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paper: 2014 HOT Tech Notes
Thread created automatically to discuss a document in CD-Media.
2014 HOT Tech Notes by Adam Freeman Back after a one year hiatus is the 2014 version of the Heroes of Tomorrow Tech Notes. Describes our game analysis, design, and robot features for our 2014 robot HOTBot SS. For further details on the robot see: http://www.hotteam67.org/WordPressTest/2014-hotbot-ss/ CAD models coming soon... Any questions feel free to ask in the thread or PM me. |
Re: paper: 2014 HOT Tech Notes
Whoa. Pneumatics.
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Love the design (and the pneumatics), but why only 50 pounds on the springs? Our design uses the same spring style, but 160 pounds which gives us a larger range and a flatter trajectory. Pretty much the same displacement as well. Also, how are your bearings set up? We tested with 80 pounds of springs and had no where near 15 ft of range.
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A really well thought-out design based off your priority list. Beautiful integration of the sub-systems. Good luck, Adam.
(The catcher arms remind me of 2056's robot arms from 2008) |
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Nice tech paper, i love the physic details.
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Great robot as usual Adam. You guys always manage to put together one hell of a robot and this year isn't looking any different. Can't wait to play with it at Lansing and MSC!
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See, 2415? HOT already has cupholders on their bot.
Great job Adam and Team 67! |
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Adam, fantastic document. I shared with my team...hoping they read it cover to cover like I have.
I am interested in that projectile motion spreadsheet. The document said it was posted on CD...but I'm not sure where (and I searched to the best of my ability!). Any way to share a link to it? |
Re: paper: 2014 HOT Tech Notes
Interesting design analyses.
I thought 254's '08 bot was a much better bot to emulate for this year's game than 1114's '08 bot. Simple lift, softer launches and a similar roller intake/outake - much more controllable than a punch. I suppose c.g. would be an issue, but with the ball in the 'up' position c.g. is an issue with 1114's design too. Turns out either would work for specific robots, but 1114's probably better for the high goal. Yet I was more biased towards being the best ball handler than the best high goal shooter. Tom, here you go: http://www.chiefdelphi.com/forums/sh...2&postcount=12 |
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Beautiful machine HOT. That backwards fire is so clutch, can't wait to see that win you some matches. Squeezing every second out of a cycle is key and it looks like you guys have it |
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Parabolic vs Air Drag Trajectory revC |
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FWIW: Using the launch numbers in your paper: 28.5 ft/sec launch speed... and running an air-drag simulation assuming a 37.5 ft/sec terminal velocity for the ball resulted in very nearly the same ball height at 12.5 feet from the launcher. http://www.chiefdelphi.com/forums/sh....php?p=1353376 |
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As Chris mentioned, we basically started with the claw concept and designed around that. One of the biggest benefits we saw in the 1114 design was the ability to get balls out of tight spaces. It's still pretty true....but the top roller with out side bars does require a higher level of driver precision than the Bombsquad (top roller and side bars design). 1114 had one of the best drivers EVER in 2008. Teams should take that into account when they are evaluating designs from past games. We will probably need to add something to our design to assist with ball centering to make it easier to collect the ball. Right now that is one of the areas we can improve on greatly. |
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Great read. I always love looking at any robot 67 builds. You guys have made some great marvels of engineering and this year is certainly up to that standard.
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Thank you so much for this. When our team did terrible in 2013, I spent days looking over things like this. I ran into your tech notes and it was like I struck gold. I showed this to our head engineer and we decided to do what you did. We used waterjet 5052 1/16" aluminum and lowered the pneumatics use. We also did our own little spin by adding some mounting holes, cable management holes, and some strain reliefs built in to the chassis. We even had to buy our own 5052 stock because Chrysler (or fiat now ;) ) only had 6061.
In short, thanks. This really helped us get a good base down to start tinkering with. |
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We were really impressed with your machine and driver's at Howell. Keep it up! Looking forward to seeing you in Lansing. -Adam |
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Adam,
Thanks for sharing the Tech Notes again this year. I finally got a chance to read them, after watching some of your matches of course. It is always cool as an engineer to know how something works and some of the thoughts throughout the process. Good luck the rest of the season and hopefully I can see this beast of a machine at Champs! |
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Since we weren't able to finish our premier night reveal video in time, we waited until we had additional footage to publish a video.
