Never Do This, and Other Good Ideas Gone Bad

[Chris is me]

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.

[MattC9]

Doing swerve before prototyping in the summer 'nuff said

[PAR_WIG1350]

Originally Posted by cire

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.

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.
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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.

[Dillon Carey]

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.)

[JamesCH95]

Originally Posted by Dillon Carey

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.)

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.

[TD912]

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.

[apalrd]

Originally Posted by TD912

We always were worrying about running low on air, even with the onboard compressor and 4 accumulator tanks.

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).

[Andrew Schreiber]

Originally Posted by apalrd

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

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.

[thefro526]

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.)

[TD912]

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:

[Alex.q]

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.

[s_forbes]

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.

[sithmonkey13]

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.

[legogeek24]

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.

[The Cyborg]

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.