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Hey guys.

Im looking to build a large drumming robot for a festival installation.  I want him to be slightly larger than human (probably about 7 ft tall) so the mechanism to hit the drum will be large and probably quite heavy.  I also want the mechanism to be very visible, so you can see the arm hitting the drum.

Bearing all this in mind can someone recommend a mechanism for doing this? eg linear actuator/compressed gas etc..

thanks in advance
Rich
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You may get more responses if you post under the projects discussion heading.
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Good call @zoomkat.  Topic moved to its new home.  May it find a plethora of helpful replies...

@rich_brighton: After a few days, if your post gets no replies, bump it and I'll move it to Robots.
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A standard linear actuator is likely to be too slow; pneumatics would be the likely way to go.

Note that if you do go this route, that new cylinders, solenoid valves, air dryers, etc - will all be fairly expensive. Your best bet is to go surplus.

You will probably want to use single-acting cylinders with spring-returns (depending on the motion you need to achieve), and a 2 or 3 way solenoid valve. The valves typically run on 12 or 24 volts (some are continuous duty, and some are intermittent). If you go with a 2-way valve and a single acting cylinder, you'll be able to have "on" and "exhaust" settings; 3-way will allow for "on", "exhaust" and "hold position".

If you go with double-acting cylinders (with ports on either end), you'll need valves for both ends. You'll also need a compressor with a tank (or a tank of compressed air, or CO2 -and- a regulator; note that regulators alone, brand-new, can cost close to $100.00 alone!), plus the air-dryer/filter components, etc.

Even surplus, expect to spend a few dollars...

You might also be able to do this with DC motors (and gearboxes), provided they can be back-driven, and you supply a spring return (so you can "pulse" them to "hit" the drum, and the momentum of the arm/striker will carry thru, then the spring will return it back to position); you'll probably need a hefty high-amperage driver (one that can take the back EMF of the "pulse", too - you'll be driving the motor somewhat abnormally).
« Last Edit: March 05, 2012, 11:21:06 pm by cr0sh » Logged

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Just to wet your appetite-
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nice 1 guys and thanks a lot cr0sh specifically!

i will be starting this in the next couple months now that it seems possible (just about!).

cheers!
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Pneumatic actuators are probably the most economical solution, especially if you already have a compressor.  But, they can be clunky/noisy, and difficult to "control".   You can control the speed to some extent by regulating air pressure, but otherwise it's just "move" and "move back".    I imagine you could use some feedback to get servo-like control, but I don't think there's anything like that available off-the-shelf.

I don't know if it's still done the same way, but "100 years ago" when I worked for the company, the characters/robots at Chuck E. Cheese were pneumatically operated.  If there's a Chuck E. Cheese near you, you might check it out.  (If they still have those animated characters, and if they are still pneumatically operated, you should be able to hear the actuators activating,)
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If it's just a regular beat you want then a camshaft on a motor can drive the motions. Using pull against springs, fishing line as ligaments attached close to joint pivots -- you can get very fast moves from short pulls. If you need to vary the beat then really strong solenoids to pull the strings would work. That or find cheap clutches for the cams! I move my arm 30 cm, my muscles change length much less than 30 cm. With this you have the power of constant turning motor and flywheel.

I've seen balloon like sacks used as robot muscles long ago. Each balloon uninflated had two 'ends' tied to two arm sections and a valved hose near one end. When the balloon was given air, it shortened the length between the tied lines and the arm moved but it wasn't anything like industrial with the amount of spring. OTOH for your robot if the arm down to hit the drum position is a bit 'deep', it won't drive the stick through the drum but just hit a little harder. That would be more expensive, maybe but could also run off 1 compressor (and many valves) and have the power stored in the air tank. The cool part is you would see his muscles move even under clothes. Just remember that arm movement starts with the upper torso.

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