# Pulley system for an axworthy ghost



## toozie21 (Aug 23, 2012)

So one of the new things I was kicking around for this year was a simple axworthy setup for Halloween with Zero the dog on it. Then at Christmas I might do something with a skiier or snowmobiler if it works well (so lower to the ground).

I was watching this video and kind of like how small his pulleys were (the big bicycle wheels always scare me because of this being lower to the ground.





What I can't figure out is, the piece at the 1 min mark is homemade I think, but i really like how it drives the axworthy by keeping tension on the line. Does this item remind anyone of anything? I have to imagine that I can repurpose something from real life to function as those three pulleys and then add a wiper motor to drive it....









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## corey872 (Jan 10, 2010)

Well, it sort of reminds me of an old reel-to-reel film projector with the play-out and take-up wheels and tensioner arm. But I suppose by the time you find one of those and convert it, you'd be money ahead to just buy the basic components and build something similar.










He seems to mention some somewhat obscure components...castor from Marshalls, Pittman motor, etc. I suppose you could try and track down a similar castor. I'm not familiar with Marshalls, but seems like Harbor Freight has something that might be similar:

https://harborfreight.com/5-in-polyurethane-heavy-duty-swivel-caster-69852.html










I could also see the thing running with some old lawnmower tires... seems like that would be about the right size, too.

As far as the motor, he says 'Pittman' - again, foreign to me. Searching it, seems like they make a whole line of DC motors.

https://duckduckgo.com/?t=ffab&q=pittman+motor&atb=v149-1&ia=web

I would worry that a wiper motor might turn too slowly with such a small pulley - unless you want the ghosts to really creep along. After a quick search, it looks like the average walking speed is ballpark 330 feet per minute. So looking at that 5 inch diameter castor:

5 inches / 12 inches per foot x pi (which is 3.1415) = about 1.3 feet of axworthy line for every rotation.

330 feet per minute / 1.3 feet per rotation = 250 rotations per minute.

So you need the 5" pulley to turn about 250 rpm to propel the ghosts at walking speed. Seems like I remember wiper motors might be in the mid double digit rpms for high speed?

If there is any gear reduction between the motor and the pulley, that also needs to be figured in. So even something like a 3:1 or 4:1 reduction could mean the motor spinning at 750-1000 rpm.


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## bfjou812 (Aug 15, 2008)

The drive system look like part of it is from a dryer drive belt tensioner. I know a lot of these were made with sewing machine motors as the drive motor. for the pulley system. You might try to get Spinman to see if he has any info on this.


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## toozie21 (Aug 23, 2012)

Hey guys, thanks for the info.

That is a good equation for rotation/wheel size. That RPM amount is a concern. That is way faster than I was thinking, the wiper is definitely not doing that. I had found an AC motor in my stash that I had thought would work, but I think it is 60 RPM.

I get the sewing machine, but I worry about the torque and constant running. I've read some people complaining about using them, but of course I see people complaining about all the difference pieces of this prop....

I think I need to start mocking some stuff up and get a feel of movement, torque, and grip. I don't need a lot of speed, but I think Zero needs to look like he has a decent speed. 

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## toozie21 (Aug 23, 2012)

So a couple of things to add to this Here is a great diagram to reinforce Corey's math:








from http://ravenmanor.com/projects/axworthy.html

(btw, Corey's math works out for sure, 250RPM with 5" wheel => 5.45ft/s)

Here is a stupid video of my looking at a wiper motor at 5V on the "fast" speed setting which is supposed to be ~20RPM with a 6in wheel. The math says it should move about ~0.524ft/s, and you know what, it seems about that painful.

I know I wanted to keep things small, but if I went with my 60RPM AC motor and a 12in wheel, I think I would get about 3ft/s. Still pretty slow, but a 6x increase from what I have now. The only reason I Want to test this is because I have the parts on hand.


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