I've written about my use of 10' long light kevlar (turns out I bought 100# strength) in my LPR, and by LPR most of mine are BT55 and BT60 size but still very light. That's a lot of "string" to stuff into a tube a few inches at a time and I've also worried about tangles which I've had one time out of about 10 flights. I tried to think of something to wrap the cord around that would still allow it to unroll easily. Last year I came up with the idea to use a spool so I made a prototype out of cardboard. I cut 3 rings and fit over a small piece of 18mm motor, the OD is about 1" so it would fit easily into a BT55.
I put a small piece of twist tie on it so I could theoretically switch from rocket to rocket but it would otherwise be captured by the shock cord. I put the spool at the midpoint of the shock cord and wrap both sides of the cord around it at the same time. Essentially when the cord tries to straighten one piece pulls one direction, the other piece pulls the other direction, the spool spins and reels out the cord (second photo below). I've flown it twice and it worked great. (The cord in the photo is actually single strand kevlar bowstring material, somewhere between 50# and 75# actual strength and very thin, still in use in a couple of my rockets.)
This one was too difficult to make, I think I could just cut a couple of disks instead of 3 rings and put a couple of pieces of balsa in the middle as spacers. I don't think it requires 2 compartments, I think it would work with just one compartment.
I will do more experiments but so far it is looking good. I will make a bigger one for MPR, maybe 1.75" diameter for my rockets.
I put a small piece of twist tie on it so I could theoretically switch from rocket to rocket but it would otherwise be captured by the shock cord. I put the spool at the midpoint of the shock cord and wrap both sides of the cord around it at the same time. Essentially when the cord tries to straighten one piece pulls one direction, the other piece pulls the other direction, the spool spins and reels out the cord (second photo below). I've flown it twice and it worked great. (The cord in the photo is actually single strand kevlar bowstring material, somewhere between 50# and 75# actual strength and very thin, still in use in a couple of my rockets.)
This one was too difficult to make, I think I could just cut a couple of disks instead of 3 rings and put a couple of pieces of balsa in the middle as spacers. I don't think it requires 2 compartments, I think it would work with just one compartment.
I will do more experiments but so far it is looking good. I will make a bigger one for MPR, maybe 1.75" diameter for my rockets.