The spread of pinching rollers this year
 

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.

Re: The spread of pinching rollers this year
 

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.

Re: The spread of pinching rollers this year
 

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.

Re: The spread of pinching rollers this year
 

Calling these sorts of things?

If the ball stayed on the ground it was legal.

Re: The spread of pinching rollers this year
 

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.)

Re: The spread of pinching rollers this year
 

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.

Re: The spread of pinching rollers this year
 

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.

Re: The spread of pinching rollers this year
 

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.

Re: The spread of pinching rollers this year
 

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.

Re: The spread of pinching rollers this year
 

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.

Re: The spread of pinching rollers this year
 

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.

Re: The spread of pinching rollers this year
 

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.

Re: The spread of pinching rollers this year
 

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.

Re: The spread of pinching rollers this year
 

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.

Re: The spread of pinching rollers this year
 

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.

Re: The spread of pinching rollers this year
 

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.

Re: The spread of pinching rollers this year
 

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

Re: The spread of pinching rollers this year
 

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 :P

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.

Re: The spread of pinching rollers this year
 

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.

Re: The spread of pinching rollers this year
 

Thank you very much! :)

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.

Re: The spread of pinching rollers this year
 

148/217
-971
-973
---294
-1625
-1771
-33???
-67

1114

254/968
-233
-971
-115

1073
-177

27

910

Updated

I compiled what we have so far. Anyone from Team IFI care to elaborate if one team found it first, or it was found separately.

Also, 1073, 27, 67, anyone else with the setup, care to share how you came across it?

Re: The spread of pinching rollers this year
 

We didn't originally have a bottom bar. We had a lot of trouble grabbing balls with our roller and before our first competition we added the bottom bar. It still didn't work well, but after tweaking the positions of both bars a bunch, we had a decent ball possession system.

Edit: 67th post! I just shouldn't post anymore so that my post count will stay at such an awesome number.

Re: The spread of pinching rollers this year
 

Would you mind posting who inspired you to add the bottom? I'd like to completely map this out.

Re: The spread of pinching rollers this year
 

I believe our idea for a bottom bar was developed independently of the other teams. We knew during the build season that we could add a bottom bar if we found that our top roller was not effective enough at grabbing the balls. Seeing that our first competition was during week 1, we didn't get the chance to see how well the bottom bar worked on other machines before we added ours.

Re: The spread of pinching rollers this year
 

After SVR, we realized how much more important ball possession was than we originally figured, and with help from 254, we had a design in place for pinch rollers.

After a bit of testing, though we realized it didn't help much in our set up, all we needed was the top roller and 2x2 angle centered at the center of the ball. The magic in our setup was a mechanical slip clutch. Worked great kept the ball on the ground.

Re: The spread of pinching rollers this year
 

You are missing 910. They had my favorite as they had the highest surface speed on the top roller of any of the teams I talked to. This allowed them to acquire the ball at a run while most of us had to take it at a walk. In general, on a collector, a top roller that engages a ball to the floor should have a surface speed equal to or greater than 2x the robot traveling speed. Our original top-spin roller was a 10 FPS surface speed which corresponded with our 5 FPS low gear. Our pincher was somewhere between 1-2 FPS SS. I think 910 managed a system with around 8 FPS SS on their roller.

1718 had a great pincher system as well.

Re: The spread of pinching rollers this year
 

233s final configuration was inspired by Karthik (1114) and the Poofs/RAWC (254/968). We started out with a floating top roller on linear bearings and a fixed lower bar. This worked well and the ball stayed in contact with the floor all through testing. However we found at UCF that the ball was lifting when we went onto the 1/2" plywood transition at the base of the humps. We did fine as long as we stayed off those transitions. 233, as always, was in continuous improvement mode @ UCF and we were still working out the bugs until they through us out of the pits long after the finals of competition that Saturday. We then attatched the lower bar to our linear shafts which allowed the ball to stay on the ground even if you pick the robot off the ground. We also changed our top roller covering to Kanagasabapathane, please correct me Karthik if I misspelled that.
Hope this helps you Adam,
mike d

Re: The spread of pinching rollers this year
 

Team RUSH dual-pathed ball possession mechanisms this year during prototyping.

We were working on a single-roller design, as well as a setup consisting of 2 powered rollers.

