PBT: Not Reel not Bungee

[Mr Epee]

I've never had a chance to crack one of these open...

PBT Tower Reel
Anyone know what's going on inside?

[DHCJr]

I have been unable to see what you are asking. I tried using the URL, you provided, this does not show the picture. The URL uses the adress www.fencepbt.com. The problem is you are directed to that by www.pbtfencing.com AFTER you sign in. I for one am not interested in signing up for PBT, just to look. If you could post the picture, that would be helpful.

Also, I did notice the length of the cable is 18 meters. I would look at how much it would cost to change that. The minimum length is 20 meters (M.55.3).

[Zilverzmurfen]

Is this what you mean?

PBT Fencing Reel, Model no. 44-800 (jpg).
Drawing instructions for 44-800 reel (pdf).
Safety instructions for 44-800 reel (pdf).

[Mr Epee]

Sorry, the link worked when I tried it originally.

Yes, ZZ, that's the one.

As best I can tell the cable is looped through 5 pulleys and I can't figure if the pulleys work independantly or if they are all on one pin and move together as a group on the other end.

[DHCJr]

Since the picture is not to detailed, I will try and guess. I would imagine they are independent and work like a multi-spring reel distributing the load. It appears to be a bungee system in a box. I can see from the instructions part of the reasons for the short cable. There should be at least 2 meters of runoff, which is greater than 6 feet. It appears to be a good idea for a club with a permanent site.

I remember a thread a while ago about wanting to set up a bungee system, but could not because of a high ceiling. This might work. How it works over the long term, I don't know, but it would be interesting to find out.

[Joe biebel]

I also can't see the detail of the mechanism in the picture, but it appears to be a gravity system. A weight or weights that supply the tension with very little change in tension when extended as opposer to springs or bungees. Very reliable, however, if gravity ever reverses, all bets are off.

[Larrison]

My guess is that it's a compound pulley system, with what looks like 6 or 7 loops in the pulley system. From the description, the enclosure is around 2 meters long, so giving it around 1.5 meters travel distance you'll get
around 17 -19 meters (11 or 13 loops with 1.5 meter on each loop) available cord travel -- which seems to fit with the description of the unit.

Offhand, this ought to work -- put a weight on the end of the lower of the compound pulley, and it will retract with pretty much constand tension. However, you'll probably want to run the lower end of the compound pulley in a track to keep it straight and use a fairly heavy weight (or bunge on the lower pulley) to give good tension. And of course, friction in the pulley system will need to be considered -- so high quality pulleys and probably some type of bearing system to minimize the pulley friction, else you'll get binding in the pulley system and it will go out of alignment.

[dekko]

The wire actually pulls the pullies together, then loosens when the fencer retreats. They are spring loaded but not in the typical way as many think about it. Kind of a neat system and uses a much less space than typical reels and these don't get stepped on.

They are kind of pricey but very neat.

[reawl]

Dekko, can you go into a little more detail how the springs are used? I was thinking about a floor version of this when I first read about it, something you could pack up at the end of the night. But I was also under the impression it was weight operated and had to be upright.

[rsy]

Originally Posted by Larrison

My guess is that it's a compound pulley system, with what looks like 6 or 7 loops in the pulley system. From the description, the enclosure is around 2 meters long, so giving it around 1.5 meters travel distance you'll get around 17 -19 meters (11 or 13 loops with 1.5 meter on each loop) available cord travel -- which seems to fit with the description of the unit.

This is similar to a device used in sailing manufactured by Harken and known as a magic box. Magic boxes can have up to 8:1 purchase with about 15 inches of travel inside the box and handle loads up to 1,000 lbs. It was designed to apply the purchase so that heavily loaded lines and stays could be easily tweaked, but if you turn it around it and increase the size (say 6 ft of travel inside the box) it would work very nicely to pay out and retract a reel cord under constant tension. Clever idea.

-r

[dekko]

Originally Posted by reawl

Dekko, can you go into a little more detail how the springs are used? I was thinking about a floor version of this when I first read about it, something you could pack up at the end of the night. But I was also under the impression it was weight operated and had to be upright.

It's been a while since I discussed it with the PBT folks here in the USA but as I recall the pullies are 'normally' at either end of the rectangle then move closer together when the connection moves away from the unit, then....

I will ask if I can see the inside then I can describe it better. The PBT folks have a couple set up in their club.

I will let you know.

[Robert Smith]

I just looked at the price on these things. Neat idea, but $500 each?!? I'd think you could make your own for much, much less. With a six-sheave pulley at top and bottom, say, you could hang 10 Kg off the bottom set and still have less than a kilo tension on the cable. No need for expensive marine pulleys for that. Just a dozen cheap pulleys, say 8-10 cm. mounted on rods with the top set fixed in place and the bottom set free to rise and fall. Cable anchored at the top of the 1.5 m tall box, to drop to the bottom sheaves first, then up, down, with the last turn off the top sheaves leading to a fixed pulley at a suitable height for easy connection to the body cord.

Only issues I can see right now would be
- keeping the cable on the pulleys if the box were tipped over or the cable were long enough to allow the lower sheaves to hit bottom;
- something to prevent someone releasing the cord at the wrong end of the strip and having the connector smack into the box. Maybe just an appropriate length of bungee between upper and lower sheaves? Foam rubber block in the base of the case? A teensy parachute?
- storing the things. We use a school's gym, so our storage space is limited to - literally - the volume of a shower cubicle.

Could be an interesting project for the summer, huh? One sheet of 1/2" ply, 15 m or so of cable, a dozen pulleys, a few other odds and ends and away we go...

[CvilleFencer]

Notice that if you are a non US customer these spiffy tower reels are only about $380 so they are comparable to other reel systems. Insert usual rant against rediculous PBT USA markups and the unfairness of it all here.

They have a warning letter an a rather unhelpful line drawing on their main website here: PBT Hungary Just check out the listing for the 44-800 reels and these are them. Sounds like a cool system but the fact that they need to send out a warning letter and that the reel cable is rather short for some od reason worries me a bit. Still, if I did not or could not do an overhead system and the space worked out I may consider them, or better yet my own version if it worked out to be practical...

[Larrison]

Ya know.. just an idle brainstorming idea, you could really do a cool version of something like this with a long vertical hole in a wall. Feed the cable in, with a weight on a rolling (or sliding) attachment at the middle of the cable with both ends at the top of the tube. As you pull the cable out the weight moves up in the tube, but pulls the cable back in as needed. Constant tension, etc controlled by the weight. This would only work in multi story buildings of course -- say around the third floor, or the 2nd floor if you can use a vertical drop to a basement.

Random thought.. probably totally useless.