Horseshoe Turret
Introduction
A project that had a lot of potential, but was scrapped due to lack of funding from my team. The horseshoe turret was a design I had with my robotics team to create a shooter design that had a wide range of motion and a variable shooting angle. It was complicated, but I knew if we were able to pull it off it would help our team become more successful in the coming years. The only other team I knew that had a design like this was Team 254, The Cheesy Poofs, so the goal for this project was to learn how to reverse engineer someone else’s design. I wanted to be able to look at a design and have a general idea of how it works and then take those ideas and then convert them to a CAD model. This would help me become a more intuitive engineer
The cheesy design
Let’s take a closer look into the Cheesy Poofs design.
The 2016 Cheesy Poofs robot was called Dropshot and it featured a turret design with a retractable hood, and 270 degrees of motion. Luckily, Cheesy Poofs document their robot design very well so I was able to go into their technical documents and get a better understanding of how their design worked.
Shooter hood design
Their shooter hood, the one that retracts, worked by having the retractable portion geared to a motor and gearbox. Knowing this, I was able to incorporate these ideas into my own design. At the top of this design is a little gold piece that I determined was the encoder, allowing the team to know how far the hood has travelled and then stop at the right position. The gear reduction that was circled allowed the motor to have more precise positioning than if the motor was directly geared to the hood.
shooter flywheel
The shooter flywheel had an interesting design choice with two motors on each side of this assembly. After some reasoning, I deduced that the reason two motors were required as if only one motor was used, once a ball goes through the flywheel and the speed of the flywheel was reduced, it would have taken too long for the flywheel to get back up to speed with one motor so two motors were necessary to ensure that the mechanism was fast and consistently fast.
Shooter turret
Finally, we head over to the shooter turret -- where all the magic happens. One of the biggest hurdles was understanding how the turret assembly was able to move around without a giant bearing underneath it. The leftmost circle shows that the horseshoe itself was suspended on three rollers: A small one sandwiched by two bigger ones. This allowed the turret to run along a circular path. Said circular path was attached to the gearbox and motor assembly as seen in the rightmost circle. The encoder isn’t 1:1 to the horseshoe itself so to ensure motion is understood the gear ratio needs to be recorded.
The reengineered version
With my design, I had the design limitation of reduced funding and materials so it was more meant as a pitch for the feasibility of the design to secure more funding and resources to make it happen. As a result, these parts were designed to be manufactured out of MDF and with a laser cutter in mind.
shooter hood design
With the manufacturing limitation in mind, to ensure that the hood can move along a set path I decided to create a slot in the hood part to allow it to ride along the two bosses at the bottom. The shooter hood was geared for a direct drive motor system (Potentially stepper motors) to help reduce costs and improve manufacturability of the device.
shooter flywheel
This was one of the few assemblies that I had the chance to manufacture in-house, so designed it using aluminum 6061.
I intended to either bend the plates or use L brackets to secure the assembly to the horseshoe gear, however, due to the pulley system location these were not possible solutions, so instead I designed these parts to be machined on two different planes. The top holes that can be seen are M3 threads that can be secured to the gear through fasteners.
As another cost-cutting measure, this assembly only features one motor which would affect spool up time and consistency of launches, but since this is a pitch device, this seemed like a worthwhile tradeoff.
The wheels used were compliant hex wheels found on AndyMark. They were the stiffest versions available as I felt they would help with the launch of the balls (Foam this season)
Shooter turret
I initially wanted to use bearings as the smaller discs used to reduce friction and improve overall speed of the assembly, but since the goal was creating the horseshoe turret as cheap as possible, those were forgone for the use of sandwiched discs. This disc is intended to be machined in one go on the laser cutter so all the cuts are present on a single plane.
The turret would be directly driven by a brushless motor and had 280 degrees of rotation available to it. Calibration of the turret was a huge factor to consider, so this current design had the idea of endstops at the limits of the gearing that would be activated each time the turret was turned on. Overall the design reduced the cost of the Cheesy Poofs design while attempting to maintain the most functionality possible.