After testing both prototypes, we realized that the "pinch" was working much more effectively than the single roller design.

After a little more testing we discovered that having only one roller powered and a bottom bar gave the same effect as both rollers powered, so for simplicity's sake we powered only the top. We also had a flat hard stop to prevent the ball from going > 3" inside our frame perimeter.

We spring loaded the bottom bar down to ensure ball contact with the floor at all times but still received several carrying penalties (most courtesy of Richard :p), but with a bit of tweaking mechanically and of driver actions we managed to avoid them entirely after our first 2 events.

Re: The spread of pinching rollers this year
 

We did not develop our "pinching roller", independent of other teams. Our ball-magnet was inspired by the incredible design and prototype team of 148 & 217. JVN and I have been discussing this since week 2 at Cass Tech....he's been waiting for me to give them props. :p

Our original design concept and prototype had a lower bar incorporated, but somewhere in the design finalization and build process the lower bar was discarded. Why? Not sure, it wasn't my sub-system to design.

We ran driver tryouts with the practice robot, after the build season was completed (yes, we are always way behind schedule), and determined that the top roller only design was ineffective for the way we wanted to the game.

Around the same time, the 148 video was released. Looking at how they were able to grip the ball, drive, spin, and kick...it was exaclty how I wanted our robot to perform. I started disecting the video to determine how they were able to do it. After reviewing the video many, many times....I determined 148 and 217 were using a similar setup to our roller, but with a lower bar. I then attempted to determine how their setup worked....it wasn't until Paul Copioli posted this statement:

"If the normal force between the ball and the floor is less than the normal force generated between the ball and the "magnets", then the ball will stay possessed by the robot. This doesn't mean the normal force between the ball and the floor is zero."

That the light turned on for me. I cut a peice of 0.5" AL rod, drilled two holes, bolted it to the frame and our practice robot had a "ball magnet".

We went to Kettering with a plan to incorporate the lower bar onto the competition robot. The frame was slightly different where the lower bar bolted on, so we had to use aluminum angle bolted to the frame, then bolt the bar too the angle. As IKE eluded too, it took us about 2-3 matches, before we finally tuned in the "ball magnet". After that we just had to keep adjusting it each match to make sure it would work.

(After Kettering we changed the lower bar from AL-6061 to Heat treated Stainless Steel, since the AL bar kept getting bent in during matches, to increase the stiffness.)

Friday evening, we were called to the field the robot, for the refs to give us the paper test. We passed everywhere, except when the front of the robot was on the 1/2" plywood bumps near the large bumps on the field. We were told to adjust our style of play to avoid carrying a ball. We adjusted by bumping the ball and allowing it to roll back to us before we grabbed it. I don't think we were called for carrying at Kettering (I could be wrong).

After Kettering, I contacted Karthik about how they avoided carrying near the plywood....he send me pics of their spring loaded design. We decided against modifying our design before seeing how it would be called at other regionals. In the end, I think the calls were less and less strick the later the season got.

Eventually, we started grabbing the balls near the bumps and backing away without worrying about penalties. Were the balls off the ground? Theoretically, probably a paper thickness. For how long? Whatever it takes for a robot to cover 6" @ 6-8ft/s. Our ball grabber wasn't really good enough to hold a ball across those bumps anyways...we usually lost it, then reaquired it quickly afterwards.

The final specs on our ball magnet were top roller, powered by a Window Motor with a 5" pulley to a 1" roller, connected by round belting that slipped on the window motor pulley to keep constant tension on the roller and ball. Top roller was mounted to the frame, with bearing blocks slotted to allow for vertical adjustment of its position. Lower Stainless Steel bar, basically mounted to the frame and adjusted via washers.

So in the end the HOT team once again owes its success to the IFI guys. Without their videos, we would not know what level we need to perform up too before the season starts. Thank you 148/217!

