Perfect spiral, every time

[Carmine] let us know about his team’s Automated Football Launcher. Their goal was to combine a football launcher with motion tracking, to allow a player to practice running and catching with the perfect throw. Unfortunately, and we’re not quite sure when, they ended up changing out the Jugs machine for an air cannon, which resulted in the use of foam footballs and the loss of throwing factors such as spiral. Somewhat defeating the purpose but we’ll let it slide; only because we know its going to be shooting potatoes eventually.

The project comes together by using two cameras giving distance and color tracking, combined with a rotating platform (and the best use of garden hose ever), an accurate set-top for their launcher. As seen in the video after the jump, it works out quite nicely.


  1. medix says:

    Rifled barrel + potato = huge distance with tons ‘o accuracy. Now just gotta figure out how to rifle a piece of PVC.. ;)

  2. Hacksaw says:

    Same way you would rifle a steel barrel with a rifling cutter. Did the writer of the article go to school with Al Gore? there is no “e” in POTATO

  3. mixadj says:

    @medix thats exactly what I was thinking…… Maybe they could drill into the pvc itself to create a kind of reverse rifling? Another option might be to use a kind of cart that rides on a set of helix shaped tracks within the barrel to give the ball spin as it speeds up…..

  4. Ramon says:

    Nobody spelled “potatoes” wrong in this article, and neither did Al Gore. Perhaps Hacksaw is unaware of plurals and the fact that Dan Quayle is the one who famously corrected a student for properly spelling potato.

  5. biozz says:

    ITS SPELLED POTATOES not potatos

  6. Jason says:

    To Hacksaw:

    “Did the writer of the article go to school with Al Gore? there is no “e” in POTATO”

    Error 1 to the writer of the article.

    Error 2 to you. Dan Quayle is not spelled A-L G-O-R_E.

  7. Jason says:

    @ blozz
    Error 3 goes to me for not reading the article and realizing that noted error 1 didn’t exist. : )

  8. userjjb says:

    It always bothers me to see the low quality/dangerous air cannons that appear here, especially in contrast to the usual amazing craftsmanship that is the standard here.

    Even _pressure rated_ PVC is not designed to carry pressurized air, just pressurized water, (Pressure is pressure for the purposes of material failure point, but the energy contained in a volume of compressed air is much higher than a volume of water because it is far more compressible) though that in itself isn’t terribly damning.

    However the reducers that they are using aren’t even pressure rated, they are DWV rated (drain/waste/vent), these are cell core, not solid core PVC and are dangerous to use in pressure applications.

    Safety considerations aside, the use of a solenoid actuated sprinkler valve is severely limiting their performance. At the very least modding the valve to be pneumatically actuated would make the valve open perhaps 10-20 times faster.

    Additionally, sprinkler valves are chamber sealing diaphragm valves and limit flow quite a bit. If you need a drop in commercial solution QEVs are leagues better and may actually be even cheaper than the sprinkler valve. If you are willing to spend an extra hour on construction you can easily build a piston valve (with no machining or special parts required, just some creativity) that will have millisecond opening times and will have no flow obstructions.

    A higher performance valve will enable lower operating pressures (maybe as low as 15-20 PSI) and a much smaller pressure chamber (maybe 4 or 5 times smaller than what they are currently using). This means greater launch frequency, increased operating safety, and a far cheaper/quieter compressor.

    Those interested in serious design/construction of air cannons should check out an excellent tool called the Gas Gun Design Tool (GGDT). Just google GGDT, it’s the first result, or see

  9. Doug says:

    Thanks, userjjb, for the break down of how bad these electrical and computer engineers did in materials class.
    The point of the project is that it tracks color and motion to shoot something. Nice work in that respect.
    If you read the final project summary, they list trade-offs of using this design. The jugs machine was not available. Designing a football launcher wasn’t even in the scope. They wanted to rent a jugs machine and just implement the tracking software and controls. Cost also became a factor (as did time (with finals week next week) I’m sure).
    Also nice to see GT students on HaD.

  10. Addictronics says:

    Check out they have rifled pvc barrels.

  11. andrew says:

    It’s strange that they calculated z-distance based on the y-axis height. They had two cameras so why not calculate z based on x-axis offset of the tracked blobs? Either way, their obtained accuracy is decent along the z-axis.

    If an application of this is to help train receivers, the tracking should actually try to predict the receiver’s future position based on their past trajectory and the best guess of how long it will take the ball to get there. It seems like the current tracking algorithm only finds the receiver’s current position.

  12. Jake says:

    @andrew I know the guys that worked on this and they didn’t calculate z-distance based on y-axis height. They used the x-axis offset as you said, where did it say they used the y-axis?? Also, it did try to predict the future route, I’m not sure the video does a good job at showing that, however.

    Also, they aren’t mechanical engineers and built everything themself so I guess you can’t really blame them for not building a completely up to par propulsion system.

  13. Hirudinea says:

    As for the spin problem, why not rifle the barrel and put a football in a sabot, spin the sabot and when it splits away after firing, spining football. And speaking of sabots, why do I suspect that the Army will be adapting this into an automatic artillery system?

  14. aEx155 says:

    @userjjb –

    You have to remember that a sprinkler valve is the most common, easily accessible electronically-controlled valve. While the valves you mentioned would increase performance greatly (as you said), they can’t be electronically controlled as-is.

    Another suggestion would be breech loading. Having to ramrod projectiles down long barrels is time-consuming. (even better would be to make it semi-automatic)

  15. underwood says:

    @aEx155 i love how this has gone from training football players to semi-auto, rifled barrel football cannon. :)

  16. anon says:
  17. Physics-Dude says:

    Hey look, this guy rifles barrels for potato launchers. I bought from him before for stuff for my “Tater Tosser”.

  18. foamy9210 says:

    I would love to see them add in some way of measuring speed so that the guys could run at full speed like a real football player would but still great work

  19. Diymaker says:

    it would be more grateful if it have automatic reload feature.

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