Building a pool stroke machine

DaveK

DaveK

Still crazy after all these years
Silver Member
So I've been toying with the idea of building a machine that can execute a pool stroke. I've got a little shop, and a table in the basement, and enough spare time over the next few winters to do this project ...

In general the machine would be to satisfy my own anal engineering mind, but I suppose the machine could be used to test various cues to some extent. There is one nagging design issue, and would appreciate any and all comments. Should the motive force stroking action be a pendulum (an idealized human stoke with no movement other than a pivot around an 'elbow'), or a straight slide ? From a construction point of view I have workable designs for both approaches. I believe that instrumenting the straight slide stroke would be easier, but that is not how real people stroke. The pendulum stroke will require slightly more complex instrumentation and set-up procedures, but might be more 'real world'. Whadaya think ?

Also, for those who have seen a pool robot (or whatever you want to call such a beast), how do the balls get positioned on the table to maintain a consistent set-up over many strokes ? I have some ideas, but would love to hear how any others do it. OK, even if you haven't seen one in action, how might it be done ? My concept is to reference the cue ball to a corner using a couple of micrometer-adjust hard stops (at right angles to each other).

Dave
 
IMO you must incorperate the wrist aswell as the elbow so the cue remains level through the stroke.
 
I would design it so it could test different strokes as well as different cues.

Also closed bridges -vs- open bridges.

And the tip radius (dime, nickel, quarter). I have read that tip radius will have an effect on cue ball deflection, but I have not read about any testing being done in this area.

For draw shots, I place my hand all the way on the back of the butt of my cue and use a closed bridge. I read somewhere that placing your hand at the back of the cue changes the up/down action of the tip. I've also been experimenting with placing my hand slightly forward of normal on the butt for force follow shots.

I have tried open and closed bidges for cue ball frozen to the rail shots.

And it seems to me that a dime shaped Moori tip works better for draw and that a Moori S, M, or Q (hard) tip works equally well for draw. And that otherwise, soft tips work better for draw. Also that soft tips work poorly for long bank shots.

I guess the thing to do would be to come up with a set of questions, then design a stroke machine which would be designed to answer those questions.

So...

Does a light hand grip on the butt make for better shooting than a firm grip?

Is following through necessary for a machine? Maybe for draw shots?

Does a closed bridge work better than an open bridge for some shots like draw, force follow, extreme English, frozen to rail shots, and shooting over a ball shots?

Is a nickel radius better than a quarter radius for draw shots, English, etc.?

Does tip softness/hardness have an effect on shots like draw or English?

Does a Moori tip work better than a leather tip for English/draw?

Does tip radius (dime, nickel, quarter) change cue ball deflection?

Does the size of the shaft/ferrule (11mm, 12mm, 13mm, 14mm) matter for any shots?

Does placement of your hand on the butt; forward, normal, or all the way back make for better shots with draw or force follow (due to changing up/down motion of tip)?

Is chalking after every shot necessary, or just for certain shots?

Backhand English?
 
FYI - Here are some links to other research/testing...

Answers to: Which Break Cue is the Fastest?, Which Shaft Deflects Least?, Which Chalk Works Best?
http://www.platinumbilliards.com

Great technical paper on cue ball deflection and testing thereof: Everything You Always Wanted to Know About Cue Ball Squirt, But Were Afraid to Ask...
http://www.sfbilliards.com/Shepard_squirt.pdf

High Speed videos of various pool shots...
http://www.engr.colostate.edu/~dga/pool/index.html

Book: The Science of Pocket Billiards...
(Discusses his testing proceedures as well)
http://www.amazon.com/exec/obidos/tg/detail/-/0962289027/103-4994865-2850221?v=glance
 
DaveK said:
... Should the motive force stroking action be a pendulum (an idealized human stoke with no movement other than a pivot around an 'elbow'), or a straight slide ?...