Re: The spread of pinching rollers this year
 

Thanks. We went through a lot of the same iterations as other teams. Our original design had a single pvc roller on top with nothing on the bottom - the intent was to spin the ball in place in front of the robot. If we backed up, the idea was that the backspin on the ball would keep it rolling toward us. This proved to be very finicky depending on the surface and ball conditions and we would often roll right up on the ball. Adding a backstop didn't work as we would just kick the ball away from us more than anything. We then added a second pvc roller and messed with all different heights; from low to up on the middle of the ball, all with the same results. We then spent some time trying a vacuum system, but after blowing out a couple of f-p motors we gave up on that idea. It became clear that we needed something on the bottom to help grab the ball. This was now after bag day if I recall correctly - we were also still working on the hanger arm, but that's a different story. We'd seen the design of 148/217 online previously and after going to watch events at Kettering for week 1 we noticed teams such as 27 and 67 with the pincher design. We were able to get things designed a ready to put on the robot before the start of our week 2 event at Cass Tech. Two 1/2-inch steel bars, the bottom stationary and the top powered with a window motor. It was driven with a vacuum belt that would slip when it grabbed the ball so we didn't stall the motor. The bars were wrapped with tennis racket tape which seemed to give us just the right amount of stickyness. We wouldn't get a death grip on the ball - if we turned or maneuvered too fast we would lose it, but we were able to grab it enough to turn, aim and shoot. I think the only carrying penalties we took were when we accidentally would drive the ball up the bump and hold it in the air. Of course, the couple times that happened, our driver was sure to shoot it just to make sure the refs noticed it. :ahh: From that point on the only changes we made to it was to make a more rigid bracket for the bottom bar and to adjust it's position to get the best grip on the ball without carrying it. Luckily, our rocker on the wheels was only 1/8" so that didn't cause any problems with carrying the ball.

Re: The spread of pinching rollers this year
 

To add a little more to what Scott was saying:

What started out as a front/back single roller after 5 iterations morphed into what we have today. Front and back software clutch variable torque pinch rollers with pneumatic ball gates and a drivers station ball sensor. In theory the ball gates allowed the driver to close a gate so we couldn't intake more than one ball. The gates also centered the ball once captured to our small 3" kicker. The ball sensor allowed the driver to know he had captured a ball even if he could not see it. It took too long to center the ball which is why you didn't see us use our kicker too much. But that's another story.

What made our roller unique was the fact that our rollers are on the front and back of the bot. We use a Jag connected to a CIM and chained up the front and back rollers. We could grab a ball on the front or back of the bot by reversing the rotation of the CIM. We pulsed the speed of the top roller then we sensed current to the roller CIM to change the amount of torque applied once we captured a ball. We also tied in forward/reverse ground speed of the robot to the amount of torque applied and also the torque applied to the ball when we fired the kicker. This gave us our ball loft trajectory. We also used the circuit board in the KOP to add a LED light to the drivers station to sense ball captured. This was helpful when Scott couldn't see the ball.


It took use awhile to figure out how to program the CIM to our control loop. At SVR we found that crashing into a wall would reset the Jags and we would lose the ball and the bot would stall. The Jag has a 3 second default once a fault occurs. That can be changed to .5 sec. We also monitored the amps to the Jag and found out we were hitting a 80 amp spike when we hit hard. Once we figured out the Jags were resetting we changed out the drive train Jags to Victors and wrote in code to prevent the roller CIM to run full power.

The materials we used on the rollers was found by a lot of trial and error. We used tennis grip, duct tape, bicycle hand grip. I think the Poof guys finally showed use what they were using. Water proof electrical tape from Home depot(the magic material) We later changed the top roller material to a polyurethane tube that had a durometer of 30.

So in the end we had over 36 " of ball intake that could pick up a ball going full speed and stuff it into a goal. You will have to ask Scott about learning to drive backwards to stuff a ball in.

Here's a pic of our roller:

http://www.bmf.com/frc%20971/2010%20...s/DSC_7689.htm


Roy

Re: The spread of pinching rollers this year
 

I find that somewhat interesting, because we had an 1/8" drop as well and received penalties as a result. We were told that as we accelerated and decelerated quickly our rock would lift the ball up ever so slightly during gameplay.

I'm not trying to imply the wrong calls were made on either of us, but that's ultimately the reason we removed our center drop and swapped out the rear plaction wheels for slick wheels for MSC on.

I harbor no ill feeling whatsoever towards any ref who may or may not have called incidental carrying penalties such as the ones we experienced, but I do feel that the way it was called at the Championship, i.e. you only received a penalty for carrying a ball an extended period of time, was more within the intent of the rule in my opinion.