Fresh from the HOT Team Promotional Department is a video featuring our robot at the Howell District: https://www.youtube.com/watch?v=pHBzLlr8aso Additional videos from Waterford can be found here: https://www.youtube.com/watch?v=-AGQ...zK-g_bv4hkgwwd Enjoy! |
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But, I am not suprised that us and 148 would choose similar music: http://instagram.com/p/jUvPJGn23l/ |
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Typical CAD disclaimers apply...not everything is 100% accurate to competition robot. This is the most complete CAD model we have created. But, most of the robot was designed in AutoCAD then Solidworks models were created to help find integration and assembly issues. We are by no means CAD/modeling experts. Enjoy! |
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Wow, this is a great set of notes. It looks great as well, super attractive cover page. I like how you laid out every step of your process including game analysis, concepts, and design. Fantastic work, and thanks for sharing.
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Adam, great robot this year. I look forward to reading through your design process and stealing ideas that we think will improve our process. Hope to see you guys again next year.
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I love that I still read every word of the Tech Notes even though I know most of it. As a new mentor its nice to have these resources around. Thanks Adam love the robot and the team.
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Adam, The step file looks great. Not so sure I'm glad I saw this, I won't be getting much sleep now!
It always amazes me how well designed your robots are and how you can push something right to the limit. The first thing I noticed is that you don't direct drive any of your wheels on the drivetrain. Is there a specific reason for that? Or do you just want to keep the weight of your Cims and gearbox centered? Also, I am impressed with the 9 mm belts, seems like that is just too close to breaking, but I like that you were able to do that. In the model it looks like you raised the outerwheels about 1/8"? Is that what you went with or did you need more and shaved the wheels a bit? Thanks for posting this! |
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We actually switched from the 9mm belts to 15mm belts after we broke a belt practicing before the season. We had quite a bit of practice time on that belt and only one side broke, so I would guess something might have happened to that belt when it was re-installed (we had just replaced wheels before it failed). We ended up using 15mm kevlar re-inforced belts to ensure that we didn't have any drivetrain issues. We had the space and weight, so better safe than sorry. The only drivetrain issue we experienced this year was picking up some debris in the drive that flipped the belt over and shredded it. We stayed with the 1/8 raise on the outside wheels. We didn't shave the wheels, but the turning performance did increase as the outside wheels wore down. We had some issues throughout the season with popping the main breaker, which I'm sure the turning scrub had quite a bit of influence. Overall we weren't extremely happy with the chassis performance from an agility standpoint, getting out of t-bones, avoiding defense, etc. We will probably do a complete re-evaluation of the chassis size, shape, # of wheels for next year. |
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Was this a VP belt that snapped? I ask because we ran belts on our intake this year and ended up having to replace every single VP belt at least once. We had one non VP belt from a different supplier (SDP-SI?) and it survived the entire season. Trying to see if our experience was unique or if others have seen that the VP belts have a shorter lifetime than those of other suppliers or if there was something different between the runs. * And anyone who is worried, VP belts are probably fine for anyone who does a sane season. 125's was NOT sane. |
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We ran at least 6 other 9mm VP belts/robot that survived an entire season (2 on intake, and 4 on outer drive wheels). I'm pretty confident that something else happened to the one belt that snapped. We had just replaced the wheels that afternoon. Right after that, they called me and said the belt broke. I think they tried to roll the belt on to the pulley and cut it, instead of assembling it correctly with the belt on the pulley. |
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I've been analysing a lot of drive train design this summer and I've been meaning to ask since watching this year's Einstein matches. Where It seemed your drive had the worst time in escaping t-bone pins. Do you think there is a simple method to improving an 8WD to escape t-bone pins so that the power and robustness of the drive can be maintained.
