I want to "hit" a fixed spot with a physical object over
relatively short distances (< ~20 ft).

This must not present a danger to nearby bystanders (in the
event of a "misfire"). "Weapons" are out of the question.

And, the object must be of sufficient size to be clearly
visible in transit. This also suggests a low transit
velocity.

I figure I need a bit of mass to ensure aerodynamic
effects don't bugger the calculations. E.g., a softball
would be better than a softball-sized hollow ball
which might exhibit more nonlinear behaviors as it
transits from projectile to ballistic motion.

The target is (effectively) a "spot on the floor".
I.e., not a vertical "hoop" to pass through (like
goalposts in soccer).

Accelerating a significant mass would likely prove to
be a challenge so "lobbing" the object seems more
practical. It would also *seem* to be more tolerant
of aiming issues than something HOPING to travel in a
straight line (like a bullet).

So, conceptually, a tube ("barrel") to guide the
initial segment of flight and some sort of mechanism
to propel the object from the tube.

Pneumatic, hydraulic, mechanical, etc.

Will the control over the propulsive force be the tougher
challenge or the precise aiming of the launch tube?

[You are given (r,theta) to target and no feedback as
to proximity of strike -- unless a direct strike. The
target -- or launcher -- will move after each attempt]

Of course, "you" is a machine...

On Saturday, December 25, 2021 at 6:47:51 PM UTC-6, Don Y wrote:
> I want to "hit" a fixed spot with a physical object over
> relatively short distances (< ~20 ft).
>
> This must not present a danger to nearby bystanders (in the
> event of a "misfire"). "Weapons" are out of the question.
>
> And, the object must be of sufficient size to be clearly
> visible in transit. This also suggests a low transit
> velocity.
>
> I figure I need a bit of mass to ensure aerodynamic
> effects don't bugger the calculations. E.g., a softball
> would be better than a softball-sized hollow ball
> which might exhibit more nonlinear behaviors as it
> transits from projectile to ballistic motion.
>
> The target is (effectively) a "spot on the floor".
> I.e., not a vertical "hoop" to pass through (like
> goalposts in soccer).
>
> Accelerating a significant mass would likely prove to
> be a challenge so "lobbing" the object seems more
> practical. It would also *seem* to be more tolerant
> of aiming issues than something HOPING to travel in a
> straight line (like a bullet).
>
> So, conceptually, a tube ("barrel") to guide the
> initial segment of flight and some sort of mechanism
> to propel the object from the tube.
>
> Pneumatic, hydraulic, mechanical, etc.
>
> Will the control over the propulsive force be the tougher
> challenge or the precise aiming of the launch tube?
>
> [You are given (r,theta) to target and no feedback as
> to proximity of strike -- unless a direct strike. The
> target -- or launcher -- will move after each attempt]
>
> Of course, "you" is a machine...

A horse shoe probably wouldn't be what you're after.
A bean bag for a corn hole game?
Build a gun using electrical conduit? An 1 1/4" piece with end caps on it
might fit tightly enough in a 2" or 2 1/2" to be blown out
with an air gun.

On 2021-12-26, Don Y <blockedofcourse@foo.invalid> wrote:
> I want to "hit" a fixed spot with a physical object over
> relatively short distances (< ~20 ft).

> Accelerating a significant mass would likely prove to
> be a challenge so "lobbing" the object seems more
> practical. It would also *seem* to be more tolerant
> of aiming issues than something HOPING to travel in a
> straight line (like a bullet).
>
> So, conceptually, a tube ("barrel") to guide the
> initial segment of flight and some sort of mechanism
> to propel the object from the tube.

mini trebuchet, catapult, or springboard.

> Pneumatic, hydraulic, mechanical, etc.
>
> Will the control over the propulsive force be the tougher
> challenge or the precise aiming of the launch tube?

friction on the insides of the tube unless you use plenty of lube or
some sorte of sabot. (hence my favouring open designs)

--
Jasen.

Don Y <blockedofcourse@foo.invalid> wrote:
> I want to "hit" a fixed spot with a physical object over
> relatively short distances (< ~20 ft).
>
> This must not present a danger to nearby bystanders (in the
> event of a "misfire"). "Weapons" are out of the question.
>
> And, the object must be of sufficient size to be clearly
> visible in transit. This also suggests a low transit
> velocity.
>
> I figure I need a bit of mass to ensure aerodynamic
> effects don't bugger the calculations. E.g., a softball
> would be better than a softball-sized hollow ball
> which might exhibit more nonlinear behaviors as it
> transits from projectile to ballistic motion.
>
> The target is (effectively) a "spot on the floor".
> I.e., not a vertical "hoop" to pass through (like
> goalposts in soccer).
>
> Accelerating a significant mass would likely prove to
> be a challenge so "lobbing" the object seems more
> practical. It would also *seem* to be more tolerant
> of aiming issues than something HOPING to travel in a
> straight line (like a bullet).
>
> So, conceptually, a tube ("barrel") to guide the
> initial segment of flight and some sort of mechanism
> to propel the object from the tube.
>
> Pneumatic, hydraulic, mechanical, etc.
>
> Will the control over the propulsive force be the tougher
> challenge or the precise aiming of the launch tube?
>
> [You are given (r,theta) to target and no feedback as
> to proximity of strike -- unless a direct strike. The
> target -- or launcher -- will move after each attempt]
>
> Of course, "you" is a machine...

