# Trinket Powered Rover ## Red Rover... Red Rover... Science, Technology, Engineering, (Art) and Math (STEM / STEAM) curriculum is gaining momentum in K-12 education. It's exciting to see so many new makers and engineers learning how fun it is to make! I wanted to design a low cost robot that anyone could build if they have access to a 3D printer. So... here it is - an autonomous micro rover based on Trinket. ![](https://cdn-learn.adafruit.com/assets/assets/000/013/373/medium800/trinket_IMG_0973.jpg?1388636372) It's inexpensive and fun, and looks adorable! # Trinket Powered Rover ## Tools / Materials When I started designing the rover, I ran into a significant obstacle trying to find inexpensive tracks / treads. I had some success 3D printing ones with [flexible filament](https://www.adafruit.com/product/3222) but the total cost was too high. That's when I stumbled into these... '[chain bracelets](http://www.orientaltrading.com/christmas-chain-bracelets-a2-13663854.fltr?Ntt=chain%20bracelet)' from [Oriental Trading](http://www.orientaltrading.com/). You can buy a dozen for less than ten dollars; which will make six rovers. ![](https://cdn-learn.adafruit.com/assets/assets/000/013/367/medium800/trinket_IMG_0885.jpg?1388616238) The pattern is slightly different on the inside and outside; rounded (left) and flat (right). The rounded side fits in the wheel / sprocket perfectly. ![](https://cdn-learn.adafruit.com/assets/assets/000/013/368/medium800/trinket_IMG_0886.jpg?1388616256) This guide builds on three others... [Introducing Trinket](http://learn.adafruit.com/introducing-trinket) [Modifying Servos for Continuous Rotation](http://learn.adafruit.com/modifying-servos-for-continuous-rotation "Link: http://learn.adafruit.com/modifying-servos-for-continuous-rotation") [Trinket Servo Control](http://learn.adafruit.com/trinket-gemma-servo-control/code) Ready? Here is a list of materials you will need. - 1X [Adafruit 3v Trinket](http://www.adafruit.com/products/1500 "Link: http://www.adafruit.com/products/1500")(you can substitute for an Arduino Micro if you like) - 1X [Tiny Breadboard](http://www.adafruit.com/products/65 "Link: http://www.adafruit.com/products/65") - 1X [4xAA Battery Holder](http://www.adafruit.com/products/830) - 2X Continuous Rotation Micro Servos - 3X Female / Male Jumpers - 3X M3 10mm Screws - 1X M3 Hex Nut - Double-sided Foam Tape For distance measurement, you can use a [Parallax Ping))) Sensor](http://www.parallax.com/product/28015), [Grove Ultrasonic Ranger](http://www.seeedstudio.com/depot/grove-ultrasonic-ranger-p-960.html), or [Maxbotix Ultrasonic Rangefinder](http://www.adafruit.com/products/980 "Link: http://www.adafruit.com/products/980"). _Let's get fantastic with some plastic!_ # Trinket Powered Rover ## 3D Printing The rover is comprised of seven plastic parts... the stache' is not optional! ![](https://cdn-learn.adafruit.com/assets/assets/000/013/370/medium800/trinket_rover_001.png?1388616567) The model archive includes a small and large chassis and three different sonar mounts. ![](https://cdn-learn.adafruit.com/assets/assets/000/013/371/medium800/trinket_rover_002.png?1388616584) You should be able to squeeze all of the parts into a single print. [3D Models (.stl files)](http://learn.adafruit.com/system/assets/assets/000/013/044/original/TrinketPoweredRover.zip?1387765228) Source files are available on [Github](https://github.com/rwinscot/TrinketRover). Or, you could try a re-mix with some elements of [designs](http://www.thingiverse.com/thing:15528) on Thingiverse. # Trinket Powered Rover ## Assembly You might need to tap the axle holes... better safe than sorry. ![](https://cdn-learn.adafruit.com/assets/assets/000/013/344/medium800/trinket_IMG_0910.jpg?1388615568) Or, you could warm / soften the plastic with a hand torch and thread the hole with the screw. ![](https://cdn-learn.adafruit.com/assets/assets/000/013/345/medium800/trinket_IMG_0907.jpg?1388615601) Make sure that the wheel on the front doesn't bind; you might need to sand around the axle a