Never Do This, and Other Good Ideas Gone Bad
 

So the scissor lift reminded me that there are a lot of designs experienced teams have tried once, and forever sworn off. This thread is meant to be a compilation of "Ideas gone bad" especially the ones you see year after year. Add your Gone Bad designs, and please explain details:

I will let someone else cover scissor lift. My favorite is the big hopper of balls with a single slide open door. These always work in your head, and they always fail in practice. Typically FIRST picks a compliant ball that wedge together and jam at the exit. This leads to frantic ramming in order to unjam the hopper.

Re: Never Do This, and Other Good Ideas Gone Bad
 

No idea what you're talking about with scissorlifts. Our team's rookie year was 2010, and we had great success with our scissor lift (Designed to climb the tower).

Re: Never Do This, and Other Good Ideas Gone Bad
 

I know my former team, 27, in both '06 and '09 refused to do an Archimedes screw after what happened to them in '02. I don't think they'll ever return to that idea. It does have great potential though, it's made it to Einstein, it's all about implementation I guess.

Re: Never Do This, and Other Good Ideas Gone Bad
 

I agree, it's more the implementation than the idea. Several years before I joined the team, they created a robot that remains infamous to this day. Its name was Scorpio. In 2009, several ideas were thrown out because they had failed on Scorpio. In competition, though, we saw them done well. The implementation was flawed, not the concept.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Historically, Drive-trains have not been our strong suit.

In 2002, 2004, and 2005 we used 4 wheel drives using rubber wheels on all 4 corners in a long base configuration. None of those robots turned very well at all, and one of then had a tendency to leave the ground while attempting to turn...

In 2006 and 2007 we decided we were going to try out Omni Directional wheels coupled with IFI High Traction Wheels. For some reason, still unknown to me, we chose not to power the omni wheels and only powered the traction wheels... These didn't turn all that well either...

Since then, there have been two unspoken drive-train rules on our team: No long base 4WD and No Un-powered Wheels.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Relying on gravity to do anything other than to give your robot weight. If it moves down (an arm, an elevator, a ball in a hopper), make it powered.

Ditto scissor lifts and "many-to-one" hoppers. I've seldom (but not never) seen implementations of each that were effective.

Mecanum wheels are on the verge of making the list, too (for the same reason).

Re: Never Do This, and Other Good Ideas Gone Bad
 

Our team will not likely use vacuums, or conveyor belts due to flawed execution and/or excess time we spent fixing parts. We will also never make a robot with less than an inch of ground clearance again (got stuck on the field repeatedly last year).
I agree that almost anything can be successful if done correctly, some ideas are just more difficult to implement than others.

Re: Never Do This, and Other Good Ideas Gone Bad
 

I think this is true for pretty much any design idea. There are few designs that are universally bad in all cases. A design may be poorly suited to a particular game, or the team may fail at execution, but given the right situation and great implementation, even the much-maligned scissor lift can be done successfully.

That being said, I do have a list of designs I will avoid unless I REALLY am convinced they're necessary. Among them are: mecanum drive, holonomic drive, scissor lifts, the aforementioned "big hopper of balls" with a single (small) door, 3+ axis arms, and high reduction BaneBots gearboxes on high-torque applications. Most of these I learned firsthand, over my college years.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Cantilever shafts, try and avoid. Especially over 1.5"-2", try and support both ends of shafts.

Re: Never Do This, and Other Good Ideas Gone Bad
 

I would argue with this one... If designed correctly, you can rely on gravity. The elevator we built in 2008 was powered up, and gravity down, and the only time it failed to work as anticipated was when the motor literally broke off its mountings at a pre-ship event. Other than that, it always went up AND down when we told it to, at a consistent, reliable speed.

Re: Never Do This, and Other Good Ideas Gone Bad
 

I accidentally tip your robot over with your gravity-down lift up. Oops, your lift doesn't go down anymore.

330 always adds a "gravity" cable to lifts for the case where you're tipped over and you need to unblock the field. It also helps to retract the lift for other cases like hanging on a bar. It's not that hard to add to the drum, either, if the winch is sized right.

Scissors lifts can be really nasty to get right. If you do get them right, they work OK... but they do have their weaknesses. I've seen a single-joint arm clean game pieces off the top of a scissor lift with one sweep, back in 2005. Hit a scissors lift so that it sways and... well... not pretty.

330 does have one team rule: All deployables shall be retractable (exception--we decide it's not necessary to pull them back in). Reason: We don't want to have to be dragging something around all match because it deployed too early by accident--and it's really surprising when we pull up ramps and go defend a spoiler (2007) or do other similar things.

Re: Never Do This, and Other Good Ideas Gone Bad
 

What difference does it make that a gravity-lowered lift no longer works when the robot's been tipped over? Talk about not seeing the forest for the trees.

It's usually not difficult to power lifts in both directions and it's sage advice to do that whenever possible, but not doing so is not necessarily a catastrophic decision. There are all sorts of things that can be done to mitigate any problems that might arise from relying solely on gravity.

Re: Never Do This, and Other Good Ideas Gone Bad
 

If a gravity-lowered lift is up, and the robot is tipped over, that lift is now blocking the field. Because it's gravity-powered, it can't go down (robot-relative) any farther. This can lead to penalties (the 84" cylinder, for example--a gravity-lowered lift that falls over while trying the top peg could easily be over 84" from the floor, causing a cylinder violation) or difficulty in getting the robot upright (longer moment arm, so more motion needed to go the same rotation).

If it could be pulled down relative to the robot (not the floor), then there is less chance for penalties, it's easier for a partner to get the robot upright, and depending on design, the robot itself may be able to assist the righting process.

There have also been some comments--some time back--that dirt could jam the guides, or some other such things, that would interfere with gravity.

Can you mitigate it? Sure. But Murphy says that the problem will happen when the mitigation isn't happening right.

Re: Never Do This, and Other Good Ideas Gone Bad
 

I think anytime you have balls in an open hopper you are asking for trouble. Look at 254/968 in 2006. While they had a big hopper, they several belts at the bottom to get them moving towards the shooter.

