Shock Cord Mounting

[James Owen]

Hello everyone. recently, I got a Wildman Darkstar Jr. kit, which I am excited to fly on some of the more potent L1 motors (and maybe some L2 motors some day). eager to fly it at the next club launch, I got started building immediately.
here's the problem.
I'm only just now realizing, AFTER I've epoxied the motor mount into the booster tube, attached the fins, and done all my fin fillets that in my excitement I forgot to mount the shock cord to the motor mount.

has anyone else done this before?
does anyone have any ideas of what to do that wouldn't require taking the rocket apart? if it helps to know this, I'm planning on setting it up for single-deployment via motor eject and using a chute release for recovery from higher altitudes, so it needs to separate at either A) the avionics bay or B) the nose cone but if I separate at the nose cone I'll have to use the avionics bay as a normal coupler and put the avionics in the nose cone so that motor ejection works. all avionics would just be for data-logging purposes and I don't plan on doing dual-deploy in this rocket.

hopefully my problem makes sense, and thanks in advance for any help you can provide.

James

 

[sharkbait]

Hello everyone. recently, I got a Wildman Darkstar Jr. kit, which I am excited to fly on some of the more potent L1 motors (and maybe some L2 motors some day). eager to fly it at the next club launch, I got started building immediately.
here's the problem.
I'm only just now realizing, AFTER I've epoxied the motor mount into the booster tube, attached the fins, and done all my fin fillets that in my excitement I forgot to mount the shock cord to the motor mount.

has anyone else done this before?
does anyone have any ideas of what to do that wouldn't require taking the rocket apart? if it helps to know this, I'm planning on setting it up for single-deployment via motor eject and using a chute release for recovery from higher altitudes, so it needs to separate at either A) the avionics bay or B) the nose cone but if I separate at the nose cone I'll have to use the avionics bay as a normal coupler and put the avionics in the nose cone so that motor ejection works. all avionics would just be for data-logging purposes and I don't plan on doing dual-deploy in this rocket.

hopefully my problem makes sense, and thanks in advance for any help you can provide.

James

Go to Giant Leap rocketry’s website and that a look at the Hard Point Shock cord mount, if you decide to go that route, install it high enough so it’s a couple inches above the longest motor you plan to use. I have installed them with JB Weld and have also installed them with pem nuts and button head screws

 

[James Owen]

Go to Giant Leap rocketry’s website and that a look at the Hard Point Shock cord mount, if you decide to go that route, install it high enough so it’s a couple inches above the longest motor you plan to use. I have installed them with JB Weld and have also installed them with pem nuts and button head screws

thanks, just ordered one.

 

[Banzai88]

Meh, I would just use a mount to an eyeball in the motor forward closure.

 

[Handeman]

I would build this as DD. The DD will be much better for apogee deploy than any motor eject can be done. I'm sure you will be very happy with it as DD. Especially when flying on large I and baby J motors over 6,000 ft.

This is very similar to my scratch built L1 rocket I did with DD. I can't imagine flying that with motor eject. DD all the way!

 

[sharkbait]

Meh, I would just use a mount to an eyeball in the motor forward closure.

I don’t do motor eject, can that be done on the forward closure with motor ejection ?

 

[sharkbait]

Hello everyone. recently, I got a Wildman Darkstar Jr. kit, which I am excited to fly on some of the more potent L1 motors (and maybe some L2 motors some day). eager to fly it at the next club launch, I got started building immediately.
here's the problem.
I'm only just now realizing, AFTER I've epoxied the motor mount into the booster tube, attached the fins, and done all my fin fillets that in my excitement I forgot to mount the shock cord to the motor mount.

has anyone else done this before?
does anyone have any ideas of what to do that wouldn't require taking the rocket apart? if it helps to know this, I'm planning on setting it up for single-deployment via motor eject and using a chute release for recovery from higher altitudes, so it needs to separate at either A) the avionics bay or B) the nose cone but if I separate at the nose cone I'll have to use the avionics bay as a normal coupler and put the avionics in the nose cone so that motor ejection works. all avionics would just be for data-logging purposes and I don't plan on doing dual-deploy in this rocket.

hopefully my problem makes sense, and thanks in advance for any help you can provide.

James

With using the chute release, I would break in the middle, build the coupler with 2 AV bay bulkplates and you could always add an altimeter and convert it to a full E-bay later if you want to

 

[prfesser]

My L1 rocket was adapted from a 2.5" PML kit. Their recommended shock cord mount was a 3-4" length of nylon, knotted at both ends and the ends epoxied to the inside of the airframe. Shock cord (elastic) was attached to this loop. Apparently it worked very well for the H/I/J end of high power.

My point: there are undoubtedly better ways to attach a shock cord. Today's wisdom is to attach to the MMT or the centering ring. That's probably best, but the older ways still work. I wou.ld not worry overly about it.

 

[Banzai88]

I don’t do motor eject, can that be done on the forward closure with motor ejection ?

You'll need a different closure and the matching eye bolt, and eliminates motor ejection.

https://wildmanrocketry.com/collections/38mm/products/38fcpt
Once you get to 75mm motors and above, they're all lacking any motor initiated deployment charge, and many many folks attach the harness to the forward closure eye bolt without a second thought. If it works well for L2/L3 size rockets, I assure you it's more than sufficient for L1 size rockets.

