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In my Student Choice Project 3 offered by my Engineering Concepts class, I was given the chance to select a project of choice on something related to engineering. I decided to pick a project that not only would challenge both my mechanical and technological knowledge but would also benefit one of the robotics teams I oversee as Wheeler High School -- CircuitRunners Robotics' Director of Operations.
Here is some specific information about the criteria and constraints regarding this project:
Overall Objective:
The overall goal is to build a mechanically functional coaxial swerve drivebase for use in the FTC environment. This drivebase must be easily manufactured and utilize little external manufacturing methods besides a 3d printer.
The drivebase must be rigid. The wheels and/or bearings must not shift or have a lot of play for consistent movement, especially in something like autonomous.
The drivebase must be precise. Repeatability with a GoBilda motor must be within 1 degree every time.
The drivebase must be easily manufacturable. 3d printing takes a priority here as an easier way to manufacture parts.
Resources Required?
-Is there additional knowledge you will need?
-What materials will you need for this project?
-Are there any special tools you will need?
No additional knowledge, just time spent in CAD.
Fusion360, 3d printed parts, steel ball bearings, screws, motor and servo, and other external electronics.
A 3d printer.
Proposed Project:
In contrast to a differential swerve, more often than not a coaxial swerve module prioritizes speed over precision, although at lower speeds it may be able to accomplish the same. Rather than using two motors like the differential does, many coaxial modules in FTC utilize a motor-servo assembly so that precious motor ports can be saved for other assemblies. This allows for a higher speed than differential due to it relying on a motor-wheel gear reduction rather than a motor-differential-wheel gear reduction.
Below is some of the work I put into building the module:
Completed Module
Dual Pulley Assembly
Utilizing a 90 degree turn in order to provide the translation of motion like a bevel gear without the backlash of a bevel gear.
Compact Pulley Spacings
Completed Project - The Coaxial Swerve
In the completion of this project, I learned a lot about the mechanics of rotated belt pulley assemblies as well as learning a lot about standoff assemblies. This project uses nearly entirely 3d printed parts, and besides for belts (which can optionally be printed) and aluminum parts, steel nuts and bolts, ball bearings, and the motor/servo and wheel, all other parts can be made on a traditional FDM printer. The project incorporates a custom radial bearing into the dual pulley assembly in the top plate, and uses a custom thrust/radial bearing combination in order to support axial and radial forces. There is almost no compliance in the system due to the 4mm thick plates and the stoutly spaced standoffs providing a lot of rigidity.
I now have left to finish printing the parts and editing the internal module in order to make sure that the material in the rotation module doesn't interfere with the pulley/belt motion. The module, when broken in by running using a motor for a few minutes, runs extremely smooth and the white lithium grease used as lubrication performs well. I do need to test whether or not the rotated belt assembly works, but the mockup I tested appeared to work fine, though the TPU belts are not performing as expected.
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