Good bumpers are hard. How do we make them easier?

Do you mind sharing your process for the Cricut vinyl? Material, choice of iron, and length of time you apply heat?

I bought a Cricut EasyPress 2 this season to go with our Cricut Vinyl cutter. We had an extremely hard time getting vinyl to stick on Cordura all year using Siser Easyweed HTV. We settled on 5 seconds pre-heat, 30 seconds, remove transfer sheet, 30 seconds, turn over and do another 30 seconds from the back. This was after a lot of testing on everything in between and consulting with other teams and either not having any adhesion or they’d adhere but fall off in practice. The 5-30-30-30 appeared the best by the time our first district came around.

In the end our bumpers got trashed and we had to replace our red set entirely before champs and they disintegrated again this offseason.

We ended up just using the vinyl cutter to make large stencils and spray-painting. It’s a little more work in prep time but I feel more confident in these. Curious what luck other teams had to consider trying HTV again, but we might be on team paint for good.

1 Like

Here’s a thought. We already have a mandatory light on the robot - the RSL. Instead of the current yellow panel light, use a similar red or blue light. Or a stack light with yellow for RSL visibility and red/blue for alliance identification.

Personally, I still prefer a non-light solution. Bumpers do seem like the obvious choice.

1 Like

The whole idea of colored lights gets lost on audience displays and streams. It’s easy to show “red bumpers vs blue bumpers” but not so easy to follow the barely visible lights.

7 Likes

Additionally, as someone who WAS around the last few times non-RSL lights were used:

The LED red/blue squares were pretty much invisible from anything >3’. (2004-2008 or so–after 2005 only 1 was needed and it was the RSL not the alliance indicator.)

The cop dome lights were bright enough, but heavy (1 lb each) and prone to suddenly putting the team on the WHITE alliance when they shattered due to impact.

With that said, if the RSL were to be replaced with a red/blue unit, it might be OK…

1 Like

The problem my team has ran into most is mounting—it required a lot of precision that we weren’t able to execute well. Measuring and aligning the “stock” AM14U5 bumper kit didn’t go too well and we ended up needing to really jam in some of the long bolts when we changed bumpers in the pit. A better COTS bumper mounting solution would have saved us (and likely quite a bunch of other teams) a whole lot of trouble. Though, also, we did the classic “leave bumpers till the end, don’t explicitly design them, and build them just based off of the manual’s specs”. That one’s on us.

1 Like

I tried to edit my reply with how-to links from 5 days back to add this, but apparently there’s a time limit on editing replies.

Here’s another great resource shared a while back by @SurfGear
Bumper fabric & How to Make Your own Bumper Numbers

Reversible bumpers paper by 2809:
paper: K-Botics 2809 Reversible Bumpers

Would COTS 2-way bumper fabric be possible? If made from sailcloth, then you could also have a COTS solution to the stick-on dacron numbers. Add great instructions and a mounting solution, and a “just add 0.75 plywood” COTS single 2-way bumper solution might be possible.

In my experience getting the ends cut square (using a miter saw) is far easier to get right than cutting the long dimension (with a table saw or heaven help you a handheld saw of some type).

It’s great that your team has a miter saw. Not all teams have one. Many of the ones I have seen in team shops are not set up correctly and don’t make cuts that are perpendicular to the fence (many have drill presses that are also set up incorrectly). Your experience with your team is one data point and is not necessarily representative of the situation for other teams.

1 Like

As I said, “YMMV”.

Like @Joe_G’s post, this one got away from me. I’m glad to see a group passionate about bumpers. I hear grumblings about it at events, but rarely are there solutions in the discussions on here on Chief Delphi.

To open, I have been working on a bumper solution that is accessible to most teams. It does rely on some sewing ability, which I’ve been able to train Team Members on within a competition season. This is one option, and the fun part about FIRST is everyone has ways of making it better for their own team. Check out my guide at https://docs.google.com/document/d/1uw5eNlRrA46mTpt6AEXgEAwaTSo1M8Y5zvqxpXRycUA. With that out of the way, I’ll take some time responding to some of the points in this thread.

Edited (I originally liked the idea of 1x6 wood, but @philso provides some good insight to material properties. Let’s stick with 3/4" plywood cut to a height of 5".)

It is interesting that we’re having this discussion at the end of September. I have pushed for June as the Bumper Season. By now pool noodles are hard to find. It looks like Dollar Tree is still selling them online (https://www.dollartree.com/brightly-colored-swim-noodles-47-in/329034). If you haven’t stocked up on pool noodles, order now. Dollar Tree and other retailers usually only stock them in the summer.

There have been a lot of good points brought up in this discussion. I agree that the T-nut diagram in the game manual needs to be removed. This steers inexperienced teams to a mounting solution that is more trouble than it’s worth. 1-1/2" drywall screws work great with the bumper mounting kit that comes with the KOP Chassis from AndyMark.