The drop-down wheels that have begun popping up on various team's drives offers an interesting solution, but I'd just like to hear what you think. |
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I'm not sure there is a simple solution to the problem. I don't think the issue was only b/c of the 8WD drivetrain setup. I think that the combination of the 8WD, long chassis, rectangular chassis shape, and driver ability all resulted in us getting stuck in a lot of t-bones. Drop down omnis are becoming more and more common. We entertained adding breifly them during the season (after MSC), but never really pursued it to far. It would have require quite a bit of designing and changes that would have only resulted in marginal gains at Champs. We actually started running different combination of omni wheels in the offseason that helped a little bit, but we still had issues with pins. As Glen mentioned, we will probably evaluate different chassis shapes to help lower the chances of a full on side pin. I think it will be a point of focus for our chassis design next season. I don't think we are ready to add in drop down wheels to our drive system. Teams like 469 and 254 did pretty well without them on a standard 6/8WD setup. I'd like to see more of a square chassis setup next year and some better driving to avoid defense. We haven't entertained switching to 6WD much in the past couple years, but it might be something to look into next year. |
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I've had a running theory for a while that a chassis such as that gets shoved into the carpet a bit odd under high defensive forces, contributing to the "locking up" affect. Any thoughts? |
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My thoughts are it allows wheels that shouldn't be touching to be forced to touch, causing a wheelbase longer than you're supposed to be on. Combined with the already huge lateral forces from the defender, you're STUCK! If only a bunch of teams would be willing to mount gopros to the underside of their robots for a few events... It's interesting how the drivetrain arms race has evolved. |
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I'd also be curious to see how it deals with omni directional drivetrains (mecanums or 33/78 style omnis). Guess I should get drawing FBDs. |
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As for Andrew's request, we only have rigid frames ;) |
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We have a flexible chassis from this year, for Andrew's testing! But we used mechanums and therefore we weren't as concerned with frame stiffness. I don't know for sure that is was a good idea though. I think the hard part was that the loading would change on each wheel therefore changing how it drove. We would keep contact with all 4 wheels though. Also in our third event we changed from mechanum to traction and kop wheels (4wd) to try to play more defense for other newer teams. Worked well, but not sure I'd do 4wd drive again. Too much power with 8 motors in the drivetrain and we tripped the main breaker in our last two matches.
It is interesting in the drivetrain wars, how much it has changed the forces the robots receive. There is much more involved than picking motors and gear ratios, the frame is definitely part of it and maybe the Bees were onto something with the Omni wheels. Maybe the frame doesn't need to be as stiff and that weight can be used elsewhere with the omni directional drivetrains. Or you have to go in the other direction of stiffness. It's always a tradeoff. |
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But, anything is possible we've never looked at a corner to corner stiffness in the vertical direction. My honest opinion is that we put ourselves in bad positions during the match which lead to a lot of easy t-bones for the defense. |
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When some teams are in t-bones, their robot vibrates and shakes as its pushed sideways from the wheels getting and then losing traction with the ground, and it's almost impossible to get out of these pins. From what I've seen, it happens to robots that don't rock, like swerve (4 wheels in contact at all times) and 8WD (4 wheels in contact at all times).
I agree that avoiding defense is pretty important. We had issues with getting pushed in circles from the side and we had a traction limited 6 CIM drive with 2" wide McMaster blue nitrile tread on our wheels, like 254 does. 254 weighed well under 120 lbs, but didn't have too many defense issues because they were very smart drivers. 118 had a similar strategy. They were geared VERY high and had a single speed gearbox that would most likely trip breakers very quickly if they got into a pushing match, but they focused on avoiding defense, and it worked pretty well for them. |
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Even though we practiced a lot with 368, I never took notice because it wasnt a full field of robots and with defense from multiple robots. Swerve is another direction we might move towards, as we tinker with drivetrain setups during the off-season. We already built a swerve back in 2009 but never implemented it into a real design for an FRC challenge. |
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This might not make a difference at all, but maybe so. When I find myself in a pin, I always shift into low and turn into them. It may all be in my head but every time I have tried turning away from the pinning robot, it seems as if my front wheels are on ice and my rear wheels are bolted to the ground. I really need to start testing these things aha. And it was a 6 WD WC set up using VP versa wheels.
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