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I am interested in putting together a tennis ball launcher.

It's accuracy/precision are not important. Even varying distance by ~50% or more per shot doesn't matter (it's for my dogs).

What type of solenoid can I use to drive this in a hollow tube, like the picture?

If this is impractical please give an actual reason.

I would also like to be able to drive this with a reasonably sized battery (12-24V; I could use a car battery but hopefully that is not required).

A tennis ball weighs (58.5g). Lets say that it needs to launch the tennis ball upwards ~6m

$$ H = v^2/(2g) = 6m $$ $$ v=\sqrt{(12*g)}=10.8 \frac ms $$ $$ E_k = (m*v^2)/2 = \frac{58.5*117.6}2 = 3.43 J $$

Likewise the energy stored in a capacitor is: $$ E_c = \frac{C*V^2}{2} $$ If I discharge from a capacitor to achieve this energy quickly, (lets say 24V) $$ C = \frac{E_c}{2V^2} = 3mF $$

Rough sketch: goofy sketch

Any inputs are appreciated

jbord39
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  • This isn't really on topic, but the easiest solution to implement would be a flywheel powered by a motor that propels the ball. Think of a pitching machine. – 3871968 Jul 25 '16 at 22:21
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    Tennis ball launchers are readily available. Why should we be bothered to engineer a new one? Besides, this is more of a mechanical design question than an electronic one. – Dave Tweed Jul 25 '16 at 22:25
  • Most of the questions asked here are related to things readily available; I am not asking for you to engineer a new one, just asking if there is an electrically controlled component capable of pushing 3.43J into a tennis ball. And my question pertains more to the electrical side, imo, because I am asking about electrically controlled actuators. If I have to go the flywheel option I would ask on me.se – jbord39 Jul 25 '16 at 22:27
  • So, do you just want to pop the ball up into the air, or do you want to give it some horizontal velocity, too? – Dave Tweed Jul 25 '16 at 22:30
  • I just assumed straight up because the math is simpler. But I would rotate the whole thing to give it some horizontal velocity (it would no longer rise 6m, but even just going up 3m and over 3m before bouncing would be fine). – jbord39 Jul 25 '16 at 22:34
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    I'm voting to close this question as off-topic because this is mechanical engineering – Scott Seidman Jul 26 '16 at 00:45
  • Not really, it's EE. I am asking about electrically controlled devices, and the currents/voltages required to push this ball using them. Similarly upvoted threads: http://electronics.stackexchange.com/questions/95557/what-sort-of-electric-motor-would-i-need-to-launch-a-puck/95571#95571 http://electronics.stackexchange.com/questions/28878/long-solenoid-50cm-stroke http://electronics.stackexchange.com/questions/10314/solenoid-relative-force I could add more but seems unnecessary – jbord39 Jul 26 '16 at 00:49
  • You're going to find a solenoid impractical for the job. Every mechanical contrivance you can come up with can be electrically activated, but that doesn't make them electrical engineering. I suggest the general engineering stack, if it's still open – Scott Seidman Jul 26 '16 at 01:17
  • Why would a solenoid be impractical? – jbord39 Jul 26 '16 at 01:22
  • Scott's right, jbord39, sorry. You'll find that they don't have the force, or the speed, or the actuating distance to do what you want. You could easily hook one up to a lever arm to make a great ball thrower, but that really is a mechanical issue. – bitsmack Jul 26 '16 at 01:24
  • You've done all the right math, though. Kudos for doing the homework. – Scott Seidman Jul 26 '16 at 01:34
  • So because you three say solenoids cannot be used the question is put on hold? Other engineers disagree. This is getting to be ridiculous. You are just saying it is IMPOSSIBLE to get this to provide enough energy, without giving any reasons or explanations. I do not want to build a hook or lever arm. I am asking about electronic components. Sorry if you cannot understand that. – jbord39 Jul 26 '16 at 02:04
  • Here is what I would devise for the launching mechanism. Use the tube as you sketched as the ball holder / guide. But drop the solenoid idea. Instead make up a mechanical arm that has an suitable spring tension to it that when released can impart enough kinetic energy to launch the ball. (Envision something like how a cross bow works). Then use a small motor with a lead screw assembly that is used to pull the spring arm in tension. The lead screw gives huge mechanical advantage and thus low energy needed to prime the mechanism. A trigger mechanism, which could be a simple trip (continued) – Michael Karas Jul 26 '16 at 02:08
