Durability in FRC
 

As many new areas are going into District format, I would like to remind folks about designing for durability.

In the past, if you went to one regional, you could expect 8 qualifying matches and hopefully at least 4 Elims matches (making it to semis). Basically, you could plan on 12-20 matches.

Now, playing districts, you might see 12 qualifying, and have an even higher likelihood of making it into elims. Plus you will be doing at least 2 events which means a high likelihood of 30-40 matches. Plus another 12-20 if you make it to a district championship. plus another 20-ish if you play a third district. Plus another 12-20 if you make it to championship...

Last year FRC33 had 92 official matches at teh end of the World Championship. Throw in a few practice matches at each event, and they likely exceded 100 matches.

Then with offseasons, teams may see another 20-30 matches. Suddenly you have a need for a robot to last 150 matches instead of 15-ish...

Total run time changed from under 1 hour to around 7 hours.

What (if anything) are teams doing now that they are seeing a lot more matches?

Re: Durability in FRC
 

Our team generally tends to make things very durable (arguably too durable). Our frames are made to stand up to the most abuse imaginable (even a pyramid fall). We make our drive-trains low maintenance and easily swap-able (we usually have an entire fully assembled extra set of wheels/motors/gearbox/bracket assemblies on hand every regional). Our systems are independent and modular to allow for easy repair/replacement. We have generally been going to 2 regionals and an off season competition (worlds eludes us every year) and our robots end the season more than capable of spending 2-3x longer under stress.

Re: Durability in FRC
 

During 2013 and going into 2014 we are keeping maintenance in mind.

This past year our shooter was very easy to maintain with an easy access panel for changing shooter wheels. Our shooter motors were mounted to a separate plate that we could undo four bolts to drop out the motors and swap it with a spare assembly if a motor died. Our climber was also attached using 3 bolts so a replacement was an easy swap.

Our drivebase wasn't the easiest to keep up over the course of two regionals, Champs, IRI, and 2 off-seasons so we are working on a simpler base that is reliable but makes it easy to replace parts.

Re: Durability in FRC
 

We have been thinking more and more about useing easy to find parts. Light and costom is great but from autozone is often better.

Re: Durability in FRC
 

This is one of the main reasons I argue for a practice bot. Not only does it provide spare parts when something inevitably breaks, it provides a much better sense of how much wear and tear your parts will see (just like a durability car). Practicing at least 4 or 5 hours a week (as most teams who build 2 robots do) means you've hit or exceeded your competition bots life cycle in 1-2 weeks. If the design failed after 5 hours of practice you know what you have to watch for on the real robot.

Re: Durability in FRC
 

Definitely a large increase in design for durability and maintainability. Ball bearings where bushings used to be enough, better wiring methods, and a focus on wear points.

Re: Durability in FRC
 

This hits on a very important point IKE hinted at but didn't outright say. Yes you're competing in more matches, AND the turn-around between your matches is shorter. I know there have been times in Districts where we only had a four match break. So easy access for quick repairs is something we've started to highly prioritize.

Re: Durability in FRC
 

After building FRC robots for years it still amazes me how cars, that only cost 4 times as much can stand up to 100's of thousand of miles of driving over years and still hold up reasonably well when our robots are always barely hobbling along by the last off season. :P

Re: Durability in FRC
 

I have only rarely seen robots that are "barely hobbling along" by the end of the season. Perhaps teams who experience this need to re-evaluate their construction methods?

Re: Durability in FRC
 

A few things to consider first is that most of the parts FRC teams use are rated in industry to be used much longer then they will ever see in FRC. For example ball bearings have life ratings in the millions of rotations (As long as they are used within load and speed ranges) and pneumatics are rated in miles of equivalent travel. So we don't need to change much because we are already operating well within the expected life of those parts.

Bumpers also made a huge difference in longevity.

If I had to pick one thing, i'll echo what has been brought up already and that is access access access. But we should all be designing that way whether you plan on playing 20 matches or 200.

Re: Durability in FRC
 

Maybe that wasn't the right phrase, but every team is always fixing something in the pits between matches and it just gets worse as the season goes on. Things you never thought would break break ect...

Re: Durability in FRC
 

Last year (our rookie year), during our regional, we never had to fix anything until elims.

Of course, during elims is when our slider attachment method broke. :( LOL.

At Worlds, we only had 1 instance where we had to repair some damage due to a crash with the pyramid. That doesn't mean we didn't have any problems at Worlds, but ours were almost entirely field/software issues.

For the most part our bot is still running at nearly 100%.

So going back to what the O.P. asked, if you design for durability you should have fewer issues.

