Never Do This, and Other Good Ideas Gone Bad

[IKE]

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.

[Numbers]

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).

[Mike Schreiber]

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.

[demosthenes2k8]

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.

[thefro526]

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.

[Jared Russell]

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).

[Dkt01]

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.

[Jeff Waegelin]

Originally Posted by ICanCountTo19

It does have great potential though, it's made it to Einstein, it's all about implementation I guess.

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.

[Jonathan Norris]

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

[Jon Stratis]

Originally Posted by Jared341

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.

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.

[EricH]

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.

[Madison]

Originally Posted by EricH

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

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.

[EricH]

Originally Posted by Madison

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.

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.

[Ian Curtis]

Originally Posted by IKE

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.

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.

[Tom Line]

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.