We had fair success keeping them in line (i.e. a tube with a width equal to the diameter of the ball so they couldn't bunch up), but even this clogged on us a few times in 2006. So in 2009, we always kept a grip on them.

Moral of the story: Keep something you can power on gamepieces at all times. Leaving them "to do their own thing" will only lead to heartbreak.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Ah, the number of spectacular failures we've had.

In 2006, the Pi's rookie year, the team had a belting company sponsor us. The team decided on treads, and the company supplied us the softest durometer natural rubber they had. At 30 lbs the robot was pushing people across the carpet. At 120, when it turned, the treads went straight and the robot stepped right out of them. They pulled the treads mid-competition, refit wheels, and never went back. However, they had a single match where they hadn't finished yet, so they put the bot out on the field without any wheels. No one said they had to move, right?

In '07, we had a spring counterbalancing the arm. The spring was strong enough, but the 1/4 bolt holding it wasn't really. I wasn't there for the catastrophic failure of approximately 400 lbs. of spring tension. Thank goodness. Gas shocks are your friend.

'07 banebots. 'Nuff said. Never went back - but we're giving them another shot this year. We have Andy Mark planetaries already here as a backup, because when you buy from Andy Mark you just know it works.

In '08, we went for a 6 wheel omni wheel setup. 4 oriented front to back, and two sideways. Unfortunately, we didn't have the foresight to make any spring loaded. Ever tried to make every leg on a 6 legged stool touch the ground at once? Our drivetrain was quickly rebuilt and frankly was never where it should have been that year.

Also in '08, we built a forklift. We ordered Bishop Wisecarver ball bearing linear rails. They strung us along for 4 weeks, telling us the parts were coming, before finally telling us we'd never see them. We built the entire 3 stage lift system out of igus slides, and used them in a manner I'm pretty sure that Igus never intended. To this date, we don't talk about Bishop Wisecarver without nasty glares.

In '10, we tried a linear kicker. Linear bearings from Mcmaster car on precision ground steel rods. Total stroke of 6 inches. 3 inch wideup with a 3 inch slowdown after hitting the ball. It worked great on paper. In reality, we shot 1/4-20 bolts across the room into a couple 4x8 plate glass windows.

Re: Never Do This, and Other Good Ideas Gone Bad
 

from 2006, 1086 has sworn off making another turret. just not our strong suit. and since 2007 we said no more elevators after making ours that year. but then we decided buying a premade system would still be possible.

Re: Never Do This, and Other Good Ideas Gone Bad
 

The main problem with the scissor lift is that this year you have to lift 9 and a half feet to get to the top middle peg. To make this scissor lift, you would most likely have to have 2 connected at the joints to eliminate sway. Then when the robot raises this 9 feet, you have an amazingly top-heavy and unwieldy robot.

Also, as our coach likes to point out, more joints=more places for failure.

Archimedes screw is fantastic if implented correctly our team used 1 in 2009 to raise the balls from lunacy from the base of our robot to the shooter. We used a 2.5" piece of PVC that had a garden hose nailed to it in a spiral to provide traction.

Re: Never Do This, and Other Good Ideas Gone Bad
 

On 397 the running joke for NEVER DO THIS was giving the Schreiber brothers access to gas shocks. I would like it noted that no one was ever seriously hurt despite dealing with 1000lbs of force...

NEVER make absolutes in an engineering discussion.

(ignoring the first one)

Never rely on gut feeling, check the numbers or don't build it.

Never trust an engineer to do the numbers right the first time, have a couple people look at the numbers.

"If you need slip rings in FRC you are probably over complicating it" - said by 397's old lead mentor. Totally true for our team.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Never build a permanently top-heavy robot. In '08 we ended up having to drive backwards because the lifter/ball-hitter was too far back, and we'd flip if we drove forward.

Re: Never Do This, and Other Good Ideas Gone Bad
 

2003... Never use #25 chain for your drivetrain. It may seem like you will never hit that several hundred lb limit, but when you throw in missalignment and shock loading, well lets just say we went through a lot of chain that year.

2004 - Never use 4wd in the 4 corners with high friction wheels... as somone else mentioned it is very bouncy when you try to turn - you DO drive straight very well though! We ended up wraping zip ties arround one set of tires which sort of helped..

2005 - Ropes don't belong on robots. We had at least 4 ropes on our robot holding things in place, although we managed to get it down to just the winch by competition, which worked pretty good.

2006 - Trust your numbers calculations (after you have checked them 5 times).. We made a ball shooter, calculated the theoretical speeds using 6" wheels, which fit well within our limits. Somone decided it would be better with 8" wheels - Our shooter ended up shooting too fast and we couldn't use it at the competition.. Another lesson is to make your design adjustable - There was literaly no way to take apart the shooter without taking apart half the robot.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Here is a list of 2791's don'ts with some explanations beneath it.

1. No Set screws
2. No Jags
3. Don't put non graded bolts in drive train.
4. Always account for force of pre-charged pistons
5. Don't put taps where they aren't 200% unavoidable

1. Set screws. We learned the hard way at FLR in '09, tightening the set screws before and after each match. Needless to say, by the time we hit Friday in Atlanta, every last set screw had been replaced with a cotter pin.

2. Jaguars. In '09 we blew at least 4 Jaguars, maybe even more if you count off-season work. Until we are convinced Jags are as tough as Vics, we won't put another one on our bot.

3. Never put any non graded bolts in a drive train. Every last bolt head sheared in '10 and took 3 hours to replace Saturday morning.

4. Never put a piston on your robot until you are sure it can handle the load. Last year every time our piston pre-charged, it bent our entire chassis. 15 lbs. of 8020 later, it still bent our entire chassis.

5. Taps. '10 was our first and maybe only experience with 8020, and we overkilled on the taps. It took forever to fix anything on our chassis, and by the end of the season, the screws had been put in and taken back out so many times the taps were loose.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Nope - the cylinder falls over with your robot.

