2014 FRC's Biggest Loser

[Michael Yeh]

Our robot hit 110 lbs on a very old bathroom scale today, which is almost exactly what our CAD said. We plan to acquire a better scale, but we had some people with known weights "calibrate" that one. Our structure is pretty simple but is mostly heavy 2x1x.125" tubing and we're using all 6 CIMs, 4 miniCIMs, and a pair of AM 9015s on the PG-71 gearboxes (no, we don't plan to pop the breaker every match )

The tubing is mostly solid so we may try to make some sort of jig to swiss cheese our unbagged parts. Life would probably have been much easier if we used the thinner Vex tubing, but they were out of stock until the day we placed our order. We may also switch out the miniCIMs with banebots motors in versaplanetaries or CIMiles if we can afford it.

[piersklein]

Rookie team here and we WAY over built (the team takes durability way too firmly). We are at 110lbs and do not shoot. We are using 3 by 1.5 in double extrusion for arms which weigh in at 50 lbs. And do not have much to save weight in. On the plus side, we can *accidentally* be a battering ram.

[Master Mac]

And if we ever meet on the field I sure hope you are full of Gracious Professionalism, because this comment is not what first is about, and as a rookie team you will not go far with this type of comment. I wish if I was a robot inspector in your regional you never make it to the field if I had seen this post.

Originally Posted by piersklein

Rookie team here and we WAY over built (the team takes durability way too firmly). We are at 110lbs and do not shoot. We are using 3 by 1.5 in double extrusion for arms which weigh in at 50 lbs. And do not have much to save weight in. On the plus side, we can *accidentally* be a battering ram.

[DELurker]

Originally Posted by droswell

We learned a valuable lesson about being 2" under frame size and ALWAYS weight your bot _before_ showing up to a regional.

Our current weighing method is to take two students, weigh them on a pair of bathroom scales, then weigh them while they are both holding the robot. Subtract out the student weights and you get the answer +/- 1 lb. If you then rotate the robot 90 degrees and repeat, you could actually figure out the location of the center of gravity of the robot in the horizontal plane. I'm not a fan of turning the robot on its side to get the vertical axis of the CG...

[Chadfrom308]

Originally Posted by DELurker

Hoping you mean Lexan/polycarbonate/Makrolon... Plexiglas is prone to shattering.

Yes, I couldn't think of the name for it!

[BoilerMentor]

Originally Posted by wilsonmw04

I would do this first.
I fail to see the significant benefit of 7lbs. vs. what 6 cims give you.

The drive train is geared for 6 CIMs. That is precisely the problem with removing them. It is also a surprisingly large amount of work to remove them as well. You can't get at them from the outside of the gearbox, so we'd probably have to remove our drive modules, remove the transmissions from those, split the transmission, remove the motors, then reassemble. Compared to most of the other items on the list it is much more difficult.

Also, it would hurt our strategy pretty severely and go completely against an important lesson the team learned last year regarding the value of defensive play.

Lastly, the robot should cross the field (calculated including wheel slip with all six cims) in 3.25 seconds. In the case we have to cycle by ourselves they will be fast cycles.

[DELurker]

Originally Posted by BoilerMentor

With the current position HBR has found themselves in, I thought this might be a fun thing to look at.

Share your robot weight situation and describe your remedy.

On paper, with the battery, 6 lbs of bumpers, and without bolts or wires (we're not going to model them), we're at 102 lbs. Our method was lightweight parts, thin Lexan, and perforated PVC panels. That, and an intense desire to break the three-year trend of being within 0.5 lbs of the upper weight limit at weigh-in ... since our shop scale broke.

[TheFrozenSlink]

Our robot weighs 72.75 pounds. If anyone would like to send us weight go right ahead

[BoilerMentor]

You guys are making me feel self conscious about our robot weight...

[MechEng83]

Originally Posted by BoilerMentor

You guys are making me feel self conscious about our robot weight...

we weighed systems last night and are coming up with 120 lbs... We're still missing some important items like the sponsor panel, which is also the entire front of our robot.

Luckily, we designed in some weight savings opportunities should the need arise. looks like we'll be diving into that.

On a completely unrelated note , anyone know where we can get a 26" long 1/2" keyed aluminum shaft? The longest I can find right now is 24"

[JamesCH95]

We weighed in at 110lbs fully loaded.

Originally Posted by MechEng83

we weighed systems last night and are coming up with 120 lbs... We're still missing some important items like the sponsor panel, which is also the entire front of our robot.

Luckily, we designed in some weight savings opportunities should the need arise. looks like we'll be diving into that.

On a completely unrelated note , anyone know where we can get a 26" long 1/2" keyed aluminum shaft? The longest I can find right now is 24"

I would be tempted to stick two chunks of shaft together with a ferrule insert to couple them, using a key to ensure that the two shafts' keyways lined up.

Like this:

[nathannfm]

Originally Posted by JamesCH95

We weighed in at 110lbs fully loaded.

I would be tempted to stick two chunks of shaft together with a ferrule insert to couple them, using a key to ensure that the two shafts' keyways lined up.

Like this:

I am not quite sure what this is, but it got me thinking, you could get 2 pieces of shaft, tap the ends of both and connect them with a piece of threaded rod. Same concept I think.

As for hex shaft, I have found that the Vex hex shaft is extremely high quality and precision, you may want to look into that.

[Oblarg]

Originally Posted by nathannfm

As for hex shaft, I have found that the Vex hex shaft is extremely high quality and precision, you may want to look into that.

Unfortunately, I have found that the probability of a vex hex bearing fitting on a vex hex shaft without issue is about 50%, though I might just have really rotten luck.

[JamesCH95]

Originally Posted by nathannfm

I am not quite sure what this is, but it got me thinking, you could get 2 pieces of shaft, tap the ends of both and connect them with a piece of threaded rod. Same concept I think.

As for hex shaft, I have found that the Vex hex shaft is extremely high quality and precision, you may want to look into that.

That's a technique for sticking carbon fiber tubes together to make longer carbon fiber tubes.

It is the same concept, but there are two reasons to not use a threaded rod. First, the keyways would have a negligibly small chance of lining up with each other. Maybe a problem, maybe not. Second, you would have to make darn sure that threading never came apart, or even loosened a little bit. If it did, you'd have threading in bending, and that is a very bad time.

[magnets]

Originally Posted by Oblarg

Unfortunately, I have found that the probability of a vex hex bearing fitting on a vex hex shaft without issue is about 50%, though I might just have really rotten luck.

First try deburring the edges. Then just sand down the hex shaft. You loose the fancy paint, but it fits!


As for the long shaft source, you could go with McMaster, which sells some .500 aluminum rod with the "ground and polished" finish. This will be the exact diameter, but doesn't have the keyway cut into it. You could then cut your own keyway, use a roll pin, or make some flat parts on the shaft, and use a set screw.