Team 2980 2013 Open Source Robot

[Nuttyman54]

Originally Posted by eedoga

Hey Nuttyman,

SO...the tri-wheels were a sort of...all or nothing sort of idea. The kids made something out of legos...but as for a genuine prototype I don't think they did anything. I'm sort of hoping they got it right. They modeled it in inventor and are going to town building it/ordering parts...At this point it might be a suicide mission where they end up with no robot. I'm sort of hoping that isn't the case. In the least the idea is that they will keep fixing/figiting until it works.

As for the transition...I'm not sure the kids have figured that one out either. The original idea was to just ram into the pole...There is an arm mechanism that mounts on the top and folds down which they will probably end up using, and they are planning on having the tri-wheels whirring away as they drive into the pole. Worst case they are going to mount a teflon-V in the center square to slide onto pole.

Absolute worst case situation the kids will add a pusher to the back to help tilt the robot up.

great...now I'm worried.

Edoga

Lego prototypes are often sufficient, and any prototype is better than nothing. most of your weight is centered around the bar or below, so you shouldn't be dealing a large torque trying to pry your robot off the bar.

As far as getting on to the bar, if driving up it with the tri-wheels spinning doesn't work, I could see a wheelie-bar linkage or two (Like 33's stinger last year) that just props the front of the robot up on omnis and drives on the rear wheels towards the bar. You've got plenty of space on the top of the robot if you need it.


All-or-nothing designs are not inherently a bad thing, and neither is letting the students try and fail. If they're excited about it, that's what matters. If it works, they've really accomplished something. If it doesn't, failure is a very good lesson if you analyze what happened. As long as they learn something either way, it's a successful exercise. Some of my most memorable design lessons came from things that DIDN'T work in FRC (ie don't use set screws instead of keys on a CIM shaft to transmit torque to your drivetrain).

What's your estimated weight at? With all these 5-gallon bucket, pneumatic fed, small wheel banebots shooters we're seeing here on CD, I wouldn't be surprised if you could fab one of those quickly and slap it on top of the robot for a quick HP load 2 or 3pt shooter. If I recall correctly, Discotechs 1099 had a video on youtube where they used the kit-channel as shooter guide rails with great success. Just some food for thought, if you've got the weight I'm not convinced this has to be an all-or-nothing design.

[Paul Copioli]

So I am going to post some things to consider since I really don't want this thing to fail to an unrecoverable point. Here are some questions / suggestions:

1. Are you depending upon the actual weight of the robot to generate the normal force required for the wheels to drive up? If so, please realize that you will need a coefficient of friction greater than 1.732 (tan (60)) to get enough traction no matter what your weight.

2. If not, then your coefficient of friction + other method has to generate an effective coefficient of friction of 1.732 or this will not work.

The above is THE limiting factor for this type of design. I have analyzed this to the nth degree and it is a undeniable fact that you must figure out the traction problem before proceeding down this road. These poles are slippery, really slippery.

I hope it works ...

Paul

[eedoga]

Originally Posted by Paul Copioli

1. please realize that you will need a coefficient of friction greater than 1.732 (tan (60)) to get enough traction no matter what your weight.

2. If not, then your coefficient of friction + other method has to generate an effective coefficient of friction of 1.732 or this will not work.

I hope it works ...

Paul

I shortened the quote but I hope I didn't change the meaning at all.

Hey Paul, I hope it works too, The kids did a bunch of math and then ordered a specific rubber from McMaster Carr. A few sheets of it are here and to be honest it doesn't seam very sticky to me, but if I put any weight on the sheet it is relatively hard to slide across my counters. I'm hoping it is sticky enough, if not I hope we can find a way to find softer/stickier rubber in time.

We may have to go with a stinger or wheelie bar idea, and in I have an idea as to how we could maybe do it, I'll have to look at the cad drawings.

As for the room in the top of the robot, there is a bucket that goes there for dumping disks in the top of the tower.

Thanks for the advice, I'll share it with the kids!

Edoga

[BJC]

Originally Posted by eedoga

I shortened the quote but I hope I didn't change the meaning at all.

Hey Paul, I hope it works too, The kids did a bunch of math and then ordered a specific rubber from McMaster Carr. A few sheets of it are here and to be honest it doesn't seam very sticky to me, but if I put any weight on the sheet it is relatively hard to slide across my counters. I'm hoping it is sticky enough, if not I hope we can find a way to find softer/stickier rubber in time.

We may have to go with a stinger or wheelie bar idea, and in I have an idea as to how we could maybe do it, I'll have to look at the cad drawings.

As for the room in the top of the robot, there is a bucket that goes there for dumping disks in the top of the tower.

Thanks for the advice, I'll share it with the kids!

