Need Some Halloween-Engineering Assistance

[Bruzilla]

It's that time of year, and I need to get busy making this Halloween's Big Build. This year it's Pumpkinhead... this guy:

We got most all of the static build issues worked out, but I'm getting kinda tired of totally static figures and want to make Pumpkinhead wag his tail. So, how does one go about making about a 10-foot long tail wag?

The best idea we've gotten so far, and you're going to have to use some mental powers here, is to use Solo cups and ping pong balls. If you think of holding a tall stack of Solo cups, if you tilt them they will lean. Now think of putting a ping pong ball between each cup to act as a bearing, and the stack of cups will lean a lot. Put a small hole through each ball and in the end of each cup, and run a string through each ball and cup from front to back, and we should have an easily bendable tail-looking appendage.

The next step is to put four small holes spaced around the base of each cup. at 12, 3, 6, and 9 o'clock, and run four strings from front to back through those holes. That way if I pull the 9:00 string, the tail will pull to the left, 3:00 will pull to the right, 12:00 will pull the tail up and 6:00 will pull it down. That part is pretty simple. What isn't simple is how to pull the strings.

So here's the dilemma... what can we make that will put tension on four strings, one at a time, and then release pressure as another line gets pulled tight, and will fit into the body of a mannequin? Think of essentially a four-cylinder engine's crankshaft in operation.

 

[HT413]

Looking at the solo cups, say 12 o'clock is vertical. I'm thinking you use a static fishing line at 12 o'clock to keep the tail up off the ground. Then at 9 o'clock you use a slow RPM motor to turn and pull on a fishing line each rotation. At 3 o'clock you use an elastic cord to resist the motor and return the wag, and maybe use another at 6 o'clock to keep the tail taut against the 12 o'clock fishing line.

Just adjust the length of the servo arm and RPM to make it look natural.

 

[HT413]

Another idea would be to use a really whippy fishing rod. The rod would provide its own vertical support and return action, then attach fishing line to the loops and connect to the motor for the wag.

cat tails wag mostly at the ends, like a whip, and most fishing rods are designed to flex most at the tip, so this might look really natural.

The issue would be creating a shape that looks like a real tail, vs the arrow straight look of a fishing rod...

 

[plymouthman72]

This may be a really dumb idea but could you hide an oscillating fan behind it or use the motor/mechanism somehow?

 

[HT413]

So here's the dilemma... what can we make that will put tension on four strings, one at a time, and then release pressure as another line gets pulled tight, and will fit into the body of a mannequin? Think of essentially a four-cylinder engine's crankshaft in operation.

I've never seen the movies, is it necessary to wag in 4 directions? Perhaps the primary wag is side to side, using one actuator motor and a return spring / elastic cord. Then you set another motor at 12 o'clock at a different rpm and lever length to get a different type of motion. Then just use a return spring / elastic cord at 6 o'clock.

 

[texas69bee]

^^This^^ Use the actuator idea but use something like a spring cable that you would find on a drain cleaning tool or even part of a garden hose.

 

[Bruzilla]

What I was thinking of using for a motor would be a turntable motor for a microwave oven. These are very high-torque but low RPM, like 2.5-3.5. They also reverse direction when they lose power, so we could put a power cutoff switch in the power line that would cut the power intermittently and cause the motor to reverse.

The motor usually has a stem that comes off it, and that something can skip over... usually a plastic piece that the turntable sits on, but we can also attach a swing arm or disk, so the question is how to get it move the strings.

 

[Bruzilla]

I've never seen the movies, is it necessary to wag in 4 directions? Perhaps the primary wag is side to side, using one actuator motor and a return spring / elastic cord. Then you set another motor at 12 o'clock at a different rpm and lever length to get a different type of motion. Then just use a return spring / elastic cord at 6 o'clock.

I was thinking about that. If we had a A shape attached to a rotating disk, it could catch a string and pull it upwards as it follows the A, then release tension as the strings comes down the other side. If we use bungees or springs to keep the 12 and 3 strings in tension, the tail would be up and to the right in a normal state, and would get bent down and to the left as the animation.