Re: Never Do This, and Other Good Ideas Gone Bad
 

During Overdrive, our team decided on using a pivoting arm with one or two 80lb constant force springs, along with an underpowered gearbox, Chinese cast iron gears and "pwm cables" aka painted string, and a broken anti-back drive mechanism. It worked about once, and then the gears sheared off half their teeth, the anti-back drive pins fell out, and a cim burnt out in the manor of seconds. We switched out all of the motors with pneumatics between two competitions, and some of our problems went away. Later that year it knocked me out twice from a blows to the head, one time during a presentation to a middle school, as well as being just terrifying to be around in general. All of those problems pretty much stemmed from a few simple issues: a lack of prototyping, a love of cheap parts, and miscalculations in math. If we spent another week prototyping and a few hundred more dollars, and double-triple-well-beyond-the-point-of-redundancy checked our math, we could have done great that year. So, pretty much anytime you think something will work, despite how sure you are of it, try it and make sure it works.
Also, large amounts of force absolutely suck to work with, try to avoid designs that use them, as they tend to fail in some way after a sometimes very short while.

Re: Never Do This, and Other Good Ideas Gone Bad
 

I'm curious about the gear specs and the load you put on those gears; would you mind explaining further? (Besides, I also want to know the supplier of the gears, so that I can consider avoiding them!)


188 broke about 13 strands of ANSI #25 in 3 events that year. Of course, we didn't exactly have the best setup—small drive sprockets on very powerful transmissions,* rigid and convoluted chain guides instead of idlers, and a bit of misalignment.

On the other hand, on a different drivetrain, ANSI #25 chain can be a perfectly reasonable choice—this year, for example, with all the high-speed driving, teams can probably expect substantially less chain load, especially if they've got room for big sprockets on their big wheels.

*Actually, as far as I know, they were the most powerful transmissions on any FIRST robot to that point; each transmission had a CIM, a Bosch drill motor and a Fisher-Price motor.

Re: Never Do This, and Other Good Ideas Gone Bad
 

I don't have the exact gear specs, but I beleive the gears which broke were something attune to:
*80 and 16 tooth
*face width of a quarter inch
*14.5 or 20 degree presure angle
*pitch of either 16 or 20
*Made of cast iron, cheap cast iron.
There was maybe about 20 to 40 ft-lb of torque going through them, but its hard to say exactly because really nothing is left of that robot (cad, docs, notes, pictures) excpt for a stripped out frame and a single, half bald gear on our wall of shame. As for where we bought them, all I remember was that they came from some Chinese distributor and had BOSTON embosed in them. Unless you are constantly looking up cheap items and can read Mandarin, you probably won't come accross them.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Based on my years on Aces High (FRC176) and Division by Zero (FRC229) heres my list of things to avoid in season:

Never Agains:
1. Sissor Lifts
2. Tank Treads
3. Vaccuum Devices

Avoid at nearly all costs:
4. Cast Iron Worm Gears
5. Gravity Fed Hoppers
6. Gravity Dependent Lifts/Arms

And until done completely and perfected in an "offseason"
7. Crab Drive/4 Wheel Steering/Holonomic Drive

Re: Never Do This, and Other Good Ideas Gone Bad
 

In previous years, this wasn't always the case.

Re: Never Do This, and Other Good Ideas Gone Bad
 

As many have noted "Never" is a really strong word. Most posters got the intentions of this thread which were to talk about some ideas that should ahve worked, but had major issues in implementation.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Although the games lately haven't brought out shopping cart wheels on the front of a robot, don't use them. They are especially bad when the game has an uneven playing surface. The robot goes where the wheels tell it to go so you can't climb a ramp with shopping cart wheels.
Don't ever believe someone who says "of course that's legal, we have been using them for years." That is why at least one team will be down hearted when I have them remove their Globe motors this year.

Re: Never Do This, and Other Good Ideas Gone Bad
 

No Jags... without using the CAN interface to limit the rate of voltage change allowed.

http://www.chiefdelphi.com/forums/sh...k#post9 47848


Team 241 had 3 Jaguars short out in 2010 and one in 2009:
All resulted in the circuit breaker on the associated Jaguar breaker trip continuously that made the rest of the robot uncontrollable- (caused variable lag time of one to three seconds on all other functions on the robot).
We guessed that the failure mode was caused by voltage spikes caused by attempts at wide voltage swings too quickly.

One failure occurred at BAE unveiling event ; (less than 5 minutes total use prior to failure)
One at the Granite State Regional ; (less than 10 total minutes use)
One at the Connecticut Regional ; (less than 40 minutes total use)

The first two were on our drivetrain (CIMs).

The last on was on our ball magnet roller (Fisher-Price).

At Manchester, we added a CAN control to limit the rate of voltage change so that the Jaguar would not be swung from +12V to -12V too quickly (and vice versa).
Since we make that change, no more the Jaguars blew on the drive train- Because we had 2 blow out of 40 minutes total use (10 minutes times 4 CIMs) and we have not had any more blow after 240 minutes total use- we think the workaround helped.

But due to an oversight, our CAN workaround to baby the Jaguars did not get put on the Jaguar driving the fisher-price until after we blew another Jaguar.
After we put the CAN workaround on the roller, we have not had another Jaguar blow. (16 minutes use without a failure).

---update---

In over 8 hours of off-season use, not a single Jaguar has blown since we put in the CAN workaround.

Re: Never Do This, and Other Good Ideas Gone Bad
 

In 2005 we used casters on the front of our robot. When we would go to the loading stations if they got on the raised part of the loading station we would get stuck.

I have seen many instances of caster problems on robot so "no casters is a fixed rule for us.

#1 No casters
#2 No scissor lifts.
#3 No elevators (I have seen many instances of very effective elevators but not from us)
#4 If balls are the game piece they must always be under the influence of at least one moving part.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Lots of good ones out here already, but my personal favorite:

NO SET SCREWS

I will never ever trust a set screw alone to retain something to a shaft on a FIRST robot.

