Robot Width

We’re a rookie team and made a bit of a mistake in our design. Our chassis is exactly 28" wide. The problem is, there are a few bolt heads sticking out beyond the 28". Are there any tolerances with the measurement? Our bumbers will still fit flush against the robot.

I’ve tried posting this to the Q & A, but I can’t seem to get permission to post with my account.

The sizing box is exactly 28" inside, so your robot probably won’t fit in it. Can you countersink the bolt holes, and use flat head bolts? or possibly shorten the frame members and put it back together an inch or two smaller?

You will have to reduce the width. During inspection the robot is placed inside a box like structure. All parts must fit inside this structure.

What you are learning is to build your robot at least 1/2" under size to allow for the bolts and other protrusions.

As Jim said, there is absolutely no flexibility in the 28" measurement (or the 38" and 60" measurements for that matter)

A couple suggestions:
-Try a countersink/counterbore if possible, it will require the least amount of reconfiguration of your design
-Is a rivet head small enough that by switching to rivets your in the mark?

Lesson learned: build your bot slightly under the dimensions. We build ours half an inch under in each dimension.

Not only bolt heads cause problems. If you build too close to max dimensions the inevitable “slightly out of square” will put you over the limit.

We always build at least an inch under, just in case.

As a mentor, I would like to say that this team has the opportunity to learn a valuable lesson: always design with margin. You will need to fix your robot, but more importantly, remember this general lesson in coming years.

I agree with Indy Sam, we also try to build 1" under all the given dimensions but our robot seems to grow some.
With monocoque you have to allow for the bends in the aluminum. We didn’t. Our bot is only 1/4" under size now :ahh:

As the others have stated, there is NO TOLERANCE at all on the dimensions, and your robot will also NOT be perfectly square which will eat up a little of the width.

We were in the exact same position you are in our rookie year with team 1858. Unfortunately we did not find it out until we were in inspection!! Save yourself a lot of grief and do whatever you have to and fix it now!

As others have said, the tolerance is 28" MAXIMUM. In other words, you will have to rework your chassis. But better to find out now than on the Thursday of the competition.

Also, the only account that can post questions on the Q&A is the username and password given to you by FIRST on the team information (TIMS) site.

Good luck.

As stated above the sizing box is a physical limit on size. Inspectors have no options on this critical issue. Weight and size are the first things checked during the inspection process, followed by bumpers. If you would like to PM me, I could offer some suggestions depending on what material your structure is assembled from and what the hardware is used for. As you can see, many of the experienced teams, build to specified dimension less at least 1/4" as two objects cannot occupy the same space at the same time (robot and sizing box wall). If you are using tubing, it is a simple matter of drilling a larger hole in the outside of the tube and moving the bolt head to the inside. If your bolts are used for mounting sheet material (aluminum or lexan) you may be able to use rivets and stay within the dimensions. Or you may be able to move the sheet to the inside of the frame. It is better to take care of this before ship, instead of during inspection.

Since everyone else handled the dimension issue, let me address this one (since I’ve been there myself). You need to get your Q&A password from the TIMS system. That will allow you to post questions on the FIRST forum. Without the account and password, you’ll be facing gobs of frustration with Q&A.

PM me if you need additional instructions on this.

And don’t feel too bad… there were a few experienced teams having trouble with the sizing box in Atlanta last year. Things twist, bend and get repaired during the competitions and… well we try to work on a 27"x37" robot if we can and always try to finish a few pounds under weight.


My experience is use a 26x36 bot. It always fits.

A couple of suggestions for reducing this that wasn’t mentioned above:

  1. Weld, who needs bolts?
  2. Instead of bolting directly, use two plates(also angle work in a similar way). One on top and one bottom. Bolt the two members that are currently bolted to the plates instead. That will give you a good durability without extending outward.

The first is ideal if you have the ability, the second is a quick fix that may add a few pounds but will get the job done with relative ease.

One thing that must be considered is your BUMPER PERIMETER (which is defined by a string wrapped around your frame). Due to the rules this year, robots cannot extend beyond their BUMPER PERIMETER at any time during a match.

This simply means that while your frame can be less than your maximum dimensions, its size also determines how big the REST of your robot can be horizontally.

That’s what we thought, until last year…our robot was about 27" wide near the top, and it poked outside the sizing box. The best part is that when we turned the robot around, it poked out the same side of the sizing box at the top.

Yup, the sizing box was not square.

Lesson learned: make the top considerably smaller than the bottom.

(we always start at 26 x 36 but it seems to grow a bit)