Adv.Info. from GRCS/Hobbs"drop"test"

[Frans]

After dropping the Volvo station wagon and this big Euc. log into both the GRCS & the new Prototype Hobbs device, we compiled the different films from all the camaras and then examined the footage with some surprising results.
Both devices took the loads of the Euc. log fine. But when we slowed down the film to frame-by-frame viewing what we noticed was the new Hobbs device allowed the rope to walk into the middle of the capstan.

(This new Hobbs is now officially the replacement device, the old one is out of production and will not be sold or made any more)

The new Hobbs is slightly concave in the middle. Under excessive forces, the rope is forced away from the base plate to the middle of the capstan. This transfers the load farther out on the capstan.
At some point we will have this thing on DVD and available for viewing
Frans

 

[Tom Dunlap]

So...what's the feeling about transfering the load away from the base? Is that desirable?

Seems like this might set up a bad loading angle, pulling the device off the tree.

Maybe not though...

Tom

 

[Frans]

Yes It pulled the bottom of the device away from the tree. This resulted in the base plate bending.
It is real interesting to view this footage. What happened at the moment of impact was too fast for the naked eye to pick up. But when the film was slowed down we could see the forces in action.
On the log drop the Hobbs forced the rope under itself on the wrap and the rope failed. We suspect because of thermal breakdown because the wrap did not move that much. When we get the footage from the fixed bollard on the GRCS I'll check if the same type of action on the rope is repeated or if the cylinder does not "walk" the rope. I dont think it will because the GRCS bollard is a true cylinder, not an hour glass shape like the Hobbs.
Keep in mind all these forces are way above what any one should be subjecting their devices to and the rope failures are because of this. No device on the market should be used in this type of drop manuver and in fact with these forces something (the tree, the rigging, the blocks) will fail, not maybe fail.
Frans

 

[Joe]

Frans: how did the grcs react to the drop?

Joe

 

[Frans]

No problems with the Log part of the test, but with the ratcheting capstan the rope blew through the fairleads and pulled the bottom of the base away from the tree, then the rope pulled/ sucked the outer part of the ratcheting capstan off the device. However the gears/pawls were not affected at all.
The rumor that the ratcheting part of the GRCS was not as strong as the Hobbs is not true. They are just as strong.

The manufacturer does not recommend using the ratcheting capstan for dumping wood but use the fixed bollard for this application. I'll have the results of the fixed bollard volvo drop test shortly
Frans

 

[TheTreeSpyder]

When mounting a wench to truck etc., and winding a reversible, you always want the winds to start near the mounting/anchoring/baseplate. From the bottom of reel pulling in puts enough leveraged pull against the anchor/truck/mount, without giving further distance from pivot of mount and reeling in on the top side of a bottom horizontally mounted winch.

So, as rope walks to center of capstan, the pull of the line is the same, but takes more leverage against the mounting of the baseplate in similar fashion as above. Same as keeping the line pulls to back solid axis of carabiner, the farther out the pull comes (in correct position) towards the gate side and not the back spine, the more leveraged force that same line is placing on gate, as opposed to being towards back spine. The larger area across in a wider D carabiner, can give the gate more leverage to hold the short axises from bending, but, as the line pull comes more and more towards the gate, the line is gaining leverage as the gate loses it i think.

Would, placing a tilt or wedge board under and across top of plate against tree, give leverage against twisting up, and force line to ride in correct position too?

 

[Frans]

You know what Tree Spyder? With all due respect I just cant get through all that verberage, sorry.
What I did pick up was you are asking if the strap could/ should be wrapped either on top of, or on the bottom of the spool. Bottom being closest to the tree.
Greg Good tried it both ways and discovered under heavy loads the top wrap configuration works best. If however you are wrapping the strap around a Huge girth, such as over 90"Dia. the bottom wrap might be better I dont know just an opinion. I would call Greg Good he is much more knowledgeable about such things than me
Frans

 

[TheTreeSpyder]

In all winches mounted to anything, even a 4 wheel drive with cable, you always want the cable to wind, feed closest to the baseplate/mount; any other position alows more leveraging/twisting on baseplate/mount from the line pull.

So, when line finds it's way to center of capstan, it is farther from the baseplate, more leveraged pull is incurred than if line rode on capstan position closest to baseplate on tree.

The bending up happens easier at this point. The top of baseplate mount under such loads becomes compression side, the bottom tension side. 2x as much force at compression as balancing pivot. Perhaps placing slight raise/wedging on top under baseplate to tilt slightly/ fight twist up and slant capstan slightly to give some pressure to make line ride towards baseplate. Then, the bottom side would get most of the binding. Liike compression/tension in hinge.