  • (from above) when the lead screw pulls past a certain point would release the trigger and let the arm whop on the ball. The motor would reverse the lead screw to reengage the trigger at the spent position of the arm to ready for the next cycle. The end of the arm would run in a slot down the side of the tube. The cycle process of the arm could also open a door to allow an auto loader funnel from above to feed down a ball in front of the arm as its approaches its maximum tension point. – Michael Karas Jul 26 '16 at 02:13
  • @Scott Seidman: from the question help center, I am asking about a specific electronics design problem: "How to use a solenoid to provide 3.43J or greater of force as quickly as possible". From the same help center: insist that opinion be backed up with facts and references. So please re-read the link for details on proper questions and answers. I don't take your opinion as fact just because you've spent more time and years posting on here than others. – jbord39 Jul 26 '16 at 02:18
  • @DaveTweed: So we cannot ask questions about reed switches either? They are truly a mechanical device which is electrically actuated (very similar to a solenoid). Or do you just arbitrarily decide what devices are "electronics"? – jbord39 Jul 26 '16 at 02:23
  • @bitsmack: from the wiki on proper questions/answer: insist that opinion be backed up with facts and references. "don't have the force, or the speed, or the actuating distance" You close the question and break a rule at the same time; what hypocrisy. – jbord39 Jul 26 '16 at 02:25
  • @jbord39, we're doing our best to get your question to where you can get real solid help. Note that the flywheel suggested, as well as the pneumatic solution suggested, both of which are better solutions than a solenoid, can both be electrically controlled, but you don't consider them EE. The equations you offer are straight out of a MechE text. You're trying to find a way to launch a projectile. It's ballistics. Take a peek at solenoids, and convince yourself that they won't provide the energy you need at reasonable size and cost. – Scott Seidman Jul 26 '16 at 02:45
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    I'm sorry you're getting so worked up; truly. I'm impressed by your question and your research. As Scott said, we're trying to help you out. You already have two answers, one of which says to go mechanical. And a bunch of experienced people trying to lead you in a helpful direction (to the appropriate tech, and the appropriate Stack). Before you claim hypocrisy, please note the difference between comments and answers. I think your project is cool. I hope you make something work. And if you can do it with an unassisted solenoid, come back and show us! Maybe we're all missing something... – bitsmack Jul 26 '16 at 03:23
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    Oh, and by the way, nobody thinks your question is a bad one! That would manifest as downvotes ;) Having it closed so it can be asked elsewhere isn't any kind of insult. – bitsmack Jul 26 '16 at 03:26
  • How much longer will this be on hold? I'm toeing the court baseline here, waiting for a serve! – Kaz Jul 26 '16 at 04:25
  • Solenoids and reed switches are examples of interface devices (transducers) that form the bridge between the worlds of electrical engineering and mechanical engineering. But your question is clearly about the mechanical side of that interface, which is why we're trying to guide you in that direction. – Dave Tweed Jul 26 '16 at 04:27
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    Thanks for the comments, sorry for misunderstanding the intent. – jbord39 Jul 26 '16 at 06:19
  • @jbord39 I'd expect this to be doable with a solenoid, but I'd expect that one of the solutions listed in my answer from 2014, which you have cited above, would serve you better. (Cheaper, easier, ...). Something which accelerates from rest over a useful distance storing energy in a mass which then strikes the tennis ball is liable to provide a better "mechanical impedance match" than a short very sharp impulse into a compressible target. A windscreen wiper ... – Russell McMahon Jul 26 '16 at 11:32
  • ... can be arranged to complete one output shaft revolution and stop at the same place each time. Speed/energy can be significant. [Tip: Wiper motors with high / low speed select using a ground and two Vin wires may run "extra fast" by connecting Vin between tge two Vin lines. [Ask me how I know :-) ]. Longevity not guaranteed. | To show what a solenoid can do here is a datasheet for a != 220W input solenoid with 20mm stroke and force ranging from 6 to 25 Newton. Ball acceleration = Newton/kg = say 10N/0.06kg = – Russell McMahon Jul 26 '16 at 11:37
  • ... ~= 160 m/s/s or 16g. Alas, that's for only 20mm so vertical altitude = Stroke Gacc/Ggravity = 20mm x 16g = 320mm. Sounds wrong but even if so, it's not marvellous. | Browse here for ideas - but you need 'gruntier'. | Some of the ideas in my cited answer are liable to be more useful. [[E&OE]]. – Russell McMahon Jul 26 '16 at 11:41