Re: Durability in FRC
 

Nathan,
High volume production cars (50,000+/yr) work as well as they do for as long as they do due to testing, refinement, and good processes. Over the years, as problems arise, they build new tests to run cars through. For instance, several decades ago, there were a lot of suspension failures in a particular area of Mexico... So the proving ground engineers brought Mexico to Chelsea Michigan. Here is a link about them "Fixing the broken road" http://blog.chryslergroupllc.com/blo...=entry&id=1303
Cars will go through various "life tests" that attempt to simulate the life of a vehicle in a short timeframe. Sometimes these are referred to as "HALT" or Highly Accelerated Life Tests. In the short time span of developing a new car, they will run a couple iterations of early product through these tests in order to verify that they would be good for customers. For a car, there are thermal test, vibration tests, electrical interference tests, several different body/chassis durability tests, several component-subsystem-vehicle level powertrain tests....

They also had us (when I worked there), design for 150,000 miles. What that used to mean was for a normal distribution of failure modes, but the average part life was 150,000 customer miles. This typically meant few failures under 3 years/36,000 miles, but due to normal distributions, you would frequently have some issues creeping in around 90,000 miles. This is in part why a used car looses so much value around the 100K miles.

The final round of testing on "production" cars typically runs into the first 4-6 motnhs of production. That is why you will often hear about a new car getting service bulletins to add or modify a brake line clamp and a wire harness rub shield. It takes that long to get those final cars made in the plants and tested, and reviewed. Guards and clamps will be added to reduce the risk of failure due to rubbing through (hose, wire insultation or ...)

I find it interesting the "issues" taht sometimes arise with customers. For instance, My father-in-law had a trunk seal wear out on his car with only about 40K miles on it... I did a quick estimate on the number of opens/closes I would think a trunk would see in the course of 150K mile vehicle life. 2/open/close cycle on 50% of trips with an average trip around 10 miles thus about 15,000 open close cycles/150K of mileage. I then asked him about his usage. He opens an closes his trunk to put his lunch box in the trunk. this means 4 open/close per day. He only uses that car to commute to work, thus he was at about 4X my estimated usage... or another way to put it, he had 160K worth of open and closes in 40K of driving... (sometimes you get lucky with your math). After that discussion he felt better about his seal wearing out so quickly...

Re: Durability in FRC
 

Never underestimate the price breaks of super mass production. Also, engineers spend A LOT of time just shaving off any dollar they can. For example, in 2012, over 400000 Ford F-150s were sold. So for every dollar off their BoM cost saves $400,000, well worth spending the time on. However, in FRC, price has the habit of playing second fiddle to other things like size and weight. If we REALLY tried to, I bet we could really drive down the price of an FRC robot. It's just not a priority.

Re: Durability in FRC
 

You had to go pick on my product, didn't you :D . Companies like Ford pay a fraction of the price that a person would for most components. When they work out a contract with a supplier, the supplier is guaranteed a certain number of parts at a certain price. As a result, they can supply at a much lower cost because they know the amount of product they will sell.

Some commodities like fasteners can be an order of magnitude less expensive for a major manufacturer.

$500 robots sound nice, don't they?

They'd also be made at a rate of a thousand or two a day....

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).

Re: Durability in FRC
 

Fair enough; but they're rules to which I hold fast, because I work with teams that are quite limited re: machining capability, student experience, and resources. Mind you, never breaking the "keep it simple" rule is not, as I mentioned, equivalent to restricting yourself to trivial challenges. Rather, it's much more a guideline for execution and for specifics of the design.

Yes, you've got to jump at some point; but I try as hard as I can to always err on the side of caution. In my experience, it is absolutely no fun to be over-ambitious and have a mechanism which does not function. I've experienced it many times, as a student and as a mentor, and it's one of the things I strive to avoid.

That said, we ourselves at 4464 have a fairly ambitious drive project we've been working on during the offseason, and we'll hopefully be implementing it in the coming build season (pending success of the current design iteration), so don't take this as if I'm saying that you should never be ambitious; you should simply be very wary of ambition at the cost of reliability.

If you have a very capable team with lots of experience, you can push the boundaries. This is certainly true, and I'd have done better to qualify my advice to reflect such. That said, human psychology being what it is, it is exceedingly easy to abandon proper caution and overextend, and the results from doing so are neither fun nor satisfying. It is a constant struggle to keep your ambitions in line with what is actually feasible, and in my experience (both in FRC and elsewhere) failing to do so is probably the single most common mode of design failure. I'd much rather be overly-strict in my adherence to KISS than be not strict enough, based on my experience with the outcomes of both.

Re: Durability in FRC
 

Long post on Estimating Duty Cycles and Fatigue.

