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Champion
 
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| Anyone know a cheap and easyish way to provide movement to a prop jaw for example? I cant say what its specifically for, but in the future I need to make a mouth move on an item... as its not a mask it wont be as easy as just linking it to a mouth of a wearer. It needs to be independant and not require a hand to operate. It doesnt need to talk or move rapidly, just move a little...
--------------------------------------------If the Gods didnt want us to eat people, then why are they made out of meat?Grumf Kikuto - United Tribes of New BantustanSir Nathaniel Holt - The Fallen
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Knight
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Likely the easiest option would be to have the mouth hinged and held shut with an electro-magnet, when off the mouth falls open under gravity, then if you keep the distance reasonable small it will close back up when the magnet is reactivated.
A refinement on this ideal would be to use a solenoid with the bar mounted inside the coil connected to the jaw. Alternating the direction and strength of current will produce a jaw motion. With a bit of practice and a variable control setup one could produce a variable movement effect - strength of the action would depend on the size, quality of solenoid and strength of current.
There would also be options for hydraulic/pneumatic action or conventional electric motors either some manner of direct motion or to a mechanical setup like a cam or similar.
If anyone is interested please let me know and I will expand on these suggestions.
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Champion
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Sounds interesting... where would I get the parts? What would they cost?
--------------------------------------------If the Gods didnt want us to eat people, then why are they made out of meat?Grumf Kikuto - United Tribes of New BantustanSir Nathaniel Holt - The Fallen
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Knight
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In case anyone needs the basics.
http://www.societyofrobots.com/actuators_solenoids.shtml
Although a wide range of industrial solenoids are available one could be easily made or scavenged.
Scavenging - the most common household location for solenoids are as the motivators of speaker cones and one from a large bass-speaker can provide the all the force you will need. The disadvantage of this is that speaker solenoids tend to have a very small amplitude of motion, because they only move small distances within the speaker.
Making your own - fairly simple but you might have some difficulty with producing one with enough force, not that it cannot be done but it might take some experimentation.
You will need four primary components:
Power supply - a large battery should do the job.
Fixed pole magnet - needs to be straight, not horse shoe - ring shaped ones are good for mounting the rest of the mechanism.
Coil - this can be made from any wire but a thin one with little insulation will provide the best results
Alternator - to allow you to reverse the voltage and cause the movement.
All this is entirely possible to make at home from very low cost materials.
My tea-break is over but I'll stick up a few plans if you want after work.
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Champion
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Thanks that would be great, I have lots of old speakers oddly enough  I also have several earth magnets laying (erm sticking) around.I know maplin do a electromagnet but its very small and I doubt it would be sufficient...
--------------------------------------------If the Gods didnt want us to eat people, then why are they made out of meat?Grumf Kikuto - United Tribes of New BantustanSir Nathaniel Holt - The Fallen
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Knight
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Rather large image, sorry, if it is a pain for anyone let me know and I'll reduce it a bit.
The rotating cell is the simplest way I could think of that could produce an reversible current from simple home technology. A battery mounted on a central pivot allowing it to turn 360 with two 'pins' reaching out to touch two contact plates. A refinement of this could to use a coil of high resistance wire which would help damp the system.
The magnet is attached to the 'jaw-bone' via a connecting rod if the range of motion is quiet large the connecting rod will need a second pivot where it joins with the magnets so that the magnet does not shift within the solenoid shaft. The solenoid itself can have a body of near any material but I would recommend thin plastic piping possible with holes drilled out to reduce weight. Non-ferrous (non-iron) material will probably work best otherwise it may interfere with the magnetic field. The coil should be a tight and regular with as many turns as possible in order to get the most strongest magnet field.
I hope this gives an idea how to do this, a lot of it will be experimentation to get it spot on for the particular job you have in mind. I have tried to cover the production as using the most basic components available within the home, for increased ease but more cost industrial components will be available from either Maplin or RS. Linear actuators tend to be rather expensive. I am sure there is a better way to create an alternating current with a pre-made component.
I would take care to try to use as low a voltage as possible and certainly not use the mains (even if transformed), there is a chance that with higher voltage the coil may create some quanity of heat.
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Apprentice
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Really we need to know some more information about how this jaw is to be set up. I wouldnt recomend solenoids until these questions have been answered as they dont provide as much movement as you think they do and they take a lot of electricity to do what they do.
Where is the device to be located? Is it going to be in a field and run off batteries or do you have a wall socket nearby.
Do you want the device to be silent? Do you mind if it had the mechanical noise made by servos etc.
Where is it going to be operated from? Are you going to be watching it at all times or is it moving on its own.PM me the exact details and I'll try to see if I can help you out. I'm sure my degree in robotics will be useful for something. Off the top of my head I would drop the solenoids and go with hydraulics. Take two syringes and connect the nozzles with some tubing. Fill the system with water and watch the second syringe move when you move the first one. Simpler and easier but it may not be what you want. Martin
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Knight
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I happily defer to Martin's judgement on solenoids.
With fresh thinking on the problem, if you are just after basic motion with no fine control of over the exact nature of the action, a motor and cam beneath the jaw would probably be the simplest method. Disadvantages would a slight noise of motion and that the system will only work if relatively light and in an upright position.
My preference for electronics comes from durability and ease of repair in the field, a loose wire is quickly fixed but a loose hydraulic tube can be far messier
Hydraulics I would use for heavier systems that did not require and fast motions as syringes can have a high resistance from their rubber components slowing the movement down - proper pistons would be faster but more expensive. Hydraulics are also good for applications were a good level of variable control is needed, they can easily stop, reverse and move to certain points within their cycle by easy manipulation of the control cylinder - this does require an individual to manage the motion so it cannot be independent of operator. Hydraulics based around a syringe are certainly easily made at home.
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Wag
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