Help With Marshmallow Launcher

Technical Technical Discussion
#1

So this year during the off-season my team has been asked to build a robot that launches marshmallows.

We are considering launching them by just putting the marshmallows into a barrel and then letting compressed air into it, like most t-shirt launching robots. Any thoughts on other ways to launch marshmallows, and any other considerations if we do use a t-shirt launcher style?

#2

Wait. A robotic… marshmallow launcher???

Do you have any sort of range/rate-of-fire specs?

I’ve seen marshmallow blowguns (PVC–don’t use this for compressed air–these were powered by lung power) that were simply a small-diameter tube with some sort of magazine. Marshmallows being round-ish with flat ends, make sure they’re lined up to go along the barrel. Low pressure would be a really good idea–a quick puff through the aforementioned blowgun could easily send a small marshmallow across the room. (Though you’d want to do some testing.) Possibly send multiple marshmallows in one shot…

Personally I’d suggest a multi-barrel, for cool factor. Just don’t cross the steams…

Honestly, the really easy way would be to build a small catapult, drop a bag of marshmallows onto it, and let fly.

#3

We were thinking bursts of mini-marshmallows, though a continuous stream would be awesome!

We were thinking of using a catapult, but we weren’t sure if the marshmallows would have enough momentum.

#4

If you want to go for a more standard FRC projectile route, you can use flywheels. I have a feeling marshmallows would work well with a single-wheeled flywheel, but a multi-wheel should do the trick. Some experimenting with different speeds and wheel types should give you some decent results. (EDIT: you’ll probably want the grippiest and most-conforming wheel possible like a fairlane, AM compliant, or WCP flex wheel) You should be able to get them to launch about as far as you would with an air cannon, and you’d be designing a mechanism with greater applicability to FRC (since air cannons aren’t allowed*).

*standard disclaimer about rules in the future possibly changing

EDIT:

Enough momentum is relative. It will depend on how far you want them to go. A few feet? A catapult should do the trick. Across the room? You’ll probably want something stronger.

#5

I’m largely with Eric - fast moving (not high pressure) air sounds like a great way to go, and preferably a rapid-fire system.

I see two big problems with rapid marshmallow launching, whether mechanical or air-powered:

  1. Indexing marshmallows sounds like a recipe for frustration. Because marshmallows compress rather easily, I’m guessing that a largely horizontal, modest speed centripetal indexer would be more successful than the systems we saw for fuel this year.
  2. How far can you propel a marshmallow, anyway? Marshmallows have rather small density, and negligible flow-through, so the ratio of air friction to momentum is rather high. The air drag around a solid object goes up as the square of the velocity, and it probably rises considerably faster around a flexible marshmallow which may spread out as the air pushes against it. This, in particular, makes me think that having the marshmallow embedded in a stream of fast-moving air would be more successful than a ballistic launch which required the same energy.

I would try a fairly large squirrel cage fan, with the output throttled down to a tube slightly larger than the marshmallows, with an index/loading tube which always has a marshmallow inside to prevent the air stream from splitting.

I’m really dubious on flywheels - marshmallows compress rather in-elastically, which means that the contact force on those flywheels will be reduced, reducing the propelling force which can be generated.

(In case I wasn’t clear enough, I have never done this before, just thinking out loud.)

#6

There are toy marshmallow guns like this one, which use air to launch(provided by a built in hand pump, one pump per shot.) I’m thinking some sort of a slingshot mechanism might work well, either to actuate the air pump forcefully or just slingshot the marshmallows directly. Another thing that might work would be a pneumatic cylinder or an elastic-powered piston that pushes the marshmallows out of the barrel. A cylinder might be a good option for a rapid-fire design, at least as long as the air lasts.

#7

Would making it like the ping pong ball machine guns work where the air launching the ping pong ball also drags the next on it or ar marshmallows too sticky for that. If the former is true that would be quite an amazing way to launch them, rapid fire marshmallow launcher mounted on a robot just sounds amazing. If you don’t know what I’m referring too go watch Adam Savage’s video on the Tested YouTube channel.

#8

Thanks for all the ideas! I think my team will experiment with a blower/squirrel cage blower as well as a direct compressed air methods.

#9

Put the marshmallow(s) into a sabot(s) that either falls away, or doesn’t, after launch.

“Launch a marshmallow” doesn’t necessarily mean that the marshmallow is the projectile. Maybe instead, the marshmallow is the payload, or is one part of the projectile.

Astronauts would be disappointed to learn that launching an astronaut into space meant that they had to ride atop a rocket instead of inside the top of one.
:wink:

Blake