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Re: paper: 2014 HOT Tech Notes
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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. |
Re: paper: 2014 HOT Tech Notes
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. |
Re: paper: 2014 HOT Tech Notes
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Re: paper: 2014 HOT Tech Notes
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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. |
Re: paper: 2014 HOT Tech Notes
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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? |
Re: paper: 2014 HOT Tech Notes
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Re: paper: 2014 HOT Tech Notes
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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. |
Re: paper: 2014 HOT Tech Notes
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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. |
Re: paper: 2014 HOT Tech Notes
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Re: paper: 2014 HOT Tech Notes
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As for Andrew's request, we only have rigid frames ;) |
Re: paper: 2014 HOT Tech Notes
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. |
Re: paper: 2014 HOT Tech Notes
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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. |
Re: paper: 2014 HOT Tech Notes
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. |
Re: paper: 2014 HOT Tech Notes
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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. |
Re: paper: 2014 HOT Tech Notes
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