Golf ball challenge! Help appreciated.

[jrrdw]

Well with the rule set, the 1st thing you need to learn is "keep it simple stupid"! You'll remember the phrase?

No mysticjbyrd, I'm not calling you stupid so don't get the wrong idea. I just think since you admitted your new to this the guys are getting to technical and don't need to be.

Well I suggest a sprinkler valve with a 2 inch pvc tank a a sdr 21 barrel

Seems to be your best option so far, simple to build, well with in your budget.

Thought: It hasn't been clarified if first impact or final resting point of ball counts.

That's a major problem with any launcher, you need to be clear on that and what kind of surface the callenage is taking place on. It's going to make a big difference.

Someone not in the class will fire the device.

I'm guessing this is why it has to be stationary and can't be moved in between shots?

Just another reason to keep it simple.

[Technician1002]

@jrrdw, I was guessing the stationary rule was not to prevent aiming, but to prevent it from hitting targets simply by calibrating to 50 meters and simply move the launcher back 50 meters from each target. They will need to calculate the distance to each target and adjust the parameters to hit it. This prevents for example a single release slingshot from winning by making all shots 50 meters.

If there is a challange website, it would be nice to see it.

[mysticjbyrd]

The contest site will be held on a football field in December.
Elevation is roughly 600 meters above sea level and wind is very likely going to be a factor.

My original plan was to try to work with a low angle to eliminate wind and flight time. I was also thinking of trying to figure out how to make a good piston valve as it seems like it would give the most uniform amount of air all around the ball.

I also had an idea of maybe making a second piston, made of foam, that gets shot out the barrel behind with the golf ball. I was thinking this could help get a little more power and eliminate any error in the air affecting any 1 part of the golf ball more and sliding it off trajectory.

But like I said I am a noob to this stuff and these ideas might be completely wrong.

[jackssmirkingrevenge]

I was also thinking of trying to figure out how to make a good piston valve as it seems like it would give the most uniform amount of air all around the ball.

I would go for a sprinkler valve. It might not be the most powerful but that is irrelevant in this case, you don't need much energy to get a golf ball 50 yards. Most importantly, the fact that its electronically actuated means that it will be more consistent than any manually triggerred valve.

I also had an idea of maybe making a second piston, made of foam, that gets shot out the barrel behind with the golf ball. I was thinking this could help get a little more power and eliminate any error in the air affecting any 1 part of the golf ball more and sliding it off trajectory.

An unnecessary complication in my view, find a barrel that is as tight as possible and you're sorted. If you're worried about muzzle blast knocking the ball off course (unlikely as I predict you'll only need a small chamber with low volume) a couple of perforations at the muzzle should be more than enough to avoid the issue


.

[mysticjbyrd]

I just ran some numbers with air resistance just for examples.

Vo = 25.82 m/s + 45 degrees = 50 meters
If I can keep the initial velocity to plus or minus 1 meter per second.
(I have no idea what this is in PSI.)
-+1 m/s = +-2.8 m

If I am off on the angle by 1 degree.
+1 degree = +.1 meter off
-1 degree = -.2 meters off



Vo = 40.9 m/s + 10 degrees = 50 meters
If I can keep the initial velocity to plus or minus 1 meter per second.
-+1 m/s = +-1.7 m

If I am off on the angle by 1 degree.
+1 degree = +2.9 meters off
-1 degree = -3 meters off


Unless I can find a really accurate pressure gauge for relatively cheap, than my certainty in the initial velocity seems like it is going to be limiting factor.

[jackssmirkingrevenge]

(I have no idea what this is in PSI.)

This depends on the individual characteristics of the launcher live valve, barrel length, chamber size etc.

Personally I think you should stick to a fixed pressure and alter the launch angle.

[Technician1002]

(I have no idea what this is in PSI.)

This depends on the individual characteristics of the launcher live valve, barrel length, chamber size etc.

Personally I think you should stick to a fixed pressure and alter the launch angle.

It's much easier to set a fixed angle (integrate a spirit level for repeatable setup) and graph range vs pressure from say 10-50 PSI in 5 PSI increments. From there bring an optical rangefinder with you and pick your distance from the graph. Use an accurate gauge for pressure. Use as low pressure gauge as possible to hit your farthest distance.

http://naturalhighs.net/waterfalls/rangefinder.htm

[jackssmirkingrevenge]

It's much easier to set a fixed angle (integrate a spirit level for repeatable setup) and graph range vs pressure from say 10-50 PSI in 5 PSI increments.

Mechanically it's certainly easier, the question is if it will be reliable with less-than-optimal regulation.

[mysticjbyrd]

Yah there are way too many variables to calculate initial velocity from PSI. I plan on trying to find an enclosed area where I can run some tests and calc an average Vo for a given pressure.