I'm loving the slip into alcoholism posts you make.

On Saturday, December 25, 2021 at 10:01:03 PM UTC-5, Jasen Betts wrote:
> On 2021-12-26, Don Y <blocked...@foo.invalid> wrote:
> > I want to "hit" a fixed spot with a physical object over
> > relatively short distances (< ~20 ft).
> > Accelerating a significant mass would likely prove to
> > be a challenge so "lobbing" the object seems more
> > practical. It would also *seem* to be more tolerant
> > of aiming issues than something HOPING to travel in a
> > straight line (like a bullet).
> >
> > So, conceptually, a tube ("barrel") to guide the
> > initial segment of flight and some sort of mechanism
> > to propel the object from the tube.
> mini trebuchet

+ 1

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

On 12/25/2021 6:55 PM, Dean Hoffman wrote:
> On Saturday, December 25, 2021 at 6:47:51 PM UTC-6, Don Y wrote:
>> I want to "hit" a fixed spot with a physical object over
>> relatively short distances (< ~20 ft).
>>
>> This must not present a danger to nearby bystanders (in the
>> event of a "misfire"). "Weapons" are out of the question.
>>
>> And, the object must be of sufficient size to be clearly
>> visible in transit. This also suggests a low transit
>> velocity.
>>
>> I figure I need a bit of mass to ensure aerodynamic
>> effects don't bugger the calculations. E.g., a softball
>> would be better than a softball-sized hollow ball
>> which might exhibit more nonlinear behaviors as it
>> transits from projectile to ballistic motion.
>>
>> The target is (effectively) a "spot on the floor".
>> I.e., not a vertical "hoop" to pass through (like
>> goalposts in soccer).
>>
>> Accelerating a significant mass would likely prove to
>> be a challenge so "lobbing" the object seems more
>> practical. It would also *seem* to be more tolerant
>> of aiming issues than something HOPING to travel in a
>> straight line (like a bullet).
>>
>> So, conceptually, a tube ("barrel") to guide the
>> initial segment of flight and some sort of mechanism
>> to propel the object from the tube.
>>
>> Pneumatic, hydraulic, mechanical, etc.
>>
>> Will the control over the propulsive force be the tougher
>> challenge or the precise aiming of the launch tube?
>>
>> [You are given (r,theta) to target and no feedback as
>> to proximity of strike -- unless a direct strike. The
>> target -- or launcher -- will move after each attempt]
>>
>> Of course, "you" is a machine...
>
> A horse shoe probably wouldn't be what you're after.
> A bean bag for a corn hole game?

A bean bag has several useful qualities as a projectile:
- weight, size and density are all adjustable
- shape can be tailored (with/without dynamic consequences)
- "skin" can be adjusted to facilitate travel through launcher
- skin can support different launching technologies (e.g.,
pneumatic/hydraulic without intervening "piston")
- easy to "dampen" its response on hitting another object
(including a "miss") as well as audibly "indicating"
- can be made highly visible, even with diminished size
- *likely* well tolerated if accidentally striking a bystander

Reloading may be a bit of a challenge. But, I suspect
you could design a magazine that held some number of them
and facilitated *reliable* loading of successor "rounds"
as the launcher/target are being moved.

OTOH, the damped response means misses will tend to pile up.
This might require some other mechanism to clear them away.

> Build a gun using electrical conduit? An 1 1/4" piece with end caps on it
> might fit tightly enough in a 2" or 2 1/2" to be blown out
> with an air gun.

I think that would be hazardous to bystanders. Imagine the
machine's targeting malfunctioning and mistakenly hitting a
bystander.

A slug of *water* is almost ideal in that it "disappears" after it
makes contact (hit *or* miss). And, range could be adjusted directly
via (water) pressure.

But, pretty messy. It would also require a higher launch velocity to
remain intact in transit (a stream wouldn't be acceptable)

And, would likely be difficult to make visible (unless you relied
entirely on the final "splash")

On 12/25/2021 7:45 PM, Jasen Betts wrote:
> On 2021-12-26, Don Y <blockedofcourse@foo.invalid> wrote:
>> I want to "hit" a fixed spot with a physical object over
>> relatively short distances (< ~20 ft).
>
>> Accelerating a significant mass would likely prove to
>> be a challenge so "lobbing" the object seems more
>> practical. It would also *seem* to be more tolerant
>> of aiming issues than something HOPING to travel in a
>> straight line (like a bullet).
>>
>> So, conceptually, a tube ("barrel") to guide the
>> initial segment of flight and some sort of mechanism
>> to propel the object from the tube.
>
> mini trebuchet, catapult, or springboard.

