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Golf ball challenge! Help appreciated.

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Unread postAuthor: Technician1002 » Sun Oct 04, 2009 9:31 pm

mysticjbyrd wrote:
jimmy101 wrote: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 isn't 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.


Use air, not propane. The regulator is a high quality regulator designed to hold a stable pressure and not wander like the cheap air tool regulators. My little regulator on my compressor sets somewhere within about 15 PSI of where it is set. My welding regulator on the other hand holds set pressure to within maybe 1/4 psi or less.
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Last edited by Technician1002 on Sun Oct 04, 2009 10:54 pm, edited 1 time in total.
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Unread postAuthor: irisher » Sun Oct 04, 2009 9:33 pm

Technician1002 wrote:
mysticjbyrd wrote:
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.

Why not just use a protractor?
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Unread postAuthor: Reactor4 » Sun Oct 04, 2009 9:37 pm

yea protractor sounds good, maybe with a steel pin or something attached to the stand so when adjusted, it moves along the outside of the protractor and points over the incriminates. Oh, and you should probably go with the sprinkler valve or QEV, i saw somewhere else in here that using a ball valve will throw off your aim, and indeed it will.
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Re: Golf ball challenge! Help appreciated.

Unread postAuthor: rcman50166 » Sun Oct 04, 2009 9:46 pm

mysticjbyrd wrote:So... I am doing a golf ball challenge for an engineering class and I would like a little inside info on air cannons from the pros I am a complete noobie to this material, so please feel free to give me the dumbed down version at first.

Here are the rules of the competition.
• Max distance is 50 yards
• Min distance is 20 yards
• Budget is $160 if all new parts however you are free to use any parts that you wish
• No chemical reactions (this means rocket engines, combustion, hair spray, starter fluid)
• EVERY DESIGN MUST BE SAFE OR YOU WILL NOT BE ALLOWED TO COMPETE!
• The base must be less than or equal to 4 ft by 8 feet, but other parts may extend beyond but not over 2 ft overall outside the 4 x 8 ft footprint .
• No part can extend beyond the start line during launch.
• Device must be free standing and sit on the ground.
• Device cannot be moved back or forth between to adjust for distance.
• Cost of air compressor not counted if using compressed air.
• Two practice shots at first distance, no practice shots are on second and third distances.
• Anything attached the golf ball must “fall off” before the ball hits the target.
• Someone not in the class will fire the device.
• Three scoring shots per distance.
• Making minimum distance 1 points
• 7.5 ft ring is worth 3 points
• 5.0 ft ring is worth 4 points
• 2.5 ft ring is worth 5 points
• We will have competition no matter the weather conditions.
• Tie breaker will be a fourth distance.


There will be 3 targets laying flat on the ground at anywhere between 20 and 50 meters away. The class will be separated into groups and the team with the most accurate setup, most points, wins. The winning team gets a score of 100 with each proceeding team losing 5 pts per rank.


Anyways thanks for any help in advance.


Slingshot. Simple, powerful, adjustable, and only one moving part.
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Unread postAuthor: irisher » Sun Oct 04, 2009 9:49 pm

Would you trust your grades to the slingshot skills of a stranger?
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Unread postAuthor: Reactor4 » Sun Oct 04, 2009 9:50 pm

hahaha nice one rcman50166! I like it! :D keeping Murphys law in mind i see?
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Unread postAuthor: rcman50166 » Sun Oct 04, 2009 9:53 pm

Reactor4 wrote:hahaha nice one rcman50166! I like it! :D keeping Murphys law in mind i see?


Correct. In engineering part of the concept is to keep devices as simple as needed to complete the task at hand. I'm in my sophomore year of becoming a mechanical engineer and I couldn't agree more.

irisher wrote:Would you trust your grades to the slingshot skills of a stranger?

Sure, you just indicate how far it needs to be pulled. A monkey could do it.
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Unread postAuthor: Moonbogg » Sun Oct 04, 2009 10:11 pm

irisher wrote:Would you trust your grades to the slingshot skills of a stranger?


Have a latch in place that holds and releases the poutch so there is no guesswork.
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Unread postAuthor: rcman50166 » Sun Oct 04, 2009 10:25 pm

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Perfect Latch
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Unread postAuthor: D_Hall » Sun Oct 04, 2009 11:38 pm

Not really a perfect latch... Does the person open it quickly or slowly? That WILL affect the output of a mechanical system such as a slingshot.
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Unread postAuthor: jackssmirkingrevenge » Mon Oct 05, 2009 5:09 am

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


The bubble level should be used in conjunction with an adjustable base to ensure that the base is always level. To determine elevation, a protractor fixed to the barrel with a plumb line from its centre are all you need.
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Unread postAuthor: rcman50166 » Mon Oct 05, 2009 8:31 am

D_Hall wrote:Not really a perfect latch... Does the person open it quickly or slowly? That WILL affect the output of a mechanical system such as a slingshot.


The time taken to release will be nearly a negligible variable if I understand what you are talking about correctly. The time it takes to slip off the latch will be a small portion of the total time of the system, which includes the acceleration of the projectile. I personally think the latch shown would be fine for the job.
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Unread postAuthor: D_Hall » Mon Oct 05, 2009 8:42 am

jackssmirkingrevenge wrote:The bubble level should be used in conjunction with an adjustable base to ensure that the base is always level. To determine elevation, a protractor fixed to the barrel with a plumb line from its centre are all you need.

Which, if you have a fixed elevation, is not required.
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Unread postAuthor: D_Hall » Mon Oct 05, 2009 8:44 am

rcman50166 wrote:The time taken to release will be nearly a negligible variable if I understand what you are talking about correctly. The time it takes to slip off the latch will be a small portion of the total time of the system, which includes the acceleration of the projectile. I personally think the latch shown would be fine for the job.

IF the person opens the latch briskly.

If they don't, then the mechansim will allow the projectile to move forward a half an inch or so before it is effectively released.

IOW, you're leaving a variable (stretch length) slightly open to operator error.
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Unread postAuthor: rcman50166 » Mon Oct 05, 2009 9:10 am

D_Hall wrote:
rcman50166 wrote:The time taken to release will be nearly a negligible variable if I understand what you are talking about correctly. The time it takes to slip off the latch will be a small portion of the total time of the system, which includes the acceleration of the projectile. I personally think the latch shown would be fine for the job.

IF the person opens the latch briskly.

If they don't, then the mechansim will allow the projectile to move forward a half an inch or so before it is effectively released.

IOW, you're leaving a variable (stretch length) slightly open to operator error.


Perhaps we are thinking of two different things, I'm thinking there is some sort of hoop behind the sling that has a single point of release (a solid rope or cable)
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