# rod lengths for props



## alewolf (Nov 5, 2012)

Morning all,

Already started looking at 2016. Lots of props to repair or repurpose and some new ones I want to work on. I was curious about how people determine the length of rods/shafts etc they use in projects.

I find I spend lots of time with binds and similar issues. Was hoping there were some basic rules that might reduce the time I struggle with them. Leering skeleton is a good example, I never got it up this year. I kept thinking I had it settled in my coffin. Then I would develop a bind at some point. 

Thanks.


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## halstaff (Nov 18, 2009)

This site may be of help - http://www.robives.com/mechs


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## Diabolik (Apr 19, 2007)

alewolf said:


> Morning all,
> 
> Already started looking at 2016. Lots of props to repair or repurpose and some new ones I want to work on. I was curious about how people determine the length of rods/shafts etc they use in projects.
> 
> ...


Do you happen to have any pictures of the mechanism you are having an issue with? Sometimes binding issues are simply a result of the hardware used and can be easily fixed.


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## alewolf (Nov 5, 2012)

Unfortunately no, seems to be a regular problem of mine. I am always having issues with trying to create linkage. The leering skeleton was a "T" pvp pipe that sat on a cap or screw. Then 3 linkage arms to a reindeer motor to get the turning motion (one linkage arm was the pvc pipe fitted into the T). I was getting binds all the time. I have tried similar things and if I go much past a FCG set up, I have issues. Something simple I am missing, spacers or lengths are what I am thinking.


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## Diabolik (Apr 19, 2007)

Yep. Sometimes the hardware itself will be your biggest enemy. On any linkage I typically use metal washers on the outside and a nylon washer in between the linkages. Like materials tend to want to bond and bind. I also always use nylon insert lock nuts on everything to keep it from tightening itself down. 

I just ordered 2 sets of prototype machined parts last night for a compact turner mechanism based on our Watchman prop. It uses no linkage and is powered by a reindeer type motor. I'll post something back here once I get the parts and assembled. It has a very small footprint of about 4 X 8 inches.


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## Fiend4Halloween (Aug 28, 2008)

Thanks for that info Halstaff. I was curious too and I appreciate the info.


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## Diabolik (Apr 19, 2007)

alewolf, Here is a quick video of the turning mechanism I was talking about. I got the machined parts in today and put one together. It is a little jerky because the balls in the bearing plate are huge and there is no load on it. This is a proven design we use on our Watchman kits and totally eliminates the rods and any worries about binding. The motor is just a 6 RPM deer type motor.


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## alewolf (Nov 5, 2012)

The web page I was referred to by Halstaff was also helpful. It made me think about other combinations. This would qualify as the Scottish Yoke? Wish I had known, perfect for my application and I even have some of those parts laying around. Picked up some from you last year.


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## Diabolik (Apr 19, 2007)

alewolf said:


> The web page I was referred to by Halstaff was also helpful. It made me think about other combinations. This would qualify as the Scottish Yoke? Wish I had known, perfect for my application and I even have some of those parts laying around. Picked up some from you last year.


I think it could be considered a Scottish Yoke. 

We are going to have this kit available very soon.

If you have any questions about the mechanism or parts used, just let me know and I'll be happy to help you out.

Ryan


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## neverhart (Sep 5, 2011)

There's an app for that: Autodesk ForceEffect Motion for iOS and Android. 

You design a simple line-based illustration of the mechanism with real-world dimensions, then set the actuator type (motors, linear) and linkages and watch it move. Changing lengths/angles is a snap. The learning curve for the layman is not trivial, but there are tons of videos and tuts online, and it really saves a ton of work in the shop.


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## alewolf (Nov 5, 2012)

Diabolik,

What are those little hollow spacers you use called? I have seen them on a number of props and I can see where they would be very helpful. I thought I might try to some.


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## Diabolik (Apr 19, 2007)

alewolf said:


> Diabolik,
> 
> What are those little hollow spacers you use called? I have seen them on a number of props and I can see where they would be very helpful. I thought I might try to some.


Depending where you buy them they are called nylon bushings or nylon spacers. You can find some of them locally at Lowes and Home Depot. We actually have some of ours made since we need specific sizes. There are plenty of stock sizes that can be used.


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## Diabolik (Apr 19, 2007)

You might also want to pick up some flat nylon washers.they work well as spacers when building linkage assemblies. Having nylon between them helps keep things smooth as 2 like materials rubbing together tend to want to bond (such as aluminum or steel linkage).


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