FRC Bumpers
A Guide to Easily Building Quality Bumpers
The Case for Bumpers
Nobody in FRC seems to like bumpers. Those pesky safety devices that FIRST requires on every robot in most all games, why is it so. In some opinions, they are only a crudely engineered method of absorbing shocks. Whose idea it was at FIRST HQ to strap pool noodles to the sides of robots so they could make contact games, I don’t know. But I was on a team that had some bumper issues, and I mean serious bumper issues. We were on the instructional slide for how-not-to-do-bumpers 3 times, on the same slide. Like any engineer would, I took a bad thing and made it better. Also like an engineer, I found that other people wanting to adopt the better thing want documentation. The guide below will show how to easily construct robust, compliant, good looking, and easy to use bumpers, this time recommended by Lead Robot Inspectors. To be clear, the instructions will show how I build bumpers for my team’s robot, not yours. I will make it clear when and where to modify the design for your particular design. There are a lot of options when it comes to materials, suppliers, and fabrication methods, and most work just as well as another. Choose what works best for your needs, and if you aren’t sure, ask.
robots and pizza,
Tynan Purdy
FRC 4468, Fernbank LINKS Robotics
What You’ll Need
Hardware
3/4” wood screws
2” wood screws
1/4-20 Machine screws and T-nuts
Materials
1/2 sheet of 3/4” plywood
1x5”x1.5” or 2”x2” 90º Aluminum Angle 1/8" thick
1"x1" 1/8" Aluminum Angle
Equipment
Staple Gun
Power Drill with phillips driver and countersink drill bits
Drill Press (preferable but not necessary)
Miter Saw (can be replaced with a hacksaw and wood hand saw or bandsaw)
Digital Calipers
Tape measure
Sewing Machine (depending on design)
Sharpie, pen, and pencil
Fabric
There are a variety of choices for good fabric, depending on the amount of friction desired and how you plan to attach numbers.
Twill
Pros
Low friction
Iron on compatible
Adhesive type can be used for easy fabric numbers
Cons
Very thin, can sag if not pulled tight
Adhesive back can be hard to work with
Nylon Fabric
Pros
Thick, durable
Things
Cons
RoboPromo
Pros
Stiffness of rubber makes pulling tight easy, often smooth result
Cons
Rips more than other fabrics
Wood
Anyone who has tried to shop for bumper wood knows that finding exactly ¾”x5” planks is nearly impossible. The simplest solution is to buy a half sheet of ¾” plywood and rip it into planks on a table saw. While it may seem like using hardwood will result in stronger, stiffer backing, it really doesn’t make a difference in performance on the field. Note that plywood is not the same as particle board, which is not legal according to the blue box in R30. Keep in mind the Bumper Rules in section 8.5 of the Game and Season Manual, especially R24, R29, R30, and R31.
R30. BUMPERS must be constructed as follows (see Figure 8-6):
A. be backed by ¾ in. (nominal) thick (~19mm) by 5 in. ± ½ in. (~127 mm ± 12.7 mm) tall plywood or solid, robust wood. Small clearance pockets and/or access holes in the plywood backing are permitted, as long as they do not significantly affect the structural integrity of the BUMPER.
Note the specific requirement for the height of the wood planks is a range between 5.5” and 4.5”. In the experience of 4468, the ability to build 4.5” bumpers allows for smaller and lighter bumpers without sacrificing functionality. Short bumpers also, subjectively, look a lot more stylish. On the other hand, if big and heavy lends toward your overall strategy, perhaps as a defense bot, you can certainly rip wider planks up to 5.5” if you so desire.
Fasteners
Again, there are many ways to do this. The best combination of ease of use and structural rigidity that 4468 has found is these slide snap latches from McMaster. Incorporating them into a bumper assembly is very simple, but does require precision and some planning.
T-nuts are a simple and robust way to attach mounting brackets to the wood of your bumpers. #10 size t-nuts and socket cap bolts are small and light while offering plenty of structural rigidity.
The brackets that the slide latches will be attached to uses 1x1” ⅛” thick aluminum angle extrusion. Angle can be purchased from any variety of hardware stores or McMaster.
Prep Work
Robot Dimensions
In order to cut lengths of wood and manufacture brackets correctly, there are a few key pieces of information about the robot frame that are needed.
Length and width of the robot frame
Length of bumper segments around bumper gaps
We have to keep in compliance with two specific requirements when it comes to the dimensions of the bumper frame.
R23. ROBOTS are required to use BUMPERS to protect all outside corners of the FRAME PERIMETER. For adequate protection, at least 6 in. (~16 cm) of BUMPER must be placed on each side of each outside corner (see Figure 8-2) and must extend to within ¼ in. of the FRAME PERIMETER corner. If a FRAME PERIMETER side is shorter than 6 in. (~16 cm), that entire side must be protected by BUMPER
Gaps
Configuration
Fabrication
Appendix
Appendix A: FIRST Robotics Competition 2018 Game and Season Manual
While rules may vary from year to year, general bumper rules hold true and are not likely to change significantly. Please refer to the current game manual and examine the bumper rules before construction to ensure you are compliant.
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