Re: PVC Swinger target stand

by MickeyK on Thu Nov 03 2011, 10:22

JD,

That's a cool site to look around on. I'm always amazed at what can be found on the web.

Can't wait to see how yours works. Swingers and poppers and paper targets (stationary) are all weak points for me in shooting.

Keep us updated.

MK

by Golfer on Thu Nov 03 2011, 10:55

JD - leave it to youto find this ! All that match was to complicated for me, but this looks cool. Thanks - will have to make one !!

by Will_M on Thu Nov 03 2011, 11:11

JohnHeiter wrote:Way to think outside the box JD. Pretty impressive.

In my experience with the swingers we have, adding weight to the counterbalance side does cause the target to present faster when the swinger is released. Does it actually cycle back and forth faster with more weight? That I don't know. I know that moving the weight further out from the pivot point (or lengthening the slats the target is on) causes the back and forth cycles to be slower and less jerky. I don't have math or science to back that up, just my personal observations. Could it have something to do with the fact that we're not really talking about a pendulum here? If there were no target above the point of rotation it would be a pendulum but that's not really what we have?

Anyway JD, cool idea. If you're interested I think Matt and I are going to be doing some welding this weekend after the match. I finally found a source for the steel I needed to fix a bunch of our busted poppers. I can't claim to be an instructor but you're welcome to join in and maybe get a feel for it. Steel targets are a great thing to learn on because it really doesn't matter how ugly your welds are and the steel is thick enough that it's hard to really damage.

Yeah I screwed that up royally.

And I may be staying afterwards for a crash course in welding.

by DBChaffin on Thu Nov 03 2011, 11:39

Will_M wrote:
SubGunFan wrote:Increasing the mass at the end of the swinging unit WILL increase the swing velocity. It makes the unit more unbalanced. The increased mass should also allow the unit to cycle more times.

.

No disrespect intended, but I'm gonna need to see the math/hear some reasoning on that. Here's mine:

First of all, since gravity is what is causing the swinging, increasing mass will not change the period (time for one oscillation) due to the formula:

v=g*t
where v is the velocity, g is the acceleration of gravity (9.81 m/s^2), and t is the time elapsed. As you can see, mass is not present.

If we want to take it a step further, it becomes a basic conservation of energy equation. The sums of kinetic and potential energies must always be equal. In the following formula, potential energy is on the left, kinetic is on the right.
m*g*h= (1/2)m*v^2
where m is mass, g is acceleration of gravity, h is the height from the weight to the ground, and v is velocity.

As you can see, mass is present on both sides of the equation. Meaning it cancels out. No matter what mass I use, it will always cancel out. Whether I use 1 pound or 1000 pounds, it won't change anything.

The only reason the mass is there is to counterweight the mass of the target and target sticks so that it doesn't simply fall to one side.

Science.

I agree 100% with your math related to true pendulums and think you are right as far as the period of the swinging target, but as John mentioned pendulums are not all that is at play here, right?

Since there is a target and slats above the pivot point, we actually are dealing with a lever, right (albeit one that just so happens to be able to swing through nearly 180 degrees)?

It's been a long time since I took physics, but in a lever, m1 × d1 = m2 × d2 (with m and d referring to mass and distance on each side of the fulcrum), for everything to be balanced. But what we are dealing with is the moment or torque, which equals force times distance, right?

Ok, I am a lawyer and getting way over my head in this math stuff, but from my experience adding weight alone cause the target to appear faster when activated (first half of the first swing) as mentioned by Dan and John, because you have increased the force operating on the lever with all other variables being equal. However, it consequently is slower "changing directions" in the second half of the swing, and the total period of the swing (time it takes to go from start to complete one full swing) does not change with added mass alone. The accelleration is different and if this is what "Subgunfan" meant by "swing rate", then I agree with that. I witnessed this when we tried to "speed up" a swinger by adding weight. While the target moved faster during a portion of its swing, it didn't swing faster overall, if that makes sense. I most definitely agree that changing the length of the arm, both above and below the fulcrum or pivot, can change the speed, period, acceleration, etc. Lots of factors to deal with, including frictional losses.

by Myers on Thu Nov 03 2011, 11:48

What did you/they use on the pivot point to reduce friction between the PVC? It would be interesting to see if a race/bearing setup could be concocted. Like a crude needle bearing of sorts.

by jdphotoguy on Thu Nov 03 2011, 13:09

Myers wrote:What did you/they use on the pivot point to reduce friction between the PVC? It would be interesting to see if a race/bearing setup could be concocted. Like a crude needle bearing of sorts.

