Bumper Mounting on a Hinge Legal

Can anyone tell me if this hinge mount would be legal during an FRC inspection.



Sure, the inspector who inspects it can tell you.

Since it doesn’t appear to let the bumper articulate, it’s probably legal. But since you asked, you must have a concern about a specific rule? Tell us what your concern is, maybe we can help you figure it out.

The usual disclaimers apply.


What fastens the other side of the hinge to the frame? If it’s a bolt head, wing nut on a stud, or something that very tightly clamps down to prevent it from moving, and essentially making that hinge turn into an angle bracket, it should be totally fine.

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A 1/4-20 Nylon Lock Nut attaches the bumper to the frame.

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If it were me inspecting that, with a 1/4-20 nylock holding it in place, I would be fine with that.

As a suggestion to prevent deforming that hinge part, I would add a washer under the nylock.

This is my opinion, and again, if you were at an event where I was inspecting that, I don’t see any issue whatsoever. It’s clamped tight to the frame, thus negating any movement the hinge may have. And with the nylock, the chances of it wiggling loose during a match are slim. Now, the nylocks wear out after repeated use, so you will probably have to replace them occasionally.

R408G could be interpreted to make this illegal in that it is not a rigid fastening system. However, if the hinge is effectively rigid while the bumpers are installed, I’d pass it.

But I am curious - what’s the advantage to a hinge over a bracket?

It could allow the bumper assembly to slide vertically past some robot superstructure, which would otherwise interfere.


This is valid, and I’m also inclined to say I’d pass it as long as it’s effectively rigid when connected, which I think would depend if there’s any kind of connection between the plywood at the corner.

Just to be safe, if the rationale is as simple as “we had a hinge, but not a bracket, and a hinge makes a good makeshift bracket,” (I’ve been there), maybe just dab some glue on the joint to make it rigid?

Are you by chance wanting that part of the bumper to not be at 90 degrees from piece you are mounting it to?

Now the questions are moving toward practical effect. Consider what might happen when a robot with one of its bumper segments mounted this way pushes against another robot with its corresponding bumper segment mounted rigidly; i.e., such that the bumper segment is held vertically? Is there an advantage to the robot whose bumper can pivot vertically on a hinge? And would that advantage come in violation of a rule?

I see what you’re saying there, and if the bumper with the hinge were longer than that short section, I could definitely see that happening. With the rigid (hopefully) corner right there, I wouldn’t anticipate a whole lot of flex, but I could be entirely wrong there.

I agree. However, there’s no rule requiring a rigid corner. See the detail from Fig. 9-3 BUMPER corner examples:

So maybe the hinge as an element of the mounting system satisfies R403 and R408G, IF the corner is rigid?

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Good point. And I would agree with that. But with such a short section of bumper that they have, it would be very strange if it wasn’t mechanically connected in that corner. Still, a valid question and worth taking note.

I am often guilty of overthinking a problem. This topic may be a case in point. A simpler way of looking at it might be, if the BUMPER satisfies R403 (i.e., it doesn’t move) then the mounting system is rigid. Usually that is not a difficult or controversial call for an RI, but in a questionable situation the RI or the team can call in the LRI to settle it. I would try pushing on it with about 150 lbf on the top pool noodle; if the bumper segment doesn’t create a “ramp” effect (see the blue box under R408C) then the BUMPER mounting system is rigid enough.


:point_up: Barring a contradictory Q&A or a rule change, that’s also how I read it. If it can’t be articulated during a match, it isn’t articulated.


Another advantage is that a hinged bracket is less cumbersome in the Pit.

EXACTLY! This is the method we are using.

Really like this idea.

FWIW, we are also doing this. One hinged bracket on the center of each side of the robot and triangular brackets in every corner of the robot (one-piece bumper).

Well, that’s a slam dunk. Even if the hinges are ruled as not being rigid, those four triangular brackets certainly are. And I don’t recall seeing anything outlawing additional mounts, as long as they’re within weight and other bumper rules.

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