Re: The spread of pinching rollers this year
 

It may have also come down to weight distribution. 397 had 1/8" drop and a pinching rollers. There was some concerns with us accelerating hard but because our weight was almost exclusively centered in the back of our robot we only rocked forward when we stopped fast. I don't know 1718's weight distribution but RUSH's looked like it was more centered on the middle wheel (I could be wrong this is just based on my memory of 27's robot) This would cause you to rock forward or backward.

Our pinching rollers were similar to 67's. We also stole the idea of tennis grip from 1718. (And the fact that one of our mentors is a tennis coach)

The only times we got a carrying penalty was when the ball was forcibly inserted into our frame. We had figured that the ball would not compress enough to do this... we were wrong. This was fixed with some steel cable running across the back of our intake. Never had a problem with that.

Re: The spread of pinching rollers this year
 

I agree that that may have been an issue we experienced that teams like yourself or 1718 did not experience. We attempted to distribute weight as evenly as possible, and that could have contributed to us rocking, and/or lifting the ball up, more.

Re: The spread of pinching rollers this year
 

If I remember correctly we calculated ours to be dead center of the bot; it might have been shifted ever so slightly backwards, but no more than an inch.

Re: The spread of pinching rollers this year
 

I don't know about that. It was a piece that many teams copied over from regional to regional. But...

Anyone remember the week 3 video from 121 in 2008? How many teams copied them entirely?

Re: The spread of pinching rollers this year
 

Like...5? Maybe 10?

There were probably 100 or more pinch rollers inspired by 148 and 217's initial video. It's not even close.

Re: The spread of pinching rollers this year
 

I would agree that there were a lot of teams copying the pinch design, but I can't say I'm surprised.

The idea is quite simple, and easy to implement, but it was in the execution of this idea that really made the best systems stand out.

While there may have been 100+ teams that copied the design successfully, there was still a very wide gap in effectiveness between most teams with a pinch roller system and teams like 254, 971, 1114, or 148/217.

Re: The spread of pinching rollers this year
 

One thing to consider is that we were an 8 wheel drive with the center two wheels dropped as opposed to 6 wheel with only one dropped wheel. It's much easier to rock back and forth on 1 wheel obviously. I think we may have had less of a tendancy to rock back because of that. We also had the advantage of not playing in the 1st week when they were really watching for it...it seems the calls on that loosened up a bit as the season progressed.

Re: The spread of pinching rollers this year
 

Ah, the fact that you guys were 8 wheel drive slipped my mind. I would also assume our tendency to rock would be greater than yours.

Re: The spread of pinching rollers this year
 

Our "ball magnet" was inspired by a video posted on CD. We prototyped and shipped with a driven roller wrapped with a high-friction material that contacted the ball above center when it was 3" inside the frame. We had an idler that contacted the ball in the middle to prevent incursion of the ball >3" beyond the frame.

At our first regional in Pittsburgh, we found that we did not have as good possession as we intended and desired. We modified the design to increase the top roller speed, while allowing it to slip on the drive pulley; then we stalled our center mounted roller and coated it with carpet tape.

It was an improvement; however, not as good as we would have liked.

Re: The spread of pinching rollers this year
 

2016 followed suit of the design after our dallas collaboration with 148. we learned a lot from them on their mechanism and seeing its effectiveness we could not resist but to transition for the big stage in Atlanta.

I think we see this every year though, last year we saw teams shoot to dumpers later in the year. So there is always one key mechanism advantage, however for us I noticed that it took a while for our drivers to get used to it and actually use the new system correctly.

That is the biggest disadvantage with changing mechanisms after having gone through one or two regionals.

Re: The spread of pinching rollers this year
 

If my aging memory is correct, Foley had a rocking problem also at Kettering and may have even flattened their drive train there.

I'm guilty as charged for calling a fair amount of carrying penalties, but like all my calls, I call 'em as I see 'em and try to be consistent. :) As all the refs do I believe.

I do think many of the early match calls were very correct because the rules were clear on the definition of carrying and ball magnet designs needed to eliminate that possibility. Without that direction, too much subjectivity is introduced into penalizing a carry. Later in the season, practically every carry I saw was incidental and did not happen consistently because of the design.

