[FTC]:Finding weighted rings vs regular rings

Okay so brainstorming a bit with some friends about this years FTC game Ring It Up! We came up with 2 easy ways of measuring the different rings and seeing that it is probably the most difficult aspect of this years teleop period I thought I would share and hear what everyone else has to say.

Option 1: Using a current sensor; If a motor needs to work harder to pick up a ring that must mean its heavier so if you measure the amperage the motor is drawing and having that read into a light that turns on or off depending on if the sensor trips.

Option 2: Use a weaker actuator on an arm that cant pick up a weighted. This is a solution for both motors and pneumatic’s.

Yes I am biased towards opinion one that is why there is more text. I am anxious to here your ideas?

Create a switch that will not trigger when something weighing less than 1 ounce… Then testing every ring, it would be most efficient to find a way to pick up the ring and then have your pick-up mechanism with a sensor on it. Basically eliminating the need to set the ring somewhere else on your robot.

This is my first season as a coach for FTC, I’m excited to see the competition! I’m also excited to make an awesome robot!

Welcome To FTC!

However I would make it work for anything above 2 oz I know they light rings are .88 oz but to account for tolerance I’d say 2oz is safe.

Some type of spring loaded trap door that rings slide/roll past and heavier rings drop through…

the lighter rings are hollow so you could use a light on whatever you use to pick up the rings on the heavy rings the light couldnt get through but the light would get through on the lighter rings

Rings are sold out on andymark… Assuming some FTC teams have already purchased them can someone post a picture when they receive them?

I just found this today while looking at sensors for FTC.


From what I see, it’s like an analog touch sensor, and it won’t be available until October, but you could use it to differentiate the weight of the rings.

Great find I hope that manufacture a lot of those because I see them getting snatched up fast.

I don’t suppose they are the same rings that VEX used a couple years ago? That would be just too convenient…


Smaller, and Branded with FIRST logos. They also feel less cheap than the vex rings, probably due to their increased wall thickness.

As for sensing the wieght I have an idea for my design that would make it work. Since my robot (should) be able to pick up from both sides I would need two force sensors to figure out what the wieght one from each side. My claw would also need to pivot a smidge so that it could rest on the sensor given the orientation at any time. However instead of an automatic function I think a function for sensing should be on demand so that you can measure the wieght of said tube while the robot is -mostly- still so it gets an accurate measure without combining forces from moving around and getting ready to score. If the tube was weighted then an LED would light up somewhere on the robot to indicate that its a wieghted tube. From there you simply drive to the corner and score it.

Those are my ideas how to go about finding wieghted tubes.

  • Andrew

Exactly what I was thinking.

Hold on to your shirts kids, here comes some physics:
Force = mass * acceleration

The heavier rings will have a greater force of impact if allowed to fall the same distance as the lighter rings, and if they hit the same spot. Calculating the actual force of impact takes the rest of the kinematic equations (as well as some experimentation to figure out distance of deceleration & duration of impact. In any event, more force = more spring extension or more cantilevered polycarbonate sheet deformation.

As for the rules – I don’t believe springs are allowed. However, surgical tubing and deformation of polycarbonate are allowed.

A really popular method in my team is a spring.

If your grabbing mechanism, say, a claw, is attached to a spring that’s hooked up to a stationary point at the top of your bot, then:

  1. When the claw grabs a regular ring, it will expand by X centimeters.
  2. When it grabs a weighted ring, it will expand by 3X centimeters.

You’ll be able to see it very easily.

Consider the reality that only a limited number of successful trips between the dispenser and the scoring rack are possible in the 2+ minutes of driver control.

If a reasonable amount of rings are not scored, of what real value will the heavy rings be? Can you afford to wast one scoring cycle to place one or two 20% bonus heavy rings? We decided that only if two rings were adjacent on the dispenser pipe and could be taken together, would they be worth the time it takes to waste one cycle of scoring two rings at the rack.

The odds for a pair of heavy rings being randomly placed adjacently on the dispenser bars is fairly low based on my rough estimation. So, how many scoring rings can be dropped to the floor in order to get a pair of heavies together in order to justify the trip to the corner?

Our team concluded that unless we could first establish at least 30 pts. worth of row or column scoring bonus points, that going after heavy rings was a greater waste of our scoring possibility time, than what a heavy ring or two scored in the corner would yield.

However, having a partner can also score rings quickly and one bot that can sort out the heavy ones and put them back onto the free space of one dispenser bar, so so one bot can then take pairs of heavies over to the corner, this could prove to be a powerful scoring strategy.

-Dick Ledford

I was under the impression that just the ring scores were multiplied by the corner rings, not line scores or any other ring bonuses. We are thinking that unless the other bot can quickly score lots of 30’s, the corner bonus may not be worth it.

To the contrary, let’s say a team decides to forgo the top row completely in lieu of a simpler robot for a December competition. This is a stark reality for many FTC teams. The scoring analysis boils down to how many ‘extra’ points would going for the top row give if it were designed for instead of adding a weighted ring detector. The analysis would also have to break down how many weighted rings could be scored in the same amount of time it took to own the top row, let for now let’s assume a 1:1 tradeoff.

  • If the bottom 2 rows are filled/owned and 1 weighted ring exists on the corner peg, then the score is 126 (assumes 1 ring per peg)
  • If the bottom 2 rows are filled/owned and 1 top row peg is filled/owned and no weighted rings on the corner peg, the score is 180.
  • If the top 2 rows are filled/owned and no weighted rings are in the corner, the score is 135.