 

[HT413]

Great idea on using the microwave oven motor. Yeah now the trick is basically replacing the rotating glass plate with a piece of sheet metal or maybe using a frisbee... and fixing it to the shaft somehow.

Maybe attach the string to a washer and slip that over a stud that's mounted on the turning disc. That should give you free rotation without winding up.

 

[HT413]

Regarding that 2nd degree of motion... how about mounting a longer stud under the frisbee and each rotation it tugs on that second string?

 

[HT413]

Something like this?

 

[Yatzee]

It's that time of year, and I need to get busy making this Halloween's Big Build. This year it's Pumpkinhead... this guy:

View attachment 494495

We got most all of the static build issues worked out, but I'm getting kinda tired of totally static figures and want to make Pumpkinhead wag his tail. So, how does one go about making about a 10-foot long tail wag?

The best idea we've gotten so far, and you're going to have to use some mental powers here, is to use Solo cups and ping pong balls. If you think of holding a tall stack of Solo cups, if you tilt them they will lean. Now think of putting a ping pong ball between each cup to act as a bearing, and the stack of cups will lean a lot. Put a small hole through each ball and in the end of each cup, and run a string through each ball and cup from front to back, and we should have an easily bendable tail-looking appendage.

The next step is to put four small holes spaced around the base of each cup. at 12, 3, 6, and 9 o'clock, and run four strings from front to back through those holes. That way if I pull the 9:00 string, the tail will pull to the left, 3:00 will pull to the right, 12:00 will pull the tail up and 6:00 will pull it down. That part is pretty simple. What isn't simple is how to pull the strings.

So here's the dilemma... what can we make that will put tension on four strings, one at a time, and then release pressure as another line gets pulled tight, and will fit into the body of a mannequin? Think of essentially a four-cylinder engine's crankshaft in operation.

You sure you're on the right forum site?

 

[Bruzilla]

You sure you're on the right forum site?

Yep. I figure folks who can figure out ways to keep 60-year old cars on the road should be able to find a fix for this problem.

 

[747mopar]

I'd consider possibly even using a wiper motor out of a car, DC converters can be had pretty cheap (McMaster Karr has them). This would most likely have more torque, low rpms and easier mounting and could utilize smaller automotive switches, relays etc. To me I don't know that I'd want a wagging tail (to dog and cat like) but one that just slithered and slowly whipped, a spinning rigid cable with kinks or lumps in it inside of a flexible rubber hose would possibly achieve the look? Maybe even use a combination of cable and bent rods? This should be cool, be sure to post a picture of both the creature and the kids pissing their pants!

 

[Mike67]

You could use something like a small wiper motor with a rigid frame. It (tail) could be bent in any s type shape, have the offset crank attached to the outer circumference and allow it to rotate on that axis.
Something like a 1/2" piece of MET supported by a carrier...
Looks great in my mind....

 

[Bruzilla]

Many of my fellow Haunters use wiper motors in projects, but I don't know if this would be too many RPMs.

Also, the cup/ball core of the tail will be light, but I'm planning to cover that in Dragon Skin silicone, which is kinda heavy, so this is going to need a LOT of torque. Fortunately, all the force will be on the strings, but even so that's a bit of weight to move.

 

[67 coronet]

just wondering if you know its gonna look like he is happy to see everyone? thinking dog waging tail here.are you not a fan of the motion activated body tilt,head turn and mouth opening thing?

 

[plymouthman72]

You could build the suit for a person and then scare the living pp out of people as they approach the door. Just start running across the lawn at full speed!

 

[67 coronet]

You could build the suit for a person and then scare the living pp out of people as they approach the door. Just start running across the lawn at full speed!

did this one year as a scare crow. put a bowl of candy in my lap and a sign that said "just take one". if they took one,they were fine. try to grab more and nope.

 

[HT413]

Hey Bru, if you do this sort of thing a lot, you need to check out some arduino. An arduino Uno and a few relay modules and you can control all sorts of movements independently. Pretty easy if you can master some rudimentary programming.