Posted by Clint Dixon on Sunday, August 19, 2007 at 14:08:44 :
In Reply to: Re: Are you sure? posted by Dan Shockley on Sunday, August 19, 2007 at 12:03:29 :
Dan,
These are the kinds of conversations that I get into with the Engineers in my office on a daily basis. They have the training and can quote the facts and figures, but sometimes they do not have the practical experience that I have and can not explain the reasons behind the facts and figures in a way that I can thoroughly digest. Talking through it usually helps me to the point where I can understand and apply it by making use of my common sense vantagepoint. So bear with me if you will. ;^)
I think any time we compare PTO winches to electric winches we can not help but get into a situation where we are effectively comparing apples to oranges. Electrical winches are rated on a sum of the whole package if I am not mistaken. This package includes the wire cable, gearing, motor, electrical voltage, and capacities of components and materials used. The PTO winch, if I am not mistaken, is a little bit different animal. The “motor” in this case is the engine in the truck. Does the failure point of the sheer pin not rate the BRADEN MU2 PTO winch alone? This winch could be installed on a lot of pieces of different equipment with various sources of power. In the case of the 230 L-head engine, you have varying degrees of power available depending upon RPM as well as other factors.
When an electrical winch reaches its capacity, the motor will stall out or overheat. When the Braden MU2 PTO winch reaches it capacity, the shear pin will break usually well before the truck’s engine will stall. If we increase the diameter of the winch drum, either by design or by adding layers of cable wraps, mechanical advantage is going to be lost and the engine will have to work harder and/or increase in speed to overcome the increased load. This means the cable will now be pulled onto the winch drum at a faster rate because of both the increase in drum diameter and the increase in engine speed. At some point you will not be able to overcome the loss of mechanical advantage and the engine will stall.
If you were to drastically increase mechanical advantage by making the winch drum substantially smaller in diameter, wouldn’t this translate directly to the sheer pin and make it sheer much easier if you also increased the load? I guess I am thinking of this kind of like lowering the ratio of the ring and pinion gears in a differential. Speed is lowered and mechanical advantage increases. Now, if you add a taller rolling radius and increase rotational mass with the addition of bigger tires, parts start breaking. The driveshaft may become like the sheer pin on a winch if it is not increased in strength.
I think I may be on the verge of seeing your point. I guess my thoughts are that if you add additional layers of cable, decreasing the mechanical advantage, then the engine is going to have pull harder and this would put additional strain on the shear pin, causing it to fail earlier. So, with a shear pin failing earlier at a given load, yes, I guess the capacity of the winch would be considered lowered. But doesn’t that mean that the tensile line load would be higher, not lower, with additional wraps, assuming that the operator is compensating with more throttle applied to the engine?
Junior
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