# Motorized Grave Jumper



## Terrormaster (Sep 27, 2007)

Ok, just toying with this idea because well sometimes I like to do things because no one else has done it or just to prove to myself I had an idea that works. Also, I've never tinkered with pneumatics nor do I own or have access to an air compressor so pneumatics is definitely for at least this year.

So to solve this problem I ended up having to think in reverse than you would if working on pneumatics. With pneumatics the physics is more of a push. And the solution to using a motorized approach is to use a pull. So instead of a cocked position being the normal at rest state, its the fired position thats a normal at rest state.

To really wrap your head around this, think slingshot or catapult. The concept works on the basic notion of the slingshot and uses a windshield wiper motor to stretch it back and cock it into position. Note that I'm still toying with the idea and that these are loose concepts. There's a lot of variables to take into account such as the weight of the prop versus the tension on the bungee cords versus the torque of the motor. Plus I don't even take into consideration how I'd mount the motor.

The cocking mechanism is based on the Headless Flailer design over at Allen's Halloween page. The mechanism is quite simple actually. The hammer spins freely on the motor shaft. Mounted below it is a disk with a pin sticking up. As the disk spins the pin catches the hammer and rotates it around to a cocked position and stops. When the motor starts again it pushes the hammer around until the tension from the bungee pulls the hammer faster than the motor is rotating firing the prop. The motor continues around, catches the hammer and goes back into the cocked position until the prop is activated again.

In Allen and Tony's design, they used a limit switch and a series of relays to start and stop the motor. In the design here, I plan to use the Valeo 15094704 Windshield Wiper Motor (thanks to goes to ScareFX for pointing that motor out in another topic). This motor has a unique characteristic that it always returns to the same parked position when the power is switched off. In this design, that position will be the cocked position. When the motor receives a momentary jolt of power it will spin one full rotation back to the parked position. This power can be applied by a manual trigger or PIR.

I don't know if I'll get the chance to experiment and build this one this year. But if anyone wants to take a stab at it go for it, just let me know how it turned out for you and give me some pictures so I can see it in action.

I've included some rough illustrations below. The blueish lines are cords and the orange lines are bungee. The grayed out bars in the first diagram show the hammer in various positions in relation to the rest of the mechanics.




























I'm sure there's plenty of room for improvement and I'm open to feedback.

-TM


----------



## NickG (Sep 12, 2006)

interesting concept, especially the use of the parking wiper motor.


----------



## Terrormaster (Sep 27, 2007)

The motor is something I struggled with initially in the design. Originally I wasn't aware of the self-parking wiper motor until I came here. I was trying to figure out the relay system that Allen and Tony used for the Flailer but they didn't post any schematics. By the time I figured out the logic myself I relegated to holding off till next year due to time constraints.

Then ran into the article on Spirit's miserable mechanical Rise from the Grave prop and it renewed my interest.

But you guys have far more experience at this stuff than I do so guess I'm looking for some feedback and if its feasible I may tackle it between seasons.

Random thoughs: the PVC in the shaft area that supports the riser could probably be replaced with a blocks of 2x4 with a hole drilled through for the riser. 

-TM


----------



## edwood saucer (Aug 21, 2006)

If I'm understanding it right - that is a great concept...

yee ole bungee strikes again!


----------



## BlinkyTheHouse Elf (Apr 2, 2007)

well I hope it works out, because I dont have a air compressor either and want something like that


----------



## Terrormaster (Sep 27, 2007)

I've updated the design pics above. I'm gonna prototype this this weekend. And see how well two 8" bungees can launch up a 1"x3' PVC tube.

I'll let everyone know how it goes.

-TM


----------



## Moon Dog (Oct 3, 2006)




----------



## Phil (Sep 2, 2007)

TM, I have been working on a variation of the same notion. My return mechanism is not complete, but I have roughed out a workable solution using bike sprockets and an end-of-cycle switch. The sprockets give the wiper motor some needed mechanical advantage and the free-wheel gear provides the release. Once the hub-mounted cam is driven past half cycle, the free-wheel releases the slinger. I don't have documentation on the return mech yet but there a few photos and test video of the slinger on my site.


----------



## Terrormaster (Sep 27, 2007)

Phil,

Great minds think alike eh? Thats pretty neat and flies up pretty darn good too. Have you tested it with the load of a costumed prop yet? 

Also on your page you mention using springs in the design, do you think they would be better than bungee? Not sure if springs would work well in my design though since the bungees pass through 1/2" holes on each side of the main support holes - I'd be concerned that the coils would get caught up and jam the mechanism.

Since you're going more for the leaper than the straight up jumper I can assume the springs are on the back side of the arm. Which means the setting mechanism would have to pull from the front. That being the case do you plan on mounting the setting mechanics on the front or do you have a way to mount it in the back and not run into the spring?

-TM


----------



## Phil (Sep 2, 2007)

It tested well with the figure with no hands. I anchored the springs with nylon rope so that the tension can be increased with the weight of the figure if needed. Springs were necessary both for the weight and length of throw I wanted.
The springs are on the back of the arm, anchored to the side supports of the base (forming an upside down "V"). Theoretically it will be clear of interference from the springs, and I would like to locate the setting mech at the rear. There are still 2X4 uprights to sneak through, and my recycled parts and limited skill throw tight tolerances out the window.


----------



## Terrormaster (Sep 27, 2007)

Ahh I get it - NOICE!

Now, does anyone know if the wiper motor I picked has enough torque to handle springs?

-TM


----------