2 Answers2

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The component you are describing is generally called a "solenoid" in the EE field. Be aware that the term "solenoid" has other meanings within the EE world as well. But here I am referring to the generally available component known by that name.

A solenoid is a coil of wire wound on a tube. The tube generally has a circular cross-section. Inside that tube is an iron "plunger". The plunger is often spring loaded so it will have a preferred position in the tube.

When voltage is applied to the coil, the plunger will rapidly move from its resting position to its activated position. The displacement between these two positions is generally about 1/4 to 1 inch, but this is part of the design of the solenoid and can be made to vary according to certain geometric parameters inherent in the design of the solenoid.

Solenoids are manufactured in a wide variety of sizes and shapes for a large range of applications. They are ubiquitous in our world. For example, your personal vehicle probably has a solenoid as part of its starter motor. This solenoid is used to move the pinion gear on the starter motor shaft into mesh with the ring gear on the engine's flywheel. It produces the "click" you hear when you turn your ignition key and just before the starter motor starts cranking. Or, when your battery is dead and all you hear is that click under the hood.

Another common example is a gong - such as a commercial door bell sounder. This has a resonant metal dome which makes the actual sound. Underneath the metal dome is a solenoid. When the door bell switch is pressed, a voltage is applied to the solenoid, the solenoid's plunger flies upward, and strikes the dome, making the sound.

There's probably a solenoid activated valve in your refrigerator, gas furnace, or gas water heater. They are everywhere.

Go to www.mcmaster.com and search on "solenoid" and you will see a wide variety of stock units you can purchase to experiment with. I'm sure there are dozens of other internet sources.

To launch a tennis ball you will need a pretty large solenoid. Such a large solenoid will require a considerable amount of electrical power. You will have to experiment to figure out what's practical for your application. But, I'd start with the biggest solenoid I could find.

It's not out of the question that you can make your own solenoid. It's also possible to put a number of solenoids in series to increase the produced force. That is, a common, extra long, plunger with multiple coils you would take from stock solenoids. Though the plunger has to be built in a special way to accomplish this advantage.

That should be enough to get you started. Good Luck!

FiddyOhm
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Pinball machines have lots of solenoids in them, as further examples to the ones in the other answers.

I would design a tennis ball launcher (something that needs to deliver a lot of energy rapidly) by using a mechanical energy store which is built up using electronic parts then released quickly - eg using a motor or rubber band and then firing off a solenoid to release the energy into the tennis ball.

Also, pneumatic mechanisms are highly capable of delivering lots of energy rapidly. See brands like Festool etc that are commonly used in factory assembly lines.

goodie
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  • Thank you. What would one of the pneumatic mechanisms called? And would it require an external air pressurized air supply? I was hoping to keep this as simple as possible. – jbord39 Jul 26 '16 at 00:35
  • Sorry, I wrote the wrong company. Festo (not Festool). Here is one pneumatic actuator
    https://www.festo.com/cat/en-au_au/products_010200
    You will need an air supply.     – goodie Jul 26 '16 at 01:29