We would like to share with the FRC community these fully configurable two-piece bumpers.
However, you’ll probably notice the “This document was shared via a link and is view only.” warning when you go to copy the file. This isn’t intentional, it’s because we are on the OnShape Enterprise Education plan and we can’t share files for export outside of the workspace easily. We will happily share files outside of it if you want a copy for yourself, just ask us. We thought this particular item might be something that others would want so we are making it available here. It’s possible it will eventually diverge from the other linked one but both are available for viewing.
It employs a full sheet metal backing, based on our bumper designs from recent years, to maximize sturdiness and help keep the center of gravity low. The document also contains mounting hardware, which is based on designs we’ve found to be reliable, and enables quick replacement of the bumpers, using sliding tabs and spring pins.
This mounting hardware is in the assembly, but not all of it is part of the measured mass of the bumpers, and teams will likely need to modify it to use it in their designs, such as adding clearance for frame gussets in some of the hardware. There are other modifications that teams may find useful, such as adding additional pocketing to the sheet metal backing, changing the mounting hardware, etc.
The reason we made this is the same as it is for any other configurable subsystems – it saves future working time, since we can input some variables and make minor modifications, rather than having to design it from scratch. This time is especially valuable during the crunch of build season. Along with saving design time, it also allows us to get our quote to Fabworks in as fast as possible, allowing us to receive the sheet metal backings much sooner.
The bumpers allow for the frame perimeter width and length, ground clearance, gap between the frame and bumper backing, and the respective gaps between the front and back sides of the bumpers to be modified using a variable studio. Using a separate variable studio with formulas that use those input values, it regenerates all the parts and mates from any changes made.
In the document, we provided descriptions for the input variables, but we’ve added them below for clarity.
The first two variables are FP_width and FP_length. These control the intended frame length on the side where the bumpers split, and the side where the bumpers are not split respectively.
The third variable is frame_gap, which controls the gap between the sheet metal backing and the outside of the frame, and it is uniform around the entire frame.
The fourth and fifth variables are front_gap and back_gap, respectively, and they control the width of the opening in the “front” and “back” sides of the bumper pieces, respectively. However, keep in mind that in some cases, it is beneficial to mount the bumpers such that the splits in the bumper pieces are on the sides of the robot, so those gaps don’t necessarily have to be on the front or back of the robot.
Here is an illustration of these variables from a top view:
The last variable is ground_clearance, which is not literally the ground clearance of the bumpers, but rather the distance between the ground and the highest point of the bumpers, which for these, would be the upper gussets. The reason it is specified like this is because robot rules in recent seasons have been specified by this height and it is almost always advantageous to minimize height off of the ground to keep center of mass as low as possible.
Another important note about this clearance is that this was designed for a chassis with SDS mk4i’s with the L-plate above the frame, so the value for that input will vary depending on the type of module. For instance, to use it for an SDS mk4i with the L-plate below the frame, add 2.25 inches to the intended distance between the ground and the upper gussets. This will vary depending on the module, but the “offset” that should be added to the intended distance between the ground and upper gussets is 4 inches minus the ground clearance of the frame tubes with that module.
Here is an illustration of the ground clearance from a side view:
