[Ken Streeter]

Originally Posted by AcesPease

Not surprisingly, our prototyping showed more repeatability with horizontal wheels. ...

BTW 1519 was another consistent scorer with the horizontal wheels. Amazing accomplishment for a second year team.

Looking back, I'd like to be able to say that we chose the dual horizontal wheels after having done a "trade study" comparing the relative merits of vertical and horizontal wheels. We did do some prototyping with both wheel setups, but we found that both setups seemed to have about the same accuracy when the wheels were fed predictably.

Our reasons for going with the dual horizontal wheel setup weren't related to accuracy:

* We wanted the shooter to be as high on the robot as possible in order to ensure that shots would go over opposing robots. Since a dual horizontal wheel setup doesn't require any mechnisms "above the ball" the whole assembly can be nearer to the top of the robot.

* We felt that a turret that could adjust for both azimuth and elevation was essential. Desired azimuth rotation was about 180 degrees. Desired elevation adjustment was only about 25 degrees. (We pivoted the shooter assembly up/down like a tank's barrel instead of adjusting wheel speed for distance.) With the desired az/el ranges, the "swept volume" of a horizontal shooter was much less than that of a vertically mounted shooter. To illustrate this, picture the dual shooter assembly having the rough shape of a thick pizza box -- a horizontal mounting rotates the pizza box around the center of the pizza in the way one would normally think of spinning a pizza. However, the vertical mounting would spin the pizza box "end over end" which would have a greater swept volume. Wanting to reserve as much room in the robot for other things (ball hopper, feed mechanisms) tended towards the horizontal shooter approach.

* Feeding the shooter up from below seemed to be much easier with a horizontally mounted shooter than for a vertically mounted shooter, especially given that we wanted camera-controlled adjustments of azimuth and elevation. Many teams that used a vertically mounted shooter loaded the shooter from above or behind, rather than from below.

I don't think that the choice of vertical vs. horizontal shooter assemblies themselves was the driving factor in the success (or lack thereof) of various teams. I think both mechanisms tended to have about the same accuracy overall. Rather, I think "rate of fire" was a very important factor for the success of the top teams. Due to the different ways the two different assemblies are fed, I think the vertical assemblies generally had a better "rate of fire" than the horizontal assemblies. In Atlanta, team 1519's robot was definitely a contender, but not one of the powerhouse teams. For the postseason, however, the team doubled the firing rate of the robot while increasing the accuracy of the camera targeting system. The result was that team 1519 was either the #1 seed or the first pick of the #1 seed at the three subsequent post-season tournaments in which they participated. For the "driver control period," high accuracy coupled with a high rate of fire is a very strong combination.

The strong offensive robots on Einstein only needed to be in their scoring position for about 4 or 5 seconds to score 10+ balls -- it's very hard to beat a team that can score 30 points if you play poor defense against them for just 5 seconds!

If there is a correlation between vertical and horizontal shooters, I think it is more due to the rate of fire characteristic, rather than accuracy of shots due to backspin. Indeed, many of the top robots were not accurate distance shooters, but were instead dominant when they got close to the target and could unload 10 balls in just a few seconds.

Just my two cents...