This is a design for a small robot chassis that is very mobile. It navigates by dead reckoning, but has I/O pins available for a variety of sensors and actuators. It is small enough to run indoors, yet robust enough for most lawns and patios.

One constraint I had to deal with was keeping costs to a minimum, preferably nothing out of pocket. Fortunately my junkbox has some high quality parts and a BOE BOT I could "borrow" from. All the parts used are still available today. this will be nice when it's time to build the second and third copies. (a swarm of one leaves a lot to be desired)

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Step 1: Materials

Materials I used:

Board Of Education microcontroller board from Parallax.com
battery case (4AA cells)
4 AA battery cells
Tamyia track and wheel kit ( I got mine from Amazon)
2 RC servos modified for full rotation (mine came from my BOE Bot, Parallax.com sells them separately)
1 standard (unmodified) servo -- (optional)
5 bolts 1/4" x 3" with nuts
4 bolts #6 x 1" washers and 3 nuts each
1/8" (3mm) plywood 18" x 24"

Tools used:

PC and serial cable (for programming)
screwdriver / wrenches
Lasercutter - You could get by with a fretsaw, or scrollsaw, and a drill press, but a lasercutter is great to have access to.

Step 2: Cut Out the Structural Parts

Cut out the drive gears and structural parts. I user 1/8" plywood, but plastic would be more weather resistant. If you are cutting with a fret saw, or a scroll saw, look closely at the template and instructions as some of the cuts are not essential.

Step 3: Mount the Drive Gears on the Servos

Mount the cut drive gears on the servo horns. The servo horns that came with the BOE Bot kit fit nicely through the hole in the center of the cut drive gear. The overhang needs to be trimmed before gluing in place.

Step 4: Mount Bogies

Mount the bogies, Drive wheel and bogie wheels to the bottom level. This level is 2 pieces thick and the screws (from the Tamyia tread kit) will go through 1 3/4 pieces, holding them together.

Step 5: Install Drive Servos

Place the drive servos with the drive gear in the cutout for them on layer 1. Add the standoff spacers and the bottom half of deck 2 on top.
Shown here with tracks already in place as I didn't take pictures until I had finished putting it all together ...well a few times.

Step 6: Add Circuit Standoffs to Layer Three

Bolt the two pieces of layer three together using the #6 bolts through the holes that line up with the controller board's holes. Bolt it from the bottom leaving the end of the bolt sticking up to mount the controller board to later.

Step 7: Install the Lift Servo (optional)

Step 8: Bolt Together Assemble and Install Track

Now using the (5) 1/4" x 3" bolts and nuts, bolt together all three layers of the chassis.

Then assemble and install track. The track just snaps together. Instructions came with my kit. It is easier if the tracks are installed on the drive gear 1st then the bogies and guide wheel.

Step 9: Mount Microcontroller Board

The bolts installed in step 6 should be sticking out of the top of the bot. Place a nut on each bolt down far enough to place the BOE board on the bolts and secure with another nut. Plug the servos in.

Step 10: Mount Battery Box - Program

Mount the battery box. I just used Velcro to secure it. install battery cells and plug battery bot into the microcontroller Board. using the serial cable and a PC program as you wish. I found the code, examples, and lessons for the BOEbot from parallax.com are thorough, easy to understand, and have provided the code I have used so far. They also filled my head with great ideas for future applications.

Step 11: Going Further

above is a photo hint of where I'm hoping to take this project.

It would be easy to substitute a different microcontroller board, or make custom attachments.

Build a copy for yourself, then add to it, change it, make it better. It would be great if you wrote up an instructable of your hacks so the rest of us could gain from your insights and hard work.

Thanks for reading.

Introduction: Inexpensive Robot Chassis