-Brando

Re: Never Do This, and Other Good Ideas Gone Bad
 

Retain, or transmit torque?

Relying on set screws to transmit torque on an FRC robot is almost always a bad idea (except for things like potentiometers), but we've used them dozens of times to hold something in place (laterally along shaft) without any problems. That being said, I prefer to design around them, and either use Delrin spacers, stepped shafts, tapped shaft ends, E-clips, or roll-pins to avoid them. If we need to use them, we almost always drill for two set screw holes 90 degrees apart, use Loctite threadlocker, and only use the cone-tip set screws.

Re: Never Do This, and Other Good Ideas Gone Bad
 

What about trusting Set Screws on FRC Mini-Bots? The Mini-bot FTC kit was full of set screw based components.

Re: Never Do This, and Other Good Ideas Gone Bad
 

1.) Do not gear a drive train for >10 fps if it has less than 3 CIMs' worth of power. It does ok in a straight line, but even with a 6WD drop center it had some difficulty turning 145lbs.
2.) Do not use 80/20 for a triple-compound elevator that has 20lb worth of manipulator and game piece on the top stage. The stresses on the bottom stage will increase the friction in the 80/20 linear slides too much.
3.) Do not make a 'naturally articulating' drive train. The drive train needs to be rigid or controlled in all aspects at all times. Our 'naturally articulated' drive train pods worked 'fine' in 2010, yet they didn't quite perform as expected. By the time we were testing it, we didn't have time to change to a new design.
4.) Do not design a multi-configuration 'automode' that is configured via the little switches on a Classmate PC. The little buttons are just too durn small.
5.) Elevators that have multiple pre-programmed positions + override/tuning are great in theory, yet are very difficult to master from a controls perspective. We're going to do a multi-position elevator for the driver again, yet with a very nice twist to add some autonomy.

Re: Never Do This, and Other Good Ideas Gone Bad
 

They will require some tightening eventually. On the kids' 9:1 double shooter last year in FTC, we had to tighten the set screws about once every 3 matches.

Re: Never Do This, and Other Good Ideas Gone Bad
 

If I have no other choice I will give in to using a set screw for retaining only. I much rather use spacers, e-clips, pins, you name it before I'd choose a set screw though. Obviously transmitting torque is a massive no-no.

-Brando

Re: Never Do This, and Other Good Ideas Gone Bad
 

I really dislike the way the FTC kit handles transmitting power through the shafts with setscrews, amongst many other things in the kit. However, given the minibot rules and such, I'm sure many teams are going to be pigeon-holed into using the set screw solution. I'm sure it will work well for most teams, and some loctite here and there may help avoid any complications...still doesn't mean I have to like it.

-Brando

Re: Never Do This, and Other Good Ideas Gone Bad
 

1075's no-no's are:

NO SET SCREWS (too many things have slipped in the past)
NO POTENTIOMETERS (code runs away and busts them, alleviated by using a 10turn pot, or encoder.)
NO BEVEL/MITER GEARS (this stems from our rookie year where we used one cantilevered on the end of a 4" shaft, which shredded, and cost us the 2003 Canadian Regional because we couldn't play in the finals, because the gears were toast)

Re: Never Do This, and Other Good Ideas Gone Bad
 

From the Controls Team:

NO potentiometers - use multi-turn or continuous turn pots or encoders
NO limit switches engaging fast moving arms or other robot parts - use magnetic reed switches instead

Re: Never Do This, and Other Good Ideas Gone Bad
 

Using set screws for retainment is IMO just as bad, when you could be using snap rings.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Do not use window motors for lever arms.

339 tried this both in 2007 and 2008 with the same results: we ended up switching from a motor to a pneumatic cylinder on the day before ship.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Never rely on pneumatics alone as a fast, pushing force. Our team learned this lesson the hard way in '09.
Never forget to leave room for electronics and then try creating space the night before ship.

Also, our team has never had much success with belt systems.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Another stopgap measure (if you can't take advantage of any alternatives, and need to use the setscrews) is to carefully centerpunch and drill a small indentation in the shaft, for the setscrew to sit in. (Alternatively, you can file a flat on the shaft.) When combined with some purple or blue Loctite (on the screw threads only; not on the shaft!), this will generally make an acceptable joint. It's still going to be limited, but it's just about the best you can do.

(Occasionally, wrapping something around the hub to keep the setscrew from falling out when it loosens can be marginally useful. It won't transmit power with a screw loose, but at least you won't have to hunt for the screw.)

Re: Never Do This, and Other Good Ideas Gone Bad
 

For what it's worth, the Tetrix-brand shafts have a flat along their entire length.

Re: Never Do This, and Other Good Ideas Gone Bad
 

I've got some bad news for you, cause this years kitbot is geared for something like 14-15 fps.

Anyways, I think all my never-agains have been covered by others, what with the elevators and scissor lifts and all. Oddly, I never swore off Banebots transmissions, despite being bitten by them in '07 like everyone else. (At GLR, we had the machine shop weld the output shaft to the carrier plate in our two RS-540 trannies. Worked great, actually.)

Our most grievous faults have usually been in strategizing and focusing too much on a marginal strategy and not enough on one or two core strengths that can adapt to multiple strategies. So if something goes wrong in design, build, or competition, we haven't left ourselves enough of a fallback position.

For example, last year we thought we'd be super clever with a ramp to get someone on the platform, plus a lift that could our robot and another robot on top of us. A scissor lift, to simplify drive for the other robots, natch. So when we discover halfway through build that this thing will be monstrously heavy, we scrap it for a different lift that sorta still works with our original concept... Which didn't work out well. We should've stopped and re-evaluated the whole game plan when that major system didn't pan out, but we panicked and forged ahead anyways.

So I guess my biggest never-again is the too-clever game strategy that only works if you do A, B, C, D and E in a match. Much better to have a robot that can adapt to different strategies through a match/regional.

