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Launching Mechanism

Launching Mechanism

Launching Mechanism

(OP)
Hello Folks,

Looking for some knowledge in this fun project I have going.

I am trying to create a device that is to launch a 400grams(approximately) projectile. I have very little knowledge in robotics, so would welcome any guidance as to what types of mechanical systems I should be observing. I researched and could see that a step motor here might be beneficial. Essentially, I'm trying to control this using an ECU after integrating a few sensors and feedback devices for self calculating distance of targets. I don't need assistance in this matter as much as the actual mechanical devices I should look into for the launching mechanism.

I am not looking for a pneumatic or hydraulic system or for that matter trying to build a trebuchet or catapult - as I want to be able to control the speed, angle, and so forth.

Not sure if I was clear at all, if you all can ask me a few pointed questions, I can elaborate more without rambling.

Thanks in advance!

RE: Launching Mechanism

Have you taken a look at clay pigeon throwers?

RE: Launching Mechanism

Quote:

I am not ... trying to build a trebuchet or catapult


Why not?

A catapult is a simple and reliable way to project objects.

Store some energy in an elastic element, then apply it to the projectile suddenly.

If you want to control the amount of energy then you control the amount of initial deflection of the elastic element. Very simple to accomplish with a linear or rotary actuator and position sensor.

A second simple actuator and sensor to control the angle of launch.

RE: Launching Mechanism

(OP)
MintJulep,

I pigeonholed my idea of a catapult by thinking it had to be driven by a counterweight.

That could very well work, since I would be able to control both actuators. Any additional guidance of which elastic elements could work here? Torsional springs?

Going to research some linear/rotarty actuators for cheap, unless someone has some useful knowledge to bestow.

RE: Launching Mechanism

Had a high school Design Technology (Think Shop with some math & physics) project vaguely similar to this.

We only had to launch a 'projectile' didn't give a mass so most of us fired BB's or ping pong balls etc.

Anyway, several of us used the idea of a solenoid which pulled in a 'bolt' which then impacted the projectile and sent it flying. To get the rapid effect of the solenoid we used large capacitors which we then discharged into the solenoid.

You could also look at rail guns if you want some funwinky smile.

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RE: Launching Mechanism

Or, you can do what they've done on Mythbusters:
> Swing arm launcher
> Air cannon using large tank with high speed valves; charging pressure of tank determines max speed
> Crossbow, but you'd need to modify it to change the amount of stored anergy

plus

> tennis ball launcher
> rail gun

TTFN
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RE: Launching Mechanism

Are you wanting to build something that can be minutely adjusted?

RE: Launching Mechanism

(OP)
Hey thanks all for the contributions, and oh so quickly!

I should have prefaced this earlier; anycase, this contraption is an indoor "beverage" launcher, hence the mentioned 400 grams. I am aware of the many designs floating on the interNET, but want to try and make it simpler, but with added complexity of feedback. Before I get to the controls, I'm trying to narrow down on the relevant mechanical systems that can help me. I'm almost certain I would require 2 degrees of freedom - to accomplish the direction and distance.

Rail guns - though enticing, is definitely going to be an insurance liability for the indoors. Cool project to do in itself though.
Bolt discharging solenoid - Need a larger contact surface to discharge, even if so, it might rupture the can, no?
Tennis/cricket/baseball launcher - Would I be able to consistently control the speed and angle from a feedback system. Maybe if I placed the whole contraption on a lazy susan. Perhaps I could get some additional feedback on this.

Also, what do you guys think of a pneumatic system that I had initial reservations against? Would that be simpler? Compressor, Air Tank, Regulator, Relief Valve, Ball Valve, and a beverage loading tube. Would that pretty much sum up the primary components involved.

In the meantime, I'm gonna check out the mentioned Mythbusters' Swing Arm Launcher.

Once again, thank you very much for your feedback and inputs. My expertise is not in applications, so I guess this is a great way to learn.



RE: Launching Mechanism

For safety/liability reasons, an indoor can launcher needs to work at a tightly controlled velocity, just enough to get the projectile airborne, and not so fast as to break a lot of ceiling tile. Better to call it a can tosser.

That makes air cannons and such a non-starter.
Despite their apparent simplicity, I don't think anyone really understands the trebuchet. Only a really small one would have short enough range.
Spinning tires could work, but they can't spin real fast.
I'm thinking the required velocity is low enough that a stepping motor could push a bumper in a trough fast enough. ... and it would probably be boring to watch.

