Cutting corners (on the robot!)

Hi everyone,

Our current frame is about .25" over the frame perimeter limit (R3-A)

We’re going to cut two of the corners at 45 degrees which will put us under the 112" perimeter limit.

My question: do those two new 45 degree angles now count as sides? R19 says “If a side is shorter than 8 in., the entire side must be protected by BUMPER” I suppose it is, since the bumper is coming from the sides and front/back.

What do you think? Any precendent of teams doing this to meet the perimeter limit?



Yes they count, also make sure you are able to follow all of the bumper rules with your new frame.

So they need bumpers on these angles. How are we thinking that would work if the corners are really small? I’m thinking 0.5" long or so. Technically you need a piece of 3/4" wood plus noodles, etc. along that length. Except mitering in a 0.5" long piece of plywood there seems pretty difficult…

That’s how I currently read R26.

To be considered supported, a minimum of ½ in. at each end of the BUMPER must be backed by the FRAME PERIMETER.

If that’s true then if you cut the corners at all you have to have wood, pool Noodle, etc on that cut corner. The Q&A might be good for this or Al might give a ruling as well.

If it’s less than a 1/4" away than that would be legal by the rest of R26.

To make the example easy, if you cut a 45 degree angle (you cut off 1" from the front and 1" from the side), the length would be just over 1.4" long.

R26-A says any gap between the backing material and the frame can be no more than 1/4", so clearly something has to go there.

R19 shows the overlap of the noodle on the hexagon-shaped robot, so a vertical pool noodle attached to the new short side shouldn’t be an issue.

The bumper backing could be a robust piece of wood instead of plywood. (R21-A), so perhaps you could create the small triangular piece out of solid wood and attach it to one of the existing bumpers.

The suggestion about Q&A is also a good one.


We had to do this last year at a regional. Yes, they count as sides, the easiest thing to do is to just make curved bumpers.

You can always just use your original bumper design, it’s fine to have small gaps between the frame and the bumpers in the corners.

We always undersize our frame by a quarter inch to prevent such possibilities. I would thing that although very small they still count as sides and therefor would need fitting bumpers

Such “small gaps” at the end of the bumper segment can be no more than a half inch long.

Just out of curiosity, what were the dimensions you were aiming for? Did you try to do something like 33"x23" and it ended up over? Always plan for your robot to be out of square, so make it just a little less on each side.

Every year teams like to push the limits with sizing… one of the nice things about the old sizing box was that it kept teams from pushing them too much. Of course, that was also the bad thing, as every robot absolutely had to fit inside the box.

Now with the frame perimeter rule introduced last year, it’s a lot easier to get people compliant if they’re just a little over. For anything up to a 1/4", you don’t really need to cut off a corner… simple rounding all of the corners a little bit is usually enough to get you there, which still leaving each corner as something a normal observer would call a corner and not a side.

That said, as an inspector if I had a team show up where they made a clear decision to cut off a corner (to the point where I can easily define two corners and a side where the single corner used to be) to make the size requirement but still treated it as a rectangular robot for the bumpers, I would be a little annoyed. And an annoyed inspector is a thorough inspector!

Also be aware of R26:

BUMPERS must be supported by the structure/frame of the ROBOT (see Figure 4-10). To be considered supported, a minimum of ½ in. at each end of the BUMPER must be backed by the FRAME PERIMETER. Additionally, any gap between the backing material and the frame

Emphasis mine. Clipping the corner of the frame perimeter but still using a right angle for your bumpers would leave at least part of the end of the bumper unsupported, and the way I read the rule support has to exist from the edge of the bumper inwards at least 1/2".

They’re only taking off a 1/4" total so I’d guess this shouldn’t be an issue for them.

I have to ask what your frame is made of and perhaps you could give us a picture? There may be some other method of meeting the perimeter rule that you have not thought of. You have some very qualified and experienced LRIs answering above and they are speaking from that experience. We want you to play while meeting the rules.

sounds like an opportunity to add a steel right angle iron to your bumper to reinforce your bumper. weight goes to the bumper, not the robot and it will fill the gap in the corner.

Adding weight that can be seen as unnecessary to your bumpers can be a bad idea. You’re allowed to put as much weight in the bumpers as is necessary to build them, but no more.

(“As is necessary to build them” is a vague statement, but that’s essentially what the rule is.)

That’s not quite what the rule says. R21 specifies how the bumpers are to be constructed and what materials you can use. For example, R21 does NOT allow you to bolt a big hunk of steel to the bumper “just to add weight”. It does, however, allow you to construct your fastening system (how you attach to the robot) however you like. So if your fastening system is a big hunk of steel with some holes through it that let the bumper mount to your frame, it’s fine by R21.

Bumpers do have their own weight limit (20 lbs), though, as seen in R20.

That’s what I was trying to get at. You’re allowed to choose your own fastening system and construct it with as much (or as few) materials as required. Any weight beyond what is required to construct your bumpers (however you want) is not allowed.

What rule says this? I just read through the rules on bumpers, and didn’t find anything that limits parts or weight based on the intention of those parts or weight. There’s a 20 pound limit total (R20).

I doubt Al will give a ruling here on CD, but he will likely give great advice, and history.

R21 says how bumpers must be constructed. Plywood, pool noodles, cloth, optional angle as a cloth clamp, and a “robust fastening system”. No other items are allowed to be used to construct bumpers as that would go beyond the guidelines specified in R21.

The term “robust fastening system” is vague and generally inclusive. You are allowed to design your own fastening system using any parts you wish. Once you have your fastening system, you can’t add any additional materials to bumpers even if you’re under the 20 lb bumper weight limit.

The bottom line is you can use steel as part of your fastening system if you can meet the weight limit. If your fastening system doesn’t involve steel, you aren’t allowed to add it even if you’re under the weight limit.

R21 says that certain materials must be used (wood, noodles, fabric). But I don’t see any thing that says only these materials, or prohibits other materials.