The spread of pinching rollers this year

FIRST General Forum
1

I know it isn’t that uncommon for teams to change their design once they’ve seen other teams, but I feel like this happened moreso this year with the pinching roller intake than any other mechanism any other year.

To be clear, I’m referring to dual horizontal rollers, one above the ball below. In most applications the bottom one is fixed so it can’t rotate, and the top has some sort of clutch or current control.

I’m curious to hear who had the design idea initially, and who added it later, and if so, who did they copy/get inspiration from?

I guess it’s common knowledge that “Team IFI”, 148, 217, 254, 968, 1114 and 2056 all had the design at ship time.

We added ours a week or so after ship mostly from inspiration from 148’s video.

I know 971 added theirs after ship but before the San Jose regional and was inspired by 254.

I know 294 added theirs after San Diego but before Los Angeles from us, inspired by 148.

It’d be interesting to track the entire spread of it.

2

I was convinced that this sort of setup was illegal: Thought of it at kick-off and dismissed it almost immediately.

Later, I thought it would be legal only if it was somehow cantilevered so the ball was guaranteed to be contacting the ground.

Later, I saw that refs weren’t calling these sorts of things and we joined the crowd.

3

2056 didn’t have it ever this year. They had a single roller that deployed outside of their bumper frame for 2 seconds at a time.

1625, 1771, 2016, and 20 are the teams I saw use the design post ship, off the top of my head.

4

Calling these sorts of things?

If the ball stayed on the ground it was legal.

5

I can’t speak for the other teams, but I know 254’s and 971’s passed the piece of paper test. (Slide a piece of paper under the ball to see if the ball is contacting the ground.)

6

For many of these machines though, the balls DIDN’T stay on the ground. There were instances at regionals as well as at the World Championship where this was being inspected with a ball and a playing card.

7

We adapted to having a pinch roller, and the simplest way to go about it was put the thing on a hinge…easy solution ball stays on ground.

8

We upgraded ours on thursday at the northstar regional. due to the way our kicker was designed I couldn’t make it as wide as I would have liked but it still worked great. We decided to change from our vac after seeing 148’s video.
Our ball rode on the floor quite hard, but it was pinched in so hard it stayed there quite well.

9

We bagged the robot with a higher-speed top roller and played like this at Kettering. We then looked at several other robot’s up close, and built a pincher-roller for Troy using the practice robot as a guide. This taught us two things:

  1. pincher rollers are waaay better
  2. the practice bot is really far off of design specs

Ours was a floating design, so the entire assembly was a four-bar linkage. The two horizontal bars supported the bottom plate and top roller, one vertical “bar” was the chassis, and another held the two pieces a fixed distance apart. Using bungee, we sprung it down to avoid carrying penalties, and put some little wheels on it so metal never touches the ground. We had an issue with carrying penalties at Troy, so we fixed it in software and haven’t had problems since.

We actually had an interesting problem with ours: It had such a good grip we could no longer kick more then about 3 feet. So we fixed it in software and can now kick the full 33 feet (+ a few more) it could with the old roller.

We carefully tuned the depth of the top roller and bottom plate, as well as the distance between the two, to get the most grip while not allowing a piece of paper to go under the ball. Software helps with this: If the roller is allowed to run continuously, it will gradually suck the ball in more, and carry it. If you just kill the roller, then it will loose the ball. We implemented a duty-cycle based roller kill to pulse the roller when holding a ball (determined by a broken-beam sensor), and to continuously run the roller when going backwards (both joysticks are positive, reverse) to prevent loosing the ball. Timing this was tuned to 5 iterations on for a 20 iteration cycle.

10

That’s pretty funny - we found the exact same thing. We had this design installed about a week before ship but were tuning it right up to the day we sent the robot out. It took us a while to get the hang of setting it up so it stayed on the ground, but once we had a system of setting it up it worked well.

The first iteration didn’t allow us to kick very far either - we adjusted our backstop and bottom bar to get just the right amount of grab.

We also realized that on our practice bot we offset the middle wheels down. On the comp we offset the front and rear wheels up. Oops.

