Structural Layout / levels
Design
From bottom to top: First stage mounted the drive train, supported by 3 Omni-Wheels touching the floor. Second stage provided platform for arduinos, motor drivers, circuit boards, and ultrasound sensors to be placed and mounted. While pillow blocks and motor mounts set the height of the second stage, threaded rods provided pressure to keep them in place. Cut outs in second stage allow for wheels and motors to protrude upwards slightly, allowing overall shorter z-height.
Third stage held the flywheel subassembly, mounted to lower stages by threaded rods. Loading subassembly mounted to third stage on cardboard constructed pillars. Loading subassembly contained three levels, for stepper motor mount, ball platform (adjustable by short threaded rods and screws) and revolute gate controlled by stepper motor. All stages were cut from ¼ inch duron, with numerous extra holes for mounting sensors and threading wires between stages as needed.
Third stage held the flywheel subassembly, mounted to lower stages by threaded rods. Loading subassembly mounted to third stage on cardboard constructed pillars. Loading subassembly contained three levels, for stepper motor mount, ball platform (adjustable by short threaded rods and screws) and revolute gate controlled by stepper motor. All stages were cut from ¼ inch duron, with numerous extra holes for mounting sensors and threading wires between stages as needed.
two layers for drive train
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completed robot, will all layers
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Development process
A fixed height for the first two levels was initially considered because of the added rigidity for motor mounting. Luckily we did not encounter fundamental drive train issues such that lacking an adjustable second level would have become an issue. Initially for holding the loading subassembly up, we used tall threaded rods, but inaccuracies in drilling holes and slip in the washers made this incredibly unstable, and also took up a larger footprint to balance correctly - so a cardboard pillar was used instead and adhered to the third level. A fair amount of troubleshooting was necessary for the relative heights of the loading mechanism features, to ultimately prevent the balls from experiencing too much friction, which would have stalled the stepper motor. Thus the adjustable platform eventually became useful in that subassembly.
Drive Train
Design
Our design utilized three individually driven Omni-Wheels. Each wheel was mounted on a square shaft, held in position by VEX shaft collars on either side. Custom pillow blocks from skateboard bearings adhered to laser cut duron were positioned on either side of the wheel - press fit acrylic pieces were used to couple the small square shaft to the inner race of the bearings.
To drive the shaft and wheel, a 3D printed shaft coupler was used between the square axle and the d-shaft of the motor. Motors were screwed into laser cut duron pieces for mounting. These mounts and the pillow blocks set the height for the next stage of the robot.
To drive the shaft and wheel, a 3D printed shaft coupler was used between the square axle and the d-shaft of the motor. Motors were screwed into laser cut duron pieces for mounting. These mounts and the pillow blocks set the height for the next stage of the robot.
view of wheel from the side
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drive train from above
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Development Process
By considering what game play strategies are afforded by certain drive trains, we settled on implementing 3 Omni-Wheels, to achieve multi-directional movement without the need to pivot in place, and to cut down on cost using 4 Omni-Wheels would entail. These shaft coupling components preferable to spider couplers, as the necessary amount of preload would have added more complexity to the assembly to keep spider couplers intact. One issue we encountered with mounting our motors was that by screwing in screws for fixing it to the duron too far, we actually jammed the motor.
Launcher
DeSign
The launching device used on the final version of our robot went through 3 iterations. With each revision to the original design, we utilized the data we obtained from our tests to make the launcher smaller and more reliable. We used a flywheel to launch, fed by gravity from a evolving feeder. We were able to increase the precision of the shooter by reducing vibrations. This was done by increasing the thickness of the motor supports and using 3D-printed couplers to ensure proper shaft alignment.
launcher components before assembling
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completed launcher on robot
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Development Process
After thoroughly inspecting and testing the old robots available for display in the ME 210 lab we realized that there are two notable differences between the requirements for this year’s robots and the ones set in the previous competitions. First, in the previous years, robots were allowed to get close enough to the targets to drop balls, chips or other payload from close range. In fact, many successful robots in past competitions were the ones that took a brute force approach to delivering the balls to the targets or buckets and avoided shooting altogether. Second, a lot of the previous competitions used horizontal targets such as buckets. This year, the target is a tower with a hole perpendicular to the playing field. Our preliminary ballistic calculations and the results that we obtained from testing previous robots suggested that the optimal launching mechanism would need to propel the balls with a relatively high velocity in the direction of the target. This change in the configuration of the targets motivated us to choose the flywheel ball launcher system as opposed to the catapult based designs that were popular in the previous years.
The first step in design our launcher was to build a test platform that aided us in figuring out what components were needed for the device to meet the requirements and what parameters would require tuning. Originally, we decided that our launching system would include three sub-systems: a shooter, consisting of a wheel a tire and a pvc pipe; a pusher, consisting of a servo, to guide the balls to the shooter and a feeder consisting of a revolving plate driven by a stepper motor that would carry the balls and drop them at a specified rate. The primary criteria for optimizing our design were precision, reliability and size. The testing platform was made using the same electrical components we were planning to use for the final version of the launcher. We augmented this testing platform with a tachometer that was made up of a customized wheel containing a magnet and a hall-effect sensor. By adding a speed measurement system, we hoped to be able to more easily tune the launcher and to find out whether we would need to implement closed loop PID controller on the DC motor to achieve the precision, repeatability and response speed needed. The test platform also included a laser diode to aid us in aiming properly during our experiments.
Below are models of our first two launcher iterations:
The first step in design our launcher was to build a test platform that aided us in figuring out what components were needed for the device to meet the requirements and what parameters would require tuning. Originally, we decided that our launching system would include three sub-systems: a shooter, consisting of a wheel a tire and a pvc pipe; a pusher, consisting of a servo, to guide the balls to the shooter and a feeder consisting of a revolving plate driven by a stepper motor that would carry the balls and drop them at a specified rate. The primary criteria for optimizing our design were precision, reliability and size. The testing platform was made using the same electrical components we were planning to use for the final version of the launcher. We augmented this testing platform with a tachometer that was made up of a customized wheel containing a magnet and a hall-effect sensor. By adding a speed measurement system, we hoped to be able to more easily tune the launcher and to find out whether we would need to implement closed loop PID controller on the DC motor to achieve the precision, repeatability and response speed needed. The test platform also included a laser diode to aid us in aiming properly during our experiments.
Below are models of our first two launcher iterations:
first launcher iteration
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second launcher iteration
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