Edoga

What I believe Paul is getting at is that you can't rely on a tractive surface alone. No rubber from Mcmaster has a CoF of 1.7 on a smooth steel pole, coefficients between two objects must mechanically interlock for the coefficient to get above 1.0 and steel poles really don't offer much of anything to interlock with. Even Roughtop wheels against carpet are only 1.4 when brand new. Basically you need something actually attached/ reaching around the pole to keep the robot from sliding/falling down.. I would have your students begin brainstorming ways to do this so when the traction-only plan doesn't work out you have a plan B.

I really hope you can pull it off.
Good Luck, Bryan

[eedoga]

Looks like we are going with electromagnets run off of a solenoid breakout. I'm hoping this is a legal, and b doesn't melt the battery or cRio. Won't know until wednesday if the magnets we ordered will work, but I have fingers crossed.

Edoga

[eedoga]

http://www.chiefdelphi.com/media/photos/38508?

http://www.chiefdelphi.com/media/photos/38506?

We had a long weekend of welding and cutting, We are almost done with Fabrication and assembly at this point, we are really waiting on a couple of parts which are in the mail, and a couple of things we still need to make. The tri-wheels are going to be a serious challenge to assemble, mostly because they have to be partially assembled in the bracket that holds them into the robot, and because the tolerances of the brackets themselves are super tight. Somehow everything constraining properly in inventor doesn't square up to actual assembly.

We have also been going through mill bits like it is going out of style. For some reason the 1/8th inch bits are super easy to break and we are hand cutting the keyway for our wheel shafts out of aluminum. The goal is to save weight by using aluminum instead of using steel.

course they will still be really heavy. Hopefully not too bad though.

We lost a few hours because we were filming our "robot reveal video" Like last year this one is a doozie...It even includes "stunts" and explosions! :-)

One of the kids said that in addition to micro biology and engineering she wants to be an actor so that someone else can do her hair and makeup...From what I have seen she is a natural. :-)

I will try to get more detailed pictures as we get them.

Edoga

[eedoga]

So in looking at the robot it got ugly in a hurry. Things were coming together pretty well, but a set of brackets we made just came out much uglier than they looked in CADD...I know...aesthetics aren't everything, but the flip side is that the brackets are too narrow and the tri-wheel assembly is grinding on the inside of it. Again, this illustrates the difference between assembling something in Autodesk Inventor and making it in the real world.

So, we are lucky and our material sponsor is going to cut out new brackets for us. We redesigned them so that they are stronger and made from one piece instead of three welded together. The upside is the new brackets give us much more clearance on the inside while saving us critical space on the outside also making the whole thing a major win win...Only lose part is time...We are losing time... :-(

Our team has also become sort of fractured. We designed everything in CADD, and tried to make a layout and plan for the year, but small changes have been made by various people meaning that no one has a complete picture of the overall robot. Our programming team also took off on its own and is doing things no one but them currently understand. I am a bit worried about this.

Today we are doing a "stop build" and we are going to redraw the robot so that everyone can see the big picture. We are sort of dead in the water build wise because we have to have a couple parts made, and some other parts are still in the mail...So we might as well all get caught up and regroup.

Now is the time when everything falls apart before it comes together right!?

Here is to hoping.

Edoga

[eedoga]

Sometimes it is good to stop and take stock of where you are. It feels late in the build season, too late for us to not have seen this thing actually move. Things are going slowly but deliberately, and we hope we have thought of everything. We will post updated CAD files in the next day or so. Hope someone somewhere finds them useful.

Edoga

[eedoga]

We are officially a week behind schedule. Well, we are three days behind schedule, but it feels like a week. I really wanted the team to get the robot to a practice field this weekend, but it isn't going to happen. Looks like they are going to get to a pyramid on monday or so, and a practice field next weekend. That doesn't leave them much time for fixing anything if things don't work as expected. We finally have all of the shafts for the tri-wheels cut and tapped, and of course then tonight we couldn't find the key stock. We decided to use some of our waiting for parts time to powder coat the frame...Not perfect, but pretty darn good all things considered. So, this weekend...Final Assembly, and Monday first attempt at climbing!?

I had a dream that it worked...Lets just hope it isn't something that only happens in my dreams.

[CFTeam2980]

This is Chris, historian of team 2980. Here is a trailer of the Reveal Video. We are really excited about this year's competition!

http://www.youtube.com/watch?v=UOMP7rs3Wb8

Hope you enjoy it!

Chris

[cmrnpizzo14]

Originally Posted by eedoga

Hey Nuttyman,

SO...the tri-wheels were a sort of...all or nothing sort of idea. The kids made something out of legos...but as for a genuine prototype I don't think they did anything. I'm sort of hoping they got it right. They modeled it in inventor and are going to town building it/ordering parts...At this point it might be a suicide mission where they end up with no robot. I'm sort of hoping that isn't the case. In the least the idea is that they will keep fixing/figiting until it works.