Re: The spread of pinching rollers this year
 

I felt you were keeping us honest, and it added a new degree of challenge to Troy. I just hope the Safety Judeges went easy on you guys for being bent over so much of the match. :D

Re: The spread of pinching rollers this year
 

We started off with a vacuum when we shipped. After seeing the 148/217 videos we built a roller assembly and took it to Florida in week 2. We ran UCF with the vacuum. We installed the rollers at Palmetto and struggled all weekend getting it tuned in. We designed a new roller system for Atlanta that floated up and down. Once we dialed it in, we did well with it. One thing that inspired us was seeing the carpet tape on 67. We put double sided tape on the bottom roller and balls were easier to grab. We did notice the ref looking closely at ours one round, so we pointed out to the head ref after the round that it floated. He seemed satisfied.:D

Re: The spread of pinching rollers this year
 

I agree with Ike, thanks for keeping us honest!

Re: The spread of pinching rollers this year
 

Hi Ike,

Actually, our roller runs at over 20 ft/sec so that when we're driving full bore at 10 FPS we can grab a ball on the fly with no "bounce-back". If we reverse it at that speed it actually is quite a nice kicker! In fact, our autonomous simply does that - reverses the roller to full speed, we drive about 2 feet into the ball in front of us and it spins the ball up to a high enough speed to run it right up the ramp into the goal!

John

Re: The spread of pinching rollers this year
 

Wow, an that is why it was my favorite collector this year.

Re: The spread of pinching rollers this year
 

Can somebody explain the physics behind the "intake must run at >=2x robot speed" assertion? I've heard this before, and even designed with it in mind, but only now do I stop to think about it.

Intuitively, I don't see why running at >1x robot speed wouldn't work?

Re: The spread of pinching rollers this year
 

I'm guessing it may have come from the fact that the tangential velocity, with respect to the ground, of the top of a wheel, is twice the velocity of the vehicle to which it is connected.

So the reasoning goes: the roller must turn at 2x robot speed in order to keep the ball from escaping when backing up.

But that reasoning is flawed. The tangential velocity of the top of the wheel with respect to the robot is the same as the velocity of the robot.

There may be other reasons for the 2x number.


~

Re: The spread of pinching rollers this year
 

If you draw a ball and imagine it rolling at 1 m/s. At any moment in time, the bottom of the ball is stationary (in contact with the ground). The middle of the ball is traveling at 1 m/s. This means the top of the ball is at 2 m/s.

With a collector that touches the ball, it is the same. If the collector has the same surface speed as the robot is traveling, it will want to puch the ball forward as it draws it in. If the surfaces speed is 2x or greater, it will draw the ball into the robot. This is best seen with the backspin collectors when they are backing up. If the surface speed is 2 m/s, the robot will loose contact when its back-up speed is greater than 1 m/s. The ball still has some momentum and will continue towards the bot if the bot stops.

Normally the collectors suck the balls into some sort of feeder system. This year, there is a 3" intrusion rule. High speed collectors impart a lot of energy into the ball. This energy can cause a bounce when the ball hits its backstop. Some teams fixed this by moving from a top-spin to a lower point along the side of the ball. This reduced the rearward momentum, but induced higher normal forces between the ball and the carpet. This meant that you needed more power to keep the ball backspinning. The solutions for that were either a clutching mechanism (so that the ball did not backspin of which 1918 was extremely creative), more powerful motor, or larger ratio which meant slower surface speed. The topspin systems often used some sort of cushioned backstop to absorb the extra kinetic energy, or would have a cushioned roller mount (our original topspin, backspin system) with a lower idler roller.

With the high surface speed that 910 has, I imagine the had lots of testing with the ball rebounding out of the machine. It looks like they found a very interesting solution of compliant yet slick material. Again why that was my favorite collector this year.

If you need some diagrams, I can throw together another Powerpoint. I have a few decks of slides from our collector studies. I would have posted it up, but felt kind of silly saying, "Yeah, we did all this engineering to get this one design which was sort of OK, but then went with a design we ruled out in week 2 because we saw it was better in a video".

Re: The spread of pinching rollers this year
 

Carnegie Melon. Your design sounds like something that Carnegie Melon developed for the Robocup.