Re: How to build good bumpers
 

Why used sanded material when the other material works just as well and you'll be covering it up? That's like using high polished material when you plan on painting it anyway. Price difference is small ($19.18 vs $26.58) but I just don't see the point, does smooth plywood hold staples better than rough plywood?

And I think the rules have specified plywood for as long as I've been making bumpers, so hardwood shouldn't even be considered anyway. Plywood will take an impact better due to the crossing grain structure over hardwood, the results of hardwood would be exactly what you stated.

Re: How to build good bumpers
 

Solid wood became legal in 2013 or 2014. A typical 1x6 is perfectly legal and effective bumper material and teams don't even have to cut it to width. (bumper heights are +-0.5“). We used 1x6s in 2014 and didn't have any splitting problems. We played at 2 regionals, champs, and 5 off season events, plus demonstrations and we haven't broke any wood and our 2014 drive train had a lot of power behind it. We also used the full 20lbs for our bumpers each set weighed over 19.5lbs, with a sheet metal frame covering the top edge and 1/8" aluminum L on bottom edge.

Re: How to build good bumpers
 

Just like you would design a component of your robot, design your bumpers to be quick change.

This is a requirement on 2826 for bumpers. 1 or 2 people need to be able to replace the bumpers in 1 min.

This requirement can be met several ways and reversible is one of them but I have yet to find a set of reversible bumpers that I would be willing to put on 2826's robot.

Re: How to build good bumpers
 

There will be more than twice the usual number of teams at events this year who will need help with bumpers: rookies last year didn't need bumpers, after all.

Hmm, 6" bumper height is much desired in some cases, IMO. I'll have to look into this.

Re: How to build good bumpers
 

They will be 5.5" since a 1x6 is actually (3/4" x 5 1/2")

From the 2014 manual
Also when talking about compressing the noodles.

Re: How to build good bumpers
 

I agree, we used reversible bumpers in 2014, and they were an absolute blessing. We rarely even needed to take our bumpers off, so being able to switch colors in 30 seconds in queue gave us one less thing to worry about. Definitely would recommend.

Re: How to build good bumpers
 

I was not referring to compressing the noodles so much that they would be undersized when the clamps were released, just enough to simplify installation by not having to pull the cloth tight while stapling (1/8" to 1/4"). After the clamps are removed, there is no way to tell that they had been compressed.

I agree; we did reversible bumpers one year (2013?), and we never did get rid of the last bits of Velcro showing and several matches (especially when we were strongly defended) a corner or two pulled loose. The tensioning trick can also be used for reversible bumpers; just be sure not to staple the loose end down!

Re: How to build good bumpers
 

I definitely agree that making nice-looking bumpers reversible is harder... although perhaps even then they wouldn't be quite up to 2826 standards.

There are some teams that put the time in to make them look pretty good though... I was very happy with how our reversible 2014 bumpers turned out, although they do require a separate right and left bumper to enable the reversing (the 'reversing fold' on each side is vertical, not the more common horizontal).

Re: How to build good bumpers
 

For 2012-2014, 225 used a homemade bumper cover attached by velcro. It wasn't always the prettiest (especially in 2014 when holes got poked through the cordura almost every competition), but it made for quick color changes and wasn't too intensive to make. I'd advocate making a cover for many lower-resource teams and only dealing with one set of bumpers, that way not a lot of time needs to go into designing and building the mounting system (and you can just use steel angle or something else heavy you can easily acquire from the hardware store).

If we were making bumpers today--I would build 2 sets, primarily to make sure we could set them as low to the ground as possible. I'd also use ballistic nylon or sailcloth for the sides instead of cordura, maybe the front and back as well.

Re: How to build good bumpers
 

There is nothing more frustrating that having to futz with bumpers at a competition.

Thoughts.

1. Baltic birch plywood. Not cheap 5 ply wood from the home center.
2. Corners cut at 45 degree angles transmit impact loads better than 90 degrees, all things equal.
3. Use sheet metal corner brackets on the outside of corners. Simpson A23 or equivalent work well.
4. Use a large diameter bit (e.g., 1") to cut recess holes for hardware that extends beyond the plane of the chassis, so that you don't have to have perfect alignment of the hardware/holes. Don't put so many holes that it impairs the integrity of the plywood -- that's what the inspector will be looking for.
5. Use a pneumatic stapler.
6. Pay attention to minimum clearance between ground and bottom of bumper. In 2014 this was 2". You will want to allow a bit of sag in the fabric so don't put the backing plywood right at 2".
7. Many fabric stores carry a polyester gabardine that is suitable for bumper use. Make sure that the fabric you select doesn't have any stretch to it.
8. Pay attention to color. There are often swatches of red and blue fabric in the kit of parts. It's not an aesthetic decision -- you want your bumpers to look like everyone else's. Don't send Grandma* to the fabric store to "get some red fabric."

RockyWoods has the 1000D Cordura in a coated version for $12 a yard. "Red" and "Royal Blue" are the colors.

* or Grandpa

Re: How to build good bumpers
 

If well made bumper covers can look nice.

https://frc2175.smugmug.com/2013/201...SC04358-X3.jpg
https://frc2175.smugmug.com/2013/201...SC04340-X3.jpg

Though if proper thought is put into changing and making bumpers (and robot geometry easily allows) I would almost always choose two separate sets of bumpers.

Re: How to build good bumpers
 

Here's where I take a moment to brag. 1712 has used bumper covers every season where red/blue bumpers were mandatory. In general, I'd agree that our covers (blue) looked less professional than the actual (red) bumpers.

However, in 2013, we took a slightly different approach and ended up with, as described by another team, the "best bumpers in MAR." Instead of 1 cover that stretches around all 4 bumper segments, we made our bumpers symmetrical (2 red and 2 blue), and had a reversible cover. The result looked terrific, and largely held up to a very rough game.

Re: How to build good bumpers
 

My team has always had issues with our material. I saw the post earlier about buying material from rockywoods, and I was wondering what other places people buy their material from?
Thanks!

Re: How to build good bumpers
 

Aesthetics is not the issue. The plywood that is sanded on both sides is generally made from a larger number of thinner and better quality wood than the lower grade, un-sanded, rougher plywood. The cheaper, rougher plywood tends to have more voids in it. Often, these voids, especially those on inner layers, are discovered to be in critical locations after the pieces are cut.

My personal (empirical) experience is that the better grades of plywood do hold fasteners (staples, nails, screws) better. I also find it nicer to work with since it splinters much less when cut. For the ultimate, use Baltic birch like MrRoboSteve.

Re: How to build good bumpers
 

We have used MDF instead of plywood successfully in 2014 just to get a bit more weight down low. You just have to be aware that small screws can strip out the hole if not careful.