bit. ![](https://cdn-learn.adafruit.com/assets/assets/000/013/346/medium800/trinket_IMG_0914.jpg?1388615626) The mounting hole in the wheel is purposefully small to allow for the widest possible screw size. Widen the hole with a drill bit that is slightly larger than the threads of your screw. Insert your M3 hex nut... ![](https://cdn-learn.adafruit.com/assets/assets/000/013/348/medium800/trinket_IMG_0922.jpg?1388615681) And screw the sonar mount to the chassis. ![](https://cdn-learn.adafruit.com/assets/assets/000/013/349/medium800/trinket_IMG_0925.jpg?1388615704) Pilot holes are needed to mount the servo to the chassis. A 1/16 inch bit will do nicely. ![](https://cdn-learn.adafruit.com/assets/assets/000/013/350/medium800/trinket_IMG_0928.jpg?1388615734) Take it slow... if you hear any kind of cracking you might want to warm / soften the plastic a bit before proceeding. ![](https://cdn-learn.adafruit.com/assets/assets/000/013/351/medium800/trinket_IMG_0931.jpg?1388615762) Let's get to work on the rear wheels. ![](https://cdn-learn.adafruit.com/assets/assets/000/013/352/medium800/trinket_IMG_0939.jpg?1388615794) Servo horns are typically white or black... grab one, and trim it to fit. ![](https://cdn-learn.adafruit.com/assets/assets/000/013/353/medium800/trinket_IMG_0945.jpg?1388615819) I tried using model cement this time... which works, but it will take an hour or so before the wheels are solid enough for final assembly. 5 minute epoxy might be a better alternative. ![](https://cdn-learn.adafruit.com/assets/assets/000/013/355/medium800/trinket_IMG_0950.jpg?1388615870) Repeat these steps for the other wheel. ![](https://cdn-learn.adafruit.com/assets/assets/000/013/356/medium800/trinket_IMG_0955.jpg?1388615892) # Trinket Powered Rover ## Electronics You'll have to decide on what combination of distance sensor + microcontroller you want to use. I've tried them all, and found the following configurations to work well. - Trinket + Parallax Ping))) - [Trinket + Maxbotix Proximity Sensor](../../../../trinket-ultrasonic-rangefinder/adding-the-sensor) - [Trinket Pro + HC-SR04](https://www.instructables.com/id/Simple-Arduino-and-HC-SR04-Example/) - [Trinket Pro + Seeed Studio Ultrasonic Ranger](http://wiki.seeedstudio.com/Ultra_Sonic_range_measurement_module/) Of all the sensors that I tried, the Parallax Ping))) was the easiest to use with Trinket. All you need is GND, VCC, and 1-pin for measurement. ![](https://cdn-learn.adafruit.com/assets/assets/000/013/358/medium800/trinket_IMG_0906.jpg?1388615985) Snap the sonar into the mount. ![](https://cdn-learn.adafruit.com/assets/assets/000/013/357/medium800/trinket_IMG_0926.jpg?1388615957) The servos wires end in female connectors, which you will need to convert to male. ![](https://cdn-learn.adafruit.com/assets/assets/000/013/360/medium800/trinket_IMG_0899.jpg?1388616051) You can do this two ways, replace them with [male ones](http://www.digikey.com/product-detail/en/1318109-1/A29322CT-ND/4430539). ![](https://cdn-learn.adafruit.com/assets/assets/000/013/359/medium800/trinket_IMG_0893.jpg?1388616024) Or pull out the female connectors... ![](https://cdn-learn.adafruit.com/assets/assets/000/013/361/medium800/trinket_IMG_0960.jpg?1388616078) Extract a few pins from standard headers. ![](https://cdn-learn.adafruit.com/assets/assets/000/013/362/medium800/trinket_IMG_0961.jpg?1388616102) Insert the pin into the female receptacle. ![](https://cdn-learn.adafruit.com/assets/assets/000/013/363/medium800/trinket_IMG_0962.jpg?1388616124) And solder in-place. ![](https://cdn-learn.adafruit.com/assets/assets/000/013/364/medium800/trinket_IMG_0963.jpg?1388616147) Sweet. ![](https://cdn-learn.adafruit.com/assets/assets/000/013/365/medium800/trinket_IMG_0964.jpg?1388616171) Here is the circuit diagram to get all the wires in the right place. With the servos, remember that ground is often brown / signal is orange. ![](https://cdn-learn.adafruit.com/assets/assets/000/013/372/medium800/trinket_rover_breadboard.png?1388630983) # Trinket Powered Rover ## Source Code _"To control servos with the tiny microcontroller on the Trinket, we'll need a Servo library. The default Arduino Servo library is really only good for Uno/Leonardo/Due and similar beefy processors that can drive servos 'standalone'. Sadly, the Attiny85 can't quite do that as it does not have 16bit timers."