I thought of this with bean bags but think it is more complicated
than other approaches (because you don't need to be able to scale
up)

I'm not sure you (a machine) can reliably adjust the sling's release
point (or spring tension) to achieve a particular striking distance.

Without feedback, I think you need a mechanism that is highly
(open-loop) predictable as it (the machine) can't learn from previous
attempts (because the target will have moved in range and
azimuth).

I think getting the azimuth correct is relatively easy -- assuming
the centerline of the "barrel" truly represents the initial arc
segment (how likely for a trebucher to suffer a bias to one side
or the other, depending on how the sling release is designed?)

And, I'm not sure how the machine would reload itself though
I imagine a mechanism is possible due to the reduced scale.

There'd also have to be some mechanical stops to prevent
excessive projectile speed and/or overthrow.

>> Pneumatic, hydraulic, mechanical, etc.
>>
>> Will the control over the propulsive force be the tougher
>> challenge or the precise aiming of the launch tube?
>
> friction on the insides of the tube unless you use plenty of lube or
> some sorte of sabot. (hence my favouring open designs)

That would depend on the nature of the projectile and it's
outer surface (as well as the inner surface of such a "barrel").
A beanbag made out of a "fluffy" material would likely exhibit
a predictable drag -- and the length of the barrel doesn't change.

Something ejected with a liquid "expellant" would rely on the
liquid's consistency between shots to make the transit predictable.
[If the barrel is short enough, any "waste expellant" could
possibly be captured directly in front of the barrel's terminus.]

The predictability aspect IMO is the driving issue. Hence the
question as to where the "sensitivity" in the design lies.

Even if you design the mechanism and projectiles to be repeatable,
you still have no way of knowing how ANY of them performed, in the
wild. So, any "calibration" has to happen at time of design/manufacture
and hold true thereafter.

[You can observe the process *until* the projectile exits the
mechanism but not thereafter. E.g., you could "watch" the
trebuchet's arm's motion and release point to verify it
is happening as intended. But, of course, that defines an
historic event that can no longer be influenced!]

Note that this can be a complex algorithm as a machine is
performing the calculation(s) without the need for an operator.
But, the calculation has to *remain* valid, thereafter, as there's
no operator to tweek it based on observations!

[Of course, there may be some value to a randomizing strategy
in that it may "get lucky" more often than a repeatable one
that is "always wrong"!]

On 26/12/2021 07:30, Rick C wrote:
> On Saturday, December 25, 2021 at 10:01:03 PM UTC-5, Jasen Betts wrote:
>> On 2021-12-26, Don Y <blocked...@foo.invalid> wrote:
>>> I want to "hit" a fixed spot with a physical object over
>>> relatively short distances (< ~20 ft).
>>> Accelerating a significant mass would likely prove to
>>> be a challenge so "lobbing" the object seems more
>>> practical. It would also *seem* to be more tolerant
>>> of aiming issues than something HOPING to travel in a
>>> straight line (like a bullet).
>>>
>>> So, conceptually, a tube ("barrel") to guide the
>>> initial segment of flight and some sort of mechanism
>>> to propel the object from the tube.
>> mini trebuchet
>
> + 1

Yes. They are great fun. There is a bloke near me who has scale model
fully operational trebuchet able to lob a water melon about 200m!

It is very impressive and apart from the beam quite compact. When things
return to normal I might try and catch up with him again to film it in
action. He does charity gigs with it from time to time in normal summers
- needs a *lot* of space. (and careful crowd control down range)

This is the biggest one I have seen online and representative of the
sort of design that would work. Camera work is pretty good too:

https://www.youtube.com/watch?v=UdGqggET0o4

--
Regards,
Martin Brown

On 2021-12-26, Don Y <blockedofcourse@foo.invalid> wrote:
> On 12/25/2021 7:45 PM, Jasen Betts wrote:
>> On 2021-12-26, Don Y <blockedofcourse@foo.invalid> wrote:
>>> I want to "hit" a fixed spot with a physical object over
>>> relatively short distances (< ~20 ft).
>>
>>> Accelerating a significant mass would likely prove to
>>> be a challenge so "lobbing" the object seems more
>>> practical. It would also *seem* to be more tolerant
>>> of aiming issues than something HOPING to travel in a
>>> straight line (like a bullet).
>>>
>>> So, conceptually, a tube ("barrel") to guide the
>>> initial segment of flight and some sort of mechanism
>>> to propel the object from the tube.
>>
>> mini trebuchet, catapult, or springboard.
>
> I thought of this with bean bags but think it is more complicated
> than other approaches (because you don't need to be able to scale
> up)
>
> I'm not sure you (a machine) can reliably adjust the sling's release
> point (or spring tension) to achieve a particular striking distance.
>
> Without feedback, I think you need a mechanism that is highly
> (open-loop) predictable as it (the machine) can't learn from previous
> attempts (because the target will have moved in range and
> azimuth).
>
> I think getting the azimuth correct is relatively easy -- assuming
> the centerline of the "barrel" truly represents the initial arc
> segment (how likely for a trebucher to suffer a bias to one side
> or the other, depending on how the sling release is designed?)
>
> And, I'm not sure how the machine would reload itself though
> I imagine a mechanism is possible due to the reduced scale.
>
> There'd also have to be some mechanical stops to prevent
> excessive projectile speed and/or overthrow.
>
>>> Pneumatic, hydraulic, mechanical, etc.
>>>
>>> Will the control over the propulsive force be the tougher
>>> challenge or the precise aiming of the launch tube?
>>
>> friction on the insides of the tube unless you use plenty of lube or
>> some sorte of sabot. (hence my favouring open designs)
>
> That would depend on the nature of the projectile and it's
> outer surface (as well as the inner surface of such a "barrel").
> A beanbag made out of a "fluffy" material would likely exhibit
> a predictable drag -- and the length of the barrel doesn't change.
>
> Something ejected with a liquid "expellant" would rely on the
> liquid's consistency between shots to make the transit predictable.
> [If the barrel is short enough, any "waste expellant" could
> possibly be captured directly in front of the barrel's terminus.]
>
> The predictability aspect IMO is the driving issue. Hence the
> question as to where the "sensitivity" in the design lies.
>
> Even if you design the mechanism and projectiles to be repeatable,
> you still have no way of knowing how ANY of them performed, in the
> wild. So, any "calibration" has to happen at time of design/manufacture
> and hold true thereafter.
>
> [You can observe the process *until* the projectile exits the
> mechanism but not thereafter. E.g., you could "watch" the
> trebuchet's arm's motion and release point to verify it
> is happening as intended. But, of course, that defines an
> historic event that can no longer be influenced!]

You can measure the speed and angle of the arm when the it releases
the projectile from that you can make a fairly good guess at its
trajectory.

> Note that this can be a complex algorithm as a machine is
> performing the calculation(s) without the need for an operator.
> But, the calculation has to *remain* valid, thereafter, as there's
> no operator to tweek it based on observations!
>
> [Of course, there may be some value to a randomizing strategy
> in that it may "get lucky" more often than a repeatable one
> that is "always wrong"!]

Yeah if the target is not found it becomes a blind hunt like a game of
battleshipa. But so long as the real game is not a type of crazy golf
it's just a matter of picking the right search algorithm.

--
Jasen.

On 26/12/2021 08:17, Don Y wrote:
<snip>
>
> A slug of *water* is almost ideal in that it "disappears" after it
> makes contact (hit *or* miss).  And, range could be adjusted directly
> via (water) pressure.
>
> But, pretty messy.  It would also require a higher launch velocity to
> remain intact in transit (a stream wouldn't be acceptable)
>
> And, would likely be difficult to make visible (unless you relied
> entirely on the final "splash")

Snowballs.

But messy. Is there something with similar mechanical properties which
doesn't melt? That way you could form it into different sizes as needed.

--
Cheers
Clive

On 12/26/2021 4:07 AM, Jasen Betts wrote:
> On 2021-12-26, Don Y <blockedofcourse@foo.invalid> wrote:

>> The predictability aspect IMO is the driving issue. Hence the
>> question as to where the "sensitivity" in the design lies.
>>
>> Even if you design the mechanism and projectiles to be repeatable,
>> you still have no way of knowing how ANY of them performed, in the
>> wild. So, any "calibration" has to happen at time of design/manufacture
>> and hold true thereafter.
>>
>> [You can observe the process *until* the projectile exits the
>> mechanism but not thereafter. E.g., you could "watch" the
>> trebuchet's arm's motion and release point to verify it
>> is happening as intended. But, of course, that defines an
>> historic event that can no longer be influenced!]
>
> You can measure the speed and angle of the arm when the it releases
> the projectile from that you can make a fairly good guess at its
> trajectory.

Yes, but you would have wanted to be controlling that
at the same time; so, measurement just verifies your control
performed as intended.

>> Note that this can be a complex algorithm as a machine is
>> performing the calculation(s) without the need for an operator.
>> But, the calculation has to *remain* valid, thereafter, as there's
>> no operator to tweek it based on observations!
>>
>> [Of course, there may be some value to a randomizing strategy
>> in that it may "get lucky" more often than a repeatable one
>> that is "always wrong"!]
>
> Yeah if the target is not found it becomes a blind hunt like a game of
> battleshipa.

Except the targets don't move in Battleship. So, you could
make several attempts to hit a specific physical location by
tweeking your control, even if it is inaccurate.

I.e., "I want to hit a spot 12 ft from me in this direction.
Set control to 12, fire. If not hit, set control to 13, fire.
If not hit, set control to 11, fire. Hopefully, one of those
three control settings actually produces a 12 ft throw!"