How about a nice simple robot to open the cooler, retrieve a can, close the cooler, and just gently roll the can along the floor?


Mike Halloran
Pembroke Pines, FL, USA

RE: Launching Mechanism

(OP)
MikeHalloran, thanks for the speedy response.

Ahhh, but what's the fun in getting the can rolled. Subsequently, uneven surfaces, carpets, center/coffee tables, etc pose as obstacles.

My motivation behind this project is the feedback, so that if I program in a few sensors, I can get the can "tossed" at whichever point I'm sitting in the room. That's pretty cool, at least I think so. I haven't really seen that in any of the existing solutions.

I, so far, have the unloading mechanism within the refrigerator determined....it's the launching mechanism that I'm stuck on.

RE: Launching Mechanism

"Anyway, several of us used the idea of a solenoid which pulled in a 'bolt' which then impacted the projectile and sent it flying. To get the rapid effect of the solenoid we used large capacitors which we then discharged into the solenoid."

That's actually very similar to how the electic Airsoft guns work. They don't use caps, but the NiMH batteries have pretty impressive discharge performance.

However, anything that generates a mechanical contact shock is probably out of the question, unless you're looking a beer bath every time you open a can. Although, it might be possible to design something like a balloon like cushion that allows a more gradual acceleration to launch speed.

I don't necessarily rule out an air cannon. The drastically reduced speed simply means that the air cannon does not need to be as beefy as I envisioned. Assuming a maximum trajectory rise/drop of 3 ft, the can must travel across the room in ~0.86 s, which, assuming a 20-ft max range, requires a launch speed of 23.22 ft/s. I would think that something that resembles a human arm would be most plausible. Imagine a DC motor attached to an arm with a cradle for the can, driven to a tangential speed of 23 ft/s. Assuming a 2-ft arm, the launcher needs to spin at 110.5 rpm, which is sporty. An encoder would be used to determine the arm position, and an automobile A/C clutch would be energized at the appropriate arm angle to stop the arm. The can would continue its tangential trajectory. A sturdy base is a must.

TTFN
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RE: Launching Mechanism

(OP)
IRStuff,

I feel the same way, I don't think a pneumatic system is completely out of the question. I'm doing some preliminary analysis on it, will share that for feedback once I get it done.

Regarding the swing-arm(human arm, whatever we call it), have never dealt with an A/C clutch, but they seem quite expensive after a quick search. Are smaller application clutches? Maybe under a different lexicon?

Also, rather than looking to get such a speedy DC motor with appropriate torque, how bout using a linear actuator to drive a crank which in turn stores energy in a torsional spring, which after a release mechanism transfers the energy to the arm to the appropriate velocity. Hopefully, I haven't looked past some fundamental physics there.

RE: Launching Mechanism

Take a look at the drive arm mechanism of a shaper. For your application the return stroke will become the throwing stroke. As the crank is moved down closer to the pivot, the length of stroke and the sped of the stroke both increase.
As the crank arm rotates clockwise, the horizontal speed of the drive pin increases as a sine function. But coupled with this the radius to the pivot of the stroke arm is decreasing increasing the speed also. You may develop quite high stroke speeds with a gentle start and a much more gentle return.
Note that the stroke and return for a shaper are reversed for your application. As the crank rotates clockwise you will get high speeds to the left followed by a slower return to the right.
You may modify the action by the following changes:
Speed of rotation
Distance from the crank center to the arm pivot
Radius of the crank.
Length of the throwing arm.
With a moderate gear reduction you may be able to get the crank up to speed in 10 or 20 degrees. Start with the crank pin at about 1:00 0-clock or 2:00 o-clock.
Clockwise rotation will through to the left.
See a sketch of a shaper drive here. Scroll down on the right.
http://en.wikipedia.org/wiki/Shaper

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Launching Mechanism

Can launcher, OK so that ties things down some. You'll want a fairly smooth launch system then, nothing to jerky or your beer/soda will just be exploding froth at the target.

http://en.wikipedia.org/wiki/Range_of_a_projectile

You probably want to minimize velocity, so unless planning to use it in a large room where the ceiling would be an issue you may be able to stick with a fixed elevation launcher at the optimum range angle and just vary the energy/launch velocity.

