Never Do This, and Other Good Ideas Gone Bad

[Kevin Sevcik]

Originally Posted by JesseK

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.

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.

[DarkFlame145]

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!!!

[Hawiian Cadder]

home brew milti speed transmissions, dewalt or andymark only


anything with more than 150 ft lbs of torque

[Joe Schornak]

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!

[AdamHeard]

Originally Posted by Hawiian Cadder

home brew milti speed transmissions, dewalt or andymark only


anything with more than 150 ft lbs of torque

Many teams have done both without issue.

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

[Brandon Holley]

Originally Posted by AdamHeard

Many teams have done both without issue.

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

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

[EricS-Team180]

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.

[JamesCH95]

Originally Posted by EricS-Team180

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.

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. Ever seen a case-hardened Thomson steel shaft snap like a twig? Out 2005 experience with hard-stops and failing limit switches.

[Neil2012]

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.

[Aussie Oi!]

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!!!!!!!!!!!!!!!

[tomy]

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

[klmx30302]

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!).

[Newo95]

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.

[Grim Tuesday]

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

[XaulZan11]

Originally Posted by Grim Tuesday

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

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.