I support the idea of including all the parts for bumpers as part of the KOP Chassis. It already has the mounting hardware. The fabric wouldn’t take up that much more room. A voucher for team numbers would be nice. The wood may be harder to ship. Teams have to cut down the frame rails on the KOP Chassis, it should be reasonable that they have the tools to cut the wood backing as well.

I support the idea of being about to attach shims to the back of the bumper to conform to the frame perimeter. It is best to have as much contact as possible between the frame and the bumper. Adding wood shims to the bumper is much easier to fabricate than redesigning the mounting hardware. Shims could be glued in place easily at an event. They will need to be monitored throughout the event to make sure they stay in place. This would make one more thing easier to fix as you’re trying to pass inspection.

Personally I’m not a fan of the bumper mounting hardware that currently comes with the KOP Chassis. I think it is over complicated for what it is trying to do. This makes replacement parts extremely expensive. It’s probably time to take time to sit down with the AndyMark engineers and work on some different options.

I’m not a fan of full wrap-around bumpers. I’m not a fan of C-shaped bumpers. I prefer having four straight bumpers with miter corners. This allows for more tolerance in the manufacturing. I use backing that is exactly the same length as the frame rails, so there is the allowed corner gap behind the pool noodle corners. Yes, a four piece bumper system is more to remove and replace between matches, if you’re not using reversible bumpers.

I understand that reversible bumpers are more complicated to construct than single color bumpers. I’ve made my design and my assembly instructions available and am happy to share them with anyone interested in them. Reversible bumpers address the issue of more to swap when using four straight bumpers. They are a mount and forget option, expect for weigh-in at the beginning of the event and after the last qualification match. (I support including bumpers as part of the weight allowance if only so I don’t have to remove my reversible bumpers for the post-Qualification weigh-in.)

One of my diverse skills when I started mentoring FRC was my parachute rigging skills. When I was interested in becoming a parachute rigger, I asked a skydiving coach and rigger what the hardest part of becoming a rigger was. He said the sewing. It isn’t because sewing is hard, but because people interested in rigging don’t have any experience in sewing. As others have said here, I think the same thing is happening with bumpers. Sewing bumpers isn’t hard, but if you don’t sew, it is impossible. If you don’t have someone mentoring the team who can sew, go to www.uspa.org and follow the link to find a USPA Member Drop Zone near you. You can’t throw a stick at a drop zone without hitting a parachute rigger. Any of them can help you sew the heavy fabric we use for FRC bumpers. (Oh, and ask them about the 3-Ring Release System. The story of the engineering behind that is inspiring.) If you can’t find a parachute rigger, look for a sailmaker. They have the equipment and the skills to work with the heavy fabrics we use for bumpers. Also one more opportunity for community involvement.

While bumpers are the only thing required by the rules that could be sewn, if you know how to sew, there are many other opportunities to make team life easier. When I train Team Members to sew, I build their skills in steps. The first step is a pillowcase. It is common cotton fabric and everything is flat, straight stitches. These are then donated to a local hospital or shelter which supports our community and increases visibility of the team. The next project is a Battery Bag. It provides a handle for carrying batteries which discourages holding batteries by their cables. It has the team number giving Team Members experience aligning, centering, and sewing the numbers. It has a window where a card, like some people have on their dishwasher, can display if the battery is charged or drained. This project uses the same heavy fabric (Cordura) that we use in bumpers. It also builds a 3D shape from fabric, so the Team Members get experience working with corners in the sewing machine. Finally they are ready to sew the bumpers which are bigger, include sew-on hook-and-loop fastener, and have a 45 degree inside corner on a curved edge.

Our sewing projects don’t end there. We developed a Robot Stretcher making it easier to carry the robot on and off the playing field. We also created a fabric and hook-and-loop Kanban Board that can be folded up and stored with our robot materials since we didn’t have open storage in our workshop. It can also be packed with our pit materials and used at events. So don’t think about sewing as a minor, one-time use skill for a robotics team. Once you have the skill, there are many opportunities to use it to make the team more effective.

As for Team and Alliance identification, I like the bumpers. I’ve been a Referee for some events. During Practice Matches we don’t require teams to be in the proper color bumpers. I’ve missed fouls and mis-called fouls because a Blue robot was wearing Red bumpers, and vice-versa. Bumpers are a passive system that work well for the Referees and the Spectators. I’m good with keeping this rule for a few more years. I don’t think LEDs are as ubiquitous at Regional and District Events as we like to think they are. The RIs out there can probably address this.

