The team recently took apart its Gateway robot & wanted to share for the benefit of next season’s rookies.
https://vexforum.com/gallery/files/1/6/6/5/2012-01-104.jpg
It intakes from the bottom (or pre-loads/match loads from the top). The 4-bar lifts 20 inches, with an additional 10-inches gained from the tank-tread.
Though it’s not the most efficient of designs, it had following features in its favor, which might be of interest to rookies:
- It was built by an all-rookie team who could only meet once/week for 2-3 hours/week (competing in events in December and January).
- It was easy to drive and required minimal practice time for the drivers to score at or near capacity.
- It ranked 14th of 40 teams, then 5th of 30 teams in local competitions. The team worked on it continuously through the first competition, and by the 2nd, it performed reliably, causing minimal frustration to the drive team.
- It made use of parts we had in our repository from the previous year, with less than $100 in new parts (replacing last year’s burned out motors and cut metal). Though we received a parts donation late in the season, the team decided to stick with its old design and save the new parts for next season.
Not-so elegant feature – the “monstrosity” wheels on the front, needed for counterbalance when the intake was fully loaded. It was a quick fix, but the team now knows to design for a better COG next season.
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Nice bot! Your intake and your wheel arrangement are pretty similar to ours. I saw a few robots like this at Worlds.
Do you have any videos of your team competing?
I have always had good luck using 2 batteries as the counter weight because when you have a power expander you can put one battery at the front right corner and the other at the front left.
We used the counterbalancing wheels during Clean-Sweep. We had a lot of people ask us why the wheels were not touching the ground. Did you experiment with using different sized wheels and plate metal, or use the first thing that worked?
@VEX Raptors: No videos of competition, but we did get some video of robot movement in the classroom, which one of the students has on a device somewhere. Will try to post when we return to school in the fall.
@tabor473: No power expander, either. Wish we had one.
@DiodeTech: We tried metal bars & metal gears, but there wasn’t enough weight, and the multiple pieces were hard to anchor. The wheels worked well, because they’re a lot of weight in a single object. Also, because the bulk of the weight is raised, the center of mass is farther from the pivot point (back wheels), increasing the torque. We also “snuck” an axle-full of metal gears over the wheels. Finally, we added an up-side down L channel to the back, which limits the tipping. The counterweight was still beneficial, because it’s not good to have the back bar scraping the ground too much.
Fundamentally, using single-holed L-bars makes for a rather flimsy chassis, which is prone to bend and more susceptible to tipping. We finally raised the funds to invest in some 5-holed C-channel, which has become the pretty standard in chasses these days (at least when you’re not trying to high hang).
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I am suprised that no one last year made a robot like this, except with the belts on the other two sides and no front plate.
People did. Including one in Nebraska.
I agree. I believe of the the 1200 teams had a design very similar. Their team name was “Pi To The Face”. They did great at US Nationals.
There was also one in Michigan. It didn’t do very well… much like 438’s bot, it had some COG issues.
Blue Isolation in this match: http://www.youtube.com/watch?v=LKY7a14VTg4
Simpler designs often don’t make their way to this forum for a number of reasons:
- Low-to-mid level teams are less likely to go on the forum than higher-level ones.
- Those with simpler designs are often intimidated by teams with more sophisticated designs. They figure, “Everyone here is way past me, so I have nothing to contribute.”
- There’s less incentive to show off a simple design for scouting reasons. Teams think, “I’m not going to impress anyone enough to pick me at worlds, so why post?”
But I think there’s educational value in seeing a variety of designs at different levels. Like a '57 Chevy, a simple robot has its parts exposed so you can see what you’re looking at and how it works. (In contrast, I still haven’t figured out how the rubber-linked standoffs on 44’s fold-out omnis work).
While imitating a more complex robot might produce a higher score in the end, starting simple allows beginning builders to reach functionality at an earlier stage, which is important if you have limited time. The difference between a highly functional robot and a poorly or non-functioning one often comes down to little details like minimizing friction, balancing weight and motors, not to mention programming subtleties.
After the first competition in December, we knew we had only 1 month until the next event in January, and the team made the unanimous decision to tweak the robot we had, rather than to start from scratch with a 6-bar lift. Since January is the end of our season (Science Olympiad in March takes precedence Jan - Mar), it was a decision that served their purposes well.
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