Bumpers
Your team will need to make two sets of bumpers, one for when you are competing on the red alliance and one for the blue alliance. We made a single-piece unibumper with wood that is 4.625” tall and 3/4” thick, which satisfies R408. Keep in mind that your bumpers are allowed to be 5” ± 1/2” in height, so it is critical that the bumper wood is not shorter than 4.5” tall.
This year we decided to prioritize a lower bumper ~0.5” off the floor to prevent the robot from running over notes.
Here is the bumper BOM for a set of two bumpers:
3/4” Thick Plywood:
- Qty(4) @ 4 - 5/8 in. x 32 - ~11/16 in (4.625” x 32.7”)
- Qty(4) @ 4 - 5/8 in x 28 - ~7/8 in (4.625” x 28.9”)
Home Depot Items:
- Qty(8) 1-7/16 in. x 1-7/16 in. x 2-3/4 in. G185 18-Gauge Framing Angle (1-Pack)
- Qty(4) 3 in. Galvanized Flat Corner Brace (4-Pack)
- Flex Seal
Other Items:
- Qty(8) nylock nuts for 10-32 hardware
- Qty(8) nuts for 10-32 hardware (may not be needed)
- Gaffer’s Tape
- Qty(8) Bumper Noodles
- Red Bumper Fabric
- Blue Bumper Fabric
- AndyMark Bumper Hardware Kit
Bumper Rules can be found in Section 8.4 of the game manual.
Starting with the sheet of plywood, cut 8 sections of 4.625” strips. Then using the 4.625” strips create four 32 - 11/16” planks and four 28 - ~7/8” planks.
Bumper Assembly
Start construction by butting up a longer plank against the shorter plank of wood. Use a 90 degree angle or speed square to make sure that the wood is a 90 degree angle. Clamp the wood into place once square and install a corner brace. Add wood until you have made a rectangle, making sure to butt the longer planks against the shorter ones (the ends of the 28 - ~7/8” plank should be visible while the longer ones should not). Flip the frame over and add another corner brace at each corner. Finish by attaching a framing angle inside each of the four corners with the wood screws from the bumper mounting hardware that come in the chassis box.
Next take two pool noodles of equal length and bundle them together with 3 single wraps of tape as shown in the image on the right. Make sure not to compress the noodles.
After making your first bundle of noodles, find the midpoint of one of the shorter sections of wood. Mark the midway point with a marker and then line up the end of the pool noodle bundle with the midpoint as shown below. With the noodle centered under the short side, bend the noodle around the corner and run it along the long side. Avoid joining noodles at the corners, if the noodles end around 2-3” from the start of a corner then it is better to shorten them and use additional noodles. If the noodles come 4” or more past a corner then there should be enough room to leave the noodle as is.
Bad corner join length Allows for better corner joins but uses more noodle
3 loops of tape were used to secure the noodle snuggly to the frame while not compressing the noodles. The noodles are then snuggly wrapped around the corners and secured to shorter sections of the frame.
After securing one side, attach the other. In the previous step our first noodle bundle extended over the centerline on the shorter section of wood, this is desired. On each bundle cut one of the noodles such that the other bundle can fit in. The noodles should have a small gap between them, if they are deflecting each other (shown in the rightmost image) then they should be cut down to remove any visible bending. If the noodles do not overlap an additional pool noodle can be cut up to fill larger gaps.
Once both sides are fully attached with tape, make sure to tape the joining of the noodles in place. The bumpers are now ready for fabric.
Measure out the width of the bumper fabric. To do this, we wrapped a tape measure around the pool noodles and bumper frame. In our case, the fabric needed to be around 16”.
To cut the fabric, we laid the entire length on a group of tables and used scissors to cut along the marked line. Make sure to cut both the red and blue fabric to the same width.
Next lay the fabric underneath a longer section of the bumper wood as shown in the picture below. Selection of this position is important for the coming steps, to find the ideal location use your stencils to layout the location of your numbers. The fabric should start about 2” from the end of the last stencil. Make sure to center the fabric widthwise such that there are equal lengths of fabric on both sides of the bumper.
Once the desired location has been found the fabric can be wrapped around the bumper and stapled in place with two staples per side. It may be best to have one person pull the fabric towards the center, keeping a decent amount of tension on both sides while another person staples the bumpers in place. Alternatively one side could be fixed in place and the other side could be tensioned afterward. Overlap between the two sides is fine. Finally once the staples are in place on both sides mark the wood with a Sharpie where the staples went to assist with reinstallation of the fabric.
Next wrap the fabric around the entire wooden noodle assembly. There are two goals when doing this: make sure the fabric is tightly wrapped around each corner and keep the bumper frame centered within the fabric. The excess material can be cut off as shown below.