Re: Never Do This, and Other Good Ideas Gone Bad
 

I really dont like the idea of saying "We will NEVER do that design again!". If the First design didn't work, in the off-season find a way to make it work cause you never know when that design will be the golden one for a season. I have seen too many teams go, we tried that one once and it failed so we didn't wanna try it again. It limits your design!!!

Re: Never Do This, and Other Good Ideas Gone Bad
 

home brew milti speed transmissions, dewalt or andymark only


anything with more than 150 ft lbs of torque

Re: Never Do This, and Other Good Ideas Gone Bad
 

Here's one: don't attempt to design, construct, and implement an independently-articulated, independently-driven swerve drive during build season without ever having investigated the surrounding concepts beforehand.

We did this in 2010. Very, very bad things happened. During our initial planning sessions, we decided that swerve drive would give us an awesome advantage in speed, maneuverability, accuracy of movement, and pushing power. And hey, AndyMark's selling swerve kits! Let's use those and save ourselves all the time and effort of designing an advanced drive train while still ending up with a fully functional robot!

Things went, shall we say, less than well. We hadn't considered the problem of turning the modules, and spent the first 4 weeks making a frame and steering system that would accommodate the modules. The Wild Swerve modules are excellent products, but they assume a certain level of competency in their implementation, which we simply lacked. Given our lack of experience and fabrication skills, it was a wonder that the system worked as well as it did.

Once our decidedly not precision-machined system was mostly functional, we moved on to figuring out how exactly to get each module to turn to a particular angle using PID (proportional integral derivative) control, which uses a feedback loop to approximate a value. We used indexing encoders, which would theoretically give accurate angle readings while letting each module figure out which way was forward. Unfortunately, our design had a habit of destroying or melting the encoder discs when the modules were not properly supported, hampering testing considerably.

We "finished" construction a few days before ship date, recognizing the need to drive and test the thing before competing with it, even if it was slightly less than functional. It worked exactly as a swerve drive should for about half the time. We had the pushing power of a 4WD system in any lateral direction, and could spin frighteningly quickly in place by angling the wheels inward. However, after a short period of operation, the PID program became confused and the encoders failed to index, leaving the wheels slightly out of alignment at best, but more often pointing in completely different directions, leaving us immobile.

Furthermore, the other game-critical systems suffered while we struggled with the drive train. Our ball handler, perhaps the most important device in all of Breakaway, was a prototype that had considerable trouble holding onto a ball while stationary. Our kicker was actually pretty good, serving us well after a robot redesign in the off-season, but it was useless if it couldn't contact the ball.

The swerve drive system remains in our shop, awaiting a revisit after this build season. With our more developed base of experience and better-equipped shop, we'll probably get the thing working finally. Until then, we're sticking to mecanum for our multi-directional driving needs.

On a side note, despite not working half the time, our robot looked quite cool that year. I suppose that partially makes up for our troubles!

Re: Never Do This, and Other Good Ideas Gone Bad
 

Many teams have done both without issue.

I think a more general rule would be; don't reach beyond your team's means.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Totally agree. I've done custom tranny's with no issues as well. It's definitely a don't reach beyond your capability issue.

-Brando

Re: Never Do This, and Other Good Ideas Gone Bad
 

Don't use a limit switch in place of a hard stop. T'was the end of our 2005 season, when we launched out tetra lift clear off the robot. :rolleyes:

Re: Never Do This, and Other Good Ideas Gone Bad
 

Don't run two FP motors through a Dewalt transmission with an extra stage of reduction and expect the output shaft to survive an encounter with said hard stop. :eek: Ever seen a case-hardened Thomson steel shaft snap like a twig? :ahh: Out 2005 experience with hard-stops and failing limit switches.

Re: Never Do This, and Other Good Ideas Gone Bad
 

I have a few things that teams should avoid. First of all, catapults. In 2008, I designed one for our team, but the execution of the design was poor and the end effector team couldn't find anything that would pick up the balls well. Also, avoid linkage arms. In 2010, I yet again designed a 12 bar linkage for our team and, even though it performed to specifications, the work that has to go into making the lengths right so that it can extend to 7 feet and still fold up flat, is monumental. You can do it with math, but the equations are way too complicated for anyone at the high school level.

Re: Never Do This, and Other Good Ideas Gone Bad
 

I think that you should only do ideas that you know that work, and only do other ideas if you have been dong FRc for many yours or you know what you are doing!!!!!!!!!!!!!!!:ahh: :ahh: :ahh: :ahh:

Re: Never Do This, and Other Good Ideas Gone Bad
 

our team decided to get more batteries last year. we had to make our own cable connectors to from the battery to the robot. DO NOT MIX UP BLACK AND RED!!!! you can fry your crio. it was a great idea but not so great at the same time

Re: Never Do This, and Other Good Ideas Gone Bad
 

our dont ever do agains from last season.
NEVER speend 2 weeks argueing over the design of the robot.
NEVER just give software 6 hours with the robot.
NEVER use belt drive.
NEVER repeat last years robot (we overloaded our jags every time we turned!).

Re: Never Do This, and Other Good Ideas Gone Bad
 

In 2008 we used a pogo- stick and pneumatically actuated arms. It had 6 wheels with two omnis in the front, and chains to drive them. Unfortunately, the arm couldn't grip the ball tight enough, the chains were too heavy, and the pogo stick needed more repairs than any part on any robot since then.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Never change your design with only two weeks until ship date.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Not sure about this one. There have been plenty of teams that changed their design late in the season or during the season and have done very well. The best example of this is probably World Champion 67 in 09. Just off the top of my head others include 469's gripper in 07, 2039 in 09, 33 in 09, 16 in 09. All of those teams either won regionals or made it to the eliminations at the championshop with their new design.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Don't change your design unless you really have to and can put in the man hours to make it work. The wrong thing well is better than the right thing badly.

