Re: Durability in FRC
 

Not that the other explanations aren't very true as well, but personally, I also try to crash my car less than I do my robot. (I also drop it off fewer pyramids and drive it off fewer bridges, even accounting for the vastly different velocities and distances.)

Be safe, everyone.

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.

Re: Durability in FRC
 

Yes, they should last but remember, this program is about high school kids with hammers. Proper installation (no inner race pressure) and support pressure is a big part of this. ALSO TEAM STOP APPLYING SO MUCH SIDE LOAD TO YOUR CYLINDERS, and if you do pack 4 spares.

racecars don't last long, if your cim motor can outlast a Civic then your prolly not pushing it to is max output

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.

Re: Durability in FRC
 

Sir, you vastly underestimate the destructive power of a teenager. :p

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.

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.

Re: Durability in FRC
 

Simple, durable and serviceable are all great, but you really can alternatively approach them as trade-offs if you're willing to take the risk. If I'm not going to be simple (e.g. our swerve), I better be seriously serviceable and/or durable. We've managed both, though with emphasis on the former: we can mitigate almost any issue in an elims timeout. The modules also very durable, probably as much so as most tank drives, but if there's a failure we'll swap it and fix it off-robot. We also deliberately underbuild some other features for weight. For instance, this year our side bumper supports every 8" are very, very bent. We could have built them stronger, but we wanted the weight, so we accepted the trade-offs of the bending and necessary servicing. Speccing them was nerve-wracking, and we had contingencies if it just wasn't enough, but they've done their job.

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.

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.

Re: Durability in FRC
 

This is what offseason is for, though. If you have any doubts at all about your ability to implement a difficult drive system reliably, then the proper time to experiment with it is when there are neither strict time constraints nor serious costs to failure. Only once you have enough experience within working team memory to do it in a way which does not compromise reliability should you put it on the table for build season.

As far as my design philosophy goes, if your "big-risk-big-reward" drive truly qualifies as "big risk" (for any reasonable definition of "big"), then you probably shouldn't do it. Drive is far too crucial to baseline ability to play the game to be gambling with. From what you describe, it sounds like you now have enough experience with swerve that the risk is not significantly above what less-capable teams would experience with a much more trivial drive system.

"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.

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.

Re: Durability in FRC
 

o.O

That's pretty impressive. Bolts and pop rivets aren't exactly the most costly things in the world...

Re: Durability in FRC
 

...t-nuts probably make the list, though.

Re: Durability in FRC
 

Absolutely true, but I was attempting to define "big risk" in your context, which appeared to be "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" (emphasis mine, the risk being breaking any of those rules). For us, it is not a significantly different risk, but it is very much breaking that three-fold requirement. It's the view of them as "rules" to which I object. Viewing them as hard-and-fast imperatives sets artificial limits below what at least some teams are capable of pushing themselves to and learning from.

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.

Re: Durability in FRC
 

This brings another point: durability/reliability/simplicity is only a requirement if you make it one. It is completely possible that a team would prefer to create some crazy, out of the box drive train solely for the purpose of building a crazy, out of the box drive train. Teams can have other goals than winning matches when they build a robot (and/or a drive train, as the case may be).