Multi Speed Pre Rotator

stolking1

Newbie
I was thinking if you had a disc like a pressure plate mounted on the prop area of say a Mac engine. Instead of the drum used on the Wunderlich.
If this Disc was say 12 inches in Dia. Now if you run the pre rotator wheel against the disc closer to the center it would turn at speed "a"... now if you were to move the wheel outward it would have to turn faster now at speed "b".. Move it all the way out and it would be much faster.. now as speed "C"..
Does this make sense or am I just somewhere out there in never never land?

It looks to me like it would work.. you could run you engine at a set speed and increase the speed of the pre rotator quite a bit to get your blades poping......

JD..
 

groundhog

Senior Member
there are/where lawnmowers which use this idea for thier transmision.About the right horsepower input if not more.If memory serves the mower that forest gump drove had that tranny
 
This type of infinite variable ratio traction drive has been around since the 1800's. One common aplication is the SNAPPER riding mower.
 

brs

Newbie
by moving to the faster (position C) position the mechanical leverage becomes less so you will increase throttle to increase torque.

On the other-hand if you just leave it as a single speed (like is currently used) then you can increase throttle to increase speed and torque. I don't see a real advantage to the multi speed idea.
 
by moving to the faster (position C) position the mechanical leverage becomes less so you will increase throttle to increase torque.

On the other-hand if you just leave it as a single speed (like is currently used) then you can increase throttle to increase speed and torque. I don't see a real advantage to the multi speed idea.
I agree!:peace:
 

gyromike

Administrator
Staff member
This type of infinite variable ratio traction drive has been around since the 1800's. One common aplication is the SNAPPER riding mower.
Correct-o-matic Pete.

When I was a kid we had a Snapper dealership. I worked on several hundred of 'em.

The aluminum disc mounted at the bottom of the engine crankshaft, and the rubber clutch disc was attached to a chain drive reduction box. The reduction box would slide on a hexagonal shaft that drove the transmission on the right side. The push mowers worked just like that also. I still have one tucked away in the shed.

I can't see any advantage this would have over a 'Wunderlich' style prerotator that would offset the additional weight and complexity unless your engine is so gutless that it would need the additional mechanical advantage to get the blades started without bogging down.
 
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stolking1

Newbie
This why I love forums.. Thanks for the input. This is why I should always build a proven design and not think to much...LOL...

JD
 
Printing presses use the same application for speed control. Of course before electronic speed control. Good old AB-DICK 9800 series and they work! You can go from 1200 sheets / minute to 10.000 s/m so it is a wide range!
 

stolking1

Newbie
BRS,
After thinking about it more I don't know that I agree with your thinking. We are only talking about a small amount of travel difference on the disc. The engine has more than enough HP to turn it and if it is set at 2000 RPM then power will be no problem.
Then allowing the wheel to move out the disc would double the RPM's of the Blade spin up. It would be very simple to construct this and one could keep it light..

JD
 

Mike G

Junior Member
One advantage is that the initial start would be at a "low gear" thus reducing the wear while the "clutch" is slipping. Once the "clutch" is really engaged you can move to a higher gear at constant engine speed.
Another idea would be if you tried the Birdy short take off where he keeps the pre rotator engaged during the take off roll. Once you go to WOT and the engine accelerates you can move down to a lower gear so that the engine speed is at max and you're still driving the rotor without the "clutch" slipping.
Mike G
 

500e

Member
One advantage is that the initial start would be at a "low gear" thus reducing the wear while the "clutch" is slipping. Once the "clutch" is really engaged you can move to a higher gear at constant engine speed.
Another idea would be if you tried the Birdy short take off where he keeps the pre rotator engaged during the take off roll. Once you go to WOT and the engine accelerates you can move down to a lower gear so that the engine speed is at max and you're still driving the rotor without the "clutch" slipping.
Mike G
Also reducing torque in drive shafts with lower gearing
 
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