Examples of "you really have to" would include the pincher rollers of 2010. Every competitive team last year at least considered that change, I guarantee it.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Doing swerve before prototyping in the summer 'nuff said

Re: Never Do This, and Other Good Ideas Gone Bad
 

last year, in Atlanta, 1350 threw a chain in every match, it was almost as funny as it was disappointing (think of a car in a cartoon driving as parts fall out all over the road, but it just keeps driving [we could drive very straight with only 3 powered wheels on the ground]):( . Every time it was a #35 chain, The # 25 chain that drove our slick wheels worked perfectly, (unless the #35 chain driving the #25 chain fell off, which didn't happen as often as the chain to the plaction wheels broke).

So, in summery, #25 chain can work well in a drive train.
----------------------------------------------------------------------------------------------------------------------

Never use too many* long* chain runs in critical** systems.







*these are not terms that I can define absolutely, use your best judgement.

**if you need it to play (well) and it isn't redundant to the point that if one breaks another/the rest can do the job almost as well without it [If its failure means you cannot continue to play the game] than it is a critical system.

Re: Never Do This, and Other Good Ideas Gone Bad
 

2007: always use active accumulation devices (rollers)

Our first arm in 2007 used a claw to grab the tubes. It didn't grip very tight and required much more attention from the drivers.

2008: make sure you can replace any part of the robot in the length of a timeout

We lost Wisconsin that year due to a motor burning out and not having a spare assembly ready to replace it.

2010: always use capture rings on CIM shafts. This way, even if the set screw holding your key in comes out, the key can't come out

At Kansas we lost in the eliminations due to overheated CIM's. They overheated because a key came out of one, causing the other CIM on the same side to overheat.

2010: do not put a bearing on a hard anodized shaft.

At Midwest we lost due to our chain falling off. Don't cantilever a swerve module off of a hard anodized aluminum/needle bearing combo.

(This doesn't mean we will never try these types of systems again. These are just examples of poor implementation.)

Re: Never Do This, and Other Good Ideas Gone Bad
 

For what it's worth: anodizing makes the surface very hard. Anodized aluminum is much more susceptible to fatigue cracking, further shortening the life of a metal that already has a short fatigue life. IMHO anodizing, hard anodizing especially, should not be used unless wear is of concern.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Pneumatics can be useful, but don't make your whole robot run on it.

In 2010 we relied wayyy too much on pneumatics. Our kicker, hanger, and "special" drivetrain (see the link in my sig) all used pneumatics. We always were worrying about running low on air, even with the onboard compressor and 4 accumulator tanks.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Did you ever actually run low on air? Probably not.

We built some stuff this off-season that relied on pneumatics, and fully automated it (in C on an IFI processor). The automation was very rudimentary and would actuate a lot (if it was on the threshold it would switch very fast). We used a mini-pump (a tiny red air pump, similar to the one this year but with less output) and 1 tank, and set the tank pressure switch to about 100psi (the pump struggled to go past that). It ran fine, and we ran it hard. So hard that the pump eventually overheated and seized, and only then did we run out of air. When we put in the old pump, it ran fine indefinitely (well, until the battery died).

Re: Never Do This, and Other Good Ideas Gone Bad
 

397's original bot in 2008 relied on pneumatics to hurdle the ball, the way the old system was set up we had to run a lap while the tanks refilled. We fixed that during the off season by changing the geometry of the launcher. So, yes, I've run short on air numerous times.

Re: Never Do This, and Other Good Ideas Gone Bad
 

On the subject of Pneumatics:

One cycle of a 2" Bore, 24" throw piston at 60 psi uses the entire legal air storage capacity of a 2005-2010 FRC robot.... We tried to use one for hanging last year, without realizing that we wouldn't be able to use our kicker for approximately 15-20 seconds before firing the hanging piston or else we wouldn't have enough air at the end of the match to hang.

(A cycle being, piston extended and then retracted.)

Re: Never Do This, and Other Good Ideas Gone Bad
 

We were in the same boat at thefro526.

We had probably one of the cooler-looking but worst-functioning robots at the NYC regional. It was mainly due to improper testing, as we would need the air tanks to be full to lift. That meant no kicking near the end of the game or we wouldn't raise fast enough.

Here's a photo of our lifter.


And when it's collapsed:

Re: Never Do This, and Other Good Ideas Gone Bad
 

My 3 years in FIRST have taught me many ways of how not to build a robot.

'09: Instead of belts, we used some sort of fabric for ball collection, ending up with a burned up (globe?) motor.
Lesson 1: make sure you have enough torque
Lesson 2: Do research online of what other teams are building so that your team doesn't have to invent everything themselves.

'09: hopper + small opening + turret = I don't know how many times we were even able to shoot because it was always jammed.

'10: I'm not sure how to say this other than don't use your frame as the stopping point for a extremely strong bungee powered kicker. Especially if you cant replace bent pieces because the frame is welded. (Also, this kicker sent a mentor to the ER after cutting his hand between the "foot" and the frame. Avoid dangerous pinch points if possible)

'10: if you have a piston that resets another mechanism (in our case, the piston pushed the kicker into a gate latch than retracted), keep the piston connected to what ever it is actuating. We made a catch for the end of the piston, but this often turned sideways and hence didn't work.

'11: If you build a swerve drive, make sure you test it in game-like condition. We prototyped in the fall (never truly testing it), and due
to slow turn around time from our manufacturer, the programmers didn't get a lot of time with it. Luckily, the programming and mechanical aspects worked for the most part. Unfortunately, the one optical encoder that told the wheels which direction they were pointing was not high enough quality and returned random values. Result: our drivers never knew which way the robot would move. While we were able to fix this with a better sensor in our second regional, this problem ruined an entire regional for us.

Re: Never Do This, and Other Good Ideas Gone Bad
 

With the season wrapped up, this should be a very hot topic for a lot of teams!

As fun as it was to design and build, I would take our arm design for this year off of my list of "Things we should do again". I'm glad we were able to pull it off, but there were a lot of headaches involved.

Fortunately, I think our list of things we did right this year greatly outweighs our list of things we did wrong. Usually it seems the other way around.

