The theme for 2022’s PiWars competition was “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 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 was 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.
The robot has a front facing Raspberry Pi camera mounted in the radiator grille, just below the Pi logo. This is the primary navigation system in the autonomous games.
A time-of-flight sensor faces forward below the radiator. This is why the middle section of the bulldozer blade has been cut out.
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 the previous year’s robot to save on build costs). These motors have a built-in gearbox so that they can directly drive the track sprockets. They also have magnetic encoders which permit the use of PID motor control and odometry based navigation.
One of the main aims for PJD was to “look cool”. We also wanted it to look like a tractor for Old McDoofus’ farm.
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.
Another game implement attachment point is located on the back of the chassis.
Four bolt heads can be seen next to the tracks. These can be used to set the tension in the tracks.
More 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.
Below is the “Technical and Artistic Merit” video that we submitted for the competition.
|Main Control||Raspberry 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 sensors||Raspberry 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 control||2x 10A H-Bridge circuits.|
Motor encoder inputs for odometry
|Dimensions||235mm long x 196mm wide x 230mm high|
|Battery||3S 1,300mAh LiPo, nominal 11.1v.|
Permits up to 2 hours of development under battery power.
|Raspberry Pi||Raspberry Pi 3 Model B+|