If the robot is a hair less than 18" (height 17.98") – a part of which is shown below – cutting it too close?
We don’t have access to a robot sizing tool. While AutoDesk Inventor shows 17.98" it is quite possible that the actual robot may touch the sizing tool. Will that result in an automatic disqualification?
The robot cannot touch the sides of the sizing box (or sizing tool), so that is cutting it way to close.
A good rule of thumb that our team has created is to try to always stay under 17.5" so that we know that sizing won’t be a problem.
In my opinion, It should be totally okay, and no it wont result in an automatic DQ. You will go through inspection and if it is too big, you just have to go fix it until it works, otherwise you wont be allowed to compete. I would recommend getting a sizing tool, they are very helpful. It is good to constantly check your robot sizing.
With your robot’s height situation, the worse thing that can happen is for you to have to file down the top of the encoder until it’s short enough, so you can then pass inspection and enter the competition. I feel that 0.02" tolerance is okay. It’s fine.
building a wood box with interior dimensions of 18" cube and a removable lid is how we check our robot size. It’s easy to work with because if it fits in the box then its competition legal.
Thanks all for the responses.
For designs using Linear Slides, we’re already at 17.5". Then add the bare minimum wheel clearance – .25" – and you’re left with very little margin for error.
It would be a shame to take a hacksaw to all those 17.5" parts …
We’ve had it easy the last couple of years. I think many robots will be at maximum height, my team is 1/8 inch under the 18 inch limit.
Should be fine.
This was one of the robots from my former team at NZ Nationals, similar situation. Sure it was a bit interesting to see it get sized but it managed…
https://vexforum.com/attachment.php?attachmentid=8581&stc=1&d=1411109919
~George
0.02" is not nearly enough room, and it is simply bad engineering to design with so little margin for error.
Anyone who shows up at an event with that little margin for error could be accused of intentionally antagonizing the inspectors.
If that tower is even a little bit tilted, what is that dimension?
Are you saying your entire robot will be PERFECTLY square?
If you get hit really hard in Final 1, are you sure your robot will still be legal for Final 2?
Do your inspector and referees a favor – go smaller. You’ll be doing yourself a favor also! 
Agreed, it is too small of a margin to be good engineering, and you always want to keep the size constraints at the tip of your mind when building.
The picture I posted was not from the robot I had been working on, but the B robot on our team. I took it down the day before Nationals to get it inspected in advance for them, and it was quite a surprise, but we managed it absolutely fine. Making the lift straighter also made it a bit shorter in height (the lift was actually on a hinge at the base, similar to 1103 from Round Up, and it just wasn’t quite perfectly vertical). I’m pretty sure both the inspector and I got a fair bit of amusement about how close it was, yet it worked.
For the height of a robot it’s generally not so bad, but length, especially with fold out intake mechanisms, always aim to be comfortably in size. Too many times have I (and I know plenty others) been frustrated at how long it takes a team further up in the inspection queue to get through sizing because as they get one fold out bit up and balanced just absolutely right at the edge of the 18", a second one opens out again, and so on, and then the chassis needs to be wriggled back to be lined up… It also really slows down the match schedule at a competition when it takes so long to set up, which annoys just about everyone. This season I’ve been volunteering, I have a lot more respect for the patience required now, let’s say!
I worked on a robot that was only 12.5" wide, 17" tall, and 16" long last year, worked absolutely great. If that last bit of space can make a difference, and if you can be absolutely sure that your robot will be in size in any situation, it won’t be a nightmare to set up again, and you can test it repeatedly knowing that you won’t bug anyone at all, like the B robot picture that I posted, then I think that is absolutely fine though.
~George
Well it seems too me you’re cutting it pretty close. I my opinion, I see no problem, but you know how strict the judges are. But I recommend cutting it down at least a 1/4 inch or maybe get it down to at least 17.50. (Make sure the edges aren’t sharp either.)
Or buy some IMEs. Then you won’t need those quad encoders. But it’s up to you of-course.
Or you could keep the quad encoders and either chain or gear them to the shaft that they’re sensing, allowing you to move them further down on the robot.
Not only is that the funniest thing I’ve read here for a short while, but also illegal, following the book exactly.
Just for fun if you want to, try filing an encoder, and make it so inspectors don’t notice. 
If you sand the rubber on the bottoms of the wheels, you can lose up to 0.2".
Yeah, better to play it safe then cut it close.
Right, you can’t physically modify the sensor housings. Forgot about that.
hmmm… I seem to remember some of our encoders having been worn down on the corners when they rubbed against the wheels they shared an axle with 
Hopefully unintentional and accidental exterior modification won’t mean they’re unusable
Oh gosh, when I read your post I couldn’t help smiling. My team has had huge troubles with the size limit in the past. This year, we’re designing our robot to have enough leeway so we don’t have to adjust the robot to the perfect position to start it out. Already, we are seeing a huge improvement from last year–setting our robot up literally takes about 5 seconds, as opposed to 1 or 2 minutes from last year (no kidding). While having it 17.98 inches isn’t illegal, I would strongly suggest having it at most 17.8 to 17.9 inches high.
The most simple answer is yes. Unless you can solve the issue by the time of competition start, you will not be allowed to compete if your robot does not fit within the sizing requirements. Even if you pass inspection you still want to be careful because other teams can call you out on sizing throughout the day resulting in immediate sizing inspection on field. If you do not fit in size then you will be disqualified from the match and the competition if the issue is not resolved. Hope this helps!
Just as reminder. Refs don’t have to size another team just because your request it. It is always at the refs discretion. If the robot is 17.98 in CAD than it is likely that the ref would see the robot as needing to be double checked but it is their choice.
17.98 in CAD does not mean when its built it will be less than 18. Even perfectly built the parts have tolerances that would make this a very risky design in terms of size.
Thats cutting it super close. I know at some competitions they have an extra sizing tool for teams to use but not always. And you don’t want to find out on tournament day that you have to take apart your robot. My advice: Set a limit for your robot. Like, “Alright the robot can be no higher than x inches/centimeters” Same with the other sides.
