# Bucky skull meets toy motor



## Otaku (Dec 3, 2004)

Hi all,
I've been working on a way to use a small DC motor in place of a servo for animating a Bucky skull jaw. I used a 9-18VDC motor from RS:

http://www.radioshack.com/product/index.jsp?productId=2102827

and a standard two-arm servo horn. The horn is mounted to the motor shaft using a small plastic tube fitting that I had laying around, but there are a number of ways this can be done. The horn/adapter is bonded to the shaft with Loctite 4014 adhesive; this is the very thin viscosity superglue that is found anywhere. To power the motor I used an 18VDC HP printer power supply - these are regulated and are common in thrift stores and surplus houses.
The Bucky jaw is attached per Scary Terry's method, using cable ties. A small spring (not shown) acts to return the jaw to the closed position. Choosing the right spring is important - you have to balance the jaw in favor of it being closed, while not placing too large a load on the motor. I found that 12VDC isn't enough to do the job, but 18VDC works great. A 15VDC wart may work, but I don't have one around.
Here's a pic of the motor mounted in the skull:










I'll get video posted soon. So far, so good. I plan to use an op amp board and MP3 player to drive this guy. The op amp board is being discussed in another thread here:
http://www.hauntforum.com/showthread.php?t=26340


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## BioHazardCustoms (Aug 5, 2009)

Looks good. That's an awesome alternative to the servo motor, also.


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## RoxyBlue (Oct 6, 2008)

Make sure you use small words as you explain all this since I don't know nuthin' 'bout no servos

Being able to do a project like this is on our list of Things We'd Really Like to Do At Least Once Before We Die.


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## halstaff (Nov 18, 2009)

Great idea! 
Is the motor quieter than a jaw servo?


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## Otaku (Dec 3, 2004)

halstaff said:


> Great idea!
> Is the motor quieter than a jaw servo?


Yep, virtually silent. There is a bit of a clack when the jaw closes but this could be mitigated with a foam shock absorber.


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## tstraub (Feb 26, 2012)

This design looks very interesting. How do you control the min and max jaw positions? I know that with the servo driven jaws to had to set the positions. On the 555 timer based circuits this was typically done with 2 potentiometers one for min and one for max. And on the PICaxe based circuits you had to define the positions in the firmware before flashing the chip. Does the return spring simply pull the jaw closed until the teeth hit each other and the motor pull it open until it hits a mechanical stop of some sort? 

Tyler


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## Otaku (Dec 3, 2004)

This design will work essentially the same way that a Scary Terry/Cowlacious board works. The S-T board doesn't have any setpoint (at least on the ones I have) for the max position, it drives the servo to the full open position as long as an audio signal is present. Same thing here, so the max travel can be defined by the length of the beeps. The return spring just pulls the jaw closed. I'm planning to insert some type of small shock absorber to keep the teeth from clacking too much. One way around that may be to position the return spring such that the jaw doesn't close quite all the way.


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## JeffHaas (Sep 7, 2010)

Very nice! The servos have an obvious "whine" when they move. So we made our talking Bucky into a cyborg, but this will be better for all the other options.


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## Otaku (Dec 3, 2004)

Initial testing shows that this motor has very good reaction time, but is prone to overheating. Probably to the point of failure if run intermittently for more than about 30 secs. I stopped before I killed the motor. This may be due to the high inrush current when the motor starts. If this is the case, is there a way to "soften" the startup?
The power supply I'm using is a regulated 18VDC, 3.5A. The motor is rated to use up to 18VDC, so I'm kinda pushing it.


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## Otaku (Dec 3, 2004)

More info - I went back and tested it with a 12VDC 1A supply and got good results. Not quite as fast on the reaction time, but after a full minute of a simulated voice track (rapid intermittent actuations sprinkled with dwell times of ~2 secs) there was no evidence of overheating at all. The motor obviously could benefit from a bit more current, but this works pretty darn good. I'm gonna dig through my wall wart stash this weekend and see if I have something that is more suitable.


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## Otaku (Dec 3, 2004)

I'm also looking at this motor as a possible candidate:
http://www.jameco.com/Jameco/Products/ProdDS/232022.pdf
The one I'm interested in is the 232040 which has a stall current rating of about 4A and the dimensions are nearly identical to the RS motor I have now. Since I'm not a motor guru by any stretch, any advice is welcome. The Radio Shack motor is, well, a Radio Shack motor and as such probably not too reliable. It was good for proof of concept, but I don't trust it for the long term.
This is fun, I can't wait to get the op amp boards from Jeff and give this thing the acid test.


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## hpropman (Jul 27, 2008)

Although the servos can be noisy I still prefer the ability of complete control of the servo with a picaxe. However, if we could work out the issues with the chattering teeth you may be on to something here. What are you using to control the motor a 555 timer circuit or a microcontroller? Oh and Roxy I would be glad to help you and anyone else with the tech stuff.


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## RoxyBlue (Oct 6, 2008)

Thanks, HP, you're a doll


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## Otaku (Dec 3, 2004)

hpropman said:


> What are you using to control the motor a 555 timer circuit or a microcontroller?


I'll be using an op amp circuit to switch the power to the motor, which is driven by an MP3 player. Here's the op amp circuit thread:
http://www.hauntforum.com/showthread.php?t=26340
The motor will be either on or off, with the jaw travel determined by the length of time each "beep" runs. Short beep, short travel. For controlling a fully-opened jaw (longer beeps) I can use a hard stop (possibly adjustable) to limit the travel. Right now I'm using cable ties to attach the jaw a la Scary Terry, but I think I want to improve that a bit; nothing fancy, just not cable ties.
I agree about the control you get with servos, but the low cost of this system might make it a viable alternative.


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## Lunatic (Oct 3, 2006)

You never seize to amaze me Otaku. I've been following the OP Amp thread. It's cool to see another thread for its application. Real nice...thanks for sharing!


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## scourge999 (May 4, 2008)

This is cool Otaku........really cool.


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## Otaku (Dec 3, 2004)

The motor driver board is pretty much finished now, there's just a couple of details to work out. Thanks to pshort's expertise, the circuit is working great. I'm still trying to nail down a better jaw hinging design and get the right motor.


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