FRC95 2022 Build Thread

@pryland We did that in 2014 to reinforce 3/4in cylinder shafts that bent during testing (and we couldn’t replace with bigger ones because of packaging). The shaft support also replaced the nose nut, so it was nearly weight-neutral. Next to it is a bigger brake cylinder we used in 2017 that didn’t need any shaft support - tested by going as fast as we could (16-17ft/s) and deploying the brakes.

Most of our cargo-handling sheetmetal came in today!

Painting and assembly are charging forward.

Seeing the Mobil XHP 461 (blue) from this post swish around in a planetary gearbox made me pretty confident that we made the right call in using it for planetary/enclosed gearboxes.

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Probably not all that useful, but I bent a piston by over-tightening a fitting. I have no idea how to translate torque on a wrench to force on the piston, but I can remember/guess/make up some numbers.

I can remember/determine based on the wrenches we have that I was using a wrench about 8in long.
I was using both hands, but I don’t have a reasonable number for pounds of force exerted on the wrench… so here’s a made up one. With two hands, carrying somewhere between 80 and 120lbs seems to take as much effort as turning that wrench did. Since we want a lower bound, and turning a horizontal wrench allows for the use of more of the body than the arms, I’ll guess 100lbs of force on the wrench.
That gives ~66 ft*lbs of torque on the fitting.
If anyone wants to produce an even-less-helpful number for the force applied to the piston, keep in mind that some of that torque was a) destroying the threads and b) squashing the fitting to no longer be a regular hexagon.

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Sponsor printers go brrr…

Collector assembly revealed a (probably obvious) little issue.

Welp… oh no…

We cut the side off of one of our spares and stuck it in the middle. Seemed to do the trick.

We also encountered some bent hex stock, only discovered after we started assembling our shooter.

A few steps forward, a few steps back.

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Why do you have one motor on the bottom shaft and another on the top? Wouldn’t it be enough just to power one?

Also, have you had problems with the belts skipping off those pulleys? We’ve had a lot of trouble with that, especially with pulleys with such shallow flanges.

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Having two lets us gear the intake a bit faster and provides redundancy in case something fails.

We haven’t tested this pulley/belt combo yet, we’ll report back when we do!

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Let’s talk about batteries.

The battery is the single most critical part in the whole robot. The battery’s condition will affect every other system on the robot to some degree. We ought to care about it quite a bit! Our legal batteries are all AGM (absorbed glass mat) lead-acid batteries with nominal 18AH capacity and ~12V differential. AGM lead acid batteries are well characterized by industry at this point, I’m only going to be going over a few FRC-specific points.

Would you like to know more? Visit Battery University. When I played with batteries in a former life Battery University matched up well with all of the more serious reference materials I used and presents everything in a generalized and layman-friendly format.

Charging

Charge your battery with a smart charger of some sort. The smart charger will help preserve your batteries’ capacity vs a constant current or constant voltage charger. Most chargers sold by FRC vendors are smart (maybe all of them are?) Smart Charging Article

Batteries can be charged when they are pretty darn hot, 50C/122F. This temperature will surprise most people if they touch it. For most FRC teams this means a battery can come straight out of a robot after a match and onto the charger. However, there is arguable advantage in waiting for the battery to cool before charging: a cooler battery can charge more quickly and you remove the need for temperature-compensation in your charging system. Battery charging temperature.

Charge the battery upright, or close to upright, if you can. NEVER EVER EVER use a battery upside down (posts facing gravity). If there is a charging issue or the battery is overcharged the gas purge valve will release the pressure, but if battery acid is covering that port battery acid will be purged out. Sad times.

Charging at 2-4A vs 6A can prolong usable battery life to an extent. We charge at 6A and don’t notice bad effects over a season.

Testing
Many testing options exist. Too many. Lead acid testing.

We primarily use a Battery Beak from AndyMark because it is quick and repeatable. It will find dead/dying batteries and loose terminals no problem. It cannot differentiate well between decent batteries with a slightly diminished capacity and great batteries with full capacity.

To manage capacity loss we don’t use a battery for more than one competition season. After 1 year a competition battery becomes a practice battery.

Our criteria look like this:

Competition

  • <1 year old
  • Internal resistance <0.015ohm
  • 13V+ charged voltage

Practice

  • <4 years old
  • Internal resistance <0.022 ohm
  • 12.4V+ charged voltage

Recycle

  • Failing any practice criteria
  • Any physical damage to the case or posts
  • Any doubt about age or observed weird performance

At Competition
Name or label your batteries and use them by a schedule. This spreads out cycles across all of the batteries evenly and maximizes recharge and cool-down time.

Assign someone to manage this process. It is critical to your success.

DO NOT DO

  • Do not pick up a battery by the leads, it can damage the battery immediately
  • Do not touch wires or clips to the SB contacts, the arcing damage will increase resistance in that connector and hurt your performance. Only a mating SB contact should touch another SB contact, and only when the main breaker has been disconnected.
  • Do not the battery as anything other than a battery. Please. I know it seems like a good hammer. It isn’t.
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Where do you recycle your batteries? Do any auto part stores take them (Autozone, Advance Auto, ect.)?

