Best methods of bumper mounting?

[mentorroger]

CIS 4607 had a two piece bumper that were reversible. These mounted to the 1X2 welded aluminum frame with 1' angle mounted to the bumpers and four 1/4 - 20 bolts.
This year we were a very physical robot that focused on defense. We both delivered and took a beating every single match and the bumpers held up very nice.

[Al Skierkiewicz]

From a robot inspector who has seen thousands of attachments, a mount that is attached to the bumpers that fits into/over/on the frame and has hardware/pins/latches that are installed from the top of the robot are the best. Screws/bolts that need to be driven in from the interior of the robot frame are OK but you will eventually drop that hardware in the robot and it will take special tools to install or remove the bumper system. This year had some defense but not as much as I expected. Bumpers are meant to take the full punishment another robot can inflict. Make them secure and easy to remove.

[philso]

There have been many different excellent attachment methods mentioned in this thread. The most important thing to do is to pick one and design it in along with the rest of the robot rather than leave it as an afterthought. Otherwise that xxx-latch that worked so well for another team won't work so well when there is no room to install it, it can only be installed in a hard to reach place or there is nothing strong enough to attach it to.

Originally Posted by EricH

As did 1197.

A word of caution on wood screws: you can never have too many in your bumpers, and keep 'em tight. Experience talking (thankfully not mine...this time).



If you gotta make a mistake, go with "more secure".

Some (many?) of you may have had wood screws strip out. If so, remove the screw and drip some thin (not gel) cyanoacrylate (super) glue into the hole and wait for it to set. It soaks into the wood and makes the wood swell a little so the screws have something to grab. The CA will make soft wood as hard as maple or oak so the screws won't strip out again.

[EricH]

Originally Posted by philso

Some (many?) of you may have had wood screws strip out. If so, remove the screw and drip some thin (not gel) cyanoacrylate (super) glue into the hole and wait for it to set. It soaks into the wood and makes the wood swell a little so the screws have something to grab. The CA will make soft wood as hard as maple or oak so the screws won't strip out again.

Forgot about that trick--it's great for a quick hardening of wood when you're building a model airplane. (Actually, add a little when the screw is in there--that'll really make it hard to get the screw out.) Just don't stick your fingers together, it hurts.

[WSiggs]

Our team had a reversible bumper that wrapped around the robot, and it was secured with aluminum bumper mounts and rivnuts, which made it very easy to remove.

[dmelcer9]

We used clips very similar to the belt clips found on the back of tape measures. At first, we had some issues (Finger Lakes Regional Q15 our bumpers fell off), but then we secured the bumpers even more and haven't had an issue since. Takes a few minutes and a screwdriver (to pry off clips) to change the bumpers.

[sanddrag]

I'm a little concerned about rule R21-G with some of the things mentioned in this thread. Perhaps I'm misinterpreting the rule. The picture seems to paint a pretty clear limitation of a 1" limit on hard parts. The 1" limit in the picture is placed over the inside and outside surfaces of the bumper plywood. Many great attachment methods need more than the remaining 1/4" inside the plywood after using 3/4" plywood, thereby seemingly exceeding this 1" hard parts limit.

What am I missing here?

Is there not actually any limit to how far the "hard parts" can stick inside your robot? Can someone point me to some rule or clarification that indicates this?

[Chak]

Originally Posted by sanddrag

I'm a little concerned about rule R21-G with some of the things mentioned in this thread. Perhaps I'm misinterpreting the rule. The picture seems to paint a pretty clear limitation of a 1" limit on hard parts. The 1" limit in the picture is placed over the inside and outside surfaces of the bumper plywood. Many great attachment methods need more than the remaining 1/4" inside the plywood after using 3/4" plywood, thereby seemingly exceeding this 1" hard parts limit.

What am I missing here?

Is there not actually any limit to how far the "hard parts" can stick inside your robot? Can someone point me to some rule or clarification that indicates this?

Originally Posted by R21-B

B. hard BUMPER parts allowed per R21-A, R21-E, R21-F, and R21-G must not extend more than 1 in. beyond the FRAME PERIMETER with the exception of minor protrusions such as bolt heads, fastener ends, rivets, etc (Figure 4-5 and Figure 4-7).

emphasis mine.
Seems pretty clear to me. The 1" is counted from the frame perimeter.

I guess bumper attachment system can be ridiculously huge then, but at some point the bumpers will hit the 15lb limit.

[orangemoore]

Originally Posted by sanddrag

...

Is there not actually any limit to how far the "hard parts" can stick inside your robot? Can someone point me to some rule or clarification that indicates this?

The limit applies outwards away from the Frame Perimeter.

Question 744 is a relevant clarification.
https://frc-qa.firstinspires.org/Que...taching-a-1-x1

[Oblarg]

Clevis and reusable cotter pins. Cheap, easy, quick.

[PAR_WIG1350]

Originally Posted by Chak

emphasis mine.
Seems pretty clear to me. The 1" is counted from the frame perimeter.

I guess bumper attachment system can be ridiculously huge then, but at some point the bumpers will hit the 15lb limit.

The obvious response to this is to use the right bumper as the attachment mechanism for the left bumper.

[JesseK]

We used Rivnuts this year. In 55 matches and approximately 60 bumper swaps (including practice/etc), we stripped 3 of the Rivnuts. The last time one stripped, removal of the rivnut caused a bigger hole in the frame which then wouldn't accept a new rivnut. So we had to drill through and put in a through-bolt.

Next year, we may go to what 2363 had - see attached.

[mwmac]

Originally Posted by JesseK

We used Rivnuts this year. In 55 matches and approximately 60 bumper swaps (including practice/etc), we stripped 3 of the Rivnuts. The last time one stripped, removal of the rivnut caused a bigger hole in the frame which then wouldn't accept a new rivnut.

Steel or aluminum rivnuts?

[JesseK]

Originally Posted by mwmac

Steel or aluminum rivnuts?

Not sure. Steel bolts though.

[Michael Hill]

We had 1" steel angle (hey, heavy bumpers are allowed) around most of our bumper perimeter. We had holes in the front and slots in the back to allow for a 1/4"-20 bolt to pass through. The bolts were put through the middle our bumper mount rail (1x1 aluminum) and a nut was installed on the inside of the aluminum to lock the bolt in place. So there are four 1/4-20 bolts sticking up in the corners. The bumpers were a single piece, so it slipped on over the robot, then we tightened them down with wing nuts. It was a pretty good system, and I think we'll probably end up doing it again. The only issues we had were inconsistency in the fabrication of the bumpers, so one of them fit a bit tighter than the other (but I think that can happen with a lot of bumper designs).