RoboHead

[thestig]

I am looking into building scaled up version of the robohead for halloween. You are not allowed to view links. Register or Login (click the link with the moving,singing head on the right)

I am thinking much bigger like a 5ft X 5ft face made out of pvc and wirefence (like how I built my singing pumpkins). Anyways servos are obviously out of the question due to the size of this thing. What do you guys think about double action pnuematic cylinders. One for the pan and one for the tilt?

Is there a way to control this by DMX?


I am very new to this, but plan to start making progress once I find a way that is doable.


Thanks for any help.



Grant

[Night Owl]

What were you thinking about using as the valve to operate the cylinder?  Have you tried looking at some of the DIY Halloween sites?

[caretaker]

Short answer yes.... Pneumatic valves use a simple solenoid system to operate a valve (open or closed) so you could use a MR16 to control the valves (as long as the current the valve needed wasn't over the MAX MR16 current).  When designing animatronics weight becomes a big issue (the more weight the higher the cost of the animatronic.) as servos a relativity cheap when moving light loads but when you get to moving bigger loads the price skyrockets. Using pneumatics lowers the cost of animating a heavier object but the trade off is you sacrifice the ability for fine control of movement. One thing to keep in mind when designing your animatronic is that the control device (servo or pneumatic cylinder) doesn't have to be right next to what you want to control, you can use control cables and locate the control device in a base or somewhere more convenient to your design. 

[wwwgator]

we use whats called E to P (E=voltage to P= pressure) valves for controlling brake pressure on our splicers and infeed dancers to position rollers and things.
The problem with air actuated cylinders is that precise positioning is not possible.
 We use a PID loop  to balance web (paper)  tension counteracting roller position and vary the E-P to try to keep it stable.  Using air rams like robo bones is all open or closed, not many replicated in-between positions. I believe robo uses fluid for smoother operations, so I have read.

[caretaker]

Actually RoboBones is pneumatic, if you watch the neck cylinders they just move the head one side to the other and the same for the arm (just up and down strumming) They are just using metering valves to make sure the cylinders operate slowly instead of slamming up or down. The slower you move a pneumatic animatronic the more realistic the movements are due to less inertia. 

[NavyGator]

I know I am a bit behind in this thread but why can't you use windshield wiper motors or power window motors. You can use linkages or gears and chains. if you need more torque than one motor when using gears an chains you could use multiple motors. Just a thought.

Rich

[rm357]

Lack of positional control.

Servos have active feedback so that it knows what position it is in.

With wiper and window motors, you have no way of knowing what position it is in. You could use limit switches and just use one of the led outputs to trigger a move to the next stop...

RM

[NavyGator]

Lack of positional control.

Servos have active feedback so that it knows what position it is in.

With wiper and window motors, you have no way of knowing what position it is in. You could use limit switches and just use one of the led outputs to trigger a move to the next stop...

RM

Okay...if we go a step further. How about using a small inexpensive servo and modifying it with some external circuitry to drive the motor to handle the power needs while using the servo for positional control. I am not too savvy with this stuff, just trying to throw out some options that might be a little more inexpensive than high torque servos.

Rich

[caretaker]

Rich (and others) you can use motors (low rpm) to produce movement as I have an animated organist that uses 2 low rpm motors, one to move his head up and down and one to move the arms. You can check out my 2009 video and see the organist about 1:41 into the clip.
You are not allowed to view links. Register or Login  I also used a low rpm motor to open and close the casket lid. The skull is a Skull-Tronix 3 axis skull which uses servos.

[rm357]

It all depends on what you want to do...

If you need absolute positional control, you are going to have to use something that will give you that control. Servos excel in this capability.

If you have something that you want to move continuously or on a somewhat regular cycle, you can use a motor with cams and gears.

If you want something that has multiple "stops," you can do that with a motor, some relays, and limit/sense circuits.

Without knowing what you really want to do, it's hard to make any suggestions...

RM

[Mimir]

Another possibility would be to use stepper motors, which give you the torque and control, but they are also more expensive.

[tbone321]

The problem with stepper motors is that they require a more complicated controller and a way to index them so that the controller knows what position the item the motor is controlling is in wehn the controller powers up.

[chrisatpsu]

to elaborate on what Tom said...  a stepper motor in most inkjet printers that move the print carriage, also have a thin plastic strip with a hole or a mark on it.

in case the printer was turned off in mid print (power outage) when the printer turns back on, it retracts the print carriage following the strip until it finds the mark (home.)  Then it knows it's set back in the start position.

i know we''re not building printers, but it gives a good illustration of what stepper motors need to find where they are.

[ebrady]

In areas were a lot of torque is needed it may be a better route to use a pneumatic sensor with a linear potentiometer.  The potentiometer will read the position of the cylinder, which can then be fed to a controller to make it work like a servo.

[jess_her]

here is a wiper motor relay setup from blue point.
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Here is a thread for directional and stopping at set  points  using a cam, points and MR16.
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Here is a Servo controller from Pololu,  Using the Bobcat servo controller plug this board
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into it then drive your brushed DC motor up to 4 amps OR plug these boards (high current H bridge)
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into the Pololu servo control board.

The trick to this is servo have a feed back pot for position.
So what you want to control that's were you need to put the pot.
Most Pot for servo are 5 K Ohms and have about 270 degrees of rotation. Now you need a gear reduction box for pot If you want more than 270 deg of rotation out of your motor.

Now the thing I don't like about Pololu stuff is $$$$, To much for me for what it is.