Examples of when it is not advantageous to be lightweight

Aside from the obvious loss of friction due to a decreased normal force affecting pushing ability, I cannot think of any specific examples in FRC history when it has been disadvantageous to be as light as possible. Is there anything I am missing, and if so, could you cite a specific match that shows this weakness due to weight? Also, is there a limit with weight where, like adding motors, you reach a point where it becomes less and less advantageous to become lighter?

I appreciate all input.

[madhav]

2012 Bridge Balancing issues?

I'm tired, I'll get back to you tomorrow

[Travis Schuh]

I think your implicit assumption is that being lighter gives you a more maneuverable robot by decreasing acceleration time.

If your goal is to make your robot more maneuverable, then I could see taking weight out of your robot at the cost of raising your CG above an acceptable height resulting in a net decrease in maneuverability. If there is no option to lower CG through re-arranging components, then it may make sense to ballast the robot. It also helps if the CG is closer to the center of the robot for best handling. I think for these reasons contributed to 254 ballasting their robot this year.

There are plenty of matches where teams either outright tipped or had to drive cautiously because they were tippy (you asked for specific matches, I would say watch some of 973's 2013 matches). I bet many of these teams would have added ballast if they had weight.

[Mike Marandola]

Originally Posted by Andrew Lawrence

Aside from the obvious loss of friction due to a decreased normal force affecting pushing ability, I cannot think of any specific examples in FRC history when it has been disadvantageous to be as light as possible. Is there anything I am missing, and if so, could you cite a specific match that shows this weakness due to weight? Also, is there a limit with weight where, like adding motors, you reach a point where it becomes less and less advantageous to become lighter?

I appreciate all input.

In 2005 there were more than a few robots that would have tipped if their drive base was any lighter due to the massive arms. Although instead of maxing out your weight, you could achieve the same effect by lowering your CoG. On our 2005 bot, in addition to adding weight, we were able to prevent tipping and change the position of our CoG by having a sliding battery box.

[EricH]

That "aside from" isn't ENOUGH of a reason?


There are several scenarios I can think of where more weight is advantageous. I can't think of any examples (other than maybe 2007...)
1) CG considerations. This is more about placement than about total mass, but if you are light and tall, you're probably going to need to take a lot more care of where your CG is. I remember at least one 6' robot going over with minimal contact in '07 (max weight, 100 lb sans battery and optional bumpers). Sorry, don't remember exactly which team/event, let alone match. I want to say San Diego '07, one of the Oregon teams in attendance, but not sure. If I can find it, I'll link it.

2) More functionality (advantageous if you can use it). More functionality generally means higher weight, but you can do more. OTOH, if doing more means you do worse (or less due to lack of practice), then this is a severe disadvantage.

3) It's not that hard to remove weight. But it's a LOT easier to ADD weight. And, given the pushing matches that ensue in FRC, many a team will at least consider how to mount a steel plate low on the robot. Then, of course, they get pushed around in one match and opt to increase their normal force.



That said... maybe one of the REAL old-timers on here can give us a rundown of the classic award, "Flyweight in the Finals"!

[VioletElizabeth]

I would second the bridge balancing from 2012, as I remember adding weight that year for that exact purpose. We were maybe 20 pounds under, so balancing with robots at the weight limit was hard before weights... (Exact numbers fuzzy, I was a freshman. I seem to remember 102.)

We also added weight in 2013 so that our robot hung right when it was climbing--a different application for CG.

[Thad House]

In 2013, our robot had a high COG because of our shooter placement. In addition, all of the weight was in the back half of robot. We weighed about 100 lbs. When we added our hanger at worlds, we added about 20 lbs of lifting weights to the front of our robot, and moved the battery to the front, in order to move our COG forward enough to hang, and low enough to still be drivable. It was still very tippy, and the match we played defense we rocked so much it looked like we were going to tip the entire match.

In 2014. 70 lbs was less then 6 inches off the floor, and the robot only weighed 100 lbs. We had absolutely no rocking issues. But if we had needed more weight for pushing, we had plans on how to add it.

We realized that avoiding defense with speed was better then avoiding by pushing. So unless we wanted to specifically be a defensive robot, it would be best to plan for as light as possible, then use additional weight if needed to make sure the robot doesn't tip and remains drivable.

Originally Posted by Travis Schuh

I think your implicit assumption is that being lighter gives you a more maneuverable robot by decreasing acceleration time.

