6 Wheel Drive vs. 8 Wheel Drive

[Mr. Van]

Our 'bot this year used our standard "poor-team's" version of West Coast Drive - 6 wheels center drop, live axles, cantilevered wheels. We used the kit wheels this year after finding that they had the best traction on the Bridge - much better than any of the conveyer belt material we tried.

The axles are evenly spaced at 10" - yes, our 'bot frame perimeter was only 27" front to back (and also side to side). This meant no hangups on the Barrier. Center of gravity was very much on one end which allowed for hanging off of the end of the Bridge. We took only 18" of bridge space including bumpers - something that was crucial for our 3-bot balances.

In most years, we would try to center the cog, but this year we wanted to hang off the Bridge.

- Mr. Van
Coach, Robodox

[JesseK]

With a wide orientation, we determined that there was no difference between 4, 6 & 8 wheels for robots that did not traverse the bump, so we went with 4 wheels. At competition we realized that there was an additional tradeoff we hadn't accounted for: we couldn't be either outside bot on a triple balance.

The purpose of our drive train was to be incredibly simple and sprint from bridge to key. It used a custom frame with 4 CIMs/CIMple boxes through moderate gearing for a top speed of ~9.5 ft/s. It weighed ~21lbs. It was designed by the end of day 1 and the design only had minor modifications as we further specified what the 2-sided intake would do. The drive train was built by the end of week 1. That simplicity allowed us to focus on a shooter for more time, thus getting us further than ever in a build season. We also made it further than ever at champs (SF's). Would we have benefited from additional wheels to be able to hang off or cross the bump? The magic 8-ball is still unclear on that one.

So one cannot put "6WD vs 8WD" up for debate without debating orientation and context. 4WD wide-drive is just as effective as either as long as one accepts the tradeoffs.

[Brandon Holley]

The NUTRONs went with an 8WD this year. 5" Colson Performa wheels, 1.5" width. The main reason for going 8WD was the same as 2168's, which is to traverse the barrier without any active mechanism.

One unique thing about the drive system was that the wheels along a drive side were NOT of equal spacing. Looking at our drive side with the front being labeled as wheel 1 and the back being labeled as wheel 4; wheel 1 and wheel 2 were quite close, wheel 3 and wheel 4 were not quite as close as wheel 1 and 2, and wheels 2 and 3 were the furthest apart.

We did this because it helped to offset one of the disadvantages of an 8WD in this game, which I believe is what John is referring to. We wanted to try and get a wheel as close to the center as we could so that we could hang as much of the robot off the back as possible. We still need 6 wheels on the bridge to hang, but those 6 wheels + front bumper only require 26" of ramp space.

The entire drive system had 0.5" of ground clearance, and all of the areas that came into contact with the barrier were either wheels or delrin slides. We developed a pretty cool cutout (relief) in our sideplates that made it impossible for us to become high centered on the barrier. This was because as the robot's weight transferred over the barrier, the robot rode on an arc instead of a flat. This guaranteed that the robot could never stop on top of the barrier. You can see those cutouts in this picture:



-Brando