks, rear hub carriers and axle nuts.
In addition, the Slash does not include a transmitter or receiver. Since these are not used in our project, this provides a little bit of savings.
As shown in the accompanying video, there are several steps in preparing the TRAXXAS Slash. Most of the preparation involves removing parts of the RC Car which which we do not use. Here are the major steps:
- Remove the 4 body clips which hold the clear plastic body on the car
- Remove the plastic body
- Remove the body mounting brackets. There is one in the front, and one in the rear. Each mounting bracket is held in place by two screws.
- Remove the stock Electronic Speed Controller (ESC), which is held in place by two screws.
- Remove the receiver case. 4 screws hold the cover down, 2 more screws accessible from inside the box hold it to the chassis.
- Remove the stock front bumper.
- Upgrade the front and rear springs.
- Install a new front bumper, the Scalpel Bumper from JConcepts.
- Remove the antenna holder
The video gives detailed instructions on the modifications.
In a previous article, What is the difference between RACECAR project?, we discussed the reasoning behind building our own robot hardware. It’s simple, we want a general purpose self driving platform to better understand the different bits and pieces of autonomous vehicles and the associated software.
There are many ways to modify this build to suite any given application. In this prototype, we replace the stock ESC with a VESC. The VESC is an open source brushless DC motor controller. This provides better control at slow speeds than the stock ESC, as well as the ability to monitor engine speed. The engine speed can be used to calculate crude odometery, since there are no encoders built into the car drivetrain.
The stock plastic body weighs about 6 ounces. The build will be adding 3-5 pounds of batteries, computers and sensors. Therefore a spring upgrade is necessary. The springs shown in the video are the first attempt, but still need to be fine tuned for this application.
Many people have asked for a full bill of material (BOM) for the build. Here’s the deal: Once we’re happy that everything works and fits the bill, we’ll publish the BOM. In addition, we’re setting up a storefront where you can buy the hard to find, custom, and long lead time items. Some of the parts can take up to 10 weeks to get, so we’ll keep some in inventory at the store. We’re still a few weeks from opening the store, but things look quite promising.