# Help with an idea about a sliding tomb lid?



## mroct31 (Nov 10, 2007)

I want to build a small grave size tomb with a headstone and I want the top of the tomb to slide a bit then return to it's original position. I wanted it to move a bit slower than I think an air cylinder would let it so I'm thinking a motor of some sort but what I'm a bit stumped by is how to achieve the motion? Maybe a horizontal cam set up with a spring return or maybe a motor set up with a crank to convert the rotary motion to reciprocating may be a better way to go? Any thoughts?


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## Wildcat (Nov 3, 2007)

A rack and pinion would work well for this 





Or if you want to spend more and tinker less a linear actuator would also work.

http://www.robotshop.com/ca/standard-actuators.html


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## RoxyBlue (Oct 6, 2008)

I wonder if something like a reciprocating motion set up would work?

http://www.robives.com/mechanisms/recip

Or rack-and-pinion like Wildcat mentioned:

http://www.robives.com/mechanisms/rackpinion


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## Otaku (Dec 3, 2004)

You can do this with a simple crank arm and a slow gearmotor. Put the slab on a pivot at one end and the motor at the other. If you want the slab to pause between movements, slot the extension arm where it attaches to the slab.


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## Terrormaster (Sep 27, 2007)

I was going to do this with the tomb I built last year but ran out of time. I was planning on using the crank arm technique Otaku mentioned. The other thing you could do is pick up one of those cheap lightning fx boxes and use it as a color organ to drive the motor's power. Then use an audio clip of grinding stone. Then when the audio plays the motor energizes and the slab moves with the sound. At least that was the plan. If you go with that let me know how it worked out for ya.


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## mroct31 (Nov 10, 2007)

Otaku said:


> You can do this with a simple crank arm and a slow gearmotor. Put the slab on a pivot at one end and the motor at the other. If you want the slab to pause between movements, slot the extension arm where it attaches to the slab.


So I'm seeing in my head what your describing as sort of pendulum but reversed with the "bottom" of the stone locked at the pivot and the top moving with the motor but maybe in only one direction?

I do like the lightning fx box idea as I have an old haunt master lightning box that I could use for this prop since I've long since replaced it with an I-Zombie unit!


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## Otaku (Dec 3, 2004)

The problem with using an AC light organ is that if you use a DC motor, you have a wart in the circuit. The wart will discharge (somewhat) slowly when the power is "flickered" by the light organ, and then charge right back up again. The motor won't get a jerky, randomized movement, it'll run pretty much continuously. You can get around this effect by having longer breaks in the soundtrack. Maybe set it up so that one channel has a groaning sound that is sync'd to a beep track that drives the FX box and motor? When the slab moves you hear a groaning sound from the depths of the grave.

Yeah, I think you get the idea - the slab pivots at one end, and the motor pushes and pulls the other. The motor would have a short arm on the drive shaft, connected to another, longer arm. This arm goes to the bolt on the slab. As mentioned, if you cut a short slot in this arm to create some deadband, the slab will first move to one side, pause, then move to the other side.


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