If you wanted to use a motor mounted forward eye bolt AND maintain motor ejection, you have to use a RAS, a longer case, and this forward closure: https://aerotech-rocketry.com/products/product_fb123c37-83ac-350c-f81e-887bc7a2845e

After re-reading the OP's post, the recommendation to go with this https://giantleaprocketry.com/collections/featured/products/shockcord-hardpoint-38mm is probably the best option if one is dead set on using motor ejection deployment.

Aeropack has one as well, https://www.madcowrocketry.com/m38b-minimum-diameter-motor-retainer-38mm-with-bypass-holes/, but it's exponentially more expensive.

 

[Onebadhawk]

https://www.homedepot.com/p/Drill-A...el-Extra-Long-Drill-Bit-DWDDL18X1-4/305228494

 

[Voyager1]

Hello everyone. recently, I got a Wildman Darkstar Jr. kit, which I am excited to fly on some of the more potent L1 motors (and maybe some L2 motors some day). eager to fly it at the next club launch, I got started building immediately.
here's the problem.
I'm only just now realizing, AFTER I've epoxied the motor mount into the booster tube, attached the fins, and done all my fin fillets that in my excitement I forgot to mount the shock cord to the motor mount.

has anyone else done this before?
does anyone have any ideas of what to do that wouldn't require taking the rocket apart? if it helps to know this, I'm planning on setting it up for single-deployment via motor eject and using a chute release for recovery from higher altitudes, so it needs to separate at either A) the avionics bay or B) the nose cone but if I separate at the nose cone I'll have to use the avionics bay as a normal coupler and put the avionics in the nose cone so that motor ejection works. all avionics would just be for data-logging purposes and I don't plan on doing dual-deploy in this rocket.

hopefully my problem makes sense, and thanks in advance for any help you can provide.

James

Yes! I did exactly that a few years ago with a MC Formula54. I solved the problem quite easily by drilling a hole through the forward and aft CRs. Through these holes I fed a loop of Kevlar cord that looped around the base of the MMT and retainer. The other end of the cord was tied off outside the forward end of the booster to use as an attachment point for the chute cord. It has performed flawlessly ever since. It can also be checked and replaced easily if/when necessary.

 

[Ronz Rocketz]

I also have the 18” drill. You could also try inserting a baffle and connect the cord to an eyelet on the baffle. You’ll have to epoxy the baffle in place. This is similar to the rings above.

 

[Highpowerrocketyahoo]

Go to Giant Leap rocketry’s website and that a look at the Hard Point Shock cord mount, if you decide to go that route, install it high enough so it’s a couple inches above the longest motor you plan to use. I have installed them with JB Weld and have also installed them with pem nuts and button head screws

+1 or fet a long skinny stick and lots of JBW for an airframe mount. Lol

 

[kjhambrick]

James Owen --

I've had my fair share of lawn-darts but my Fin-Cans were almost always salvageable.

If the Rocket is not a min-diameter design then I will cut off the fin-can far enough above the forward Motor Mount Centering Ring so I could install a Couipler and then I would rebuilt the upper sections of the Rocket as necessary with new parts.

Then I secure the new section of Airframe to the Coupler with counter-sunk wood screws after hardening the holes with CA.

At the same time, I always replace the existing shock cord mount with a new Kevlar bridle.

The additional coupler is a tad heavier than the unbroken Airframe but it is worth it to me to save the fins which I always put a lot of effort into.

In addition, the deliberate break allows for shock cord maintenance.

Spock's Johnson, once a LOC Vulcanite H76, is one such Rocket and it is now going on 28 years old and two such repairs.

The second time, I just removed the screws and replaced the damaged section of tube and the Kevlar bridle ( and the decal

Maybe the cut-n-couple trick will work for you ?

HTH

-- kjh

 

[Buckeye]

Who needs a stinkin' eyebolt?

https://www.rocketryforum.com/threads/attach-harness-to-forward-closure-why-knot.159622/

 

[James Owen]

James Owen --

I've had my fair share of lawn-darts but my Fin-Cans were almost always salvageable.

If the Rocket is not a min-diameter design then I will cut off the fin-can far enough above the forward Motor Mount Centering Ring so I could install a Couipler and then I would rebuilt the upper sections of the Rocket as necessary with new parts.

Then I secure the new section of Airframe to the Coupler with counter-sunk wood screws after hardening the holes with CA.

At the same time, I always replace the existing shock cord mount with a new Kevlar bridle.

The additional coupler is a tad heavier than the unbroken Airframe but it is worth it to me to save the fins which I always put a lot of effort into.

In addition, the deliberate break allows for shock cord maintenance.

Spock's Johnson, once a LOC Vulcanite H76, is one such Rocket and it is now going on 28 years old and two such repairs.

The second time, I just removed the screws and replaced the damaged section of tube and the Kevlar bridle ( and the decal

Maybe the cut-n-couple trick will work for you ?

HTH

-- kjh

I ended up using a GLR acme shock cord mount. Rocket has flown 3 times now (including once supersonic!) with no issues with the shock cord.

 

[kjhambrick]

Thanks for the info James Owen.

I had to google 'GLR acme shock cord mount'

Nice solution that I'll keep in mind for future builds !

Thanks again.

-- kjh