Re: Never Do This, and Other Good Ideas Gone Bad
 

On 1178 (D.u.R.T.), we have successes in some areas, and some pure luck in others.

In 2008, we implemented a scissor lift that lifted the ball up to deposit on the rail. Once the drivers got used to it (the whole robot was named Manny), it worked marvelously, although it used pneumatics (several of them) to force the lift up. We still drive the robot around, as it is one of the most visually impressive robots we have.

In 2010, we learned that a powerful pneumatic kicker can and will kick itself to pieces if shoddily crafted. We also learned that bending the frame and wheel brackets made the drive train unusable in some matches.
In 2007, we used the Banebots planetary gearboxes, and they are still working (though we would not use them again if we are able to use AndyMark's or Dewalts)

2011- We decided that we would use meccanums and a continuous lift, both of which we had never prototyped before. Due to the awesomeness of AndyMark components (our whole drivetrain was AndyMark components), the direct drive meccanums worked marvelously. Also, we paid a lot attention to making the lift right and getting it working (the biggest issue was belt tension, and using a window motor direct driven to the belt).
We have also decided that until TI improves the Jags, we are not using them as they present too big of a safety hazard (we have had multiple fail this year while driving, and one caught on fire).

Sorry about the disorganization of this post, it was pretty much all train-of-thought as I procrastinate from homework.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Suction cups are a bad idea. 1569 attempted it in '07 and almost never was able to adequately pick up and place the tubes, forcing the robot to rely simply on the ramps. Awesome as they were, they weren't enough to get picked in the eliminations due to the lack of scoring capability.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Former team #65 in 2007- Using a plastic sprocket to drive the elbow joint of an arm. At the finals in their division, I believe an opposing robot rammed into the arm, putting a lot of force on the joint. You could probably guess what happened next.

Oh, and only one plastic sprocket was made for the robot.

I didn't even know that plastic sprockets existed for anything outside of toys and Vex Robots.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Epoxy works great when you use it on it's intended materials that have been properly prepared. It doesn't work work quickly at all and expecting it to hold together for the next match in 20 minutes will never work. It is also a disaster when someone loses the caps to the epoxy and then just puts it into a plastic bag at the bottom of the tool bag.

Trying to speed hole extruded Aluminum will just result in bad things.

Based off this year's experience with mini bots, don't use Tetrix motors and expect them not to fry.

Make sure to pack your controls.

Not robot related but..don't let someone handle the bookkeeping if the have no accounting knowledge. Make sure someone goes over said books before the night that the sponsorship application is due.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Don't use rigid couplings or pin shafts. Love joy 3 piece couples are great as are offset couplings.

The benefit is 2 fold, it gives you some wiggle room in case things aren't perfectly lined up (like that would ever happen on a FRC robot) and it also makes changing parts much quicker in the event of a failure, you can build spares right up to the coupling.

my $.02

On my teams I will not allow scissor lifts, mecanums, multi stage elevator lifts, winches, large pneumatics or belt type conveyors (poly cord ftw!)

Re: Never Do This, and Other Good Ideas Gone Bad
 

Every year we seem to have to relearn the same lesson: Don't engineer things too closely.

If something works but *barely* works at home (meaning that it might be fantastic, but the tolerances are very tiny), the Unmutable Laws of The Universe dictate that it will NOT work at competition.

In other words: All values are nominal values, even if they aren't nominal values.

Re: Never Do This, and Other Good Ideas Gone Bad
 

team 1126 will most likely never use a cable winch again, after failing several times, including in 2010 when i personally worked on our double-barreled (kicker and elevations) monstrosity of a winch, i understand our failures. we found that cable just frays and gets tangled much too easily

this year we used a chain winch to power our elevator and it worked GREAT, sure, there is extra weight involved, but it's worth it to not have to deal with that cable! i don't think we'll ever go back to cable!

Re: Never Do This, and Other Good Ideas Gone Bad
 

Oh, right:

NO CABLE WINCHES.

Also, AVOID QUALIFYING MATCHES WITH 1126. It doesn't seem to matter how well either of our teams are doing in any given year, if we have a qualifying match where we are on the same alliance, it is always a disaster for both teams. This has been true at every FLR since 2005. No legitimate reason -- we always get on just fine in the pits, and love each other so... But when it come time to play a QM, disaster. Every time.

Re: Never Do This, and Other Good Ideas Gone Bad
 

1) Build the most important part last:

Did this on an offseason robot last fall. It had a bucket that lifted via parallel arms. By the time the frame and bucket were done, we had no room for the parallel arms unless we used flat. The bucket never fell back inside the frame when we let it down. We almost completely rebuilt our robot after this.

2) Use flat for parallel lifting arms:

It makes things go up and down fine. It also has the unfortunate side effect of things waving around to the sides.

3) Not read all of the manual:

We used both a DeWalt and a Globe on our robot this year. Luckily I was glancing through the manual one night (procrastinating homework) and noticed. We spent the next two weeks trying to mount the window motors.

4) Have someone build a part for a design they hate:

It either will be done wrong, or just not done at all.

5) Non-Polycord belts:

We have found that they don't work for us, from slipping to coming off the roller to being so ineffective it's useless.

6) More than one gate latch on an arm:

The amount of sway and overall inefficiency as well as a horrible lack of control prevent this from being a remotely good idea.

7) Human player fed ONLY

We did this for an offseason competition. We probably would've won if we didn't have to cross the field to reload, score, reload, score, etc.

8) Build something without a definitive strategy, or a good idea of how to make it work:

Here is a list of robots we've (recently) had to completely rebuild after the first competition fro this reason;
FIRST 09 (from Archimedian screw to polycord conveyor)
FIRST 10 (kicker and hanger both didn't work)
Offseason 10 (See #'s 1 & 2)

Re: Never Do This, and Other Good Ideas Gone Bad
 

Our 2010 robot drivetrain.

Just don't.