_ If you haven't installed the [Adafruit Software Servo Library](http://learn.adafruit.com/trinket-gemma-servo-control/code) yet, read through this guide and install the library. Good to go? The following sketch uses the Parallax Ping))) Distance Sensor and is a starting point; ultra-bare bones. And this, is where all the fun begins! ``` #include <Adafruit_SoftServo.h> #define SERVO1PIN 0 // Servo control line (orange) on Trinket Pin #0 #define SERVO2PIN 1 // Servo control line (orange) on Trinket Pin #1 Adafruit_SoftServo servo_left, servo_rght; // Connect the sonar signal pin to this pin on the Trinket. const int sonar = 2; // Moderate speed forward for both servos. Given the orientation of the servos // one will be going forward, and the other backward. You may need to adjust // these slightly to get the rover to move straight forward. const int left_speed = 75; const int rght_speed = 90; // Number in cm when the rover will reverse and try to navigate around. const int obstacle = 8; // Multiplier used to determine how far the rover will back-up. const int back_track = 100; // Duration of a ping, distance in inches, distance converted to cm. long duration, inches, cm; void setup() { // Attach servos... and off we go! servo_left.attach(SERVO1PIN); servo_rght.attach(SERVO2PIN); } void loop() { // Setting servos in forward motion. servo_left.write(left_speed - cm); servo_left.refresh(); servo_rght.write(rght_speed + cm); servo_rght.refresh(); delay(15); // establish variables for duration of the ping, and the distance // result in inches and centimeters. duration = 0; inches = 0; cm = 0; // The PING))) is triggered by a HIGH pulse of 2 or more microseconds. // Give a short LOW pulse beforehand to ensure a clean HIGH pulse: pinMode(sonar, OUTPUT); digitalWrite(sonar, LOW); delayMicroseconds(2); digitalWrite(sonar, HIGH); delayMicroseconds(5); digitalWrite(sonar, LOW); // The same pin is used to read the signal from the PING))): a HIGH // pulse whose duration is the time (in microseconds) from the sending // of the ping to the reception of its echo off of an object. pinMode(sonar, INPUT); duration = pulseIn(sonar, HIGH); // convert the time into a distance. inches = microsecondsToInches(duration); cm = microsecondsToCentimeters(duration); // Long distances will cause the servos to misbehave... cap at 50 cm. if ( cm > 50 ) { cm = 50; } if ( cm < obstacle ) { // back_track * delay(15) = distance the rover will back-up during // obstacle avoidance. for (int i = 0; i < back_track; i++) { // Magic numbers... will always backup the same direction. Can you // think of a better way to navigate obstacles? servo_left.write(150); servo_left.refresh(); servo_rght.write(50); servo_rght.refresh(); delay(15); } } } long microsecondsToInches(long microseconds) { // According to Parallax's datasheet for the PING))), there are // 73.746 microseconds per inch (i.e. sound travels at 1130 feet per // second). This gives the distance travelled by the ping, outbound // and return, so we divide by 2 to get the distance of the obstacle. // See: http://www.parallax.com/dl/docs/prod/acc/28015-PING-v1.3.pdf return microseconds / 74 / 2; } long microsecondsToCentimeters(long microseconds) { // The speed of sound is 340 m/s or 29 microseconds per centimeter. // The ping travels out and back, so to find the distance of the // object we take half of the distance travelled. return microseconds / 29 / 2; } ``` ## Featured Products ### Adafruit Trinket - Mini Microcontroller - 3.3V Logic [Adafruit Trinket - Mini Microcontroller - 3.3V Logic](https://www.adafruit.com/product/1500) **Deprecation Warning: The Trinket bit-bang USB technique it uses doesn't work as well as it did in 2014, many modern computers won't work well. 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