motorised pounding mallet

[klunk]

Hi all,

I was told I could get some help here. Hope you can.

I need to make a large scale pounding mallet that can repeat a pound every 5 seconds or so. I'd be using a mallet approximately 300mm in diameter. It would pound away at a large cube of compounded dirt - a mud brick of sorts - that is roughly 1.5sqm. The velocity of the pound needn't be that forceful at all. Also the pound would be automatic.


I was referred to this early on.
http://www.youtube.com/watch?v=lCUE3htj37o

At any rate, this object is for a visual arts exhibition and so is temporal.
However I really have no idea on mechanics, robotics, electronics or even basic engineering. I'd prefer the machine to look minimal, but am not concerned if it looks crude.

Here's two variations of it. I prefer the triangular looking one.

Thanks in advance,
Klunk

[Jeffy]

It looks like you have a solid plan. However, it appears that the linkage you have shown will move it at the same speed forward and backward, is this desired?

If not, you could use a cam. Or, I'm sure someone will soon post the "1625 linkage" used in 2008 and 2010 for spring loaded mechanisms.

[klunk]

i think slow when backward would be ideal.

[Kyoshirin]

Would this sort of thing work for you? The wheel pushes the hammer up and then drops it. Doing this makes the hammer fall faster than it rises.

You shouldn't have any problem with the pyramid. You just need to put the lever just underneath the top vertex and run the axle off the supports. I can draw a picture if my words don't make sense.

[klunk]

yes please, a drawing would help.

[Joe G.]

I agree, a cam powered system sounds like it will achieve what you're looking for.

http://www.youtube.com/watch?v=1wjjRYgDZT0

[Kyoshirin]

In the 2D view, you see a trapezoid with a circle inside it. That is a single plate that holds the pivot axle. In the 3D view, you see how it is implemented. With the two plates mounted inside the supports, you can hold up the arm/lever on that pivot axle. In the video you posted, this is accomplished by two pillow blocks (grey omega-shaped things) on top of the pillar. What I am describing for use by you is called a bearing plate, which can be easily made out of sheet metal, a bearing, and three screws.
Does this make sense, or should I try another approach?
Joe G.'s video is another way you could make this automated mallet. How you want to make it is up to you.

[msimon785]

I can tell you right away that a string/motor system will prove entirely ineffective. If the mallet requires functionality, or at least any actual level of practical force, you will need to stay away from flexible parts and move towards either dynamic parts or a CAM. Either of these will work just fine. If you choose to implement a CAM, you will need to design a solid system in which bearings are placed around the main rotating shaft.
By a dynamic system, I infer something with two main positions/stages, or in other words, a linear actuator. Among these, a motorized linear actuator could work, or if you have the expertise and will, you may choose to attempt a pneumatic actuator. Automation direct sells some good actuators.

[Kyoshirin]

In non-technical language, msimon785 is saying that if you want this to be a tool instead of just a moving sculpture (I believe just a moving sculpture is what you wanted) you should use an air powered piston (with a recommendation in his post of where to get some) or any of the previous design ideas that Joe G. or I have given.

[lemiant]

Here is my suggestion: http://www.youtube.com/watch?v=U5tHtntT9gU

The constant speed stick is running at 12RPM, which will give you a pound every 5 seconds.
To achieve this I recommend using a CIM (http://www.andymark.com/product-p/am-0255.htm) running through a high reduction planetary gearbox (http://banebots.com/pc/P80K-S4/P80K-4444-0005). You can put a standard #35 chain 12 tooth sprocket (http://www.andymark.com/product-p/am-0166.htm) on the output of the gearbox, and attach a 22 tooth sprocket to the stick (http://www.andymark.com/product-p/am-0216.htm), then run #35 chain between them.
I have more ideas about the construction of it, and the exact configuration of the drive system (shafts, keys and bearings), if you would like extra details like that just ask.

PS After typing that I realized that you may or may not understand any of the words I wrote, feel free to ask for clarification and I will explain our CD jargon.

[Garrett.d.w]

The easiest (albeit crudest) way that I can think of doing this involves some 2*4 lumber, a few half inch bolts, a drill, and duct tape.

First, build two triangles out of some 2*4 lumber (these triangles can be any size that you want, as long as they are the same).

Next, mount them so that they are parallel to each other. The mounts must be sturdy if you don't want this thing to discombobulate in the middle of the demonstration.

Finally drill a hole that is a half in diameter at the same height on both triangles (this will be the pivot point for your lever.

That will be your base.

Now for the arm.

Simply take a large piece of lumber, drill a hole 3/4 of the way down the length (1/2 to match the holes that are located on the frame).

Using tape, or any other method, secure your hammer to the end of the longer side of the arm.

Attach this to the frame using a half inch bolt through the mounting holes we drilled earlier.
With any luck, it should now look like a medieval trebuchet.

Now we need to power this contraption. To do this, we will attach a short length of 2*4 lumber to a variable speed drill (this will be our cam). You will have to play around with the mounting and size of the cam. Your goal is to have the cam push the short end of the lever down (raising the other end), and then drop it so that the hammer can descend.

If you want, I can draw this all for you. It will probably be easier to understand.

[klunk]

Looks like I found the right place!

Thanks for ALL the input, kind folk. There's a lot of information here.
Back soon with questions.

Thanks again,
K

[Alex Cormier]

Originally Posted by klunk

Looks like I found the right place!

Thanks for ALL the input, kind folk. There's a lot of information here.
Back soon with questions.

Thanks again,
K

I told ya this place could easily help you out.

[klunk]

Thanks Alex!