If "12" doesn't always yield the same throw, then all bets
are off.

And, if the target can be 18 ft away when you take your next shot,
then the control may as well be random as the effect is unpredictable.

> But so long as the real game is not a type of crazy golf
> it's just a matter of picking the right search algorithm.

On 12/26/2021 5:45 AM, Clive Arthur wrote:
> On 26/12/2021 08:17, Don Y wrote:
> <snip>
>>
>> A slug of *water* is almost ideal in that it "disappears" after it
>> makes contact (hit *or* miss). And, range could be adjusted directly
>> via (water) pressure.
>>
>> But, pretty messy. It would also require a higher launch velocity to
>> remain intact in transit (a stream wouldn't be acceptable)
>>
>> And, would likely be difficult to make visible (unless you relied
>> entirely on the final "splash")
>
> Snowballs.

Snowballs would be excellent! But, I'm not sure how easy it
would be to make a machine that could form them, get them firm
enough to ensure they don't disintegrate in the launch process
and ensure they don't become (dangerous) "ice balls".

> But messy. Is there something with similar mechanical properties which doesn't
> melt? That way you could form it into different sizes as needed.

Are you assuming size can be used as a control variable? I.e.,
make a fixed strength throwing arm and vary the weight of the
projectile to adjust range?

I'm assuming (at design/manufacture time) that you can quantify the
behavior of the mechanism with a specific projectile and that it
will remain repeatable (with that type of projectile). So, you can
"learn" how to make a 12 foot toss.

And, prior to design release, can adjust the mechanism or projectile
to improve the control sensitivity/range to that which you need.

("Hmmm... throwing mechanism is too strong! Even on the lowest
control setting, projectiles fly 35 feet! Let's try making heavier
projectiles -- or, crippling the throwing arm...")

On Sunday, December 26, 2021 at 8:51:58 AM UTC-6, Don Y wrote:
> On 12/26/2021 5:45 AM, Clive Arthur wrote:
> > On 26/12/2021 08:17, Don Y wrote:
> > <snip>
> >>
> >> A slug of *water* is almost ideal in that it "disappears" after it
> >> makes contact (hit *or* miss). And, range could be adjusted directly
> >> via (water) pressure.
> >>
> >> But, pretty messy. It would also require a higher launch velocity to
> >> remain intact in transit (a stream wouldn't be acceptable)
> >>
> >> And, would likely be difficult to make visible (unless you relied
> >> entirely on the final "splash")
> >
> > Snowballs.
> Snowballs would be excellent! But, I'm not sure how easy it
> would be to make a machine that could form them, get them firm
> enough to ensure they don't disintegrate in the launch process
> and ensure they don't become (dangerous) "ice balls".
> > But messy. Is there something with similar mechanical properties which doesn't
> > melt? That way you could form it into different sizes as needed.
> Are you assuming size can be used as a control variable? I.e.,
> make a fixed strength throwing arm and vary the weight of the
> projectile to adjust range?
>
> I'm assuming (at design/manufacture time) that you can quantify the
> behavior of the mechanism with a specific projectile and that it
> will remain repeatable (with that type of projectile). So, you can
> "learn" how to make a 12 foot toss.
>
> And, prior to design release, can adjust the mechanism or projectile
> to improve the control sensitivity/range to that which you need.
>
> ("Hmmm... throwing mechanism is too strong! Even on the lowest
> control setting, projectiles fly 35 feet! Let's try making heavier
> projectiles -- or, crippling the throwing arm...")

How about a mini basketball? Maybe fill it with something besides
air if you need a little more weight.

On 12/26/2021 8:02 AM, Dean Hoffman wrote:
>> And, prior to design release, can adjust the mechanism or projectile
>> to improve the control sensitivity/range to that which you need.
>>
>> ("Hmmm... throwing mechanism is too strong! Even on the lowest
>> control setting, projectiles fly 35 feet! Let's try making heavier
>> projectiles -- or, crippling the throwing arm...")
>
> How about a mini basketball? Maybe fill it with something besides
> air if you need a little more weight.

There are myriad choices for projectiles. The problem is coming up with a
"system" (projectile + projector) that is repeatable. I.e., so a *second*
"mini basketball" performs identically to the first for a given set
of "projector controls".

(because you can't see where THIS projectile lands but, can be
reasonably sure as to where it *should* have landed, based on
earlier "design assessment")

A basketball player learns how much force is necessary to
throw the ball the estimated distance to the hoop (or,
another player). He does this by practicing -- shooting hoops
to train his muscles and vision with a "representative ball".

His skill then boils down to how well he can estimate that toss
and execute the corresponding amount of throwing force. If the
ball could suddenly changed weight (or aerodynamic properties),
his skill would be for naught.

