This tutorial will teach you how to build your very own robotic rover. I'm using a 1/10 scale electric car, a monster truck to be specific, but any type of car will do (although, some are easier to work with than others). Our goal will be to build an autonomous rover that can navigate a course on its own.
First, we will modify the chassis so that we have a platform to mount our electronics and sensors. We will mount our microcontroller to the platform. Next we will add a wheel sensor for measuring distance traveled.
- Sparkfun Wheel Encoder Kit - This is a magnetic encoder that is easy to mount and works quite well.
- Exceed RC 1/10 scale electric car or truck (from nitrorcx.com) - I used the "Infinitive" truck, but the "Sunfire" buggy is a good choice also, just depends on what you like the look of.
- Pololu A* 32U4 prime - Arduino compatible microcontroller - Pololu has several versions of this; I like it because it has a lot of power pins and other options, as well as a built in SD card reader, a buzzer, and some buttons and LEDs.
- Pololu MinIMU v3 - An optional sensor, but important as it adds a compass and gyro that give us heading information. Also, it contains a 3 axis accelerometer that lets the rover know which way is up and if it gets bumped.
- Hardware - #6 by 3" machine screws (x4) and nuts (x8); round nylon spacers for #6 screws, 2.5 inches long (I used two 1.25 inch spacers) (x4), rubber washers for #6 screws (x4).
- Plywood board - About 9" by 6" (for mounting sensors and electronics).
Step 1: Modify RC Truck Chassis
You will need a place to mount your electronics and sensors. There are many, many ways to do this; this is how I did it. First, remove the body shell off the truck. Drill a hole the diameter of your machine screws in each of the 4 corners of the chassis. Place a 3" long screw (bolt) in each hole and about 2.5" inches of spacer, held in place by a nut. A plywood platform goes on top of these nuts/screws. You will have to cut the platform to the approximate size of the chassis, so that it fits. Mark the place on the platform where each of the screws goes, it may be easier to do this using the holes that you drilled in the chassis. Drill holes in the platform for the screws. The platform is held in place with another nut (I also put a rubber washer on the bolt to help with vibrations).
Now, mount your microcontroller to a convenient location on the platform. You can screw/bolt it into the plywood, tape it down, or whatever works for you. Just make it reasonably secure. I also found it convenient to cut/drill a large hole in the center of the platform for routing wires through from the bottom.
Step 2: Add Wheel Encoder Sensor to Vehicle
In this section we are going to install a wheel encoder sensor. The purpose of this sensor is to measure the rotation of the wheels. The sensor detects the magnets that are embedded inside of a small washer. This washer will be glued onto the output gear of the vehicle's motor and the sensor will be mounted near the gear, on the outside of the gearbox.
First remove the gearbox housing (so that you can pull off the motor gear that is located inside the gear box housing) in the back of the truck, next to the motor. Take the housing off by removing the 5 screws holding it on. Then pull the gear off (after using a hex key to loosen the set screw holding it on).
Prepare the magnetic sensor washer by removing the rubber washer that came on it, you may need to cut/scrape rubber off and clean it up some.
Carefully center the magnetic sensor washer on the gear, add a little super glue (CA) and let dry.
Put the gear back on motor shaft and put the gear housing back on with screws. It may take a bit of wrangling to get the gear back on the motor shaft because the magnetic washer gets in the way, but it can be done. Also, do not tighten the set screw too much, as it could break the gear (I made that mistake). Instead of over tightening, you may want to add a little lock-tite.
Step 3: Mount the Encoder (magnet) Sensor to the Gearbox
The magnetic sensor for the wheel encoder needs to be mounted to the outside of the gear box housing, on the side close to where the magnet is mounted on the motor gear. Use double sided foam tape, hot glue, duct-tape -- whatever works. Exact placement is not critical, just get it close. Bend the wires to the sensor, so that they go around the top of the gearbox housing, and the sensor ends up against the side of the housing. The sensor wires will be plugged into the microcontroller in a following step.
That's it for now, I do plan to update this instructable will more steps as I progress on my rover. Stay tuned!