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How do I double wrap bull wheel on rope tow?

farmerkevin (Petroleum)
29 Sep 10 12:47
I've made a pretty sweet rope tow that is in need of some help.

I'd like to eliminate some of the rope tension in my design.
Presently, much tension is needed to provide enough traction to drag skiers up the hill
A double wrapped bullwheel would save the day.
I'll assume that my 26" bike wheel will have to go and a wider, smoother wheel of the same diameter will be needed to let the wrapped rope get out of its own way.  
I've tried double wrapping the bike wheel but the rope only ties itself in knots as it can get out of it's own way.  

any suggestions?

here's a quick vid of my machine in action on our little hill.
It finished up the winter on our 800 foot hill with 120' vert
http://www.youtube.com/watch?v=K32OyNa5ByA

Thanks
FK
williedawg (Mechanical)
29 Sep 10 13:39
note how these guys arranged the idler pulleys to get more "wrap" on the drive wheel...

http://www.youtube.com/watch?v=DV_6plAcRJ0&NR=1

 
MikeHalloran (Mechanical)
29 Sep 10 14:47
A small motorcycle will have a wheel of about the right size.
 

Mike Halloran
Pembroke Pines, FL, USA

btrueblood (Mechanical)
29 Sep 10 18:01
Take an old tire and roll it inverted, to get a rubber "liner" for the wheel rim.  Trim back the bead edges where they curl in.

If you need 2 or more wraps, you will need to pull the rope off the wheel, pass it through an angled guide/idler, and back onto the wheel

To make a continuous rope go "two wraps" around a pulley, without doing the above, implies that the rope must slide along the pulley axis.  Which is counter to the idea of having enough friction between rope and pulley to reduce rope tension...
farmerkevin (Petroleum)
1 Oct 10 7:22
Thanks for the ideas.
  
I'm going to mock up a twin wheel setup. Much like btrueblood describes.
Like a 10 speed bicycle, it'll have 2 pulleys .  
The pull rope will make a trip around the main bull wheel, then, make a trip around a smaller second pulley at a angle. Then the rope will make another trip around around the bull wheel and then return.  

The setup will look a bit like the setup in WillieDog's video response but will be rigged differently as to get 2 wraps on the bull wheel

I'll fab it up in the coming weeks and keep you posted.

Thanks for helping me get my brain in gear
FK
unclesyd (Materials)
4 Oct 10 16:01
Here is how it's done on pot haulers.  I may stand corrected but you may have to use a long splice in the line for this type to work properly.
The pulley on the arm assist the fairlead that allows the rope to lay on the bull wheel properly.
There are several variations of the pot haulers out there.

http://www.go2marine.com/product.do?no=99481F

You could make the system with one pulley or single purchase if you move the fairlead pulley to about 2/3 out from the center of bull wheel.  This will allow you to pull all type of things through the bull wheel.  
Try not to go over wraps on the bull wheel if you can.
 
unclesyd (Materials)
4 Oct 10 16:04
Corrections to my post:
The last line should read two wraps on the bull wheel.   
farmerkevin (Petroleum)
19 Jan 11 9:05
Thanks for kicking me in the right direction!
I have since designed, built, installed and tested my rope tow.
It now pulls like a freight train with zero slippage.

Check out the pics of the final design here
http://www.facebook.com/album.php?aid=91819&id=1066800210&l=5dd5e53cba
unclesyd (Materials)
19 Jan 11 13:00
Appreciate the feedback, it doesn't happen very often.

I like the amount of purchase you achieved on the drive sheave.  
MikeHalloran (Mechanical)
19 Jan 11 13:00
Great photos.  Thanks for the followup.
We love a happy ending.

... guards removed for clarity, of course.
 

Mike Halloran
Pembroke Pines, FL, USA

btrueblood (Mechanical)
19 Jan 11 13:12
Cool.  So, getting about 60 or 70 degrees more angle of wrap was good enough.  I like the overhead return too, keeps both sides of the tow usable.

Mike does have a point.  Have seen people get "stuck" to rope tows, whether due to panic-grip syndrome, or actual ice freezing their gloves to the rope I don't know which.  Typically there is a "gate" about 10-20' downhill from the bull wheel or return pulley, rigged to a kill switch or E-stop for the motor.

I've never seen guards per se on the pulleys, though.  Typically a fence or snow berm is enough to keep people well away from the business ends of the tows.

So, how much is an all-day lift ticket? :)
farmerkevin (Petroleum)
19 Jan 11 20:21
You can't see it in the pics but I have a dead man switch connected to a rope gate that kills the operation when someone skis or is dragged through it.  I have 3 young children that all are supposed to be professional golfers, we can't afford  any lost fingers. ha ha ha
Skiing is free for all, conditions permitting.

Thanks.
 

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