Compact Bulldog Bone

This is what I have done with mine. This works really well with Vortex. Look at the angle of the top arm. It is loaded with my weight but the arm is still in a low position. Moving the pivot hole changed the hole dynamics of the BDB. It feels like I added power steering, smooth and precise.

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Hey Dave,

That looks good. What is it doing exactly, reducing the bend radius on the top arm and thereby reducing friction on a larger diameter rope?

Or is it doing something else that would be advantageous on smaller diameter ropes as well?
 
You could put a hole 1" from the top double joint instead of the Friction link. That way you would also lessen the grip on a fat rope, but get more mechanical advantage from the release arm as well, and not have the projection at the spine and potential jamb.
 
Treegongfu, it reduces the lever arm on the top link. This changes the force necessary to activate a release as well as reducing the load on the top link. It also moves the top link closer to the spine during slack tending or ascending. This gives the rope a more straight shot path through the bottom link and reduces drag. I can clip into the tending hole with my shoulder harness and not get any increased drag like before when walking up the rope in an upright position. I have not tried it yet with thinner ropes but I suspect you would need to go at least one size larger with the ballard. I think it would slip on 11mm lines.

Gordon, I tested it thoroughly and could not get it to jam but I still plan on removing the old hole and reshaping the arm. I just left it long until I could be sure I liked the change. I also like that the top arm is shorter and think it could be slightly shorter still.
 
Hmmmmmm... Interesting, but it would have to work on thin ropes for me. Could it be that ur modification works the same on fat rope as it does stock with thin ropes. I don't feel I apply a lot of pressure the way it is stock.
 
surveyor said:
You could put a hole 1" from the top double joint instead of the Friction link. That way you would also lessen the grip on a fat rope, but get more mechanical advantage from the release arm as well, and not have the projection at the spine and potential jamb.
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With 11.5 Tachyon and 11.7 Yale (Aztec) in mind, I made a quick and dirty set of upper arms, stock length but with the hole for the friction link 1.25" from the upper pivot hole instead of the stock 1.5".

The result was an easier release with even better regulation of speed on both ropes. After a quick trial low and slow on the Aztec, I went up 20' came back down (all good), went up to 55', sat back and while removing my knee and foot ascenders, the BDB started to creep down. After starting and stopping a few times the creep went away and I have no explaination for that. More testing needs to be done before I'd recommend making a change like this to others. It also requires new arms because the holes are not moved far enough away from the existing holes.

While my first impression of this change is a very good, it reduces the margin of error and may be a bit on the edge for use in a working situation. I'll probably make another set of arms with the holes another 1/16" apart (1.3125" spacing) and see if I can hit a sweet spot for this size rope.

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Side notes...Mike's tether routing is proving to be an excellent choice. I personally feel the Yale 11.7's are better behaved with the BDB than Tachyon. Tachyon seems to be a little more 'on and off', taking more care to feather my speed.
 
Be aware that the top and bottom arms could cross load without the handles they come with.
 
Understood. I should have pointed that out for anyone that wasn't aware. These arms are for testing purposes only. When I get done 'playing', I'll put the stock arms back on or mill a set with 'handles' built in.
 
TylerHoffman said:
Hmmmmmm... Interesting, but it would have to work on thin ropes for me. Could it be that ur modification works the same on fat rope as it does stock with thin ropes. I don't feel I apply a lot of pressure the way it is stock.
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The way I have it is definitely for fat ropes only. It is amazing how much of a change moving the pivot point made. At a buck 60 I should be about average, weight-wise, for a climber but I was not totally happy with the way it preformed on 11.5 lines and not at all pleased how it worked on Vortex. My HH is as smooth as silk so it is a hard act to follow. But I do like how the BDB now runs on Vortex and it is cool to be able to take it on and off the rope so fast.
 
DSMc said:
The way I have it is definitely for fat ropes only. It is amazing how much of a change moving the pivot point made. At a buck 60 I should be about average, weight-wise, for a climber but I was not totally happy with the way it preformed on 11.5 lines and not at all pleased how it worked on Vortex. My HH is as smooth as silk so it is a hard act to follow. But I do like how the BDB now runs on Vortex and it is cool to be able to take it on and off the rope so fast.
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Were you using it without the bollard for the Vortex? That's what it took for me to be happy with it.
 
TreeLogic said:
Were you using it without the bollard for the Vortex? That's what it took for me to be happy with it.
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Yes, I was and it was OK most of the time. But occasionally on ascent or on the ends of limbs at awkward angles, I could feel more friction than I was happy with.
 
treegongfu said:
Gmcttr, did you try adding a larger bolard on the thinner ropes with the mod as DSMc suggested?
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Without the hole spacing mod, Tachyon runs better with the 5/8" bollard and that's how I ran it after the mod as well. I did not try it with the 3/4" bollard after the mod.

Aztec 11.7mm has too much 'coasting' with the 5/8" bollard and requires the 3/4" bollard even without the hole spacing mod. No way I'm going to try it with the mod and the 5/8" bollard.:eek:
 
I am using the 5/8" bollard with a new piece of Vortex. The rope is slick when it is new. It ran fine on the 7/16" on older Vortex and like I said before the pivot point change I was running the BDB with no bollard. This is sweet now the way that the top arm is right at the release point and the modulation is even more smooth.
 
I forgot to mention that I used the ARB HUT from Tree Stuff today and it worked great clipped into the BDB's tending hold. I think Gordon recommended using a bungee for advancing to ensure that the tether not stop the carabiner from loading the BDB properly. I would agree.
 
gmcttr said:
I went up 20' came back down (all good), went up to 55', sat back and while removing my knee and foot ascenders, the BDB started to creep down. After starting and stopping a few times the creep went away and I have no explaination for that.
Click to expand...
I think that the top arm can be worked like a lever for all sorts of control , on the creeping I've found when I work the lever (toparm) by moving it up it grabs perfectly. When ascending its kind of in between , so if your light wieght or not too aggressive with sitting back on it , the arms don't spread completely and slight creep is possible. Easily stopped by moving top arm up in my experience.
 
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