[He can also *see* the results of his tosses and make dynamic
adjustments to his estimating/throwing. Imagine what a game
would be like if he could only know if he'd made the shot, or
missed (no information as to whether he was long, short or
off to one side or the other)]

In article <sq8e3h$fmo$1@dont-email.me>, blockedofcourse@foo.invalid
says...
>
> I want to "hit" a fixed spot with a physical object over
> relatively short distances (< ~20 ft).
>
> This must not present a danger to nearby bystanders (in the
> event of a "misfire"). "Weapons" are out of the question.
>
> And, the object must be of sufficient size to be clearly
> visible in transit. This also suggests a low transit
> velocity.
>
> I figure I need a bit of mass to ensure aerodynamic
> effects don't bugger the calculations. E.g., a softball
> would be better than a softball-sized hollow ball
> which might exhibit more nonlinear behaviors as it
> transits from projectile to ballistic motion.
>
> The target is (effectively) a "spot on the floor".
> I.e., not a vertical "hoop" to pass through (like
> goalposts in soccer).
>
> Accelerating a significant mass would likely prove to
> be a challenge so "lobbing" the object seems more
> practical. It would also *seem* to be more tolerant
> of aiming issues than something HOPING to travel in a
> straight line (like a bullet).
>
> So, conceptually, a tube ("barrel") to guide the
> initial segment of flight and some sort of mechanism
> to propel the object from the tube.
>
> Pneumatic, hydraulic, mechanical, etc.
>
> Will the control over the propulsive force be the tougher
> challenge or the precise aiming of the launch tube?
>
> [You are given (r,theta) to target and no feedback as
> to proximity of strike -- unless a direct strike. The
> target -- or launcher -- will move after each attempt]
>
> Of course, "you" is a machine...

Build a ramp similar to a ski jump. Use a golf ball and you can adjust
the angle of the ramp and how far up you let the golf ball go from. You
can probably cut a PVC pipe in half long ways and use an elbow of 45 deg
at the bottom. Or do not cut the pipe but put holes in every 6 inches
or so to drop the ball in.

On 12/25/2021 6:47 PM, Don Y wrote:
> I want to "hit" a fixed spot with a physical object over
> relatively short distances (< ~20 ft).

 How about a tennis ball?

Solenoid launch it, easily adjusted power to solenoid, ( voltage control
or charge on a capacitor).

Provide an arch type flight, less likely to have the speed to hurt anyone.

Add a rotating mount. Might have to qualify your tennis balls for
constancy. :-)

                                Mikek

--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

On Sat, 25 Dec 2021 17:47:31 -0700, Don Y
<blockedofcourse@foo.invalid> wrote:

>I want to "hit" a fixed spot with a physical object over
>relatively short distances (< ~20 ft).
>
>This must not present a danger to nearby bystanders (in the
>event of a "misfire"). "Weapons" are out of the question.
>
>And, the object must be of sufficient size to be clearly
>visible in transit. This also suggests a low transit
>velocity.
>
>I figure I need a bit of mass to ensure aerodynamic
>effects don't bugger the calculations. E.g., a softball
>would be better than a softball-sized hollow ball
>which might exhibit more nonlinear behaviors as it
>transits from projectile to ballistic motion.
>
>The target is (effectively) a "spot on the floor".
>I.e., not a vertical "hoop" to pass through (like
>goalposts in soccer).
>
>Accelerating a significant mass would likely prove to
>be a challenge so "lobbing" the object seems more
>practical. It would also *seem* to be more tolerant
>of aiming issues than something HOPING to travel in a
>straight line (like a bullet).
>
>So, conceptually, a tube ("barrel") to guide the
>initial segment of flight and some sort of mechanism
>to propel the object from the tube.
>
>Pneumatic, hydraulic, mechanical, etc.
>
>Will the control over the propulsive force be the tougher
>challenge or the precise aiming of the launch tube?
>
>[You are given (r,theta) to target and no feedback as
>to proximity of strike -- unless a direct strike. The
>target -- or launcher -- will move after each attempt]
>
>Of course, "you" is a machine...

Ping-pong balls can be aimed well and aren't very dangerous.

I once played with the world's 16th best player. I couldn't return a
single serve and his shots did bruise. He applied so much spin that
the balls hit my paddle and exited at 90 degrees, typically hitting
the ceiling.

He was a not very good EE.

I also took a college course under the world's #1 doubles badminton
player. His rule was that if anyone ever retuned one of his shots,
they would get an A and not have to show up any more. Nobody ever did.

--

I yam what I yam - Popeye

On 12/26/2021 9:07 AM, amdx wrote:
> On 12/25/2021 6:47 PM, Don Y wrote:
>> I want to "hit" a fixed spot with a physical object over
>> relatively short distances (< ~20 ft).
>
> How about a tennis ball?

Tennis ball is ideal size for visibility, etc. But, bounces a lot.
So, detecting if it has "hit" the target becomes problematic
(did it hit the target or *bounce* into it?) This is the appeal
of something like a beanbag -- it just *sits* where thrown (more
or less).

