Build Guide 4: Vehicle Prep & Mounting

Type: Build Guide

Time to move from the bench to the workshop. In this guide you'll prepare the TRX-4, mount the enclosure, and install the camera. No wiring yet — that's Guide 5. This is purely mechanical.

What You Need

Parts:

Traxxas TRX-4 Sport (fully assembled RTR)
Waterproof IP65 enclosure
Camera mount bracket + 1/4" mini ball head
Long CSI ribbon cable (15-30cm)
Anker USB battery pack

Tools:

Hex driver set (metric — the TRX-4 uses 1.5mm, 2mm, 2.5mm hex)
Drill + small drill bits (for enclosure cable holes)
Zip ties (assorted sizes)
Double-sided VHB mounting tape
Velcro straps
Marker/pencil for marking drill points
Ruler or calipers

Step 1: Get to Know the TRX-4

If this is your first time with the truck, take 10 minutes to drive it around with the stock radio. Seriously — it's fun, and you'll understand the steering range and speed characteristics you need to replicate with the Pi.

Things to note while driving:

Full steering lock left and right — how far do the wheels turn?
The slowest speed you can maintain — this is roughly your drag speed
Where the ESC is mounted and where the servo wires route
How the body shell attaches (clips) and comes off

Now remove the body shell and set it aside. You'll be working on the bare chassis.

Step 2: Plan the Layout

Before mounting anything, dry-fit everything on the chassis. Lay out the components and think about:

Weight distribution: The Pi enclosure and battery are your heaviest additions. Try to keep them centered and low. The TRX-4 has a good center of gravity — don't ruin it by mounting everything on one side.

Cable routing: The CSI camera cable is fragile. Plan a path from the Pi enclosure to the camera mount that avoids moving parts (suspension arms, driveshafts, steering linkages). The cable should have some slack for suspension travel but not so much that it snags.

Access: You'll need to open the enclosure regularly (to swap SD cards, adjust wiring, debug). Don't mount it somewhere you can't reach.

Suggested layout:

         [Front of truck]
              |
    ┌─────────────────────┐
    │                     │
    │   [Camera]          │  ← Front of chassis, looking forward for awareness
    │         |           │
    │   [Pi enclosure]    │  ← Center of chassis, top of battery tray area
    │         |           │
    │   [USB battery]     │  ← Next to or under enclosure, velcro-strapped
    │                     │
    └─────────────────────┘
              |
         [Rear of truck]
              |
         [Drag bar attachment point]

Step 3: Mount the Waterproof Enclosure

The enclosure holds the Pi, PCA9685, ADS1115, and wiring. It needs cable entry points for:

Power cable (USB from battery)
Camera ribbon cable (CSI)
Servo cables (2-3 going out to ESC and steering)
GPS antenna cable (or the GPS module itself can mount outside)

Drill cable entry holes: Mark and drill holes in the enclosure for cable pass-throughs. Use cable glands if you have them — they maintain the waterproof seal. If not, silicone sealant around the cables after final wiring works fine.

Mount Pi inside the enclosure:

Use the brass standoffs that come with most enclosures
Orient the Pi so the GPIO pins face toward your cable exit holes
Leave room next to the Pi for the PCA9685 and ADS1115 boards

Mount enclosure to the chassis:

Use VHB tape on the bottom of the enclosure, pressed firmly onto a flat section of the chassis
Add a velcro strap around the chassis rails for extra security — VHB is strong but a backup strap means you won't lose the enclosure on rough terrain
Zip ties through the chassis rails also work as additional insurance
Make sure the enclosure lid opens freely once mounted

Step 4: Mount the Camera

The camera faces forward for situational awareness — it gives you a view of where the rover is in the yard and will eventually feed autonomous vision.

Attach the ball head to the camera bracket. Standard 1/4"-20 thread.
Mount the camera module to the ball head. You may need an adapter plate or a small custom bracket — some 3D-printed options exist, or just zip-tie the camera securely to the ball head.
Mount the bracket to the chassis. Use VHB tape on the base of the bracket, pressed firmly onto a flat section of the chassis near the front. Add a velcro strap around the bracket and chassis rail for extra security. The camera should be:
- Near the front of the chassis, pointing forward
- Angled slightly down (~10-15 degrees) so you can see the ground 1-3 meters ahead, not just the sky
Route the CSI ribbon cable from the camera back to the Pi enclosure. Keep the cable away from moving parts (suspension, steering). Use a zip tie or two to secure it along the chassis rail.

Test the field of view: Power up the Pi (on bench power for now), connect the CSI cable, and capture a test image:

# On the Pi
rpicam-still -o framing_test.jpg

Check that you can see the ground ahead of the rover and enough of the surroundings for orientation. Adjust the angle if needed by adding/removing shim material under the camera.

Step 5: GPS Antenna Placement

The GPS module needs a clear view of the sky. Options:

Mount on top of the enclosure: Simple, good sky view. Attach with VHB tape or a small bracket. Route the cable through a hole in the enclosure.
Mount on the body shell: Even better sky view, but the shell comes on and off a lot. You'd need a quick-disconnect.
Inside the enclosure with an external antenna: If your GPS module supports an external active antenna (SMA connector), you can keep the module inside and just mount the antenna on top.

Recommended: Mount the module itself on top of the enclosure with VHB tape. It's simple and works well enough for 2-3m precision.

Step 6: Battery Placement

The Anker USB battery pack:

Velcro-strap it next to or under the enclosure
Route the USB-C cable into the enclosure through a cable entry point
Make sure you can access the battery's power button without removing it
Make sure you can remove the battery for charging without disassembling everything

The TRX-4's main LiPo battery goes in its stock location — don't change this.

Step 7: Drag Bar Attachment Point

You won't build the full drag rig until Guide 7, but prep the attachment point now:

Identify a solid point at the rear of the chassis — the rear bumper mount or rear body post works well
The drag bar will be towed from here via a short rope or rigid link
Make sure there's nothing in the way of a bar swinging left-right by 30-40 degrees during turns

Checklist

Driven the TRX-4 with stock radio — understand its behavior
Body shell removed, chassis accessible
Waterproof enclosure mounted to chassis with VHB tape + velcro, cable entry holes drilled
Pi mounted inside enclosure with room for PCA9685 and ADS1115
Camera mounted forward-facing with VHB tape + velcro, framing tested
GPS module/antenna positioned with clear sky view
USB battery mounted and accessible
Rear attachment point identified for drag bar

Looking good. The chassis is ready for wiring — Guide 5: Wiring & Control Integration connects everything together.