Thinking about designing a double catapult shooter for the offseason, similar 5050 or 2881. How would I go about designing the mechanism? Would I use motors?
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Team 333 used a crank shaft (choo choo) mechanism for our double catapult, the power of the catapult is determined by the spring we use, the path/ trajectory of the cargos being launched is determined by the design of the fingers( the angle the cargos when they leave the place they are landed on)
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I recommend looking up old 2014 mechanisms for how to design a catapult. One design in particular came up fairly often called a âchoo-choo mechanismâ .
Also 2016 designs may be useful to look at, I believe catapults were used fairly often to launch the balls in that year.
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Not a good idea. But one of my favorite kickoff ideas for a catapult: A Flywheel revs up to a set speed, a clutch powered by a pneumatic brake engages it, that clutch is attached to an arm, so when engaged, the catapult arm launches.
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From pit scouting at SBPLI #1 I know that 358 had a pneumatic cylinder that would launch the balls. They could shoot from outside of the tarmac.
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5507 is the GOAT double catapult.
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Quite a few ways to actuate catapults, depending on your goals.
1675 used pneumatic-actuated catapults inspired by 148âs launcher in 2016. We had pretty decent success with it. Happy to answer any questions.
Onshape Link to the Design: Wolverine
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In New England 1740, the Cyber Colonels, had an awesome double catapult IMO. I never got a close look at it, but their reveal video shows it may be as simple as a NEO with a reduction.
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That ONE Team was a part of the double Catapult gang with pnuematic catapults. We controlled them by changing the pulse of air of the solenoids, 100ms was our full power shot at 60psi. we used a smaller pulse to eject the wrong color cargo.
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What cylinder do you use? Bore, stroke length?
Yeah, ours are super simple if you want something easy to try out. Throw a brushless motor on a gearbox with a 25:1 to 48:1 ratio (we liked 36:1 for ~24" arm), mill down a 1/2" hex collar or even 3D print an insert and shove it in some 1" square tube for an arm, then 3D print a scoop for the end (or screw on a collander from Walmart). All of that was mounted to a tower made from 2" square tube and controlled via simple duty cycle and soft limits, with brake mode upon hitting the travel limit releasing the ball. The only real improvement we made over this basic setup was cutting a slot in the hex insert so that we could clamp it on the gearbox output shaft like a hex collar to eliminate slop in the system.
It is tuned for fender shots, but has the power to hit from pretty much anywhere on the field.
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We did something similar that for the soccer ball kicker in 2010. There were dual flywheels that slammed down on the kicker arm. I wasnât around then, but there were plenty of technical challenges to getting it to work I understand.
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Oh the joy that brings to my ears that someone has tried this idea
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That is great. I looked for a while, but donât have any footage or pictures I can find of the 2010 kicker. Just a couple IRI matches, one with the famed 469 robot.
I love how simple this robot is.
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We will probably try something like this, thanks.
You might also want to check out the Behind the Bumpers interview with 2881: https://youtu.be/1_-qTczPrBY
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Yep, thanks.
Hello from team 2881, we are happy to share some info about our robot! Our catapult is mechanically simple and doesnât require any fancy code, although we have added some since our first event.
Quick overview:
Our catapult system consists of two independent catapults, each driven by a single NEO, 36:1 MAX Planetary and chain drive to connect the MAX Planetary to the catapult arm. The arm is a piece of 1â square tubing with an aluminum slug in the drive end and a flat plate with two screws to hold the cargo at the other end. Cargo is held in place slightly above the catapult arm with a sheet metal funnel that is fixed to the frame of the robot. We did this to keep the catapult arm as light as possible.
CAD for our robot can be found here
https://grabcad.com/library/frc-2881-2022-competition-robot-1
Behind the Bumpers Interview
Mechanical Details:
- We started the season with a 45:1 reduction which worked great for the close fender shot. After our first event we decided that we wanted more scoring flexibility so we tested some different reductions. Much like 1740 we determined 36:1 seemed to be the sweet spot that gave us the ability to score anywhere from the fender to about a robotâs length beyond the launch pad.
- The chain drive between the MAX Planetary and the catapult arm was mostly for packaging but also gave us the option to fine tune the overall reduction if we wanted/needed to.
- We spent a lot of time brainstorming ways to keep the throwing end of our catapult arm as light as possible while still giving us some ability to fine tune things. The sheet metal plate with two screws in it ended up being the lightest, most repeatable way to hold and throw the cargo no matter the shape or air pressure.
- The sheet metal cargo funnel does all the work to hold the cargo once we intake it and keeps the cargo lined up over the catapults.
Programming Details:
- All of our prototype testing was done with the REV Hardware Client by adjusting the soft limit, motor output voltage and current limit. This made early testing super easy and didnât require us to have any code running yet. Once they found some values that worked well we just plugged those into the code.
- Both catapults run in an automated sequence that launches one after the other and resets everything. This allows the driver to hit one button and the robot does the rest.
- Each cargo funnel has a REV color sensor that prevents us from scoring the wrong color cargo.
- For our second event we added vision tracking to target the hub and throw from anywhere on the field within our range. The delay between catapult launches varies based on our distance from the hub.
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