Team 254 Presents: Dropshot Technical Binder 2016

[Starke]

Thanks to the Cheesy Poofs for continuing to inspire our students.

Would you be willing to explain the relationship between 254 and 971? Looking at 971's reveal video this year, it looks a lot like 254's place in previous reveal videos, while Dropshot premiered in a different field.

[Cory]

Originally Posted by Sperkowsky

At champs I was doing field reset on Newton and talked to Travis a bit about it. He mentioned that they have a better set up at their school and mostly work there now. I believe he also said they missed giving students the opportunity of working at a NASA facility which is an interesting point I never thought of.

So... yea that's what I have figured out from me digging around. Ill delete this post once someone actually from 254 gives a better response.

We have been lucky that our school is committing a lot of resources to their STEM programs, including FRC. This has given the team more resources on campus. We still have a strong partnership with NASA, as we always have.

971 has been an official "house team" for the last few years. I don't know if the robotics.nasa.gov link is current but it lists 842 for NURC, not FRC. 842 has never used the NASA lab.

254 has had a long running relationship with 971. We helped with a design review for them in 2007/2008 and have been close since then, often bouncing design or strategy ideas off each other, sharing prototype results, etc. In 2015 we collaborated on the design and manufacturing of our can grabbers for championships, which was a lot of fun.

[caume]

Are CADs for Dropshot available anywhere?

[Knufire]

Originally Posted by caume

Are CADs for Dropshot available anywhere?

254 historically does not share CAD.

[frcguy]

Originally Posted by caume

Are CADs for Dropshot available anywhere?

Originally Posted by Travis Covington

We have no plans to release the CAD of the robot but are happy to answer any questions you have.

See above.

[RoboChair]

Originally Posted by Ashwin Adulla

The main purpose of the safety wire, as suggested by Team 1678, was to prevent our fairlane flywheel from expanding a significant amount past 5000 rpm. During prototyping, the fairlane wheels expanded to the extent that we were fearful of testing them out. As a result, the safety wire constrained the expansion of the wheels to a certain diameter which allowed us to ramp up to around 6000 rpm at Champs for taking shots. As for the process of installing them, the safety wire was wrapped once around the wheel, cut to its length, and then two ends were twisted together and then stuck inside the neoprene so as to prevent it from contacting the boulder. I have attached a picture of the flywheel below.

Originally Posted by lnex1357

We are throwing some fairlane wheels on our shooter for an offseason event in place of our colsons. Did you guys use round or flat safety wire and what was the rough OD or width respectively, as I would prefer not to guess and check through a series of McM orders. Thanks so much!

Round safety wire 0.032" diameter. 1678 ran 2 wraps around our wheels. It's a little bit of a tricky process. You must get the safety wire tight and squeezing into the wheel a little and you will almost definitely break some wires in the process of twisting them. Try until you succeed To stuff the twisted wire end into the wheel use a screwdriver or awl to stab into the rubber right next to the twisted end, then stuff it in.

Attempted destructive test of a shooter wheel

[asid61]

Originally Posted by RoboChair

Round safety wire 0.032" diameter. 1678 ran 2 wraps around our wheels. It's a little bit of a tricky process. You must get the safety wire tight and squeezing into the wheel a little and you will almost definitely break some wires in the process of twisting them. Try until you succeed To stuff the twisted wire end into the wheel use a screwdriver or awl to stab into the rubber right next to the twisted end, then stuff it in.

Attempted destructive test of a shooter wheel

I felt myself shying away from that wheel...
Out of curiosity, does it explode if you run it without the wire, and if so how did you find out?

[Cory]

Originally Posted by asid61

I felt myself shying away from that wheel...
Out of curiosity, does it explode if you run it without the wire, and if so how did you find out?

For us it was less about keeping the wheel from exploding and more about the fact that since we retrofitted the wheel into the shooter, the expansion would cause it to rub dramatically on the turret plate, without being safety wired.

In 2014 when testing with the same wheels we wanted to determine how much they expanded and make sure they were safe to use at those speeds. We mounted them to a shaft held in a collet chuck in our cnc mill, spun them up to ~5000-5500 rpm with no safety wire and measured the difference in size at speed vs static and saw no issues with exploding. That's substantially slower surface speed than at ~8k rpm like Devin's test though.

[RoboChair]

Originally Posted by asid61

I felt myself shying away from that wheel...
Out of curiosity, does it explode if you run it without the wire, and if so how did you find out?

We were having issues with delaminating wheels, which lets them expand far more and in a highly unbalanced way.

