# best way to build this prop: reaching hands under door



## discozombie (Jun 21, 2012)

I want to make a prop that has a series say 8 hands that reach out from under my slightly opened garage door. I dont want all the hands coming and going at the same time. I was thinking something along the lines of a cam. Anyone else have a suggestion or reference of something similar. I have on hand two wiper motors and a few other low rpm gear motors. Hoping to use one of these.
Thanks
DZ


----------



## Otaku (Dec 3, 2004)

Something similar to a crankshaft would also work, but using a series of cams gives you more options. You can use compression springs on the extension rods to give you a slow "reaching out" movement and a faster retraction. Or the opposite - just reverse the cam profile/rotation direction. Check out some of the haunted bookshelf threads for ideas for the mechanism.


----------



## [email protected] (Aug 25, 2012)

I like the spring loaded cam idea... Especially configured for a quick grab, then slow retreat.


----------



## heresjohnny (Feb 15, 2006)

I would use a long rod attached to your motor, with cams on the rod where you want the hands to be. I would use a spring strong enough to keep the rocker arm on the cam, but no stronger, and shape the cam to make the arm retract quickly when desired. Mix 1, 2 and 3 lobe cams to give the feel for random movement. I would also have some arms go back and forth, and up and down instead of in and out.


----------



## The Pod (Sep 15, 2009)

If you don't want something that looks like a continuous motion loop:

Using pneumatics, you could just attacth each hand/arm to a seperate cylinder and then use a prop1 with a random routine loop to activate the hands.

Another option would be to do something like Otaku did where he used a couple limit switches and a cam on a wiper motor to stop it at 180 degree rotation. Using one motor per hand/arm and a prop1 to extend them out and pull them back randomly.


----------



## discozombie (Jun 21, 2012)

The Pod said:


> If you don't want something that looks like a continuous motion loop:
> 
> Using pneumatics, you could just attacth each hand/arm to a seperate cylinder and then use a prop1 with a random routine loop to activate the hands.
> 
> Another option would be to do something like Otaku did where he used a couple limit switches and a cam on a wiper motor to stop it at 180 degree rotation. Using one motor per hand/arm and a prop1 to extend them out and pull them back randomly.


Though I would like the hands to be random, this sounds more complex and expensive than I was hoping to spend. Thanks for the suggestion, Ill tuck it away for a project upgrade in a year or two.


----------



## The Pod (Sep 15, 2009)

Here is another option for a somewhat not quite random look. Build each of the hands/arms using a crank slider setup like this: http://www.robives.com/mechanisms/crankslider. But for the rotating circle part, make them as plywood gears of all different sizes/number of teeth and have them all connected/rotating together off one wiper motor. This way, some hands would be coming out more often than others. Some would be sweeping left to right and others right to left. Will help keep the cost down and may give you a more random movement look.


----------



## The_Caretaker (Mar 6, 2007)

you can go here for gear templates: http://woodgears.ca/gear_cutting/template.html


----------



## R. Lamb (Oct 11, 2011)

Sounds to me like a Haunted Bookcase set up would do the trick. A single motor driving a shaft with assorted cams. instead of moving books in and out it can move arms and hands.


----------