Just a hole to apply oil to the axle, so virtually anything else would be an improvement.

by jdphotoguy on Thu Nov 03 2011, 13:11

JohnHeiter wrote:If you're interested I think Matt and I are going to be doing some welding this weekend after the match. I finally found a source for the steel I needed to fix a bunch of our busted poppers. I can't claim to be an instructor but you're welcome to join in and maybe get a feel for it. Steel targets are a great thing to learn on because it really doesn't matter how ugly your welds are and the steel is thick enough that it's hard to really damage.

Yeah, I'd be interesting in helping out. Anything I should pickup ex. protective eyewear, clothing.....?

by bsdubois00 on Fri Nov 11 2011, 08:10

i just wasted 15 minutes trying to figure WTF is going on - all I want to know is DOES THIS THING WORK!?!?!?!

by jdphotoguy on Fri Nov 11 2011, 08:41

bsdubois00 wrote:i just wasted 15 minutes trying to figure WTF is going on - all I want to know is DOES THIS THING WORK!?!?!?!

Yes, it does work. Rick and I tried it out last Friday and surprisingly it was challenging to hit, which is what I was after.

I didn't have time or sand to add some weight to the swinging part, but it still moved pretty good, I hope to try it next week with some weight added and the improvements I've outlined earlier.

by Golfer on Fri Nov 11 2011, 08:59

Yeah - it was pretty cool - and just like in a match, I rarely hit it !! Like JD said, some sand or weight will make a difference, but I would definetly recommend building one. I know I need the practice with a swinger. Hey, JD - how much do you charge for them ?

by BigDaddyQ on Fri Nov 11 2011, 11:06

To resolve your math delimma. Adding sand will effectively change the Center of Gravity which will in effect change the length of the pendelum. As this is a counter weighted system the COG is equivelent to the length of the lever arm. With that being said I think we can make this cheaper by leaving out the 4 bends at the bottom and just making the stand a little wider and putting some concrete or sand in the bottom to make it more sturdy. As far as bearings going its added expense for not much difference. You'll notice that most things in order to lower cost will use a bushing made of a more self lubricating material. In the case of steel or aluminum most will use bronze.

by jdphotoguy on Fri Nov 11 2011, 13:49

Golfer wrote:Hey, JD - how much do you charge for them ?

You buy the parts and I'll put it together for you, take a few minutes, can be done at the range.

by bsdubois00 on Wed Nov 16 2011, 13:02

JD - can you get a video of this thing in action - I may wanna build one.

B

by JohnHeiter on Wed Nov 16 2011, 13:12

Here you go. This guy slices more pie than Mrs. Smith's but you can get an idea.

http://www.parmarng.org/freeidaho/AlSkDjFhG/RockingTargetPVC/124_2461.AVI

http://www.parmarng.org/freeidaho/AlSkDjFhG/RockingTargetPVC/127_2720.AVI

by bsdubois00 on Wed Nov 16 2011, 13:16

OK - JD - I wanna make one - hook me up!!!!!

by JohnHeiter on Wed Nov 16 2011, 13:34

Why do you need JD's help? From this it looks like all you'll need is 8' of 2" pvc tubing, four T's, six elbows, a protractor, a Texas Instruments graphing calculator with IR capability, a Chinese kid who's good at math, and permission from NASA.

Done deal.

by bsdubois00 on Wed Nov 16 2011, 14:04

I don't have any of those things - or tools to make those things - and I only have a red head that is semi good at math....

by BigDaddyQ on Wed Nov 16 2011, 19:34

I've built 2 now in the past 2 days. They work good, mine aren't as pretty since I used a saw-z-all to cut with but they work. It took me 2 10ft 2in pvc pipes, 6 elbows, 4 2x2x2 Ts and to get cheaper I got 2 2x2x1.5 T's and used some 1.5 pipe for the pendulum arm.

by jdphotoguy on Wed Nov 16 2011, 21:56

bsdubois00 wrote:OK - JD - I wanna make one - hook me up!!!!!

The parts list:

2 x 10' of 2" PVC
1 x 18" of 1.5" PVC
6 x 2" T's
6 x 2" Elbows
28 or so #8 x 1/2" sheet metal screws

PVC Rocking Target plans

Be more then happy to help you set one up. Will try to make the modifications I've outlined earlier tomorrow and get some video posted of it in action.