Quote:
Originally Posted by JesseK
So generally speaking, teams who have 4 VEX motors on their drive train and a 25-lb VEX robot will typically not move as fast as an FTC robot that weighs 25lbs with 2 motors on the drive train.
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Your conclusion as stated is unassailable.
Three of the robots we sent to VEX Worlds weighed a COMBINED total of 25 pounds. Tetrix robots tend to be very heavy. I expect that it is because the wheels, motors, gears, and batteries are heavy, and, despite using aluminum, the basic Tetrix aluminum is thick, large in cross section and weighty. We actually ripped some of the c-channel into thinner pieces to reduce bulk. It's strong, but since it only comes in one real cross-sectional size, you have to use the giant c-channel even where you don't really need it. Not all tools are hammers, and not all problems are nails.
As long as FIRST recommends not gearing up the Tetrix motors (see last year's Q&A) FTC robots won't have a big speed advantage. We tried gearing up the motors last year and broke gearheads. Shortly thereafter FIRST told teams to use direct-drive or gear down, so I'm guessing we weren't the only ones with the problem. A direct-drive FTC robot with 4" wheels has about a 2.6 fps potential. Certainly no faster than the average VRC robot, but it will have substantially more "pushing power" with the bigger motors (as long as they don't stall and burn out).
Some of the big steel VEX robots can be pretty darned heavy, too. Most of these are geared for about 2 fps. Five of our six VRC robots last year were geared variously at 3.6 to 4 fps. This video is a pretty good example of what lightweight robot design can do:
http://www.youtube.com/watch?v=aIsQckNv9zM. I don't think you could build that 8-pound robot with Tetrix parts.
Someone elsewhere in this thread mentioned that they didn't like people bashing Tetrix who hadn't tried it. That is a fair point. We had three FTC and six VRC teams last year, so I suspect that there aren't a lot of programs around that have wider experience in the two platforms than we do. Given our program's goal of delivering a high-quality competition robotics program to the greatest number of students for the least money, we have chosen to focus on VRC and not FTC. Especially when you start adding up the annual fee (275+149) times our 7-10 teams, the bang for our FTC buck starts to fizzle. For eight returning teams, which takes the kit cost out of the equation, FTC would cost us $3,392. VRC registration for eight teams is $250. We could fund an additional 2.3 (or so) VRC teams for that $3k, and reach 15 more students.
I do like the sensor suite in FTC, and the FIRST volunteers here in Washington are an outstanding bunch of folks. We will still have at least one FTC team as long as we have students that prefer it. I think we should all continue to share our experiences on Delphi, and remember that engineering and science isn't about cheerleading, it's about evaluating problems and designing or choosing the best solution. As lead mentor for our program, my problem was "STEM+fun bang for the buck" not "how many weights can I hang on a beam" and so we decided to focus future team growth on VRC. YMMV.