In 2007, in order to have the giant ramps (2 ramps of 18 square feet each), weight was a very precious commodity. While the students do most of the fabrication and a lot of the design, the engineers often do the calcs. The arm and tower on that robot were constructed out of very thin aluminum (0.049" wall). At that time, we estimated the weights and torques expected to see on the arm. We figured that the arm would raise and lift at most 9 tubes per match. We were going to 3 regionals and planning on the world championship. Assuming 10 qualifying matches and 9 elim matches means that the robot was expected to play about 60 matches. With the lifting/lowering at 9/match, this would be just over 500 cycles. Assuming tuning and practice matches double the cycle count, you have about 1,000 cycles. This is not a lot of cycles in terms of fatigue strength. You can see it on a sample SN curve for aluminum here: http://en.wikipedia.org/wiki/Fatigue_(material)
Note that the 1,000 cycle point is at about 2/3 the 1 cycle failure point from a stress perspective.
The 1,000 cycles would correlate again to about 120 matches or about 4 hours of assumed operation.
We built a practice robot that year, and after about 10 hours of actual run-time during practice, the robot self-destructed. This occurred right before the championship. It was scary. *
The competition robot performed well that year, short of a joint failure right before elims at Detroit (the hand portion kept striking the ground hard and broke at Detroit, but we had a spare and fixed it in short order). The competition robot did end up failing later that year. It was after Worlds, after IRI, after Kettering Kick-off, and about 4 ours into playing at the YES expo. In other words, after a couple hours of test and tuning, approximately 100 mathces (2 more hours), and 4 hours of playing at YES... or around 10 hours.
If you compare on the SN curve, the 10 hours of operation we saw with both bots was about 2,500 cycles. Had we used 0.065 wall tubing, the stresses would have been reduced to about 75% those experienced (using thin wall assumptions). As the associated point on the SN curve linked above was 175MPa, 0.065 wall would have seen 131MPa. This stress would equate to around 40,000 cycles or 160 hours of operation. Another 25% reduction would have gotten out to 1,600 hours.
So the question then becomes, how sure are you of your assumptions, and how important is weight. Well, in 2007, for the components I am talking about, we had 16 feet of 1.5" x 0.049 wall tubing. This was about 1.34 lbs lighter than going up to 065 wall. As the robot was continuously at 119.9 lbs that year... It was a reasonable bet, but JZ asked that we never push it that close again (at least intentionally).
Something to keep in mind, the same robot that would see 2,500 arm cycles would see about 1.35 Million revolutions from a CIM motor in the drivetrain (assumes 10 hours of operation at 50% speed = 10*60*2250=1.35M revs).

*The calculations were based off of annealed 6061 alloy even though 6061 T6 was the base. The reason for this was because the welding done on the 6061 would cause localized annealing at critical stress locations.

Re: Durability in FRC
 

For those wondering (like I was) "isn't this assumption too conservative-- won't the HAZ naturally age back to some fraction of its full strength in a matter of days if stored at room temperature?", apparently the answer is no (pdf link):
Learned something new today! Quota met-- now I don't have to do homework :)

Re: Durability in FRC
 

Yep... You also get a tiny bit of thinning in the material section just outside of where the weld occurs. That is often why you will see failures just past the edge of the weld on thin section material.

Re: Durability in FRC
 

WOW! I never thought about how many matches teams would have to play in. That # is absolutely astonishing!

If there's one thing I learned from Aren Hill and the rest of our mentors during my one year on Team Neutrino, it's that you want to modularize EVERYTHING on your robot. By having modules, you give yourself a leading advantage over other teams. I was talking with some FTC teams at our state fair and encouraging them to modularize everything they could. If something were to happen to say the climbing mechanism, you could detach it from your robot and it wouldn't impact your robot.

Re: Durability in FRC
 

One of the things that the district systems has taught my team is to make cycle times faster for in between matches. Bumpers and the battery have to be very quickly changed when you are being called to get in the queue while coming off the field which happens usually once a district for us if not more. Also having the lexan siding for the robot velcroed on makes diagnosing issues on the field so much easier.

Re: Durability in FRC
 

This is a great item that I don't think has been brought up before. It is a good practice for repairability as well as adaptability.
For instance, I heard 111 made swerve modules that were easy to swap for replaceability/spares. Break a wheel, replace the module (faster/more reliable). While it costs more, it keeps those items from casting the team a championship.
Modules are also easier to replace. In 2005, the FRC 33 bot had no fewer than 4 end-efectors throughout that season (which was really tricky due to fix-it windows versus current withholding allowance), This was only possible because there was an easy and documented attachment point for the end effector.
While you don't have to have a complete CAD design of your robot, it is essnetially to have good documentation of major interfaces. In industry these are often referred to as ICDs or Interface Control Documents. ICDs can either cover the inputs/outputs/attachemnts of a module (think hand ICD & arm or forearm ICD) or the documents can cover the interface (think wrist joint ICD).

Re: Durability in FRC
 

In all of this great thread on durability (or reliability), I didn't see mention of a key item - SOFTWARE. Think about it. Any comments?