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RE: Launching Mechanism

http://www.youtube.com/watch?v=7R4W3k-GOu4

The lower connection point of the spring could be a movable point controlled by a stepper motor or other linear actuator to adjust for throwing velocity.

"Art without engineering is dreaming; Engineering without art is calculating."

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RE: Launching Mechanism

A slingshot type catapult with surgical tubing as the elastic element? If you have a fixed point for payload loading and trigger then you can make the "Y" the movable part to control the tension.

Similarly, a cross-bow.

Changing from tension to compression, something like a pinball machine plunger.

If you use a torsion element you could independently control the angle of the release point and the amount of wind-up.

I don't think the baseball pitching machine concept would work well, as it depends on friction, and you don't control friction of your projectile.

RE: Launching Mechanism

(OP)
waross

I'm definitely going to consider that as a solution. However, some immediate questions arise. A DC motor would allow me to vary the speed with PWM, but then how could I control one revolution? An encoder? If a step motor is used, I doubt I can get a cheap option for the RPM needed in this design. Any ideas as to how I could control this, since loading of the beverage is going to take place after each revolution.

KENAT

You hit the nail on the head. I'm definitely going for low velocity with the average height of a living room being the control here. Now figuring out what the most efficient(simple) mechanism would be to employ here.

MadMango

I came across that video - seems well done. Is that a stepper motor on top that's driving the arm? I think a linear actuator there could definitely work. Just curious whether I can find a low-cost option for a linear actuator with enough force. I'm going to figure this out as I get more advice.

RE: Launching Mechanism

While I doubt it's the best option, the solenoid bolt concept doesn't have to involve a sudden impact.

If the 'bolt' has a 'cradle' at one end that the projectile sits in then the bolt can be pulled into the solenoid which causes the cradle to push against the projectile and launch it.

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RE: Launching Mechanism

Is the plan to catch the can in your hand as the machine tosses it towards you?

If so, I guess that designs with swinging arms will give the catcher better cues about when and which way the can is going than things like air cannons will. Perhaps dropping a few is part of the fun, but it's going to be a royal pain when you're thirsty.

A.

RE: Launching Mechanism

An AC motor with a gear reducer and a VFD drive may work. Use a limit switch to stop the rotation after one cycle.
On the slower return stroke, there is more mechanical advantage. You may be able to pre-load the arm with a spring. The spring would be compressed during the return stroke and add to the force on the throwing stroke. The motor may be able to use the extra help.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Launching Mechanism

bhasker2, that motor in the video looks like nothing more than a $15 automotive window motor. Good solution for a linear actuator would be a ball screw actuator, maybe an acme type as those are harder to back drive.

"Art without engineering is dreaming; Engineering without art is calculating."

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RE: Launching Mechanism

(OP)
Gentlemen,

I'm now working on my second option, a pneumatic launcher:

After conducting an adiabatic expansion analysis, it seems I might need only 40-60 psi to launch the beverage. Why the wide range, well I know the adiabatic expansion analysis is at best 50-60% efficient; it doesn't consider head losses and accurate frictional account. Any case, I'm just looking for ball park pressure; since it's less than 100 psi, don't see why I can't have this system as an option indoors.

So here's the setup, please critique:

200-300 psi rated compressor ---> regulator ---> air tank (200 psi) ---> pressure transducer ---> Electro-Pneumatic High Resolution Proportional Control Valve ---> Beverage Barrel

The idea behind this setup is that the electro-pneumatic valve will allow the right(approximate) pressure to be requested for the distance the beverage needs to travel (yes, control setup will be a pain). The maximum pressure ever requested will be 100 psi.

What do you all think. Am I missing a few things here?

RE: Launching Mechanism

(OP)
I forgot to include the relief valve in the setup.

RE: Launching Mechanism

Here's another type of launcher with soapy water.
I know this fellow. He is a lot of fun. Be careful. Someone drops the "F" bomb at about 46 or 47 seconds.
http://www.youtube.com/watch?v=U11SkW84k6s
Same character; Here's what can happen if you use too much pressure in a pneumatic beer can launcher.
http://www.youtube.com/watch?v=7Zn8WGiwNCw

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Launching Mechanism

Google around for Nerf dart gun modding. Should be lots of interesting ideas in there.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com

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