I might suggest you reevaluate this one. Have a look at this robot and this robot. Both robots human loaded. Both robots played on Einstein their respective years. You can get away with human loading if you do it right.

-Nick

Re: Never Do This, and Other Good Ideas Gone Bad
 

Never use KOP servos as a means of grabbing the game piece, no matter how light the game piece may seem. "We need something really light to power the tube gripper out on the end our long multi-jointed arm... I know, servos!" Our 2007 robot was hastily dismembered after the season, and the veterans try to shut it out of their minds.

Really, it seemed like a good idea at the time.

Re: Never Do This, and Other Good Ideas Gone Bad
 

I must say our old team, 2645, used set screws all the time with no problems, we used mechanum wheels, a scissor lift, and a cable winch. All on one robot with no problems except a broken logitech controller. One of those examples of engineering gone right. :D

Re: Never Do This, and Other Good Ideas Gone Bad
 

A lot of things mentioned in this thread aren't mechanically wrong, they're just not the best way to do things (for various reasons). A robot with mecanum wheels and a scissor lift has no reason it couldn't be mechanically reliable all season, it's just not likely to keep up with a more optimal design.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Something we learned the hard way at Bayou 2010: Don't put off numbers if they have to go on the bumpers...if you're having to use paint outside, the result will look like crap.

JVN's silver Sharpie tip was a revelation this year, though that still took us a couple of hours in our shop with a small group of people tracing and going back over the numbers a few times. (I think we put at least three or four coats on our robot's bumpers, which we did with a rather thick stroke--we bought six markers and had usable ones afterward.)

I wouldn't want to do anything resembling that level of effort in the pits ever again.

Re: Never Do This, and Other Good Ideas Gone Bad
 

To make the numbering process faster, couldn't you cut the markers open, extract the plastic-wrapped felt ink reservoir, and use it like a big, wet crayon? (Who cares that you can't write with the markers anymore? And if at a competition, there will be plenty of other teams with inadequate bumpers who could benefit from the leftover ink.)

Re: Never Do This, and Other Good Ideas Gone Bad
 

I haven't experimented with this--in our situation this year, we had some time, plenty of cheap labor students, and me leading the process in clothes for work that didn't need to be silver if I could help it. :)

Unless we were in a panic, I'd probably keep with how we did them this year (better photo: http://twitpic.com/40kj4i)--the only improvement would be a true stencil. (We traced old iron-on transfers that we used unsuccessfully in 2010--but we didn't have a 5, so we improvised it using other numbers we did have.)

Of course, if someone can show how it's done (and without creating a total mess), I'm all ears.

Re: Never Do This, and Other Good Ideas Gone Bad
 

This is more of a bad idea gone bad but it certainly applies to the side topic of team numbers on bumpers. In 2007, 1766 forgot to have our numbers on our bumpers and had to improvise at the competition. Going pit to pit we found a team that had some paint and got permission to borrow it. We cut a stencil out of paper and cardboard and went outside to spray it on. In the end I held the bumper with one hand while spraying with the other. My arm had orange on it for the rest of the competition. I would give credit to the team that gave us the paint but I can't remember the number. It was a tiger themed team at the buckeye regional in 2007 if anyone else recalls the number.

My point to all this is that there is always a worse way of doing things. I never once thought of a sharpie and immediately went looking for paint.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Bumper skirt.... Bad idea. They almost got us DQ'ed at FLR.

Next year we'll be making two sets of bumpers!

Re: Never Do This, and Other Good Ideas Gone Bad
 

Also, don't use the bumpers as pillows after you have used the Silver Sharpie Technique, the numbers will transfer to your face. Not that I have first hand experience after the all nighter Monday before shipping or anything, just sayin....

Re: Never Do This, and Other Good Ideas Gone Bad
 

Pics or it didn't happen....;)


-Brando

Re: Never Do This, and Other Good Ideas Gone Bad
 

Never try to wire a robot at 3am unless absolutely necessary - Jags don't like to be wired incorrectly.

Never use pneumatic tires on your drivetrain when you need to accurately place a game piece - This one used to be "never use pneumatic tires period" after our 2005 robot (it was like riding on big springs--bounced like crazy), but 1114 showed me last year there really was a use for them on a drivetrain--driving a 140-lb. robot quickly over 12-in. bumps and surviving.

Never use tank treads for high-speed drive applications--climbing and pushing only - Don't get me wrong, they worked great for our 2008 robot, but the continuous high speeds were causing the inner treads to get stress crack (despite steel reinforcement), and those things are expensive.

Never use a high-complex drivetrain (or any system, for that matter) when a much simpler method will do - Despite the coolness factor, our 2010 robot showed us that articulating drivetrains just weren't necessary.

Never forget the six degrees of freedom - Pieces tend to shear or break spectacularly when you do.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Pics or it didn't happen.

Re: Never Do This, and Other Good Ideas Gone Bad
 

If its rated for 25lbs, it probably doesn't have a safety factor of 4, and it probably can't handle 100 lbs.
The "Little Pulley that Could," couldn't.

Re: Never Do This, and Other Good Ideas Gone Bad
 

Sorry we dont have a lot of pictures but there are some cool videos on our old website http://rprobotics.com/ under the media tab in 2010 videos. You can see our mechanum, scissor lift, and see the winch pull us up. as for set screws im not really sure how else you would attach something to the toughboxes

Re: Never Do This, and Other Good Ideas Gone Bad
 

...with the provided machine key? ...in the provided keyway?

Re: Never Do This, and Other Good Ideas Gone Bad
 

And a setscrew to hold the sprocket in place.

Wait were you guys just saying no setscrews as in no transferring of torque with a set screw?

Re: Never Do This, and Other Good Ideas Gone Bad
 

We try to avoid both, but transferring torque is the worse of the two.

Re: Never Do This, and Other Good Ideas Gone Bad
 

One thing we will most likely never use again are casters. Our rookie year, not our best year, we used caster is much the same way they are used on menards carts, two in front two in back and two drive wheels in the middle. It was very unstable and hard on the toughboxes.