Re: Durability in FRC
 

Re: Durability in FRC
 

Software is generally not going to weaken and/or break merely by being used. If it works as designed at the beginning of a competition, it's likely to still be working as designed by the end.

Programming bugs have their own agenda for expressing themselves, but they're not likely to cause issues in quite the same way worn bearings or overheated motors can.

Re: Durability in FRC
 

In the context of a thread like this, software would be in terms of error handling due to failed sensors or components. A common item would be how to mitigate a faulty encoder or having a manual override in case a potentiometer goes out on an arm controlled by state programming. Good question but probably not the right thread. How about starting a software validation thread?

Re: Durability in FRC
 

Intriguing conversation...

Software can compensate for physical durability/reliability constraints. This approach is often used in building systems that demands 99.99+ availability.

In the context of FRC robots? Here are a couple of thoughts on better handling problems with wear-and-tear.

What if we:

- use redundant sensors for critical elements (e.g. encoders for the shooter's speed this year) and reject abnormal readings automatically?

- over-sample the image data from camera so that noise can be "averaged" out for better target tracking?

- put simple checks into the amount of energy we send to the actuators (e.g. unusual range, spiky patterns) to prevent damage/reduce mechanical stress on parts?

- use a proximity sensor and accelerometer to slowdown before the robot slam into something HARD. (this must be overridable though)

In fact, I can imagine some of these design patterns can be coded into reusable libraries to make it easy to adopt.

Additional thoughts?



It takes a little bit of work, but the overall systems' durability can be improved.

Re: Durability in FRC
 

The design of a car involves hundreds of engineers over many months and tens/hundreds of millions of dollars. I get customers who ask similar questions about miniaturization. "This computer is less powerful than my phone which cost me almost nothing, why is is $12,000". Answer: Give me a couple hundred million for NRE and I can match the price point and size of your phone.

There are many great recommendations in this thread. Durability comes both from good design practices (using robust serviceable mechanisms - bearings instead of bushings etc) and good quality practices (pull test all electrical connections, tie the wiring harness down so that no terminal connection is stressed, unit test software and so on). I wish 1296 had the problem of getting a robot through 100 matches! But we do design them to be used for demos for years after each season.

Re: Durability in FRC
 

To help introduce the newbies on team 20 to design, I made a powerpoint about designing for reliability. It covers basics- nothing too in-depth, but it goes over how we built our robot last year in terms of reliability, and the mistakes we made when we were preparing for IRI.
I would love to hear suggestions, but remember, this is for the freshman, I'm not trying to give them all of ChiefDelphi's knowledge about building robots. Baby steps. :D

I'm likely to add a few more pictures of the parts of the robot I'm talking about in the future.
Attachment 15307

Re: Durability in FRC
 

I've tried to stress durability to my team over the past two years, not because of more matches in the FIRST season, but because by the time Cowtown Throwdown rolls around, our robots are barely functioning. Not only that, but then some of our robots have to be able to work longer than that, since we use them as demonstration robots.

Our oldest one still working, Trigger (Breakaway), is turning 4 in February, and other than motor replacements and small rebuilds to make it easier to maintain, it has had no problems.

On the other hand, we have Epona (Rebound Rumble), which turns 2 in February, has consistently broken down and almost everything on it has been replaced and it still doesn't always work right.

Even worse was Pegasus (Ultimate Ascent), which has been scrapped after having many problems at the end of the FRC season, the least of which was that the frame was lower than the wheels.

I'm sure you can guess which one we demonstrate the most out of these robots (I'll give you a hint, it's Trigger).

All of these reasons are going into the design of our robot for Cowtown Throwdown, Buckbeak, so that we can keep it as a demonstration robot for the future.

Re: Durability in FRC
 

Redundancy is often used to help out Durability's sibling "Reliability". Durability and Reliability are kind of like precision and accuracy. They are heavily related, but not the same thing. Sometimes they use similar units of measure. Durability is keeping something from wearing out. Reliability is keeping something from causing a mission failure. Adding a second sensor doesn't improve the durability of the first sensor, but it can improve the reliability of the sensing system (if you have good fault detection and override algorithms). Without good fault detection and arbitration software, you can inadvertently make the system less reliable.

Occasionally though, redundancy can improve reliability & durability. This is sometimes the case with pumps or motors where 1 pump at full power can do the job, but will only last a short period of time before overheating. Using two pumps allows you to reduce the load by 50% and occasionally this can increase life by as much as 1 order of magnitude (for instance 100 hours goes to 1,000 hours). Think of it as how long can you run a CIM at peak power versus same speed, but half the torque...

Often these sorts of thins can be measured in Mean Miles Between Failure (for cars) or Mean Time Between Failure (industrial or off-road machinery).