@jrrdw, I was guessing the stationary rule was not to prevent aiming, but to prevent it from hitting targets simply by calibrating to 50 meters and simply move the launcher back 50 meters from each target. They will need to calculate the distance to each target and adjust the parameters to hit it. This prevents for example a single release slingshot from winning by making all shots 50 meters.

If there is a challange website, it would be nice to see it.

Yes this is correct. You cannot setup your rig to shoot 50 meters and then simply move it 20 meters behind the start line to hit another target. That is the only real limitation when it comes to moving.

I was originally planning on putting my gun on a sheet of plywood and attacking it sort of like an antenna on a radio. Once I cut the groove in the plywood it will allow me to attach a threaded rod to my cannon. I can then place a nut on the thread all and easily adjust the angle in any direction I want.

[jackssmirkingrevenge]

I was originally planning on putting my gun on a sheet of plywood and attacking it sort of like an antenna on a radio. Once I cut the groove in the plywood it will allow me to attach a threaded rod to my cannon. I can then place a nut on the thread all and easily adjust the angle in any direction I want.

Sounds like a good system and it will enable you to make the fine sort of adjustments you require.

[Technician1002]

It's much easier to set a fixed angle (integrate a spirit level for repeatable setup) and graph range vs pressure from say 10-50 PSI in 5 PSI increments.

Mechanically it's certainly easier, the question is if it will be reliable with less-than-optimal regulation.

Use a good regulator, not one of the cheapie ones sold with junk compressors. Use one intended for precision.

I find these are very stable and highly repeatable. I picked up a spare in a second hand store for $15. You could even make a photoshop scale for it that directly reads average feet instead of pressure. I wish I was there. I would join the competition if possible.

Why combine the inaccuracy of a poor regulator with making mechanical aiming? Bolt on a spirit level so it's aimed the same elevation every time, now simply graph distance vs pressure. In the field on contest day, the setup will match your calibration setup.

[mysticjbyrd]

Do you know of a really good relatively cheap pressure gauge?

PS: Responding to another poster: The 1st hit onto the ground is the point that counts.

Tech 1002 you mentioned

A hand pulled QDV may be OK but their disadvantage is the possibility of messing up your aim when firing it, so I don't recommend one unless you modify one to use a spring trigger.

I plan on making the base of the cannon very sturdy so I think this could be a good idea. I am just curious as to what you meant when you said you modified it with a spring.

PS: How is a bubble level going to help determine elevation? Do they make ones with marks to determine angles of elevation?

[jimmy101]

A decent regulator is going to be fairly expensive. The accuracy of the reg doesn't matter much. What does matter is how accurately you can read it and set it.

How about a different approach. Instead of a compressor with regulator how about a propane cylinder? The pressure is constant for a given temperature as long as the cylinder contains both gas and liquid. Propane is fairly low pressure. A propane cylinder changes the control problem from a pressure regulator to an oven (or water bath) at a constant temperature.

A picnic cooler filled with tap water (~60F) should have enough thermal inertia, and should be well enough insulated, to hold it's temperature for an hour or two. You could also measure the baths temperature and use that to calculate (or at least correct) the pressure. Temp measurements are typically accurate to about 1 part in ~500, which is much better than your are ever going to get with a compressed gas regulator.

EDIT: Make the precise to 1:500, which is what you care about. The accuracy is generally pretty bad unless you have a calibrated thermometer.

[Technician1002]

PS: How is a bubble level going to help determine elevation? Do they make ones with marks to determine angles of elevation?

Bolt it onto a support arm at the base of the elevation triangle. Make the triangle fixed. Set it up every time with the base level. The elevation is fixed in relation to the base. Measure once and forget it. I would recommend between 30 - 45 degrees above horizon. A cheap 30 60 90 triangle would work well for layout. Base level, barrel at 30 degrees.

[mysticjbyrd]

A decent regulator is going to be fairly expensive. The accuracy of the reg doesn't matter much. What does matter is how accurately you can read it and set it.

How about a different approach. Instead of a compressor with regulator how about a propane cylinder? The pressure is constant for a given temperature as long as the cylinder contains both gas and liquid. Propane is fairly low pressure. A propane cylinder changes the control problem from a pressure regulator to an oven (or water bath) at a constant temperature.

A picnic cooler filled with tap water (~60F) should have enough thermal inertia, and should be well enough insulated, to hold it's temperature for an hour or two. You could also measure the baths temperature and use that to calculate (or at least correct) the pressure. Temp measurements are typically accurate to about 1 part in ~500, which is much better than your are ever going to get with a compressed gas regulator.

EDIT: Make the precise to 1:500, which is what you care about. The accuracy is generally pretty bad unless you have a calibrated thermometer.

That isnt a bad idea. Especially since I do not have to shoot it... but I kinda doubt the teacher is going to let someone release flammable propane around everyone else.