If your goal is to make your robot more maneuverable, then I could see taking weight out of your robot at the cost of raising your CG above an acceptable height resulting in a net decrease in maneuverability. If there is no option to lower CG through re-arranging components, then it may make sense to ballast the robot. It also helps if the CG is closer to the center of the robot for best handling. I think for these reasons contributed to 254 ballasting their robot this year.

There are plenty of matches where teams either outright tipped or had to drive cautiously because they were tippy (you asked for specific matches, I would say watch some of 973's 2013 matches). I bet many of these teams would have added ballast if they had weight.

Part is maneuverability, though the main reason is I just can't think of a reason to be heavy. 1323's resources make machining for weight easy enough, and I think it would be a useful engineering goal for the kids to shoot for in season to design for a lightweight yet strong robot if the game allows for a lightweight robot as a viable strategy. Also it would be a good way to allocate weight lower into the drivetrain to make a lower CG (which has been a clear problem for us this year).

One of the first things many mentors I have learned from tend to tell me is how to lighten a robot and that "lighter is better" (not always true, but it's a point that has been stressed enough to me in my education that I started this thread because of it, though further learning could prove differently) and while I understand the potential advantages of a lower weight, I cannot think of many reasons for increased weight. More mass in a robot just makes it harder to move, and I don't see any advantages to that, and want to learn what I may be missing.

[Kevin Sheridan]

When I was on 766 we made our robots as heavy as possible in 2006 and 2007 so we would not tip going up/down the ramps. I saw a lot of robots tip in 2006 especially because they were too top heavy. A common tactic that year was to shove top heavy robots up your own ramp on defense so they would risk tipping trying to come down the ramp during teleop.

[Caleb Sykes]

Originally Posted by VioletElizabeth

I would second the bridge balancing from 2012, as I remember adding weight that year for that exact purpose. We were maybe 20 pounds under, so balancing with robots at the weight limit was hard before weights... (Exact numbers fuzzy, I was a freshman. I seem to remember 102.)

It was certainly helpful in 2012 to have roughly equally weighted robots when balancing. Additionally in 2012, some minimum weight was required to lower the bridge. I recall a few robots that year who, when trying to push down the bridge, ended up lifting up their front wheels instead. This effect could have been avoided either by making their robot heavier all around or by shifting weight toward the side of the robot that contained their bridge lowering mechanism.

[Chief Hedgehog]

In 2013 if you designed your robot to be a climber, then yes.

In fact, in FRC 4607's rookie year our robot was designed to be a climber and could reach the 2nd rung. Our climbing apparatus was set on a 22.5lb stainless steel 1/4" slab that was positioned on sliding rails and was moved by an acme lead screw.

HOWEVER, we used black and white wiring... a no-no that we neglected to search out in the rule book. That and one of our CIM shafts stuck out 3/8" beyond the frame.

After a full thursday of not practicing and rebuilding our robot - voila! Peanut the defensive robot that could climb for 10 points!

We did well considering our failures...

[nathannfm]

Originally Posted by Andrew Lawrence

One of the first things many mentors I have learned from tend to tell me is how to lighten a robot and that "lighter is better" (not always true, but it's a point that has been stressed enough to me in my education that I started this thread because of it

I think this is always true of subsystems, including the drive, until you start to sacrifice structural integrity, but not true for the robot as a whole. When I say "lighter is better" it is usually because if it's not stressed you get to week 5 with a 150lb robot and a major sub system has to be removed because there is no time to redesign all of them to be lighter. On MOE we always have 120.00lb robots because we usually shoot for maximum functionality (do all the things!) and this usually requires more weight than a robot specialized to do a specific task. We embrace this so much that if we get to week 4 or 5 and realize we have 4lb to spare we try to think of a way to use that 4lb to make our job easier, more reliable, or faster.

[MichaelBick]

Originally Posted by Andrew Lawrence

Also it would be a good way to allocate weight lower into the drivetrain to make a lower CG (which has been a clear problem for us this year).

Drive size has a lot more to do with this than your drive weight.

[scaryone]

We added weight to the base of this year's bot to avoid tipping over. (top-heavy)

[MooreteP]

Team 148, OverDrive, won Einstein.
Low CoG, very effective at lapping. Different from everyone else.
https://www.youtube.com/watch?v=6fLf71xlVhE