As for the transition...I'm not sure the kids have figured that one out either. The original idea was to just ram into the pole...There is an arm mechanism that mounts on the top and folds down which they will probably end up using, and they are planning on having the tri-wheels whirring away as they drive into the pole. Worst case they are going to mount a teflon-V in the center square to slide onto pole.

Absolute worst case situation the kids will add a pusher to the back to help tilt the robot up.

great...now I'm worried.

Edoga

I'm not sure if you have already tested this, but our team tested a similar idea when we were making our climber. It worked very well for getting over the knuckles. I don't want to lead you the wrong way, but I think that it should be able to work if you follow Paul's advice.

Goodluck! Can't wait for the real reveal!

[josephus]

We've powder-coated the robot frame, it looks incredible. Programing is finished and the electronics board has been installed. motors are connected.
-Josephus, 2980 team member

[eedoga]

Originally Posted by cmrnpizzo14

I'm not sure if you have already tested this, but our team tested a similar idea when we were making our climber. It worked very well for getting over the knuckles. I don't want to lead you the wrong way, but I think that it should be able to work if you follow Paul's advice.

Goodluck! Can't wait for the real reveal!

Our final brackets came it at 7PM tonight. They look awesome and we will post pics tomorrow.It is tight inside of there, and things are really close to each other...The smaller brackets will be a big help in making everything fit and move the way it should.

I had a dream that the robot worked the other night. In the dream I didn't get to see it go up the pole, but everyone was really happy about it.

We are using electromagnets to stick to the pole. greatly increasing our normal force Hopefully we will be rolling by the end of the day tomorrow, and will get our first test/fitting climb in Monday night.

Edoga

[Jibri Wright]

Originally Posted by eedoga

Major Problems being worked out...

So our goal with Agent M was to drive up the pole...This would be hard enough, if the pole was just a straight shot, but with those stupid rails in the way...

Our original thoughts were that by using these weird "tri-wheels" we could drive up the pole, and when one of the small the wheels met an obstacle the entire wheel would simply flip over driving over the problem areas on the pyramid...


In the original design had four of these wheels mounted at 90 degrees, so that the wheels would sort of cup the pole as the robot drove up. The idea was that the robot would flip the wheels as it went over the horizontal bars robots can hang from.

We realized that as the wheels rotated around they would do two things...First the wheels would crash into each other and bind. Our next solution to that problem was to switch to three wheels, and off set them so that only one wheel would be flipping over at any given time. Here again we ran into trouble. As the wheels flip over the longer leg moves down into the center position. This would push the robot side ways instead of up and over. When the robot came back down it would no longer be lined up with the pole which would result in an expensive fall!

We were seriously close to giving up on the plan all together and starting over when we noticed an old robot I made a number of years ago that had a suspension system. I keep it up on top of a cabinet where I am sure it will fall off and crush me some day. :-)

In any case after reviewing how it works we came up with the plan of mounting the tri-wheel assembly's on springs. It is our hope that when the wheels encounter the barrier and begin to rotate around, as they lift up the springs will absorb the travel smoothing out the robots ascent and maintaining the wheels contact with the pyramid at all times.



The shock mounts give the triwheels 3 inches of travel. Of course we are banking on a whole lot of things working together...We can only hope that things will work the way we expect them to. If not...I guess we can dump disks in the 1 point slot.

(It will work...It will work...It will work...Our new team mantra)

Finally today we worked on making the shocks smaller. Garret and Mr. McGinnis managed to shave about three inches off of them which will give us much more room for electronics. We have to work hard to keep as much of the weight possible low and forward which means this robot isn't going to handle very while it is on the ground.

Maybe we should rename it SLOTH. :-p

I'm sure we will run into more problems as we continue on with this design and build. Here is to it all coming together in the end.

Edoga

You know that system your robot uses to climb? Maybe if you mounted that vertical on the robot and put it to the back or front of the robot, you would have room for a shooter.

[eedoga]

Originally Posted by Jibri Wright

You know that system your robot uses to climb? Maybe if you mounted that vertical on the robot and put it to the back or front of the robot, you would have room for a shooter.

At this point I think we would run up against a few things. First of all is weight. This robot is small, but dense. I am not sure we could fit anything else in and be under the weight limit. Each tri-wheel without the three chains inside weighs 6.2 pounds...So we are probably over 30 pounds for that climbing mechanism. even if we had the weight capacity adding a light weight shooter would probably be mostly ineffective.

We are also running up against time. We currently have not tested our robot climbing up a pyramid. We hope to see it climb later this week. We could develop a light weight shooter as our with holding allowance, but I have a feeling we are going to be modifying our climber during that time.

There is also the time available during a match. We aren't sure how quickly our robot will climb the pole. We probably won't have time for taking shots. Our current plan is to try to dump in the lowest slot during autonomous and then make a bee line for the half way mark so that we can load up the top dumper with the colored disks and get back to climbing.

Hope this clears things up.

Edoga