To Shift or Not To Shift, That is the Question

[wilmo]

we had a 2 wheel drive with the AM Gen-2 Servos. We tried shifting once, and we almost fell over from the sudden burst of speed, wasn't worth the weight for the 07 game, rather have more tanks for air

[DonRotolo]

Originally Posted by AdamC

that finds a balance between power and speed.

You mean a compromise, not a balance, because that's what it is. A shifter eliminates much of the compromise...but that might not be important to your strategy.

[Daniel_LaFleur]

The answer to this question has to do with your strategy and the design of the game.

Last year Our strategy was to defend the opposite side of the rack and to come back to open our ramp / platform at the end of the match.

We were not too concerned with speed because all the scoring was in the middle of the field. That meant that the scorers had to come to us.

Our solution was tank steering, 4 wheel drive, 1 small CIM per wheel, Banebots single speed transmission with 16:1 conversion, and soft 7" pneumatic tires (CoF ~1.3). This gave us a speed of ~ 6 fps and ~ 175 lbs pushing force ((120 lb robot + bumpers + battery) *CoF). We adjusted the pressure in our tires so that the tires would just break free at stall current.

In all of our compitition matches (25) we only met one robot that we could not push (checkmate, team 40).

I'll say it again, don't put in a multi-speed transmission just to have a multi-speed transmission. Design in what you need to be successful in the game using the strategy you chose.

[Ian Curtis]

Originally Posted by Daniel_LaFleur

The answer to this question has to do with your strategy and the design of the game.

Last year Our strategy was to defend the opposite side of the rack and to come back to open our ramp / platform at the end of the match.

We were not too concerned with speed because all the scoring was in the middle of the field. That meant that the scorers had to come to us.

Our solution was tank steering, 4 wheel drive, 1 small CIM per wheel, Banebots single speed transmission with 16:1 conversion, and soft 7" pneumatic tires (CoF ~1.3). This gave us a speed of ~ 6 fps and ~ 175 lbs pushing force ((120 lb robot + bumpers + battery) *CoF). We adjusted the pressure in our tires so that the tires would just break free at stall current.

In all of our compitition matches (25) we only met one robot that we could not push (checkmate, team 40).

I'll say it again, don't put in a multi-speed transmission just to have a multi-speed transmission. Design in what you need to be successful in the game using the strategy you chose.

Trinity learned their lesson about being pushed around in 2006. You can have the best darned scoring mechanism on the field, but if you can't stay in scoring position, then it doesn't matter.

Also, the shifting debate really does come down to *gasp* robot strategy. In my experience, the better you are at scoring, the faster you need to go, for two reasons. If you could be scoring, why waste time plodding around the field? Second, if you're good, and people know it, you will be a target, and its much easier to rush out of their way than to have to fight through them. Because even if they don't manage to stop you, if you spend time fighting through them, you're wasting time you could be using to score.

Take Buzz (175) at BAE for an example. During the final practice matches on Thursday, they were putting up over five tubes with ease. Obviously, this got noticed, and during the course of 8ish seeding matches they managed to only score 15 tubes. They had an excellent drive team as well, but they were just pounded non stop, and couldn't score well through all the defense. Of course, when alliance time came around, their AC made sure that defense wasn't a problem, and they essentially walked through the elimination tournament.

On the other end of the spectrum, don't make a useless gear for the game. Last year in our top gear (we had 3 speeds) we could cross the field in about three seconds. Since the rack was in the middle of the field however, it wasn't really useful, and just resulted in a banged up grabber.

Most games require precision however. Let's review the last 4 games, shall we?

2004: Line up with 13" playground balls. Line up with 3'(ish) wide chute to deposit them.

2005: With a 5 lb object swinging wildly through the air, line up about a 2' square area over a tetrahedron.

2006: Line up with a 4' hole in wall

2007: Line up a circle with a foot radius over the end of pole.

Games require precision and speed. They typically lie at either ends of a spectrum. Shifters are one way to get there. There are other ways to get relative precision in code however, which is less of an investment in time and money than buying/making two speeds, and requires a smaller time investment than shifters.

[Billfred]

I have to echo the ideas above: it's all in your strategy. We wanted to be a fast arm robot, but I've had a hand in far too many flying bricks over the years for the robot to be unable to push. AndyMark Shifters allowed us to hit that sweet spot (ours, as I recall, were set for about 12 and 5.5 fps through sprocket and wheel choice).

What we do for next season will depend on a lot of things, at least on my end:

1) The game next year. Obviously, a robot that's going rock-crawling will not be using Uppercut's drivetrain.
2) Durability of the 2008 KOP gearboxes. If we can do the job with the kit gearboxes, I'll be more than happy to put them on. But if we had another year with gearboxes showing problems, I'd start investigating alternatives fast.
3) Resources available to us. If we need the $500 difference between AM Shifters and AM Gearboxes for other parts of the robot, decisions have to be made, particularly if item #2 is in question. (Ideally, of course, this would not factor into the equation.)
4) Familiarity. Given the choice, I'd much prefer to use a system someone else has had all the frustration fun of debugging already. ("Someone else" can be us.)