FRC 95 The Grasshoppers 2024 Build Thread

The other issue with a weight limit is that it will incentivize teams to build even weaker frames in their quest to save weight and go even faster. So you’ll end up with robots carrying the same or nearly the same amount of energy, and being even more susceptible to damage when they come to a sudden halt.

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That’s a fundamental design trade off though, right? Teams need to learn that they can’t make everything out of pocketed 1/16" tubing and expect the robot to not break.

Edit: Before I get roasted, the teams that are trying to shave weight to go faster aren’t the bottom 50%-tile teams. It’s the upper 50%-tile and we need to be holding these teams to higher design standards.

From a competition design level though, I think James has it right. If you want to prevent field damage, and you want to minimize the number of teams that suffer robot damage, a speed limit is the most effective lever to pull. Weight and other levers just invite “workarounds” that will prolong the problem.

I agree that lowering the weight isn’t the right lever to be pulling.

But I also argue that that the speed “issue” is mostly self-inflicted as well. The vast majority of robot damage I’ve seen this year was due to improperly designed under-the-bumper intakes by top-50-percentile teams. The bumper rules state that they have to be “backed by the frame perimeter every 8 inches” because bumpers are not designed to be structural, but primarily to distribute loads across structural members of the frame. Yes, a 1x2" tube spanning >25" of robot width in the vertical direction and only supported at the ends is the frame perimeter by definition, but structurally it’s really as if the bumper is backed by a gap way larger than 8 inches and is effectively insufficiently supported.

Field damage can be engineered around. These robots are already right at the limit of the battery – things can’t meaningfully escalate any more from here.

Will it, or will it encourage other design tradeoffs such as using less motors or not building as complicated? At least from what I’ve generally seen in the past few years, teams have been building underweight a lot more often than they were pre-brushless and the robots that tend to reach the weight limit are the most complicated robots. Because none of the levers are mutually exclusive, I would not be surprised if some weight got moved over to the bumpers possibly in combination with a 5 or 10lb overall weight drop to tune down the impact damage without imposing extreme speed limits.

No, I’ve only had the time to post bits and pieces of theory scattered around CD. Let’s see if it makes a good manifesto here. The broad strokes are not that weight is a higher risk factor than speed, but that a reasonable reduction in weight should be good enough to lower the risks and is far easier to implement for next season than a speed limit or bumper redesign*.

(*Field design notwithstanding; I think that controlling speed through field elements or adding soft bumpers to the alliance walls would be highly effective solutions)

The nice thing, to me, is that you don’t have to lower the weight limit a lot to significantly move the average weight, because a disproportionate number of teams build up to the weight limit, even though the actual components have trended toward lighter weights. We already have the tools and processes to control robot weights at events so there’s nothing new to implement. Personally, I decided, even before this year, that this is a good tweak to the FRC design challenge and makes robots a little safer for students, in general. Granted, as a result, I’m solution-fitting it to this issue a little bit. I think teams are smart enough to adapt to the new constraint.

I do think that the influence of weight on collision outcomes is more than the square root of the influence of speed, which helps the case. The force you can apply from the wheels decreases with weight, so you increase the likelihood that your grip fails before something more valuable does. Reducing your weight relative to the field walls should also reduce how much momentum you impart into it or things on it. Yes, reduced weight allows for higher speeds in some cases but in general, robots are nearing other limits on speed, like motor or battery performance or traction. Looking at drivetrain calculators and the runways on a “typical” field, it doesn’t seem like top speed significantly increases as weight decreases. So, it should still give you a net energy decrease.

And then a big unknown is how much of a reduction is necessary to achieve an acceptable level of risk? I do think this year is a bit of an outlier - wide open field with all the action at the alliance walls, game suitable for low centers of gravity, a lot of UTB intakes, new motors introduced, significant swerve adoption - and we are probably more aware of incidents making it seem like a bigger increase than it really is. Teams are going to adapt a little on their own, the game will be different, and probably only a small additional correction is needed to get things within reason, especially when you can address a large bloc of the “worst offenders” doing something like limiting weight. (And I’ll acknowledge that I am more risk-tolerant than others in this debate.)

Know this topic has aged a bit, but some like me are still thinking about bumpers with off season events looming. This year, we had an OTB intake and competed in 46 matches this year. Took some pretty hard hits and we are still rockin our original build bumpers.

In ours and most that I’ve seen, The corners are the weak point with the wood corners wedging into the tensioned pool noodle. I can feel a split in both noodles at each corner beneath the fabric.

Back on this topic, I’ve been plying around with TPU and think that a printed corner pieces with perhaps slightly more spring rate than the noodle would be a large improvement. Discussing this locally with few other teams and bumper experts. Know this is not allowed per current rules, but hate the idea of slowing down the robots does not appeal and and I have some bumpers that need some mending before our offseason events.

Had also thought about the benefit of the mk4 SDS design when flipped around is that you could build some nice danish furniture like plywood bumpers on a router table and the noodles could hug the corner radius vs sharp corners. Curious if others had similar ideas

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If FIRST were to provide specific corner extrusion for the bumpers that’s harder, I think that would be very helpful in terms of reducing damage.

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