PiDrojon Deer

The theme for 2022’s PiWars competition is “Old McDoofus had a farm” (Doofus is the name of the little red robot logo for the competition). With this in mind, this page introduces PiDrojon Deer (PJD), our design for PiWars 2022 at Home.

We decided to try a tracked chassis this year at the request of our team driver.  He also requested that we make the robot “look cool”, so we have paid much more attention to the robot’s aesthetics.

We think this machine would be entirely right on “Old McDoofus’” farm.

PJD has been completely designed in Fusion 360.  The caterpillar tracks are made from Lego parts, but the rest of the chassis has been 3D printed in PLA and PETG.

Doof’s new tractor

The robot has a front facing Raspberry Pi camera mounted in the radiator grille, just below the Pi logo.

A time-of-flight sensor faces forward below the radiator. This is why the middle section of the bulldozer blade has been cut out.

A speaker is also mounted just behind the radiator: hopefully we’ll find some nice engine noises. And perhaps we may give Doofus a voice!

The front loader has a pair of high-torque servos to lift it. It will be one
of the attachment points for the game specific implements.

We have used two of P21’s motors in PJD (we generally recycle last year’s robot to save on build costs).  Initially, PJD’s track units included a 4:1 reduction ratio since we expected a tracked chassis to need lots of torque to make turns.  However, it turns out that this was not necessary: two motors provide plenty of torque to turn the robot on the spot, even on grippy surfaces.  A new chassis was developed that can use two or four motors with a direct drive to the tracks.  The new design can have two motors (with tracks, or wheels), or four motors (with tracks, wheels, or mecanum wheels).  Initially we will try playing the games with two motors and tracks but will swap to a mecanum setup if it helps. 

This year we have paid more attention to our robot’s aesthetics.

Instruments and control levers were included in the design and painted. Details have been included on the engine and track running gear.

The engine bonnet (which houses the RPi) includes an air-cleaner and Raspberry Pi logo radiator badge. The exhaust pipe has a motor fitted so that it shakes like a real tractor exhaust might shake, see here.

Doofus has a servo in his torso so that his head can turn.

I bet that number plate was expensive!

Another game implement attachment point is located on the back of the chassis. This is intended to be used for a tow hitch; we’re thinking of using a trailer for the obstacle course.

Four bolt heads can be seen next to the tracks. These can be used to set the tension in the tracks.

More aesthetic detailing can be seen here such as the warning chevron paint scheme and the posh number plate.

My personal favourite is the rusty old toolkit containing a jerry can, hammer, huge adjustable spanner and oil can. I like it because my son designed it.

Technical Features

Main ControlRaspberry Pi 3 Model B+ running Buster
Control code written in Python
Camera interface using OpenCV
Connection to robot via 3v3 full duplex serial and two GPIO lines
Onboard sensorsRaspberry Pi Camera Module V2.1
BNO055 Inertial Measurement Unit (IMU)
Front mounted VL53L1X Time of Flight (ToF) sensor
Hall Effect motor encoders x 2
LiPo voltage detector
Push button to provide manual RPi shutdown
Motor control2x 10A H-Bridge circuits.
Motor encoder inputs for odometry

Specifications

Dimensions235mm long x 196mm wide x 230mm high
Weight1.6kg
Top speed1.2ms-1
Battery3S 1,000mAh LiPo, nominal 11.1v
Raspberry PiRaspberry Pi 3 Model B+
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