E.g., if you allow for the transit to remain valid after the ground
has been contacted, then why not just *roll* the ball in a particular
direction and "claim" to have hit anything that it rolls over along
the way? :>

> Solenoid launch it, easily adjusted power to solenoid, ( voltage control or
> charge on a capacitor).

But, would it? That was my point behind asking about control over the
propulsive force... *if* the projectile (tennis ball in your case)
is a "repeatable" unit, can you deliver it to the same point
repeatably (just by repeating the "adjusted power to solenoid")?

> Provide an arch type flight, less likely to have the speed to hurt anyone.

Yes. "lob" not "throw"/shoot.

> Add a rotating mount. Might have to qualify your tennis balls for constancy. :-)

Yes, as the shooter is not assured that the target will be in the
direction the "gun" currently points (r,theta).

On 12/26/2021 8:38 AM, Ralph Mowery wrote:
> In article <sq8e3h$fmo$1@dont-email.me>, blockedofcourse@foo.invalid
> says...
>>
>> I want to "hit" a fixed spot with a physical object over
>> relatively short distances (< ~20 ft).
>>
>> This must not present a danger to nearby bystanders (in the
>> event of a "misfire"). "Weapons" are out of the question.
>>
>> And, the object must be of sufficient size to be clearly
>> visible in transit. This also suggests a low transit
>> velocity.
>>
>> I figure I need a bit of mass to ensure aerodynamic
>> effects don't bugger the calculations. E.g., a softball
>> would be better than a softball-sized hollow ball
>> which might exhibit more nonlinear behaviors as it
>> transits from projectile to ballistic motion.
>>
>> The target is (effectively) a "spot on the floor".
>> I.e., not a vertical "hoop" to pass through (like
>> goalposts in soccer).
>>
>> Accelerating a significant mass would likely prove to
>> be a challenge so "lobbing" the object seems more
>> practical. It would also *seem* to be more tolerant
>> of aiming issues than something HOPING to travel in a
>> straight line (like a bullet).
>>
>> So, conceptually, a tube ("barrel") to guide the
>> initial segment of flight and some sort of mechanism
>> to propel the object from the tube.
>>
>> Pneumatic, hydraulic, mechanical, etc.
>>
>> Will the control over the propulsive force be the tougher
>> challenge or the precise aiming of the launch tube?
>>
>> [You are given (r,theta) to target and no feedback as
>> to proximity of strike -- unless a direct strike. The
>> target -- or launcher -- will move after each attempt]
>>
>> Of course, "you" is a machine...
>
> Build a ramp similar to a ski jump. Use a golf ball and you can adjust
> the angle of the ramp and how far up you let the golf ball go from. You
> can probably cut a PVC pipe in half long ways and use an elbow of 45 deg
> at the bottom. Or do not cut the pipe but put holes in every 6 inches
> or so to drop the ball in.

I don't think gravity, alone, would create enough momentum to carry the ball
much beyond the end of the ramp. (e.g., think ~20 ft).

Martin Brown wrote:
> On 26/12/2021 07:30, Rick C wrote:
>> On Saturday, December 25, 2021 at 10:01:03 PM UTC-5, Jasen Betts wrote:
>>> On 2021-12-26, Don Y <blocked...@foo.invalid> wrote:
>>>> I want to "hit" a fixed spot with a physical object over
>>>> relatively short distances (< ~20 ft).
>>>> Accelerating a significant mass would likely prove to
>>>> be a challenge so "lobbing" the object seems more
>>>> practical. It would also *seem* to be more tolerant
>>>> of aiming issues than something HOPING to travel in a
>>>> straight line (like a bullet).
>>>>
>>>> So, conceptually, a tube ("barrel") to guide the
>>>> initial segment of flight and some sort of mechanism
>>>> to propel the object from the tube.
>>> mini trebuchet
>>
>> + 1
>
> Yes. They are great fun. There is a bloke near me who has scale model
> fully operational trebuchet able to lob a water melon about 200m!
>
> It is very impressive and apart from the beam quite compact. When things
> return to normal I might try and catch up with him again to film it in
> action. He does charity gigs with it from time to time in normal summers
> - needs a *lot* of space. (and careful crowd control down range)
>
> This is the biggest one I have seen online and representative of the
> sort of design that would work. Camera work is pretty good too:
>
> https://www.youtube.com/watch?v=UdGqggET0o4
>

See you and raise you:

https://www.youtube.com/watch?v=M1iPxY3FYNE

At Warwick Castle there's a copy of Edward 1's Warwolf.

Here's a similar example;

https://www.youtube.com/watch?v=4_iIfZH33MA

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

On 12/26/2021 1:15 PM, ke...@kjwdesigns.com wrote:
> On Sunday, 26 December 2021 at 00:41:17 UTC-8, Don Y wrote:
> ...
>
> How about this for some inspiration?
>
> https://www.youtube.com/watch?v=sZm9ZEpvolw

<https://www.youtube.com/watch?v=EC5mLx6_8FI>

Unfortunately, I suspect considerably more than my $600K budget!

