Bumper Wood

Technical Technical Discussion
1

Hi all, My team is building bumpers soon. In this years bumper kit from andymark the wood is not included, so we were wondering where do your teams get the wood from?

2

The building supply store (Lowe’s) right down the street. They sell half sheets of plywood, which is more convenient to carry.

3

> Team’s name is “Birch Bots”

4

1678 prefers high ply cabinetry plywood for our bumpers.

5

Both Home Depot and Lowes will rip the plywood into 5 in wide strips. Convenient if you don’t have a panel saw.

6

Generally Home Depot unless somebody wants to go to the local lumber yard while they’re open. We used to get the quarter panels, but now that the team has a panel saw and I have a pickup truck, we got a full sheet this year and used the extra to build storage in our new shop.

7

I’ll ask this on behalf of those of us that just grab whatever’s on the shelf at Lowe’s: What’s the benefit to going this route? Heavier/lighter bumpers? Improved durability*? The patch not covered by fabric looks better?

*We’ve never had an issue with the standard Lowe’s stuff, but I’m leaving it out there anyway.

8

The stuff is much stronger that the run of the mill plywood. Holds screws a bit easier. The cost increase is marginal for the improvement in quality you get. Bumpers will get hit HARD this year, our 2014 robot broke even the high ply backing twice over the season.

9

I see this game being the same, hard hit wise as 2013. The field is pretty much laid out the same, only we can’t drive through the air ship. There will be hard hits for sure, but not anywhere as vicious as what 2014 was. There are things for each robot to do this year besides play defense, unlike 2014.

That being said, make your bumpers as strong as you can while sticking to the rules.

10

Unlike 2014 there is no moment when 2/3 robots have nothing to do but defense, but also unlike 2014 or any other recent game, there is a moment (stopping the 12th gear in elims) where alliances will drop everything to play 3 on 1 defense, which could quickly evolve into a 6 robot scrum at the airship.

Defense won’t be as all-consuming as it was in 2014, but the highs will be just as if not more brutal.

11

1676 confirms. Similar team numbers must think alike.

1 Like
12

Team 900 excepted, of course.

Asked of teams who’ve had broken bumper wood: was the bumper completely backed by frame perimeter, or was this across a gap, or perhaps with a frame perimeter only an inch or so high?

13

I’m also interested because I’ve never seen broken bumper wood either. Did it break on a screw hole? Was the crack all the way through (wood disconnected) or just a sharp bend? Vertical or horizontal?

14

Of Course!

Yes and no. The bottom inch was fully backed but the top 4 were not. Our corners were screwed together with aluminum angle and were in need of glue and re-tightening after many matches. But the rules most years make it hard to support your bumpers in the middle most years.

To answer Ari: yes it was all the way through, but the high ply kept it from falling all the way apart and the break was vertical.

15

The thickness of plywood seems to be a confusing matter in the industry - they should just label actual thickness but they don’t and it varies by material-type and is not consistent.
R29 A. says: “be backed by 3⁄4 in. (nominal) thick (~19mm) by 5 in. ± 1⁄2 in. (~127 mm ± 12 mm) tall plywood or solid, robust wood.”
Can we ask FRC to spec the thickness with +/- like they do the vertical dimension ?

3/4" Nominal means anything from 0.75 to 0.688 from what I have seen in CA HomeDepot. Can we use 0.688" (we cut it already!)? Sometimes 0.688 Actual comes from 23/32 Nominal though - so wouldn’t want to be failed on inspection
 Any opinions?

16

If you go with the .688, I would bring to your inspection some packaging information / order information that indicates the plywood is sold as nominally 3/4" thick. That will most clearly demonstrate that it fits the rule as written.

17

Here’s a good thread on bumper construction from last year, that includes a discussion of materials.

https://www.chiefdelphi.com/forums/showthread.php?t=138638&highlight=bumper

I am a fan of these at each outside corner:

http://www.homedepot.com/p/Simpson-Strong-Tie-Z-MAX-2-in-x-4-in-12-Gauge-Galvanized-Medium-L-Angle-ML24Z/202071147

Connecting each corner using a 45 degree angle joint, rather than a butt joint, helps carry the load to adjacent pieces of wood. Use quality screws to fasten the bracket, that fully go through the 3/4" plywood, cutting off the excess if needed. Don’t skimp on screw length.

18

folks can sure make simple things, seem complicated! :ahh:

19

You can always ask on the Q&A - “We bought plywood sold as 3/4”, but when measured is only 0.688". Is this sufficient for R29A?"

20

I personally like your brackets, but the GDC seems to want them made out of Aluminum. :frowning:

Q353Using Hinges on Bumpers
As said in R29:F, you are allowed to use aluminum brackets to fasten bumpers together at a 90-degree angle. Would it be acceptable to use a metal hinge for the same purpose, given that both bumpers will be fastened to the frame 90 degrees from each other?
asked 3 days ago by FRC 1245

Answer:
No, hinges are not aluminum sheet or angle and thus do not meet R29-F.