Help With Spud Gun

jimmy101 · Sun Jun 28, 2009 12:46 pm

Hmm, reading everyones post reminds me that this type of measurements are a lot trickier than you might expect.

For a chest protector there are a couple concerns; total energy transfered to the protector, time over which the energy is transfered and the area over which that energy is distributed on the wearers side.

Seems to me you could make adequate armour by maximizing/minimizing any combination of those characteristics.

To get total energy transfer a ballistic pendulum (BP) is probably the easiest way to go. Unlike using a BP to measure the KE of a bullet, where the bullet must not rebound from the BP, in this case rebound would be OK since you want the energy transfered and not the bullet's energy?

To get the area part of the problem is trickier. What is the force and over how much area is that force distributed? Given enough surface area to distribute the force and you could make a protector that would dissipate the energy of a high velocity round. (As long as the round can't penetrate the protector.) Given a baseball moving at "baseball type velocities", WAG that the contact area of the baseball is 1in<sup>2</sup> then if you can distribute that force over 100in<sup>2</sup> (10"x10") on the wearer's side of the protector then you've dropped the pressure 100X even without absorbing any of the energy. The wearer's body would recoil because of conservation of momentum but the wearer is a heck of a lot more massive than is the ball so the recoil velocity would be tolerable. The large surface area would prevent bruising and/or penetration at the contact site.

nomansland · Mon Jun 29, 2009 3:09 pm

Hey Guys. So I am deciding on getting a bigger valve, and since I don't have much time now to try to build my own (as well as the fact that this cannon is for the school actually so its better I get a valve made by someone knowing what they are doing), I decided with getting the mauler vavle.
http://www.launchpotatoes.com/index.php ... oductId=26

Agree, or any other suggestions on other valves?

As you can see from my picture on the first page of this topic, my setup is linear, that is the valve input and output are 180 deg. from each other. Therefore, if I were to get the mauler, or any other valve who's input/output is 90 degree apart, then would using an elbow valve cause much flow disturbance/choke of the air as I release it.

Here is a pic of the mauler valve with an elbow valve:
http://img410.imageshack.us/img410/4830 ... 004mc9.jpg

Lastly, with the mauler valve, does the trigger assembly (if I were to get the one from the site launchingpotatoes) get plugged into the back of the valve?

Also, a comment on the speed of the baseball. We actually do have a chrony to measure the speed. However, after many tries with it, we obtained some crazy, very incosistent (beyond +/- 10%) results. The chrony uses photoreceptors that are triggered when the ball pases over the two sensors. I followed the manual by putting the chrony six inches below the projectile and putting on the white backgrounds. This can be seen in my picture on the first page of this topic. Is there something I might be still doing wrong?

Thanks for the help guys.

jimmy101 · Mon Jun 29, 2009 5:28 pm

nomansland wrote: Also, a comment on the speed of the baseball. We actually do have a chrony to measure the speed. However, after many tries with it, we obtained some crazy, very incosistent (beyond +/- 10%) results. The chrony uses photoreceptors that are triggered when the ball pases over the two sensors. I followed the manual by putting the chrony six inches below the projectile and putting on the white backgrounds. This can be seen in my picture on the first page of this topic. Is there something I might be still doing wrong?

The only thing I can think of is the light source. Are you under fluorescents lights? Does your chrony's doc's say anything about using it under fluorescents?

The variability you saw may well have been real. Especially if you were getting varying amounts of blowby and frcition depending on how the ball was loaded.

Technician1002 · Mon Jun 29, 2009 8:01 pm

jimmy101 wrote:
nomansland wrote: Also, a comment on the speed of the baseball. We actually do have a chrony to measure the speed. However, after many tries with it, we obtained some crazy, very incosistent (beyond +/- 10%) results. The chrony uses photoreceptors that are triggered when the ball pases over the two sensors. I followed the manual by putting the chrony six inches below the projectile and putting on the white backgrounds. This can be seen in my picture on the first page of this topic. Is there something I might be still doing wrong?
The only thing I can think of is the light source. Are you under fluorescents lights? Does your chrony's doc's say anything about using it under fluorescents?

The variability you saw may well have been real. Especially if you were getting varying amounts of blowby and frcition depending on how the ball was loaded.

Thanks for catching the bit on the light source.. Great catch.
http://www.youtube.com/watch?v=PnJWbE_dd48

nomansland · Tue Jun 30, 2009 10:52 am

Hey Guys. So I am deciding on getting a bigger valve, and since I don't have much time now to try to build my own (as well as the fact that this cannon is for the school actually so its better I get a valve made by someone knowing what they are doing), I decided with getting the mauler vavle.
http://www.launchpotatoes.com/index.php ... oductId=26

Agree, or any other suggestions on other valves?

So do you guys have any suggestions on this though?

Thanks.

Technician1002 · Tue Jun 30, 2009 11:14 am

nomansland wrote:
Hey Guys. So I am deciding on getting a bigger valve, and since I don't have much time now to try to build my own (as well as the fact that this cannon is for the school actually so its better I get a valve made by someone knowing what they are doing), I decided with getting the mauler vavle.
http://www.launchpotatoes.com/index.php ... oductId=26

Agree, or any other suggestions on other valves?
So do you guys have any suggestions on this though?

Thanks.

It's a great valve. I have heard of nobody having trouble with it. It should work well for consistent shots and good speed. I think you will be impressed with the change in performance. Use large pipe into and out of it. Don't choke it by keeping the fittings for the smaller valve. Go full flow.