While I was trying to see if we could make it come apart it wasn't really the goal. The goal was to make sure that the wheel would not delaminate from the steel hub at a speed the shooter would never need to reach, it did not. The wheel was pulling well over 2000 times the force of gravity expanding outward in that test and nothing failed. It managed to handle around twice the stored wheel energy than what was required on the robot. The secondary effect of reducing the expansion of the wheel was just an effect of the wire resisting the outward force to a level that the rubber could handle.

Without the wire it would have delaminated or disassembled itself for sure.

Also, when you have that much energy stored in a disk the only places the pieces can go is the plane of rotation. So everyone was well clear of that plane with further room to move away. If something did fail the only damage would be to the ceiling tiles or the requirement of fresh pants.

[caume]

How is the drive gearbox attached to the chassis frame?

[Cothron Theiss]

Originally Posted by caume

How is the drive gearbox attached to the chassis frame?

I'm not affiliated with the team in any way, so take this with a grain of salt. But it appears from the close up of the gearbox that there is a screw on either side of the output shaft that was screwed from the inside of the chassis rail into the gearbox plate that is flush against the rail. It appears to be very similar to how the WCP gearboxes are attached.

[pilleya]

http://www.vexrobotics.com/bearingblocks-g.html

A custom bearing block, very similar to that of the WCP Gearbox bearing block.

[NotInControl]

So just a few questions from your friends on 2168.

1. Can you share a little bit more about how you arrive at shooter geometry (compression, contact time, exit speed etc.) required to make the shot. Every year these factors seem to be areas teams must learn from trial and error, wondering if the poofs have a more polished process.

2. Can you share more about what drove the Team to a turret all together, as far as I know this is the first turret 254 has used in competition. I am curious what drove the design, where did 254 pull the inspiration from if anywhere, did any team mentors/students have prior experience with turrets in FRC applications in the past? I find it typical for teams to avoid certain solutions because they have never fielded them in an event and would rather choose a solution they have more experience with. That definitely is always a good approach in my opinion, just wondering how 254 gets over that idea to follow a solution they never fielded.

3. Can you share a little more about how you determine whether to go chain #25, #35, or belt. This has been an age old question, and I am not really asking which you think is better, but how do you go about choosing which one for the application. The reason I ask is some teams use belt, and use it for everything, some teams use chain and use it for everything, and other teams kind of are in the middle, they use one, have failure, and use the other, and keep bouncing around. I am wondering if 254 has a more scientific approach to the choice because it seems like 254 chooses different solutions more purposefully.

4. Going back to the chain question. I recognize that in certain years 254 has went from belt to chain or #25 chain to #35 chain etc. When this occurs do you have to redesign your drive rails or are their certain considerations into the design that makes changing from one to the other easy without much modification? (i.e certain spacing common to all)

5. Your Vision on the Nexus was stated to come out of necessity due to the unreliability of the Tegra, I am curious if the android solution seems like something 254 would use in the future or if there are equal pros and cons to possibly look for another? We did use a tegra, and after soldering come caps off to make it boot reliably we did not have an issue with the board. But again thats besides the point, looking for 254's opinion on the next best solution. Could you share some pain points, or cons/hurdles which needed to be overcome before the android solution was put into practice. I am sure many teams are testing an android solution in the off-season (we may be one).

6. Can you share more on the servo solution? How did you ensure the servo was meshed properly and never skipped? We tried to use a servo this year for our articulating hood, but slippage was a big issue so we pulled it for a multi position pneumatic solution right before our first competition. Typically on this team if it failed once we never try it again. I am curious how 254 was able to have a successful servo implementation. Would you mind sharing which servo was used, and how it was interfaced to the hood and did you have any issues with slippage?

7. How was the hood angle determined from vision? Was it based on distance to target, center of target to center of camera frame, or some other method?

8. How many drivers were used this year for the machine? I have heard that some years 254 has 2 drivers, some years 254 has 1 driver with a bunch of automated stuff. Could you share what was automated, requiring little/no commands vs what was always manual for this years bot?

Thank you very much for the answers to these questions. Truly is awesome learning from you.

[ThePoopieBandit]

WOW!

[mman1506]

Originally Posted by Cory

For us it was less about keeping the wheel from exploding and more about the fact that since we retrofitted the wheel into the shooter, the expansion would cause it to rub dramatically on the turret plate, without being safety wired.

In 2014 when testing with the same wheels we wanted to determine how much they expanded and make sure they were safe to use at those speeds. We mounted them to a shaft held in a collet chuck in our cnc mill, spun them up to ~5000-5500 rpm with no safety wire and measured the difference in size at speed vs static and saw no issues with exploding. That's substantially slower surface speed than at ~8k rpm like Devin's test though.

I guess it's only okay to use machine tools to spin up a shooter wheel when 254 does it

/S