We used a simple vacuum cleaner belt to drive the roller - once the ball hit the backstop the belt slipped on the upper roller so the window motor didn’t stall. Ours didn’t float, but we did make sure it kept the ball on the floor all the time. We never changed that belt once. $2.49 from Ace Hardware.

11

Weeks were spent in the iterative design process to ensure “these sorts of things” were physically impossible with the 254/968 pinch roller design. The mechanism was on a free pivot, such that the entire robot could lift from the floor by a significant amount (more than 1" I believe) and the ball remained in contact with the ground, such that a piece of paper could not be slid beneath it. For added security, at Long Beach, 968 added springs to actually push the ball into the ground with some force, beyond the weight of itself and the mechanism. I don’t feel that any team with such a mechanism got away with a certain “way” referees were calling anything.

12

I know we made the change after peachtree and seeing how ineffective the vacuum was compared to the awesome pinching roller of 148/217. We went into peachtree knowing we would be changing the design and ended up showing up to champs with a pinching roller with the whole assembly on linear bearings to allow ~1" of vertical play so that the ball always stayed in contact with the floor during normal play.

The roller worked incredibly well and allowed us to really play to our full potential once we worked all the bugs out about halfway through friday of champs.

Thanks 148/217 for posting the video and answering questions about the design. Both programs are quite inspiring in there dominating designs.

13

I was under the impression that 233 had a mechanism that oh so slightly lifted balls, and that caused them to miss elims at Florida.

I doubt refs ignored this when I’ve read posts about how teams were pulled to practice fields to prove balls stayed on the ground.

14

177 based our design on 1073 after we saw it a BAE as mentioned in our thank-yous thread. We designed our roller system to pass the piece of paper mentioned by others to be certain it was legal.

Edit:
I forgot to mention we had the clutch on our original possesor about a week before scrimmage on our original design. It was our own design using laser cut friction discs we custom made to work with our hex shaft.

15

2075 came up with this design on there own, and we actually got a lot of people gawking it on the practice field at Kettering. but instead of the solid top bad we used a 1/2 inch urethane cord and a piece of aluminum angle along the ground. It had the ideal coefficient of friction, as found by accident. It slipped when it needed and rolled the ball when going backwards and it also contoured to the ball to center it. Too bad we had a software issue that kept us immobile all but 2 and a half matches.

16

I realize that my initial post sounds a lot like I condoned cheating. That was not my intention. Our setup most certainly kept the ball in contact with the ground.

My intention was to indicate that I had assumed that the refs would be erring on the side of declaring legal mechanisms to be illegal, and it would therefore be unlikely to be worth the risk.

17

I was impressed with 148’s pinch rollers in their video but did not really think much of it until 971 got the robot up and running. I was disappointed to say the least at the ineffectivness of our initial single roller design compared to the 148 pinch rollers, but went home that night, took a look at the CAD and was excited to see that our kicker would clear a bottom bar for a pinch roller application. I did a few quick prototypes on the robot the night before ship and began work on the pinch rollers as soon as the practice robot frame was togeather. It took me quite a bit of work tuning the position of the rollers before I could get them working optimally, but as the driver the gain in ball control resulting in the freedom of menuvers was phenominal.

254 also helped us a lot in getting the rollers functional. We had been having alot trouble with getting enough grip on the ball until 254 showed us their magic material, which made all the difference. They also helped us tune the position correctly. Having 254’s 'bot as an example was an enormous help.

-Scott

18

115 added a second bar close to the ground at eliminations in SVR. We only got two matches to test it out though before we got knocked out by the team that showed us it works :stuck_out_tongue:

For us it helped more with herding and pushing balls rather than actually being a ball magnet. It helped us play in the first zone a lot better in Atlanta though so it was worth adding.

19

This is a long story, but one that shows the steps of continuous improvement.