Just guessing and looking, applying similar strategy patterns as to a cable winch mounted on truck.

The top binding will keep from sliding up trunk i would think, the bottom binding keep base from arcing up as top digs into tree. The farther the bottom binding was from the top, the more leverage the binding will have against twist up like in hinge i think.

 

[Burnham]

KC--I don't quibble with your basic theoretical premise on the lower/higher amount of leverage placed on a winch mount based on the position/direction of the cable feed, but no power winch on a truck is mounted as you pictured it. The mount is opposite the direction of cable feed, and either direction of cable wrap yields the same amount of stress on the mount. What I mean is, the GRCS or the Hobbs are not set up the same as a power winch...no argument with your point on those units' function, just that it isn't applicable to the truck winch .

 

[TheTreeSpyder]

i think i have seen truck winches mounted horizontally, pulling horizontally, base is on bottom, pull is on top(or capable of being on top if reeled in wrong; esp. on reversible.

Wrecker, 4x4, electric capstan on back of electric company truck etc.

These have frames that mount parallel to spool (i guess this is what ya mean?); as adverse to the capstans that mount to tree, where frame mount is perpendicular to spool (actuyally worse cuz only one side supported of spool by mount, and most leveraged angle (perpendicular to support). But, leveraged distance of line pull from mount, is still best kept at minimum in either case i think.

 

[ORclimber]

I've seen verticle capstan winches on retired davey chip trucks and old range rovers. Seems like they'd be more popular, since it's easier to lay out rope than pull cable.

Here's a link to some hourglass shaped capstan winches. http://www.littlehercules.com/catheads.html

 

[Burnham]

Nice link, ORclimber...one of those would be very useful for some jobs.

Since I have not seen every winch ever mounted, I guess I should back off from my absolute statement, shouldn't I, KC ? I sure have never seen one mounted like you describe, and the reason would be just as you say. Anyway, I take it back .

 

[TheTreeSpyder]

Heck, someone told me about it working; or rather, i heard someone else get yelled at about it, and saw plate flexing etc.
Then saw someone almost do it, and heard it again, and so it goes. Also, when installing, it is(in the few i have helped install) a mentioned factor in directions; along with the loss of leverage of the spool filling in layers in a winch, that a capstan doesn't have.


Here is the $50 Rigging Software shots that i can plug numbers into for this car drop or whatever, if someone would like to see what we got, or if the software is for them.

If picture is too small, and don't know Where the invisible picture enlargement buttons are

 

[TheTreeSpyder]

Part 2 Now the rigging options and some of how they work.

i'll have to get a picture of the capstan on the back of some of our electric company trucks. Because of heat from friction of gripping coils the bollards/spools are usually made of hi-tech, super speed temperature dispersment and strength aluminum.

 

[Frans]

The capstan on the new Hobbs (the only one you can buy new at this time) is slightly concave or hourglass shaped. This would tend to force the rope into the middle of the capstan and thus make for more leverage against the base plate. The GRCS fixed bollard is a true cylinder and does not promote rope walk.
HOWEVER
All this is a moot point and irrelevent.
When you subject a lowering device (ANY LOWERING DEVICE) to forces where this becomes an issue you are exceeding the rope failure limits and the device limits. You will either brake the rope clean at a marl or half hitch, or at the drum itself or at a friction point within the bight somewhere.
We did notice that the friction/thermal breakdown at the drum happened with the new hobbs because of wrapping. This could have happened becouse of the double wrap on the drum or because of the tendancy of the new hobbs to force the rope into the middle of the capstan because of it's hourglass shape.
You can beat this issue around as much as you like but the fact is with weights over 2-3 thousand pounds and slam dunking the weight the failure will happen, not maybe.
We tried to set the test up to mimic real world conditions not some theorectical theory.
Winches mounted on trucks with electrical power and both sides of the capstan captivated and using wire rope, are a totally different tool than the lowering devices.

Frans

 

[TheTreeSpyder]

i thought the idea of your generously shared experimeant was to raise the load to the extreme that none would, for a magnified view of the processes and effects in standard rigging and the potentials that should be bordered against from that view, applied to the smaller, less magnified projects of 'daily' rigging; in this and other forms from the lesson. i'd imagine even the manufactures and designers should be eyeing your results, of these and other items, quite a dilligent undertaking and risk, then to give away here.

Thanx,