Was this a class project? Where do you go to school?

We're all students at Olin College and the Confectionery Cannon was our project for Principles of Engineering. Check out some of the other class projects:

This website seems unfinished...

That's because it is.

You spelled "confectionery" wrong, idiot!

First, that isn't a question. Second, that's not very nice! Third, nope.

What sort of marshmallows do you use?

This kind! Though we've also used store brand marshmallows, as well as mini-marshmallows.

How is this system safe?

There is a certain risk associated with working with a used air compressor and intergrating that high pressure system with our PVC reservoir. To mitigate the risk, we added a safety release valve, preventing us from filling our reservoir with pressures higher than 30psi.

Where did you get the cabinet?

We built the cabinet with the express purpose of housing all of our components while creating pleasing aesthetics. Constructed out of 5/8" plywood, the 2' x 2' x 4' cabinet has a foam-lined door that latches shut to reduce the noise made while the compressor is running.

What were some of the challanges that you faced while working on this project?

One of the most frustrating problems we faced in our system was the inconsistency in size and shape of marshmallows. We encountered jamming, double-loading, and a variety of other problems. While the addition of cornstarch for lubrication partially solved this problem, this issue nonetheless made calibrating the automated ranging more difficult.

A second issue we faced was calculating the distance to the target. At the begining of the project we decided to use an ultrasonic range finder to get distance readings. While we tested several types of ultrasonic rangefinders, we found all of them had trouble getting accurate readings from fabric (i.e. clothing) at the distance that the cannon has its best accuracy. In the end we skipped using a rangefinder altogether and decided on calculating the distance with the size of the face that the webcam detects.

What's up with the reservoir?

It's important to remember that this might not the best way to construct such a reservoir--we took budgetary considerations heavily into account when building our reservoir. The following are a few considerations someone looking to build a similar device might want to take into account.

  • PVC isn't technically rated for gas pressure. While it can perform well in many applications (such as this one), the pressure rating on the side of any PVC pipe or fitting is only for water pressure. A reservoir made from steel pipes and fittings would be safer at low pressure at the same time as allowing experimentation with higher pressures.
  • Unfortunately, our regulator lacks precision. The regulator has issues with staying at the same pressure for a long period of time, and the output pressure varies slightly with the input. At the low pressures we require, this effect is significant--a precision regulator would make our shots more repeatable.
  • The clear tube between the output of the sprinkler valve and the barrel of the cannon has a tendancy to become kinked. We resolved this issued by adding clear acrylic rings around tube where it tended to kink. This solution is less than optimal, it'd be better to choose a tube less likely to kink.

Can you fire multiple marshmallows?

Yes! We made a small open cylinder out of painters tape, and with the addition of some mini-marshmallows, it acts much like a shotgun shell. Firing a lot of marshmallows makes it easier to catch at least one!