An easy argument to make is that for two equally-practiced teams, a team which scores the bottom two rows will be able to score faster than a team that scores the top two rows. Thus the team that scored on the bottom first will have more time to place that last ring on top.

On the surface, this seems like a no-brainer – go for the top row. Yet there are underlying tradeoffs that may allow the low-peg team to pull ahead in most situations:

  • Their lack of adding complexity for the top row gives them more time to pull of a complex autonomous routine, netting them the ability to score their own and
    their partner’s ring (+50). - The extra practice time with the intention of going for weighted rings allows them to score more rings overall, including more regular rings than a team which goes for the top row and
    weighted rings (+10-20 points) - There will be plenty of opportunities (at least one per match per field) for a double-weighted ring score to occur. When it does happen, the team which specializes in weighting will be prepared for it and have practiced it multiple times (+42 points)
  • The simple fact that the weighted ring adds an entire other place on the field on which to score (a totally different zone!) means defense will have to guess where to go next. This would be particularly devastating to that top-level team when they’re trying place that last ring on top in that VERY predictable spot. (20-40 point differential per match)
  • Match to match, if the weighted ring detector fails then in most designs* it isn’t catastrophic to run a match without it. A top-tier lift adds complexity versus a mid-tier lift, thus is more prone to failure over the course of an entire season. With a lift failure it would be catastrophic to run a match without the failed system. (probably only 1 match outcome affected over the entire season)

*Get creative! One doesn’t NEED gravity to detect the weighted rings, as my students were quick to point out to me.

Just to be clear. The probability of a weighted ring is 6/24 or .25. The probability of a weighted ring, given you have already found a weighted ring, is 5/23 or .2174. The probability of a pair of weighted rings is .25*.2174 or .0544.

That is, at the start of the game, there is a 5.44% chance that the first two rings are both weighted.

To me the key to the game is cycle time—how quickly the robot can grab two rings, drive to the rack, hang the rings and return to the dispenser. Assuming both robots hang their rings during autonomous and a lift takes 30 seconds, that leaves 90 seconds to fill the remaining seven pegs on the rack. That’s four cycles, or round-trips, for the two robots. Finding weighted rings and hanging them adds cycles.

Your strategy then depends on how reliable your autonomous is, your cycle time, how quickly you can identify a weighted ring and your assumptions about your partner’s autonomous and cycle time. Remember, to avoid wasting time and the bottleneck at the dispenser, one of the robots will need to use the far dispenser.

Now you are describing the reality of the game that I was talking about.
We plan to place two rings on each of the 2nd level scoring pegs initially.
The fourth cycle we will use this next ring pair to place one of them each on the upper and lower of one side or the other side.

This approach means that starting after the second cycle, every trip can earn at least 30 point row bonus plus 20 more for the level scoring. The fourth cycle can also earn a 30 point row bonus with 20 ring scoring, and if a 5th cycle can be done, 20 for level scoring and 90 points of row bonus – 110 in one cycle!!

So we see it as critical to get at least four scoring cycles completed. Only a trip to the corner with at least 125 points already scored and two heavy rings can give a 50 or more points of heavy ring bonus, but if it jeopardizes us from completing the forth scoring cycle, and prevents us from even being able to attempt a 5th cycle, then it is barely worth the 50 points loss that the fourth scoring cycle would have generated, and it totally kills the possibility that getting a 5th cycle at 110 points can even be attempted. So we see going for the heavy ring scoring as a sucker deal.

In the early portion of the match, we also don’t want to waste time shuffling heavy rings between pipes to try and arrange to get a pair of heavies adjacent either. It is just too critical to complete the initial scoring cycles done to have access to the possibility or reaching the stage where every additional cycle can give 5o to 90 points of row bonus.

-Dick Ledford

Further update:

After review (again assuming NO ANONOMOUS SCORING), it turns out that with proper planning, after the 2nd scoring cycle takes you to 50 points, the next two cycles (3rd, 4th) can each yield 110 points (20 rings and 90 row bonus) per cycle, and the fifth can yield 80 more pts.

Unless you have pair of heavy rings for the corner goal, to have that trip yield more than the 80 points that a 5th trip to the rack can give, requires 205 points already scored, and after three cycles 155 is the most possible.
So, there is no attraction for the corner until the 4th scoring cycle gives 265, and with another 80 still available from a 5th cycle to reach 345 – you are not going to the corner unless you KNOW you have TWO heavies to hang for the 40% bonus applied to the 265 points reached on the 4th cycle. Without two heavies, a 5th trip to the rack is the best option.

  • 1st – 2nd – 3rd – 4th — 5th
    0 1 0__0 1 2__3 1 2__3 1 2__3 15 2
    0 1 0__0 1 0__0 1 0__4 1 4__4 1 4
    0 0 0__0 0 2__3 0 2__3 0 2__3 5 2

25pts -45pts -155pts 265pts 345pts

So with this in mind, how can you even consider heading for the corner with only one heavy ring, and how can you bother to waste time sorting heavy rings when the 3rd, 4th and 5th scoring cycles can offer a combined 300 points?!!

Only with two partners that are both fast scorers, and with one of them able to detect/sort heavies, does a trip to the corner with heavy/heavies seem likely to make any sense.

-Dick Ledford


  • 1st – 2nd – 3rd – 4th — 5th
    0 1 0__0 1 2__3 1 2__3 1 2__3 15 2
    0 1 0__0 1 0__0 1 0__4 1 4__4 1 4
    0 0 0__0 0 2__3 0 2__3 0 2__3 5 2

25pts -45pts -185pts 295pts 345pts