FRC 95 The Grasshoppers 2019 Build Thread


#21

We are leaning towards a continuous elevator because the setup and cord management is a bit easier than cascade. We had good success with our continuous elevator last year.

We have had success with cascade elevators in the past, and they are much smoother to operate (see 148 in 2018). But there are more parts and more design considerations.

For those who are not immediately familiar with this terminology:


#22

FTFY


#23

:grinning:

Baby brain is a real thing. Thanks. Post has been edited.


#24

Hatch intake looking great! Just curious though, what was the reasoning for alternating green and blue compliant wheels versus all green or all blue?


#25

We’re using a mixture as well. When we use all green wheels we’ve noticed that they wear out very quickly. Blue or red will last longer and help provide support so the green wheels hold together longer. You still get the benefit of green wheel grip, with the added bonus of some blue wheel durability.


#26

Thanks! The student who put it together thought it looked cool. I can’t deny that. We bought a bunch last year, but only blue and green because of our team colors.

Interesting. We’re going to keep an eye on wear too. We have certainly noticed the green wheels slipping on the hex drive shaft.


#27

James, I am always impressed by how quickly you guys are able to churn out CAD which ends up on your finished bot. My question is how big is your CAD team and how do you break up the work between them?


#28

James, are you able/have you tried to make the hatch intake in a sort of W shape with shorter legs on the side so you can grab from the loading station bottom?


#29

So the middle snoot could grab from the bottom at the loading station


#30

I’m so glad you’re doing the build thread once again.


#31

Since 2016 the CAD team has been me until this year, where I have one student interested in CAD. We are a pretty small team, usually only 10 to 15 students at most, and we have a ‘work on what you want to’ policy.


#32

We have not. Our intent at the moment is to have a totally different mechanisms to grab from the human player station and score the hatch. Our current ground loader layout in CAD puts the hatch right at the player load height, so we can transfer between the two mechanisms.


#33

@JacobD, I was giving this some more thought over the weekend. There are a handful of ‘design style’ guidelines that we follow which help us turn out designs more quickly than we used to. We were quite cognizant of these design process changes when we implemented them circa 2014, but they have become second-nature in recent years.

  • 10-32 bolts and 3/16 rivets are our standard. Attachment point? 0.201in hole(s). No thinking needed.
  • We do not make our own gearboxes basically ever. We just find a way to make OTS solutions work well enough.
  • We use as many OTS parts as possible. We buy spacers and standoffs from McMaster, something we can easily make ourselves, but if we don’t have to we won’t.
  • We have a sheet metal + brain/belly pan build style that we use from year to year. This dramatically reduces the number of design decisions to make when creating the chassis. We also try to use sheet metal everywhere else we can. Sheet metal parts are light, can be made quickly, and with good bending can dramatically reduce the total parts count.
  • We try to find ways to reuse the same parts over and over within a given robot. Our chassis side plates are always the same, our 2018 elevator bearing blocks were left/right/top/bottom independent, our wheel modules are generally position-independent, things like that. It is super easy to make a chassis when you just build one side plate, pattern it to make a drive pod, pattern-array wheels modules into it, then pattern the whole drive pod to make most of the chassis.

For the sake of clarity, here are some screen shots:

Drive plate. There are a lot more holes than what will actually be used in any one position, but having all of the possible holes on every part lets them all be the same exact part. (That feels really weird to write out…)

Wheel module. Note that it’s bearings are captive to the axle/module and the whole thing can be installed, rather than being assembled on the chassis. The only ‘custom’ part here is the drive alxe, which is just the thunderhex model from Vex with an Extrude Cut to make it the right size.

Drive Pod Assembly. This is two chassis plates, three wheel modules, one transmission model downloaded from Vex, and some special sauce cylinders downloaded from McMaster.

Drive Base/Chassis Assembly. Comprised of two drive pods, one brain pan, and one ‘end cap’ part with 3x configurations to link the two drive pods together.

To get to this point we modeled 4x parts, one of which has 3x configurations, and downloaded less than 10x other models.

Does this style result in the optimal robot design every year? Absolutely not. We always compromise on one or more performance metric like CG, total mass, mechanism volume, etc. But it is FAST. Like, super stupid fast. We’re going to release models to our sheet metal sponsor tonight and would expect to have our chassis parts by Friday. We’ll also start machining some parts in house and maybe have elevator parts done by Saturday.

We also start cutting metal before everything is modeled in, we just try to give ourselves as much wiggle room as possible to fit things in later. We, as a team, accept this risk in favor of having our primary functions operating sooner to test and iterate. This mode of operation is a function of how small we are, we simply do not have the people-power to churn out a fully integrated model by the end of week 1 or 2. So, we work with what we’ve got!

I hope this was a little more informative/helpful than my last response.


#34

Current state of CAD:

We held a design review tonight to go over all of the CAD, and made a few revision. We’ve sent 14 models to our sheet metal sponsor, Progressive Manufacturing Inc. Now the exciting/horrible waiting game… Also sent orders to McMaster and will need to send another to VexPro.

I’m quite pleased with how well our ground collector packaged after we struggled with it for quite some time.

Two BAG motors, one for the wrist, one for the intake, with AM compliant wheels to collect. We did not model the plastic teeth in. This bolts/rivets inside of the front recess of the chassis. It snuggles right in between the bumper sections.


#35

I think the choice for a ground pickup instead of a feeder mechanism is interesting, it will be neat to see how that plays out in a game.

For CAD it looks like you’re using onshape. What kind of format do you export your sheet metal designs in so that your shop can build them?


#36

The ground pickup will compliment a human load station pickup. It flips the cover up to a position similar to the load station.

We export as solidworks, the solidworks sheet metal convert tool identifies all of the bends seamlessly (so far) and flattens the part out. Easy peasy.


#37

James, thank you for the in-depth response. I really appreciate getting some insight into what you guys do. Your team gets better and better each year and I am sure this year will be nothing but success again! Thanks for sharing.


#38

I would be interested in seeing how well the floor intake scores the hatch panel.


#39

You’re welcome, and thank you for the kind words!

Our intent is not to score directly with the ground loader. But we will certainly give it a try!


#40

It will likely be easier than the handoff, tbh.