Also, for those who have seen a pool robot (or whatever you want to call such a beast), how do the balls get positioned on the table to maintain a consistent set-up over many strokes ?...
Click to expand...
For the second part first, I think Predator uses stops as you have suggested, while Meucci uses a small hole in a thin plate.

For the first part, I don't think it makes any difference for the action, especially if you have the tip hit the ball when the pendulum is at bottom-dead-center and the stick is moving along its own axis. Go with what you can make the most repeatable.

Far more important is how the robot grips the stick. It is not so easy to get a grip that is no more firm than the human hand. Iron Willie suffered from a grip so stiff that it caused the whole several pounds of the actuator arm to get into the shot. That is totally unlike a real hand, which basically prevents the arm from really being in the shot.

You need to have a system that does not significantly increase the mass of what actually hits the cue ball.
 
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Bob Jewett said:
For the second part first, I think Predator uses stops as you have suggested, while Meucci uses a small hole in a thin plate.

For the first part, I don't think it makes any difference for the action, especially if you have the tip hit the ball when the pendulum is at bottom-dead-center and the stick is moving along its own axis. Go with what you can make the most repeatable.

Far more important is how the stick grips the ball. It is not so easy to get a grip that is no more firm than the human hand. Iron Willie suffered from a grip so stiff that it caused the whole several pounds of the actuator arm to get into the shot. That is totally unlike a real hand, which basically prevents the arm from really being in the shot.

You need to have a system that does not significantly increase the mass of what actually hits the cue ball.
Click to expand...

Thanks Bob, I appreciate your comments. As far as the 'grip' goes, my current design is to use a steel pipe, perhaps 4" (100mm) long with an ID of 1.75" (40mm) or so, with foam weather stripping on the inside. The weather stripping will compress around the butt / handle area and hopefully provide sufficient friction to accelerate the cue. Upon impact I believe that the foam will give and the cue will slip a bit. After impact the foam should allow the mechanism to push the cue's 'follow through'. I'm sure it will take a few tries to get a useable amount of compression and 'grip' without excessive slipping while accelerating the cue. One additional benefit of this scheme is that the cue will not be marked or scarred in the machine.

Dave
 
Billy_Bob said:
FYI - Here are some links to other research/testing...
Click to expand...

Thanks for these links Billy_Bob and steigweis. I've been through them all over the years, but must admit to not reading Rons paper too thoroughly. It's been 25 years since I went through EE and my math is about that rusty ... maybe when the machine is complete I'll test to see if the calculations match the observations, but first the machine :)

Dave
 
DaveK said:
T... As far as the 'grip' goes, my current design is to use a steel pipe, perhaps 4" (100mm) long with an ID of 1.75" (40mm) or so, with foam weather stripping on the inside. The weather stripping will compress around the butt / handle area and hopefully provide sufficient friction to accelerate the cue. Upon impact I believe that the foam will give and the cue will slip a bit. ...
Click to expand...
The solution in the case of the Jacksonville Project's tests on Iron Willie was to wrap the grip area of the butt with bubble wrap. I think that there was no slipping.

As far as follow through after tip-ball contact, that will not affect the reaction of the ball, since the ball will already be gone. The distance over which tip and ball move together is about 5mm or less -- about three times as much as the tip is compressed during the shot.
 
Bob Jewett said:
Far more important is how the stick grips the ball. It is not so easy to get a grip that is no more firm than the human hand.
Click to expand...
I'm pretty sure you meant something else here. LOL!!!

Probably: Far more important is how the "robot" grips the stick.

Fred
 
DaveK said:
Thanks for these links Billy_Bob and steigweis. I've been through them all over the years, but must admit to not reading Rons paper too thoroughly. It's been 25 years since I went through EE and my math is about that rusty ... maybe when the machine is complete I'll test to see if the calculations match the observations, but first the machine :)

Dave
Click to expand...

Skip the math... Go to pages 10 and 11 starting at "Squirt Measurements:". This describes a method for testing for cue ball deflection.
 
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