>>>Pi Wars 2020<<<
1OB Hull
With the motors, electronics, layout and software at a good enough point in the development, the moment finally arrived to build the hull of the platform and finally give shape to the robot.1.1Mock Up 1.0
The initial mock up was done in October when the platform still deployed four independent DC motors. The turret was also a place holder, way too small to sport the capabilities required for the Pi Wars.
Illustration 1 - Mock Up 1.0
1.2Mock Up 2.0
With a changed layout, with the boards ready and the gun mechanism is decided, a second mock up was made in to evaluate the fitting of all components.
Illustration 2 - Mock Up 2.0 Structure
The structure changed little overall. The turret turn mechanism was also decided upon. The turret was moved and increased in size. It was decided to put the RPI inside the turret since that's where the camera lay. Also, the elevation mechanism was decided.
Illustration 3 - Mock Up 2.0 Turret
There was the option to use sliding contacts to give the turret infinite 360° turn capability, but this feature was dropped due to the little practical use and the added complexity on the turret turn motor.
Illustration 4 - Mock Up 2.0 Inner Component
Placement
The rotation mechanism fits well inside the body of the machine,
requiring an additional fixture plate. The motor board and voltage
regulator can be fixed on the main structural plate that supports the
motor as well. Battery is placed in the front lower section for
protection and ease of access.2Hull
The second mock up allowed to size up the boards. Next, is the construction of the (hopefully) final Pi-Wars Hull.First choice is the material. We had both 3mm aluminium and 5mm polycarbonate sheets at our disposals. The final choice landed on polycarbonate for aesthetic reasons. OrangeBot will look fabulous with a carefully routed wires, transparent hull and strategically placed LEDs.
Illustration 5 - Cut Masks
Construction method was the same deployed for OBY, our beefiest
platform. First, paper mask are drawn 1:1 with the desired shape,
than the masks are applied to the sheet, that are cut using vertical
saws and drilled with a vertical drill. machine.
Illustration 6 - Cut Plates
2.1Hull Construction and Assembly
The main structural plate hosts the motors, the trailing wheel, the motor board, the battery housing, most of the wiring and give shape to the platform.
Illustration 7 - Main Structural Plate
Below the main structural plate there is a skirt section to protect components above the clearance line, like the battery. The biggest are side plates, that rests on the motor bracket wings. Like all plates, angular L and M4 bolts hold the structure together.
Illustration 8 - Side Plates
The front and rear plates close the skirt and together with ten angular elements and forty bolts, give the structure of the platform rigidity.
Illustration 9 - Front and Rear Plates
The front plate is lower on the ground, to allow the installation of the Joust Equipment Extension and the Barrel Mover Extension. The rear plate is higher to allow space for the Main Motor Board.
The Front Angular plate and the Rear Angular plates have no structural purpose and have a fixed M4 bolt holding them, allowing for quick dismounting of the plates. They are designed to come off quickly and allow maintenance of the equipment inside the platform.
Illustration 10 - Front Angular and Rear Angular
Plates
Closing the platform is the Top Plate. In future the plate might be modified to allow rapid extraction as well. The Top Plate hosts the turret rotating joint and the turret rotation servo.
Illustration 11 - Top Plate and Turret Joint
The turret rotation servo is placed inside the body to save space inside the turret itself. The pillar to connect the servo to the turret above is still being optimized. Cable runs by the side of the pillar inside the turret joint hole. Long M5x60 bolts allow regulation of height and hold the plate in position.
Illustration 12 - Top Plate and Turret Rotation
Servo
With the body of the platform taken care of, next step is to
construct the turret.2.2Dummy Turret Construction
OrangeBot is designed to have a main weapon as integral part of the platform, and not as standalone extension. Similarly, equipment is going to be always present beside the main weapon. A low power targeting laser, and the main camera. This gives the ability to aim quickly and precisely from the remote control interface, removing the need to look at the physical laser manually.Because of this, the Raspberry Pi 3B+ is best placed inside the turret, with a dedicated power and communication cable interfacing with the Main Motor Board.
Illustration 13 - Turret Component Placement
Since the main weapon design is yet to be finalized, the current turret design is only a place holder, meant to provide the minimal capability: Host the Raspberry Pi 3B+.
The MVP turret is composed by just two plates. A turret base plate to host the angular elements and the rotating joint housing and a vertical rear plate to host the RaspberryPi 3B+.
Illustration 14 - Turret Base Plate and Turret
Rear Plate
The dummy turret is attached on top of the turret rotating joint, with a pillar connecting the rotation servo with the turret top plate.
Illustration 15 - Turret Assembly
With the structure assembled, next step is to mount the electronics and route the wires.
2.3Install Electronic Boards and Route Wires
With the structure assembled, next step is to disassemble it, remove the protective film from the plates, and install all electronics and wirings.The bundle of wires coming from the encoders, the motors and the battery are cut to length, terminated and routed through an hole in the main structural plate.
Illustration 16 - Motor, Encoder and Battery
Wirings
Next step is installing the boards. First the voltage regulator board fits the Left Side Plate. Wirings fits below the Main Motor Board.
Illustration 17 - Voltage Regulator Board on Left
Side Plate
Next step is installing the Main Motor Board along with all the required wirings. An XT60 Connector goes to the battery in the lower front section. Two DC Motors and Encoder channels are routed to the front of the board. Power wirings are routed below the motor board and held in place by zip ties.
Illustration 18 - Main Motor Board on the Main
Structural Plate
Due to a reduction in scope, and to solve the “DISASTER: Turn”, the platform uses only two DC motor channels in base configuration. The Barrel Mover Extension is going to make use of the two remaining open loop DC motor channels.
With the bulk of the wirings in place, the reminder of the hull can be assembled.
Illustration 19 - Final Assembly
3Electrical Test
With the platform assembled, an electrical test was conducted to validate the platform.
Video 1 - Electrical Test
4Conclusions
The construction of the hull is a major step in the construction of the OrangeBot platform.With the hull assembled, the core of the platform is ready, and development for challenge specific extensions and core software components can continue.
A major focus is achieving high precision of the controls.
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