As for numbers, don’t strive to do the minimum. I build bumper numbers that are 4.5" tall, not just 4" tall. I use a typeface with a strong, consistent stroke width that is usually 3/4" wide. I don’t do this for inspection. I do this for Spectators. When team parents are in the nosebleed section of the stadium at a Regional I want them to be able to tell which robot is the one their child worked on. The bumpers are the robot jersey’s. If you can’t read the jersey, you can’t tell which “kid” on the field is yours. And when you go big on the numbers, there is no question about rule compliance during inspection, which is a nice thing to do for overworked RIs.

Please keep bumpers as an exception to the season schedule rule. Many teams have a standard chassis design, so being able to reuse bumpers between seasons helps these issues. As a community we can do a better job of highlighting bumpers during the summer and, yes, now as teams are returning to school. Thinking about bumpers outside of the competition season helps teams take their time and do bumpers right. Additionally pool noodles are for sale or on sale in June. Can we as a community declare June as Bumper Month? (Maybe we also set August as Fundraising Month and September as Recruiting Month.)

I’ve long said the KOP Chassis is good enough. The dimensions for this chassis are well established. Every team can build their bumpers outside the Competition Season, even Rookie Teams with experienced mentors or another FRC Team guiding them. If you disagree with me about the KOP Chassis, you have another chassis design in mind and you too can be building bumpers in June, not February.

Since I sew, I prefer sewn numbers over painted, adhesive, or iron-on numbers. It means this is the first thing done on bumpers, which makes pre-built, stock bumpers available as a COTS item a problem. I think they look better and they hold up better to the rigors of gameplay. I was fortunate that the team I started with had a laser cutter. We cut our numbers from white nylon fabric (Cordura) using the laser cutter. The laser cutter sears the edges of the nylon as it cuts which prevents or at least delays fraying. More teams and companies are getting laster cutters, so if you don’t have one, reach out to a community partner to see if they can cut your numbers for you. And a local company with a laser cutter may be a good team sponsor, even if all they donate is bumper letters cut from fabric and a design you provide.

There was a good point made in this discussion about problems with bumpers tend to be hard to fix at an event, particularly when you’re trying to pass inspection and everyone else is getting Practice Matches. The combination of four straight and fully sewn bumper coverings, makes it easy to pull staples, replace a single piece of plywood, and staple together a repaired bumper. The straight bumpers eliminate the need to disassemble and reassemble corner brackets. The fully sewn bumpers create a pocket for the pool noodles, which eliminate the need to tape the noodles to the frame and then wrap with fabric. And if you’re taking the time to sew the bumper numbers and the bumper coverings, then it is simple to make them reversible.

In reading some of the posts, I realized that most teams are lifting their robots from the bumpers to get on and off the field. I’ve been using a Robot Stretcher, which supports the robot by its wheels, and I hadn’t been thinking about bumper mounting supporting the robot. This means that the Bumper Mounting system is in the primary load path for supporting the full competition weight of the robot. From that standpoint, the bumpers are critical not just to pass inspection, but to make sure you can get on and off the field safely. (Still struggling with Etsy to get my shop running so I can sell Robot Stretchers as well.)

There was a mention about pool noodle sizes and availability. The pool noodles that FIRST includes in the Rookie Tote are AndyMark am-0838 (Pool Noodle Qty. 6 - AndyMark, Inc) Their diameter is listed as “approximately 2.2 to 2.5 in.” I expect if FIRST is providing them to rookie teams, they meet their bumper rules. This is the same size as those sold at a local retailer, like Dollar Tree. I don’t think the rules are intended to create more supply chain issues for teams. It may be good to include a blue box in the rules clarifying a diameter tolerance for the pool noodles that helps teams understand that what they find at a local retailer as a pool noodle, not pipe insulation, is probably good for their intended use.

@bbonner, I accept your challenge. Let me know which events you’ll be at and I’ll try to stop by and let you see my bumper design. From the other teams who have seen them, I believe they are something better than “terrible.”

I’ve seen a couple suggestions for grommets. They are not as easy to maintain as they appear. Parachutes use a lot of grommets in their construction. They can be finicky and introduce a new set of tools and a whole new skill set to get them right. Think about that tarp that you’ve used for years. How many of the grommets are pulling away from the fabric? Are you going to use brass grommets, nickel grommets, or stainless steel grommets? Have you priced out stainless steel grommets? What is the difference between a correctly set grommet and an incorrectly set one? Can you inspect the grommets before they get installed on the robot to make sure they won’t pull loose? Did you know that flat washer grommets use a different die set from spur grommets? I’ve seen teams struggle to keep track of the 5/32 hex wrench for installing 10-32 SHCS. How many stripped out metric hex wrenches does your team have? Are you ready to replace grommet dies when they are used incorrectly and damaged?

I think the ideas are in the right direction. A formed fabric pocket covering that can be easily attached and removed from the wood backing makes repairing bumpers much easier. Let’s do what upholsterers do: Staples. Incorrectly stapled fabric works pretty well. Staples are easy to remove. Staple guns are safe, readily available, and relatively inexpensive.