After the bumpers are secured, find the midsection of each bumper side, lay out the number stencils, and mark the stencil’s locations on the outside of the bumpers. Write the number in the center of the section as well so you know where each number belongs. The corners can also be marked if desired.
Once the bumpers have been appropriately marked, use a flathead screwdriver to remove the staples. Then take the opposite alliance color fabric and lay it out on the ground next to the marked bumper. Align the marked bumper end to end with the opposite colored bumper and then begin to transfer the markings onto that bumper. Using a long piece of box tube or a long measuring device is a good way to make sure that the markings line up well. Finally cut the opposite colored fabric to the same size as the one that was stapled.
Once the bumpers have been properly marked it is time to add your team’s numbers. We used a wooden template and white flex seal spray to add the team “number” to the bumpers. We elevated the wooden template off the fabric by 1/2” to reduce the amount of paint build up between the fabric and wood. However teams can also use Stick on numbers, Vinyl adhesive, or hand painting. We made sure the template was centered top to bottom and left to right before starting the spray. If you used our BOM to buy bumper materials you will have Flex Seal and the stencils. For the best look attempt to evenly elevate the stencils 1/2” above the fabric and spray from a higher distance, making sure to not to get Flex Seal on the rest of the fabric. Taping the stencils to the bumper material may also work. Make sure to let the Flex Seal dry before continuing.
Once the bumpers have been painted we can move to reattach them. Repeat the steps that were taken to attach them the first time making sure to staple them in the correct location. Make sure that all numbers are centered on the bumpers.
First we will begin adding staples to the top of the bumper. Staple in the center of each side first, making sure the fabric is centered. It may be best to add a single staple on the bottom of each midpoint before moving on. When adding staples on the bottom make sure the fabric is pulled as tight as possible. Add staples until you reach the approximate spacing from the corner shown below. Staple all sides before moving onto the corners.
Here is a method we used for having nicer looking corners. Use one hand to pull the corner fabric parallel to one strip of wood while holding scissors in the other. Use the scissors to find the corner of the wood and then mark a 45 degree angle. Fold the material towards the other side and mark the same 45 degree angle. Finally make a straight line connecting the 45 degree lines. It may be best to leave an eighth of an inch from the corner to the start of your line.
Cut along the lines created. Once a corner is cut we will start adding staples. Pull the fabric tight to one side and add staples. After one side has staples fold the fabric over itself and attempt to get the corner to like it does in the bottom photo. Add staples to complete. Do this for all corners on the top.
After the top has been completed, flip the bumpers over and begin stapling on the new top starting from the center again. Make sure the fabric is pulled as tight as possible for the best looking bumpers. Using wide vice grips can be very useful for this task. You will have noticed that one of the sides has a good chunk of excess fabric, fold it over itself, leaving some space for the corner. Staple down the folded over excess fabric.
Once all sides have staples in them and everything looks correct, use a mallet on the staples to push them further into the wood so they do not stick out.
One of the most important considerations for the bumpers this year was the mounting height. Bumpers should not be dragging on the floor but should be low enough to prevent Notes from easily being run over. Running over Notes could lead to your robot being high centered on them, getting them stuck in the drivetrain or getting stuck underneath the robot. We found that 0.5” of ground clearance heavily mitages this issue.
Note doesn’t go under🙂 Note goes under🙁
We only used the front/back brackets that come with the chassis, with two at the front corners and two more in the back corners. Note that 8 total front/back brackets will be used, 4 for each alliance color of bumpers. The brackets are secured to 1.5” 10-32 bolts that stick vertically out of the chassis. These bolts are inserted in the third hole in from the edge in the outer row of holes in the chassis front and end rails. The bumpers are set to the appropriate height by using nylock or regular nuts as spacers. Our bumpers were installed with two nuts on top of each bolt. We highly recommend using at least 1 nylock nut on the 1.5” 10-32 bolt. These nuts should be left in place on the bolts in the chassis, with only the top nuts on top of the brackets (shown below) coming off when the bumpers need to be changed.
Wood screws are used to secure the bumper to the bracket. Put the bumper frame over the robot and put it in place around the chassis. Position the bumper bracket over the bolt and add another nut to hold it in place. In order to install wood screws, you will need to drill a pilot hole for your wood screws through the fabric, corner brace, and into the wood frame so that the wood screws will be able to bite directly into the wood. Ideally, you will be able to get four wood screws into each corner.
Nylock nuts or the provided wingnuts should be used to ensure the bumper cannot come off during the match. Once one set of bumpers is undone, remove the four nuts holding the brackets down, lift the bumper set up, put the other color of bumpers in its place, and position four more brackets in place and tighten down the nuts again to hold them in place. Drill out pilot holes and then wood screw these four brackets in place to the other bumper set.
Severely compromised bumpers can result in your robot being disabled during a match (G411).