RACECAR/J Platform Preparation

RACECAR/J Platform Preparation is the second step of building RACECAR/J. In an earlier article we prepared the chassis, here we will be working on preparing the platform decks and adding some electronics. Looky here:

Background

One way to think about RACECAR/J is that it consists of two parts. The first part is the chassis, a 1/10 scale remote control car with modifications to support the extra weight of the electronics. The second part is the electronics. The electronics consist of the computers and sensors which enable the car to act autonomously.

The electronics attach to platform decks, which in the case of RACECAR/J are made from precision cut 3/16″ Delrin sheets.

The full RACECAR/J kit includes the mechanical hardware, platform decks, electronic speed controller and USB hub shown in the video. Full kits are available in the RACECAR/J shop. The video shows the “Big Mouth” kit in a MIT RACECAR configuration. The MIT RACECAR configuration mounts a Hokuyo UST-10LX Lidar at the front of the RACECAR, along with a stereo camera.

The Platform Decks and Mechanical hardware are available separately in the RACECAR/J shop.

Tools and Supplies

Here are some of the hand tools in the video:

Some paper towels and isopropyl alcohol can are useful for cleaning the platform decks. Soapy water is a good alternative.
3M Dual Lock Reclosable Fastener is used to attach the USB Hub to the platform deck. Industrial Velcro is a good alternative.

Platform Deck Preparation

If you order the Platform Decks from the RACECAR/J shop, the decks are delivered as a single piece of Delrin protected by an overlay sheet. As shown in the video, remove the decks from the sheet and remove the overlay sheet.

After removing the overlay sheet, clean the platform decks. The laser cutting process leaves a residue which tends to create a mess. In the video, isopropyl alcohol is the cleaning agent; some soap and water can be used as a substitute. Use a lintless towel if possible, you can wipe it down afterwards with a micro fiber cloth if need be.

You may notice that the Platform Deck has some surface scratches. This is normal. Delrin is an industrial plastic, and arrives from the manufacturer with some surface imperfections.

Clean Platform Deck
Clean Platform Deck

Standoffs

As an optional step, you can use a 4-40 tap to thread the holes for the standoffs. If you have a large number of RACECAR/Js to build, I have found this to be a real time saver.

Tap Standoff Holes
An Optional Step: Tap Standoff Holes

The holes drilled in the platform deck are sized such that the standoffs are self tapping. You can simply use a 3/16″ driver to screw the 1/4″ standoffs into the platform deck. If you tap the holes before hand, assembly is easier. Here is a major WARNING: Do not over tighten the standoffs!! Aluminum is a soft metal, and your super human strength may sheer the standoff. Removing the standoff remains is very unfun. Don’t ask me how I know that.

8 1/4″ 4-40 standoffs go on the top of the bottom platform deck. Here’s how it should look after installation:

Standoff Placement
Placement of 1/4″ standoffs on lower deck
Annotated Standoff Placement
Annotated Standoff Placement

Next, install the 5 2″ Standoffs with 7/16″ 4-40 machine screws as shown below:

2" Platform Support Standoffs
2″ Platform Support Standoffs Installed

Do a test fit of the upper platform to make sure everything lines up correctly.

Electronic Speed Controller

RACECAR/J uses an open source electronic speed controller (ESC). Previously this was called a VESC, but due to copyrights each manufacturer now has a different name for their particular version of the hardware. The ESC takes two forms. There are mounting hole patterns on the lower platform deck for either form. For a traditional VESC derivative, 1/4″ standoffs are used to mount the ESC. The video covers the non-traditional Enertion Boards FOCBOX installation. The FOCBOX is a more compact and better package for this application.

Here are the mounting points:

ESC Mounting Points
ESC Mounting Points

The ESC should be placed on the bottom of the platform. There are 4 through holes to mount the FOCBOX, which is held in place by M3x8 mm machine screws.

Once the FOCBOX is in place, add the extra long header to connect with the steering servo later.

Servo Header Extender
Installing Servo Header Extender

USB Hub

The next step is to mount the Amazon Basics – 7 Port USB Hub

. Turn the Platform Deck over. Four pieces of Dual Lock tape, each about 2″ long, attach the hub to the underside of the platform. First, attach two pieces of Dual Lock to the underside of the USB Hub. Second, lightly attach the mating Dual Lock tape to each. Remove the backing tape, and then place the the hub on the platform. Then remove the hub, and make sure that the Dual Lock firmly adheres to the platform deck.

When finished, run a USB cable (Micro-B to USB A) cable from the FOCBOX underneath the USB Hub mount. The Dual Lock acts as a raceway to run the cable. Attach the USB Hub to the Dual Lock tape on the platform, and then plug the USB cable in to the hub.

USB Hub Mounting
USB Hub Mounting

Lidar Plate Mount

All that remains is to mount the lidar plate. If you are using the Hokuyo, you will want to use the 1/4″ aluminum plate. The plate is included in the full RACECAR/J BigMouth kit, and available separately in the RACECAR/J shop. This plate will help dissipate the heat which the lidar generates. This step is of course a place holder until the actual lidar itself is installed.

The lidar plate mounts with 4 1″ standoffs using 7/16″ 4-40 machine screws.

Conclusion

In these first two articles, we have built the chassis and the electronics platform for RACECAR/J. In the next article, we attach the two and install the Jetson computer.

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