Line Sensors in Sack Attack

Hi VEX community, now that we’ve really gotten going into the Sack Attack season, I was wondering how teams are using the line sensors for Sack Attack autonomouses and programming skills runs. Seeing as the lines in Sack Attack are extremely useful, with most of the sacks in the open fields centered on the lines, line sensors look to be very important (but maybe not absolutely necessary) for a programming skills run.

The problem with this great sensor in Sack Attack is the tendency for sacks to get caught on line sensors extremely easily. What my team has resorted to doing is attaching our line sensors to an easily removable module (2 screws). We remove the module for matches and screw it back on for programming skills. However this is extremely inconvenient and time consuming and we’re looking for an alternative.

Are teams substituting line sensors with other sensors that can achieve a similar effect? (Ultrasonics tracking distance from the walls) Or are teams just forgoing line sensors altogether?

Our team thinks that line sensors are probably a bad idea in this game for the exact reason you stated. They have to be relatively close to the ground to get an accurate reading, and this can cause problems with getting stuck. We decided that using the quad encoders would probably be best for this year.

One of the things that I like about the quad encoders is that you can have them in a lot of places on the robot just by using chain or gear systems. I also find that they are more reliable than the line sensors (although that could just be my programming). I use the quad encoders extensively to drive an exact distance, turn, and can even use them to drive in a straight line.

My team is using mainly encoders for small distances and turns but we are using line followers for stopping at certain points and driving far distances in programming skills. When it comes to the autonomous during the actual match there is not enough time to drive as far and pick up as man objects so we only use encoders and ultrasonics.

I think either line following or wall tracking will need to be used in order to have a successful run in programming skills. (Feel free to prove me wrong. This is based on observations I have made for MY robot.)

Right, we do use the quad encoders, but we like to use a combination of all sorts of sensors to get the most effect out of them. Line sensors may be less reliable because of lighting or what not, but I think if you calibrate at the competition fields and make sure they work 100%, they are more useful than quad encoders, though we definitely use both for many of the reasons/functions you have stated.

Agreed completely, if you have completed a programming skills in the season so far, how are you dealing with the line sensor issues I talked about in my original post?

Our team would really like to use them this year. We already have a low chassis, so getting them low would not be a problem.

One small problem is that our field tiles are “rainbow” colors. If it werent for that, we would use them.

We are using 4 IME’s, and 2 Pot’s to help us with our Programming Skills run. (Our run is ±10 of the current APAC Programming Skill Score ;)).

I think having those would help out tremendously.

You could place black tape lines running parallel and immediately next to the white tape lines (i.e. a border). Or, you could place black tape lines. During competition, you would flip the triggers (from greater than to less than).

We actually do not have to worry about them. We leave them on at all times. Our robot has very low clearance (on purpose) so sacks do not get under our drive and we intake anything in our way so we rarely ever get sacks caught inside the drive train.

Sounds like a very successful programming run so far! Yes, we used to have the same rainbow colored tiles and had a very tough time with that. Hopefully you can put edjubuh’s advice to good use, as it is a very good workaround for that. However nothing can replace the real field conditions.

I’ve seen teams try low-clearance drives, but I’ve always liked high-clearance. I understand the whole “picking sacks up instead of driving over them” but there just seem to be so many situations in this game where you could end up getting jammed up on a sack, that it seems more convenient just to avoid the problem altogether.

A specific example would be this. You’re trough is full of sacks and you go out to grab another load to score. On your way back to score, the opponent robot descores everything right in front of you. Since you have a low-clearance drive, you are now cut off from your trough unless you have an extremely strong drive or a fair amount of reach.

So your saying that right beside the White Tape we add black electrical tape, or duct tape?

Something that will help contrast the colors between dark and light (so ideally, something black, like black electrical tape) Here’s a diagram: the green is the field tile, the white is the white electrical tape and the black is the black electrical tape.

Alright. Thanks :wink:

My team has always liked low-clearance. (Team Preferences. I am not saying you are wrong.) We have been to two tournaments so far (one this weekend) and we have only had one instance where we were stuck on a sack (which was due to poor driving under stress).

Our robot happens to have both. :wink:

Aloha All,

We have gone over using line sensors this a few times year. I would have personally liked them used, especially for programming skills and autonomous. After much discussion our programmers have decided that using the encoders paired with the gyroscope was better for them. Since the students have worked with the encoders and the gyro in the past, they felt more comfortable with the programming for that approach.

The biggest reason for not using them was the possibility of getting stuck on sacks.

In our first tournament of the year we had a fairly low chassis and got stuck on a sack and it nearly cost us the match. After that incident the students were adamant about not using them. In fact they remade the chassis higher after that tournament to avoid stuck sacks.

I like the idea of having them on a removable mount. But in doing this, you are supposed to have your robot re-inspect between skills and matches. Not always time to do this…

Better yet, how about or on a lowering device. Perhaps a team will take on a spring or pneumatic lowered line sensor array.

Any takers?

24C has used Line Following Sensors in the past, especially during Round Up. We were able to write some nice code using them, and it worked very accurately and consistently. However, both this year and last year we have not been able to use them. Last year, they just didn’t fit anywhere on our robot, and although we could fit them this year, we do not want anything that low to the ground on our robot, as has been said in this thread. I love the Line Followers, but I believe that the combination of IME’s and Gyroscopic Sensor we have right now will be enough to get a consistent Programming Skills run working. Although we have not done much testing, from what I have seen, it is very accurate and consistent.

I will miss working with Line Following, but it seems like we will be able to make do without it.