Build & Week 1:
To add a little to what apalrd already said, we tried about 7 collector concepts. We made no fewer than 4 “final” systems. We initially didn’t believe the over under pinchers would be legal. We built a vertical set (similar to 71), but felt that it had too limited a range for a 6x6 drive system. We had several other concepts that looked really promising, but once applied to the robot were quite frankly failures. Our vacum required too much driver precision, and our center feeding belt system (while excellent in prototype phase) bounced the balls off of itself during the implementation phase. At that point we went to a high speed wide overhead roller with a lower reaction roller that allowed for the ball to reverse idle. This took several days of tuning to get it to collect at high speed without bouncing the ball out. In the end, it worked pretty well, but the ball would occasionally cam out during turning maneuvers, and would often pop free when hit by another robot. Our team lead had been pleading for us to try an over under system, but that would require a floating mechanism (8" wheels) I didn’t think we could get done in time. Moving over the bump smoothly was a key component of our strategy and a lower reaction bar really needed 4" traction wheels. Then came the 148 video. I didn’t sleep that night. I may have posted it as “nightmares”, but they were nightmares of the best kind. The next night (two days before ship-date), the kids and I made the first version of our pincher collector. With only 1 days worth of development, and Kettering being week 1, we decided not to chance it, and shipped with the overhead roller. At Kettering there were 3 teams with pincher style of collectors. Initially 2 of the 3 fumbled the ball more than our backspin roller (one is now a multi-time national champion). Then they got them tuned in, and they were amazing. Each one of the 3 got at least 1 penalty that weekend for an inadvertant carry, but it was clear that was a better solution. The backspin would have worked much better if our spin center was about our nose (think 4x4 with grippys on one end and slicks or omnis on the back). Unfortunately, our CG ended up 2 inches rearward of the middle wheels instead of forward. If we had 4 more pounds, we could have changed this, but we were at 119.8 lbs.

Troy Week4:
Its a funny thing having the robot in a bag for 3 weeks. It is agonizing not being able to tinker with it, but so much fun to plan the time that you will get with it. With the 6 hours of unbag time, we made some improvements and installed our pincher grabber. We had very little time to develop it, but it looked promising. Troy (week 4) was the first competition that the pincher premeired at. There it was a Ref magnet, and a penalty collector. Due to the nature of our backstop, the ball could wedge itself against the backstop and manage to lift as much as 1" off the ground even with 10+ pounds of downbungee on the collector. One match we had soo much downforce, the floating assembly actually lifted the front wheels off the ground, and we could no-longer traverse the bump. We weren’t the only ones getting penalties that weekend for carries (the reffing was quite diligent), but we did get more than most. With 12 matches, there are a lot of opportunities for experimentation. After 8 matches, we were basically penalty free, and the mechanism was way better than our backspin roller. It is what allowed us to take on that infamous alliance in the finals at Troy.

Week 5 MSC:
For MSC, we found another lb or two and switched the back wheels to omnis to add some maneuverability. this change allowed us to remove most of the rock in our system ans still turn well. MSC is also where apalrd’s software was fully implemented. We had been looking for a clutch mechanism, but couldn’t find what we wanted so Andrew fixed it in software (chaning some 0 to 1s was a lot lighter and cheaper than most of the clutches I found). I think we recieved one penalty and it was after being double-teamed and knocked around. The reffing was a little more lax as twice, I saw us grab a ball as we were headed over the bump from the far zone. Both times the operator kicked it as soon as she saw it, but clearly the ball was lifted off the ground for an ever so brief moment.

Atlanta:
For Atlanta, there really weren’t any changes. It seems like it takes 3 competitions for a Killer Bee to find its place. This is true since I have been on the team. If there were 2 regionals, then there would be changes for the Championship. If there were 3 regionals, then the Championship would mostly be refinement. This year was earlier calm. There were a couple software upgrades, but the biggest improvements were working with the comp team to set the robot up better for auto-mode, and discussions of which balls to leave alone on the field.

Continuous improvement turns good to great. Continuous tinkering can lead to inconsistent behavior and headaches.

20

(the reffing was quite diligent)

Thank you very much! :slight_smile:

I will never forget the last minute of match 80 and having to call a carrying penalty on you. I had no idea of the score of the match but Jim was quick to point out that it was a huge penalty. And it was. But you were professionals and handled it as such. Thanks.