The spread of pinching rollers this year

[EricVanWyk]

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.

[Scott Bahl]

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

[blayde5]

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

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.

[IKE]

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.

[ExTexan]

(the reffing was quite diligent)

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.

[AdamHeard]

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?

[JABot67]

Originally Posted by AdamHeard

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

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.

[AdamHeard]

Originally Posted by JABot67

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.

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

[JABot67]

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.

[rahilm]

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.

[IKE]

Originally Posted by AdamHeard

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

1114

254/968
-233
-971
-115

1073
-177

27
67


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?

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.

[Triple B]

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

[Josh Fox]

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 ), but with a bit of tweaking mechanically and of driver actions we managed to avoid them entirely after our first 2 events.

[Adam Freeman]

Originally Posted by JABot67

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.

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.

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!

[Craig Roys]

Originally Posted by IKE

1718 had a great pincher system as well.

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. 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.