Taut fabric helps in giving your bumpers a clean, not saggy, appearance. Don’t be afraid to cut the pool noodles slightly larger than needed (no more than 1/4"). Then pulling the fabric taut and stapling it to the wood backing is a two-person job. One person pulls tension on the fabric while the other staples. Make sure you’re talking because you don’t want to staple your teammate’s finger. This doesn’t have to be a strength contest. Just keep the fabric taut as you staple it to the wood. I put the staples in at an angle, close to 45 degrees to the edge of the wood backing. This creates two separate load paths for the tension in the fabric. It also distributes the load across different weft and warp threads in the fabric.

I hope you got to this point. I think there are some great points in this thread. I’m glad to see bumpers getting some constructive attention here. Thanks for your consideration.

7 Likes

We’ve used Stahls gorilla grip vinyl for the past few years (pretty sure suggested by @katiyeh07 / 125). Heat Transfer Vinyl CAD-CUT GORILLA GRIP II | Stahls’

I cut our numbers on a cricut too, this year I found a used heat press on Craigslist that sped up the process. I’ve found that with ironing on numbers how much pressure was applied made a difference. Also note that the Stahls vinyl is a cold peel- so after applying the numbers you let it cool before pulling off the plastic and setting with heat again.

I’ve used the cricut and siser vinyls on our practice bumpers and the numbers always come loose eventually.

One of the problems mentioned before in this thread is lack of pool noodle availability. Also, the typical 2.5" noodle you can buy on Amazon breaks down pretty quickly in a season of heavy defense. Solid noodles are more expensive, but definitely last much longer than the cheap noodles.

2 Likes

Seeing how well yours and 125’s numbers hold up we might give them one more try.

Thanks!

I saw a small quantity of pool noodles at a local swimming pool supply store last November or December. They were willing to bring more out of their storage space and were happy to give a significant discount if a whole carton (36?) was being purchased.

Imgur
Here’s how FRC Team 1501 does bumpers.

7 Likes

We’ve had two releases this week of custom bumper mounts… both for custom chassis configurations. What I’d love to see are strong solutions teams have come up with for the kit-bot chassis aside from the AndyMark bumper mounts. Generally speaking, the teams that i’ve seen have trouble mounting bumpers are using the kitbot, not custom chassis.

4 Likes

I really don’t think that bumper mounts per-se are the biggest challenge to building bumpers. We struggled for years to build bumpers that fit the chassis reliably, and had mounting holes in accurate places. Eventually we asked a sponsor to make full-size sheet metal liners for our bumpers, as shown below.

These have many advantages:

  • They match the frame perimeter exactly (with ~1/8" clearance), so they go on without any drama. (We know right away if the plywood and fabric aren’t built to the correct size)
  • they can extend above the plywood, so we can mount to frame structure (rails above the wheels) that is usually above where the bumpers can reach
  • they provide dozens of (countersunk) holes for wood screws, so that the load is distributed over many fasteners, and there’s less chance of stripping any.

I recognize that not every team has access to a sheet metal sponsor, but this might be worth spending some money on an online service like sendcutsend.com

11 Likes

Most definitely! Serving as a RI at several events in each of the last 4 years, I have noticed that it tends to be the teams that struggle to get a robot running that also have trouble with their bumpers when they get to their competitions. Often, they don’t do any CAD so they are not likely to come up with a mounting system like what @nuclearnerd showed. Many are still learning to build with some moderate level of precision and repeatability and have trouble getting the second set of bumpers to work properly.

One of the teams I saw this last season used the brackets from AndyMark but had installed them on the bumpers at random heights so some of the brackets could not be attached to the chassis. They had to remove the brackets and reinstall them while they were lined up with the chassis before they could pass.

4 Likes

We have a dream of integrating a bumper build into the Kickoff Day robot quick build session.

It’ll take Some Doing, to have rookie teams show up with enough students & leadership capacity to do work on multiple fronts at the same time during the Quick Build, and enough trainers at the workshop.

2 Likes

our team uses these, and they are cheap and pretty good, very durable, and they are very quick when changing bumpers out https://www.mcmaster.com/snap-slide-latches

4 Likes

The bumper rules have improved greatly over the years. But the GDC seems to be too nit-picky. I.E. not allowing steel brackets because the rules stated AL brackets. While realizing the rules need to be the rules the GDC should be more accommodating in this area.

Noodles: Please define noodle size more completely that "nominal 2-1/2 in. Leaving the definition of nominal to the LRI stresses both the LRI and teams who have to buy noodles long before the LRI is available to consult.

Better clarify the bumper attachment rules. For example do the interior parts of the bumper of the bumper attachments have to stay in the bumper zone height restrictions.

Have a manual of best practices like the pneumatic manual that can provide more detail than the rules can.

5 Likes