Robot Development

2022-2023 Power Play

Chassis Development

We developed two chassis in parallel at the start of the season, one with a low center of mass (COM), the Standard chassis, and one with a high COM, the Clearance chassis. We attempted to design chassis and mechanisms with the build systems that we had, rather than basing it off of parts we didn't have and hoping we'd be able to get them in time for competitions.


Design requirements from the start of the season:

The Standard Chassis

Based off of our Freight Frenzy chassis, the Standard Chassis was designed to just be a holonomic chassis capable of holding a lifting mechanism and moving around with it.

The Clearance Chassis

The Clearance Chassis was an original concept designed to be elevated 6-7" off the ground in order to be able to clear cones placed on ground junctions.

Pros

Cons

Pros

Cons

Assessing the Designs

After using the Clearance Chassis in our first two league meets, we found that the instability and high COM was too much of a detriment to our mobility in a match, and we decided to develop the Standard Chassis over the Clearance Chassis. Additionally, after developing each chassis with Rev parts and a Pitsco rack and pinion slide, we decided to switch to GoBILDA, as it would allow greater compatibility with GoBILDA parts like the pulley-rigged Viper Slide.

Moving into GoBILDA

Once we got all of the GoBILDA parts, we developed a version of the Standard Chassis, which we used in our third league meet and in the B&T tournament. We found that our new GoBILDA parts were much better for matches, as they ran more smoothly compared to the Rev and Pitsco parts. The chassis was more dynamic on the field with the new motors and Mecanum wheels, which allowed for more accurate positioning of the robot, as well as faster motion in general.


After the B&T Tournament, we noticed that the weight of the slide was not evenly distributed throughout the robot, and that it was starting to bend the U-channel it was mounted on. We decided to rework the chassis into a triangular shape so that the slide would be better supported and more embedded inside the chassis.

Enter the Triforce Chassis

The Triforce Chassis was designed to have the very center of the robot raised upward, with the front and back angled to be down closer to the ground, such that its profile would resemble the Triforce from popular video game series The Legend of Zelda. This chassis maintained our low COM and centered the front-to-back weight distribution such that the robot could move more quickly while the slide was fully extended.

Elevator Mechanism Development

We started designing an elevator mechanism using Pitsco's TETRIX MAX Rack and Pinion Linear Slide Pack. We found it to be a sturdy slide, but it was very slow and heavy, to the point where it struggled to lift itself. Additionally, it required multiple stages to fit within the 18" size limit while compressed, but also extend up to reach higher junctions. Even with 2 stages of the slide (which required 2 separate motors), it wasn't high enough to reach the highest junction, so we added a 4-bar linkage to raise our intake mechanism up above the high junction.

With the height of the slide and the 4-bar, it became very difficult to precisely control the positioning of the robot, as it was very unstable with such a high COM. The weight of the TETRIX C-Channels and our intake mechanism, combined with the overall lack of constraints in this chassis, made nearly every robot motion unstable.

The Double-Reverse Four-Bar


We briefly explored the idea of attaching our intake mechanism to a double-reverse four-bar system, as it was a compact way to easily add a lot of height to our robot's reach.

We decided against the Double-Reverse Four-Bar, as there wasn't an easy way to mount it without creating a third chassis from scratch built specifically to hold the mechanism. Additionally, the heavy TETRIX C-Channels were a challenge to lift under a motor's power, even with using gear ratios to apply higher torques to the system.

Looking Elsewhere for Elevators


We began looking into Rev Linear Slides and GoBILDA Viper Slides, and we were lent a 4-stage Viper Slide from 11563 (RoboWranglers), which was more lightweight and faster to extend and retract. However, like the other designs, the Viper Slide was not immune to problems. 


The first problem was that the extension and retraction cables kept getting tangled together while operating the slide. To counteract this, we moved the position of the spool up and mounted it on the back of the slide, as seen in the picture. Our spool only had an extension string, as gravity would be doing most of the work for retracting the slide.


The second problem with the Viper Slide was that the cables in the slide's pulley system kept snapping. For a while, we just kept a crimping tool on hand (also lent to us from 11563) and replaced the snapped cables as they happened. However, when the cable snapped during a match, we decided that we had to figure out a more permanent solution.

Cable-Driven Slide

Belt-Driven Slide

Pros

Cons

Pros

Cons

Incorporating Sensors

Another problem during matches was that the positioning of the slide relative to each junction was variable. The slide occasionally lowered itself while the robot was moving because the tension in the system was not being kept. An encoder was placed on the slide motor to track the rotational position relative to the height of the slide. Since a certain amount of rotation in the motor always corresponded to a certain height of the slide, we used the encoder to map specific motor positions to the four heights necessary for each of the cone stacks, as well as the heights of the three junctions. Using the motor's RUN_TO_POSITION mode makes the motor hold its position under power, so once it reached its target it would stay there. This level of automation gave the drivers more freedom to focus on positioning the robot relative to the junction, with the press of one button setting the height of the slide and holding it there until another was pressed.


To further increase the accuracy of the slide, a touch sensor was added at the base of the slide, so that every time the slide was retracted, the encoder position was reset to zero to negate the effects of the belt slipping on the motor and ensure that the slide would reach the proper height every time it was extended.

Intake Mechanisms