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[on:]

I'm in the planning stages of a costume with a large head which I want to have hands-free control of.  The plan is to use servos of some kind along with some combination of accelerometers, gyros, flex sensors, rotary encoders or whatever to match the motion of the head with that of my own. 

My best guess is that the head will weigh 3-4 pounds, will be approximately 24 inches long, with the pivot point 6" in from the back of the skull.  It will taper to the snout but not by much so the mass distribution can be approximated as a box 24x12x12 in size.

I don't know if adding a spring or additional weight to somehow counterbalance it would help any with the torque. 

Anyway, what I'm wondering is if there are servos that aren't thousands of dollars which can lift this kind of weight?  There won't be room for significant leverage, but a 4" lever may be possible.  A servo doesn't rotate very far though, so the lever idea might not work out since the head wouldn't rotate very far.

Stepper motors I suppose are also a possibility.  I don't have experience using them but I don't have to build a circuit from scratch to control them either.  I'm not sure how one would attach something like a head or a level to a stepper motor shaft though.  What would one use? 

Any ideas for servos / motors or even a way to control this with only head movements would be helpful.

[Reply #1 on:]

Hm... I found some not terribly expensive servos on Pololu which have the kind of torque I need.  I think.  $40 each, with 416 oz-in of torque... I think that translates to being able to lift a 4.3 lb load that sits 6" from the center of the servo.  I used 6" because the mass of the head is not centered around the servo, it is shifted to one side, and the average distance of the unbalanced mass on the one side is 6" out.  The weight of that unbalanced mass, and indeed the entire head should be less than 4.3 lbs. 

Not sure how I would mount the head to the servo, but I guess I could attach an arm to a pivot rod somehow, and use one of those servo rods to pull on that. 

Now I've just gotta figure out how I would mount the head so it could rotate side to side.  Some kind of bearing?  With a rod going down through it?  And an arm on that rod for the second servo to pull on? 

[Reply #2 on:]

Servo city has some heavy duty camera pan/tilt units.

[Reply #3 on:]

Some large inexpensive servos.

http://www.hobbyking.com/hobbycity/store/__9617__Turnigy_Metal_Gear_Servo_60g_15_5kg_16sec.html

http://www.hobbyking.com/hobbycity/store/__16643__VS_11_Vigor_Extra_Large_Servo_19sec_19kg_103g.html

http://www.hobbyking.com/hobbycity/store/__8496__Turnigy_S8166M_Servo_154g_33kg_21sec.html

http://www.hobbyking.com/hobbycity/store/uh_listCategoriesAndProducts.asp?idCategory=291