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#16
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Re: Durability in FRC
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Be safe, everyone. |
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#17
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Re: Durability in FRC
You guys spend more than $500 on your robots? If we add the price of all three years robots our team wouldn't hit the $3500 season limit... This year, I actually listed KOP items (including the cRIO) on our BOM to try to make it and still didn't get there.
Maybe we need to step up our fundraising a notch or two to find out what we are really capable of... At the same time, we've never had a major breakdown that couldn't be fixed with a little time or a few rubber bands. We had two repairs this year, a pneumatic solenoid block and two wheels. The pneumatics weren't properly tested and we had a defective solenoid, and the wheels were the result of a 6 foot dismount from the pyramid. Even then, we replaced the wheels because the had a small crack and we had an hour to kill, not because they were destroyed. I think in average design for these robots, teams just need to think about what they are asking the machine to do. If it is strong enough to do the task, it should be able to handle any abuse a 16 year old with a joystick can throw at it. Last edited by MrBasse : 03-10-2013 at 19:53. Reason: I wanted to |
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#18
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Re: Durability in FRC
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racecars don't last long, if your cim motor can outlast a Civic then your prolly not pushing it to is max output |
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#19
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Re: Durability in FRC
Estimating the full value of a FRC robot is a fun exercise! To get close to the real amount you should also count the volunteered labor. Each dedicated engineering mentor is probably donating $5-10K of his or her time annually.
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#20
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Re: Durability in FRC
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#21
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Re: Durability in FRC
As a drive mentor, this is pretty much the single most important design constraint I deal with in FRC. I don't care how impressive-looking and feature-packed your drive is; if at any point it fails during a match, it has cost you more than the added features could have possibly given you over a simpler design.
Keep it simple, keep it durable, keep it serviceable. You cannot break any of those rules, ever, if you want your drive to do its job. If you've got a choice between overbuilding and underbuilding, always choose the former. It is far better to have to cut features due to weight constraints than to have your robot break down. Keep in mind that "simple, durable, and serviceable" does not mean "unambitious" or "trivial." I've seen many ambitious, nontrivial drives executed in an elegant, robust manner. Most FRC drive concepts can be implemented in an extremely reliable way if you execute them properly (though a few, such as swerve, may require somewhat prohibitive team ability and investment of resources); it is, as always, a matter of details. But, as a rule, if you ever find yourself doing something which looks at all like sacrificing reliability for added features, you are doing it wrong. An afterthought: If you are a team with durability issues, and you tend to make lots of parts out of 80/20, the two are very likely related. 80/20 is a fantastic prototyping material. It is not a material for finished robots. I learned this the hard way during my time on 449's drive team; no amount of tightening, loctite, or lock washers will keep things in t-slots from eventually coming loose. Fix your dimensions and attach things with through-bolting or pop rivets. |
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#22
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Re: Durability in FRC
Not gonna lie, our robot could not handle 100 matches this season. We had to unbend and put new braces on the intake aftwr every event, sometimes during. The rest of our robot would have no problem handling more matches. Everything inside the frame perimeter is very durable and pretty much never breaks or fails. However, designing parts that can withstand high speed impacts outside the bumpers all season is quite a challenge.
Also the reason that cars last so long compared to robots is because you're not smashing them together at full speed for their entire lives. Comparing the ratio of durability to total g forces over the life of the product, robots are far more sturdy than cars. |
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#23
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Re: Durability in FRC
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Back in 2010 (our first year of swerve drive), if the goal was to perform well on the field that year, our complexity-based failures probably "cost you more than the added features could have possibly given you over a simpler design". But I doubt you could find anyone wouldn't do swerve that year if given another chance. Why? Well, one, the students loved it and learned more than they had in any other design. Moreover, we wouldn't be where we are today if we didn't start somewhere. This year, ok, we've had a couple in-match failures, maybe one even cost us a match. But I seriously doubt we would have been on Einstein without the swerve--it was just so integral to our strategy/alliance. There were of course other strategies which were very successful (and 6 that were more), but I doubt we could have implemented them to better effect than the one we chose, in part building off that under-performance in 2010. In short, there are big-risk-big-reward drive features that really are worth it, even if there's a risk of "if at any point it fails during a match". It's just that in some cases, you have to be willing walk the longer arc of history. |
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#24
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Re: Durability in FRC
We have found that solenoid -related failures are usually not irrepairable. We had a solenoid that failed to actuate regardless of input, manual or electrical. I entirely disassembled it and found some metal debris jammed in the mechanical slider valve. This could be caused by a number of reasons, all pointing to someone's negligence. I cleaned the valve with a paper towel, and put it back together. Presto! it worked just fine again. We also had to replace a damaged o-ring inside the slider a different solenoid, which we have a little box of assorted little o-rings. they are a pretty standard size, I think, and these are much better solutions than $60 buying a whole new one! Just be sure to tighten every screw well when reassembling.
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#25
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Re: Durability in FRC
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"If at any point" was intended heuristically and is hyperbole, and perhaps I should soften it: the loss of drive ability in a match is a crippling blow, and sacrificing anything other than very small increases in its probability for added functionality is very likely going to have negative utility. For the vast majority of situations, "do not sacrifice reliability for features" is going to give you a reasonably optimized decision. Re: intentional underbuilding, bumper supports are one thing, and the actual drive is another; I'm not sure I'd personally be comfortable with bumper supports that I didn't know would stand up to FRC impacts, but I could understand the justification for doing so. But I am very sure I would never put anything in the drive train if I doubted that it would last. Last edited by Oblarg : 05-10-2013 at 16:14. |
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#26
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Re: Durability in FRC
I've easily spent more than $500 just for fasteners for robots, or just in pneumatic solenoid valves, or just in speed controls.
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#27
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Re: Durability in FRC
o.O
That's pretty impressive. Bolts and pop rivets aren't exactly the most costly things in the world... |
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#28
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Re: Durability in FRC
...t-nuts probably make the list, though.
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#29
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Re: Durability in FRC
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As for off-season prototyping, certainly (and we did pre-2010), but no matter what--if you're iterating the way you should--the first year's always going to be more risky than the following. At some point you've got to jump. We probably would've had a better first year performance if we'd spent another off-season waited until 2011, but we also probably wouldn't be as far along as we are now, and another year of students wouldn't have had the swerve experience. Again, it depends on your goals: we might have done better than semifinalists and 10-12-1 in 2010 with a tank drive, but it was also our second-ever award and an altogether amazing and inspirational (as well as very challenging and somewhat frustrating) experience. All in all, the point I'm trying to make is teams shouldn't be inherently afraid to think outside the "safe" box, even when the safe box is outlined by very smart people who have their best interest at heart. Basically, what he says*. I'm not claiming that Karthik would agree with what I say here--and you can back up from the linked time for the KISS context--but I agree with him, so feel free to view this through the "Effective FIRST Strategies" lens. *For anyone who's never watched this entire presentation, you are missing something very important from your life. Just saying. |
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#30
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Re: Durability in FRC
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