# Length of Motor Arm For Animated Spider



## liftngwaght (Sep 27, 2011)

I have one of the small black 12VDC motors that Dave used for his head pooper prop. I also have a large, 84", spider I bought from BigLots that I would like to animate with said motor. This particular spider screams to me to be animated. The legs are lightweight but sturdy metal, covered in fake spider "fur" and are attached to the body in some way that allows them to move freely/independent from the body.

My thinking is a simple crank mechanism. Take a piece of plywood say 80" wide and maybe 24" deep (basic dimensions of the spider I guess). Put the motor in the middle with 8 eye bolts placed around the side of the board. Fishing line connected from said motor to each leg. Basic enough.

How do I determine how long to make the arm that attaches to the motor? This is the arm that attaches to the motor on one side and has the free spinning washer on the other. Is there some type of calculation or is it trial and error?

Thanks for any advice on my first prop build!


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## niblique71 (Dec 2, 2009)

I looked up your spider, and I am a little concerned that the little black "Vent" motor will do what you want it to do. It might not be strong enough. But I don't know how much the legs weigh.

However, If you still want to give it a try, I would make a 6" crank arm with extra holes so you can move the string "Teather" closer to the motor for greater mechanical advantage. I always drill extra holes when I'm experimenting with motors and crank arms. It's a lot easier to adjust when the extra holes are already drilled. Good luck and let us know how this works out.


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## liftngwaght (Sep 27, 2011)

Thanks for the multiple hole suggestion. VERY good thinking!

The legs seem pretty darn light. Im not looking for extreme leg movement so hopefully the little motor works. Are they pretty sissy? From the videos i've seen they seem to so a decent job at light stuff.


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## liftngwaght (Sep 27, 2011)

Oh sorry, you are correct Max. Body will be stationary (held up by it's own set of wires) while the legs will be the only thing the motor is supporting.

Thanks for the help guys! Experimentation is in order. I get to try my hand at wiring the motor this afternoon.


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## hedg12 (Jul 6, 2008)

The length of the arm will depend on how much movement you want in each leg, and how much power your motor has. The longer the arm the greater the movement, and the greater the load (it will take more power to move the mechanism with a longer arm.) The amount of movement in each leg will be twice the length of the distance from the pivot point (motor shaft) to the point on the arm where you attach the fishing line.


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## BTH (Jul 2, 2006)

One other consideration will be where on the leg do you attach the string. Closer to the body will give more movement while moving the string out towards a spiders foot will decrease movement. Here's a video of the spider I did a couple years ago. Wood legs and now they are dried out and extremely brittle. They still work though. As you can see, I get maybe 2 feet of spider toe travel with a 5" or 6" crank. The legs are also counterbalancing each other so your vent motor will work just fine.
Crankspider video by indianaholmes - Photobucket


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## paulcav151 (Nov 15, 2009)

Have you seen this site? http://softlyspokenmagicspells.com/halloween/dcs.html


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## liftngwaght (Sep 27, 2011)

I'd actually seen both the video and the site. Im a Google machine! It seems like everyone puts the motor on one side and the spider on the other. I was thinking of centralizing the motor with the spider body hanging directly below the motor, approximately 30" below the motor. The crank would be 6" and the 8 eye hooks would be approximately 30" away from the end of the crank.

The spider has 4 leg segments and I was going to connect the fishing line between the 2nd and 3rd segment.


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## liftngwaght (Sep 27, 2011)

Madmax, your instructions were PERFECT. Worked like a charm! I now have a working motor.

Went out today and purchased all the materials for the couple of builds im doing including this spider build.

I'll report back once construction gets underway.


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## Todd (Sep 1, 2007)

Here is my 2 cents.

First hang the spider torso at the desired heighth. 
Only attach one leg line at a time, I used clothes pins to temporarily hold lines until I could check for desired motion. 
I connected my legs in opposing pairs so I only had 4 points of connection.
You may find that you need to route your lines around the perimeter of your layout and come back into the washer from the outer edge.
Make sure your lift points are directly above your attached point on the leg or you will have problems with swaying motion that wil cause the legs to bang together
Oh yeah wire up a momentary contact switch while your under construction. This will allow just quick shut down during trial runs..... in case _____ when somthing goes wrong.

Good Luck.
Todd


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## liftngwaght (Sep 27, 2011)

The spider is UP! I'll try and get pictures up in the next day or two. Was a definite learning experience. I was not made to be an engineer I now know.

Things I learned.
1. The reason people don't build the spider under their motor is that you can't hand a spider if it's under the motor. Duh, right? We'll I didn't think about the motor being in the way. In the end the motor holds the entire weight of the spider and does well. Instead of the legs moving up and down with the body stable, the spider more or less "waves" from left to right. I don't have any sway which is nice though.
2. The lengths of the line from the motor to the spider legs should be the same length. This was mentioned by Todd but I just kinda guesstimated when I tied the string to the legs. Only after measuring correctly did the spider stop swaying.
3. People like moving props. Tons of people stopped their cars to watch this 7 foot spider move back and forth.

Along with the spider I took 2 Big Lot skeletons, wrapped them with cyran wrap and then wrapped them with spider webbing to be cocooned figures. Hung them upside down on either side of the spider. 

I still have to make LED custom spot lights and finish up my monster in a box build. Like I said i'll try to get some pictures/videos up tonight showing stuff off so far. Thanks for everyone's help!


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## Spooky D (Oct 4, 2011)

Just when I thought I was done building for the year. That's pretty cool, wonder if I have time to build one before Halloween it would go great with my animated spider victim.


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## liftngwaght (Sep 27, 2011)

Finally got a video up. The spider was a huge hit for the kids! For next year ill change where the spider is located so it isn't directly under the crank. That way the body will be supported by it's own string and the legs will move independent from the body.


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