Our teams don’t usually do reveals, however, I wanted to post about a recent design that was built by a freshmen team as it’s a good example of how a competition robot can be relatively simple yet still be competitive.
This design was created with the following goals.
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Drive system using mecanum wheels. No other reason here other than that we have them and wanted to try them out.
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Height under 15 inches so as to be able to drive under trough.
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Scoring in trough only, no attempt to score in the high goal. This was to simplify the design.
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As light as possible.
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Finish building with enough time to practice (wishful thinking).
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Try and use as many uncut standard structure pieces as possible.
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Modular design that separated the three major sub-systems (drive, lift and intake) and allowed them to be worked on independently.
So with this in mind the following design was created.
Drive system
The drive is based around a standard 25x25 steel chassis. Aluminum could have been used but we have a number of these that came with classroom kits and were available. Version 1 of the drive constructed the chassis in the standard way, after testing it was decided to push the front wheels forward to create a larger wheel base and help keep the center of gravity behind the front axles, more on that later, this meant replacing the front angle with a C channel behind the wheels. Power for the drive comes from four 393 motors geared for torque directly driving the four mecanum wheels.
[ATTACH]6912[/ATTACH]
Lift System
The lift system is a simple (2-bar ?) arm that uses two small turntables as the final pivot points for the arm. Another of our teams had tried to use the turntables last year but were unsuccessful, this time the idea was to try and put the arms outside the chassis so as to theoretically be able to drive them a full 360 degrees. I posted some details of the compound gearing used in the design this thread;
https://vexforum.com/t/compound-gearing/22130/1
power for the lift comes from two 393 motors and we stuck with the 8.33:1 gear ratio that was initially chosen. The lift has a potentiometer on both sides for positional feedback to the software.
[ATTACH]6908[/ATTACH]
The lift attaches to the drive using 5x10 aluminum (or steel) plates, this allows some amount of forward/backward and height adjustment. Some additional bracing was added after the final position was determined.
Arm
The arm is very simple, 1x2x1x35 Aluminum C channels, scoop driven by two 269 motors using HS chain with a 4:1 ratio to provide more torque to rotate the scoop. Several different scoops were tried before the final simple design was arrived at. The scoop has a quad encoder so the software can “electronically gear” the scoop movement as the arm raises.
[ATTACH]6909[/ATTACH]
The three sub systems come together as follows.
[ATTACH]6911[/ATTACH]
[ATTACH]6913[/ATTACH]
The 1x5x1x25 C channel at the back is ballast needed to counteract the weight of the sacks.
Part 2 will look at the center of gravity and force needed to lift the arm.