On Sunday, December 26, 2021 at 6:01:36 PM UTC-6, Don Y wrote:
> On 12/26/2021 1:15 PM, ke...@kjwdesigns.com wrote:
> > On Sunday, 26 December 2021 at 00:41:17 UTC-8, Don Y wrote:
> > ...
> >
> > How about this for some inspiration?
> >
> > https://www.youtube.com/watch?v=sZm9ZEpvolw
> <https://www.youtube.com/watch?v=EC5mLx6_8FI>
>
> Unfortunately, I suspect considerably more than my $600K budget!

NASA spent 10 Billion dollars on this thing.
<https://thefederalist.com/2021/12/22/nasa-to-launch-telescope-stronger-than-hubble-that-can-see-back-in-time/>
Over budget and behind schedule, of course.
<https://www.cbsnews.com/live-updates/james-webb-space-telescope-launch-12-25-2021/>

On 12/26/2021 6:05 PM, Dean Hoffman wrote:
> On Sunday, December 26, 2021 at 6:01:36 PM UTC-6, Don Y wrote:
>> On 12/26/2021 1:15 PM, ke...@kjwdesigns.com wrote:
>>> On Sunday, 26 December 2021 at 00:41:17 UTC-8, Don Y wrote:
>>> ...
>>>
>>> How about this for some inspiration?
>>>
>>> https://www.youtube.com/watch?v=sZm9ZEpvolw
>> <https://www.youtube.com/watch?v=EC5mLx6_8FI>
>>
>> Unfortunately, I suspect considerably more than my $600K budget!
>
> NASA spent 10 Billion dollars on this thing.
> nasa-to-launch-telescope-stronger-than-hubble-that-can-see-back-in-time

------------------------------------------------^^^^^^^^^^^^^^^^^^^^^^^^^

Maybe they can use it to sort out where their cost overruns were?

> Over budget and behind schedule, of course.
> <https://www.cbsnews.com/live-updates/james-webb-space-telescope-launch-12-25-2021/>

On 26/12/2021 10:47 am, Don Y wrote:
> I want to "hit" a fixed spot with a physical object over
> relatively short distances (< ~20 ft).
>
> This must not present a danger to nearby bystanders (in the
> event of a "misfire").  "Weapons" are out of the question.
>
> And, the object must be of sufficient size to be clearly
> visible in transit.  This also suggests a low transit
> velocity.
>
> I figure I need a bit of mass to ensure aerodynamic
> effects don't bugger the calculations.  E.g., a softball
> would be better than a softball-sized hollow ball
> which might exhibit more nonlinear behaviors as it
> transits from projectile to ballistic motion.
>
> The target is (effectively) a "spot on the floor".
> I.e., not a vertical "hoop" to pass through (like
> goalposts in soccer).
>
> Accelerating a significant mass would likely prove to
> be a challenge so "lobbing" the object seems more
> practical.  It would also *seem* to be more tolerant
> of aiming issues than something HOPING to travel in a
> straight line (like a bullet).
>
> So, conceptually, a tube ("barrel") to guide the
> initial segment of flight and some sort of mechanism
> to propel the object from the tube.
>
> Pneumatic, hydraulic, mechanical, etc.
>
> Will the control over the propulsive force be the tougher
> challenge or the precise aiming of the launch tube?
>
> [You are given (r,theta) to target and no feedback as
> to proximity of strike -- unless a direct strike.  The
> target -- or launcher -- will move after each attempt]
>
> Of course, "you" is a machine...

A nerf gun.

On Sunday, December 26, 2021 at 12:55:39 PM UTC+11, dean...@gmail.com wrote:
> On Saturday, December 25, 2021 at 6:47:51 PM UTC-6, Don Y wrote:

<snip>

> > And, the object must be of sufficient size to be clearly visible in transit. This also suggests a low transit velocity.

When I was an undergraduate people did drop paper bags full of water on people passing below.

A longer range variants of this was rubber party balloons full of water.

We launched few from a ten foot long catapult - lots of rubber bands in series and in parallel - with a leather bucket to cope with the acceleration forces. The water-filled balloon contracted away from the leather bucket as the acceleration fell away.

> > I figure I need a bit of mass to ensure aerodynamic
> > effects don't bugger the calculations. E.g., a softball
> > would be better than a softball-sized hollow ball
> > which might exhibit more nonlinear behaviors as it
> > transits from projectile to ballistic motion.

The water filled balloon has a fairly stable shape - after a bit of initial sloshing around.

> > Accelerating a significant mass would likely prove to
> > be a challenge so "lobbing" the object seems more
> > practical. It would also *seem* to be more tolerant
> > of aiming issues than something HOPING to travel in a
> > straight line (like a bullet).

Everything travels along a parabolic path. Air resistance does eat into the momentum and velocity, but not that much.

--
Bill Sloman, Sydney