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Auto parts place. The one I use gives you a $10 store credit for each battery.

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We go to AutoZone and cash them in for $10 and buy tools or whatever else we might need on the spot, usually.

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That’s awesome! Thanks for the information!

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Lots of progress today after Friday being lost to snow.

When we got the colletor mounted on the chassis we weren’t happy with the stiffness of the 1/4in PC linkages.

Fortunately we had two spare sets, so we laminated them together with VHB tape. (Slightly more than) doubling the thickness increases stiffness by 2^3 = 8x, at least if they’re fastened or laminated properly and not loosely bolted together.

Oops…

Putting the pit back into pit crew. Or #justbrainpanthings

We got the shooter assembled and wired, collector assembled and wired, singulator assembled and wired, then we taped a bumper on and got to testing.

Just a simple few feed-thru tests at first.

Then off to the practice area for some torture.

We’ve got some work to do to keep belts from popping off, but overall we are quite happy with the initial results.

Some outstanding tasks include:

  • Sorting out spacers for the collector mounts, all of that was tossed out the window when we laminated the links
  • Real bumpers
  • Add in and calibrate color and line-break sensors to automate cargo handling
  • Dial-in shooter
  • Wire and calibrate LimeLights
  • Drivetrain characterization

And, you know, a million little things…

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Due to laminating our collector links all of our planned-out spacers were not useful. We tested without them letting everything float. And we learned about bending stresses.

After a 2-day delay from snow we got most of our latest batch of parts and got to painting last night.

The climbing latch/hooks are one of the only parts we’ve had lasered out of 1/4in aluminum.

We experimented with different ways of springing the climber joints open. We have settled on torsion springs nested inside the joint. Unfortunately we’re going to have to order a different size to fit the way we want it to.

We did a little welding too. These are some of the brake pad weldments, a SS flanged nut and washer fused together with TIG.

@Wesley created a well-packaged voltage divider harness for our line-break sensors to be used in the indexooter.

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Let’s talk about talking. Specifically discussing/debating/arguing.

We have a few basic rules when we have discussions on our team:

  1. Do not ask “what if…?”

This means you haven’t thought about the merits or detriments of your idea and are asking the audience to do your thinking for you. Not a good look.

Instead, present: “if we do A then X and Y get better, but Z might need attention to avoid failure.” This shows you’ve thought through some of the implications of your idea and have considered the upsides and downsides.

Also okay: “I know this is insane, but we could use W to do T and F, but J and K are huge issues.” Sometimes you need to get the bad ideas out to make room for good ideas, presenting them will help you move on. This may also inspire a good idea in someone else.

  1. Do not ask: “why don’t we…?”

This simply invites negative criticism. Your audience is already starting out with the thought of ‘we shouldn’t do that because of reasons.’ You likely won’t appreciate the feedback you get, and you are handicapping a potentially great idea by encouraging all first thoughts of it to be negative.

Instead: see above.

  1. Once you present an idea it is the team’s idea, not yours.

This helps divorce ownership from an individual, makes criticisms less personal, and workload-sharing easier. We have someone besides the idea presenter name the idea to help with this.

“Gear Runner is a more competitive robot than Baller Hippo” reads a lot better than “James’ idea is better than @Andy_A 's idea” for example.

  1. You DO NOT need to defend or even respond to any criticism beyond acknowledging it. This can… perhaps obviously… lead to a lot of defensive language. My favorite responses to criticisms include:
  • That’s a good point, we’ll make sure to evaluate it in testing.
  • Is there a change you might make to avoid that?
  • Let’s do some math to see.
  • Thank you for the input.
  • YOLO! (Kinda joking, but only kinda. Sometimes we want to do something because it’s fun, not because it’s the best idea ever.)

Finally, we do our best to avoid logical fallacies, and there are a few of them. I found a lovely chart covering them using ROBOTS. Adorable.

Essentially all of these fallacies can be disproven through testing/math/analysis, so we try to do as much of these three as we can. In any event: screen arguments through this list to make sure that the argument is valid, made in good faith, and effectively proves the point. If it doesn’t pass this sniff test maybe a different tact is a better choice.

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This the the real post we need to talk about. Many teams, including ours are struggling from communication right now!

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Bad example. I will defend Baller Hippo as I would my own child.

Baller Hippo is more then just a dumb name for a dumb robot archetype. Baller Hippo is love. Baller Hippo is life.

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…and what was “Baller Hippo”?

(not that it really matters)

In 2017 a design was proposed to completely ignore gears and only shoot fuel. The robot would be super fat, hungry for fuel if you will…

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I think the more important aspect, and the one that earned the name, was that it’s only auto move was to immediately trigger all the field fuel hoppers. The sole purpose was to make a huge mess of the field then careen around having a good time. If it scores points, so much the better.

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I took 5 old batteries to Auto Zone today. Was told that they only accept automotive batteries for cores.

I ended up taking them to a scrap yard, along with a bunch of aluminum scrap pieces we have accumulated over the years)…they gave me $7 for the batteries and $16 for the aluminum :man_shrugging:

Ah, you need to call them “motorcycle batteries” :wink:

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