Why do E-bays appear overbuilt?

[ep29030]

There is one valid argument for overbuilding an av bay: So it will survive a lawn dart event, or a late chute deployment. I had one of those late deployments that ripped the fins off the rocket, but the av bay survived. But I'd also admit that som av bays are overbuilt for even those kinds of events.

 

[OverTheTop]

There is one valid argument for overbuilding an av bay: So it will survive a lawn dart event, or a late chute deployment.

That's the beauty of 3D printing. You can just press "print" again .

 

[ep29030]

That's the beauty of 3D printing. You can just press "print" again .

But you can't do that for your altimeter

 

[OverTheTop]

But you can't do that for your altimeter

Sometimes yes, sometimes no.

 

[SDramstad]

An aerotech G55 (is actually a 49% G) and 2 of them get you just under 125g

According to thrustcurve.org an Aerotech G55 is 63 grams propellant and 120 ns. 2 would be well into H territory and 1 gram over the 125 gram limit.

 

[prfesser]

According to thrustcurve.org an Aerotech G55 is 63 grams propellant and 120 ns. 2 would be well into H territory and 1 gram over the 125 gram limit.

Does anyone know where the 125 g limit came from?

Some have suggested that it comes from the Gun Control act of 1968. Here's the relevant text:
------------------------------------------------
(4) The term “destructive device” means

(A) any explosive, incendiary, or poison gas

• bomb,
• grenade,
• rocket having a propellant charge of more than four ounces.
• missile having an explosive charge of more than one quarter ounce.
• mine or,
• device similar to any of the devices described in the proceeding clauses;

(B) any type of weapon (other than a shotgun or shotgun shell which the Secretary finds is generally recognized as particularly suitable for sporting purposes) by whatever name known which will, or may be readily converted to, expel a projectile by action of an explosive or other propellant, and which has any barrel more than one half inch in diameter; and

(C) any combination of parts either designed or intended for use in converting any device into any destructive device described in subparagraph (A) or (B) and from which a destructive device may be readily assembled.

The term “destructive device” shall not include any device which is neither designed nor redesigned for use as a weapon…
---------------------------------------------------------

"propellant charge of more than four ounces" does not refer to model or high-power rockets. The phrasing of 4(A) refers to "any explosive, incendiary, or poison gas rocket having a propellant charge of more than four ounces." We don't launch explosive rockets, incendiary rockets, nor poison gas rockets, period. So the four-ounce limit doesn't apply.

Furthermore, the last line says very specifically that a device that isn't designed/redesigned as a weapon is not a destructive device. Possibly an authority would charge a model/high power/amateur rocketeer with some other infraction of the law, but it appears that a charge of "possession of a destructive device" (referring to our rockets and activities) could be tossed out of the courtroom by a sharp lawyer.

 

[dhbarr]

Does anyone know where the 125 g limit came from?

Some have suggested that it comes from the Gun Control act of 1968. Here's the relevant text:
------------------------------------------------
(4) The term “destructive device” means

(A) any explosive, incendiary, or poison gas

• bomb,
• grenade,
• rocket having a propellant charge of more than four ounces.
• missile having an explosive charge of more than one quarter ounce.
• mine or,
• device similar to any of the devices described in the proceeding clauses;

(B) any type of weapon (other than a shotgun or shotgun shell which the Secretary finds is generally recognized as particularly suitable for sporting purposes) by whatever name known which will, or may be readily converted to, expel a projectile by action of an explosive or other propellant, and which has any barrel more than one half inch in diameter; and

(C) any combination of parts either designed or intended for use in converting any device into any destructive device described in subparagraph (A) or (B) and from which a destructive device may be readily assembled.

The term “destructive device” shall not include any device which is neither designed nor redesigned for use as a weapon…
---------------------------------------------------------

"propellant charge of more than four ounces" does not refer to model or high-power rockets. The phrasing of 4(A) refers to "any explosive, incendiary, or poison gas rocket having a propellant charge of more than four ounces." We don't launch explosive rockets, incendiary rockets, nor poison gas rockets, period. So the four-ounce limit doesn't apply.

Furthermore, the last line says very specifically that a device that isn't designed/redesigned as a weapon is not a destructive device. Possibly an authority would charge a model/high power/amateur rocketeer with some other infraction of the law, but it appears that a charge of "possession of a destructive device" (referring to our rockets and activities) could be tossed out of the courtroom by a sharp lawyer.

https://www.ecfr.gov/cgi-bin/text-idx?rgn=div5&node=14:2.0.1.3.15#se14.2.101_122"
§101.22 Definitions.
The following definitions apply to this subpart:

(a) Class 1—Model Rocket means an amateur rocket that:

(1) Uses no more than 125 grams (4.4 ounces) of propellant;
"

 

[gtg738w]

I just use a 3D printed sled with holes on the end for the shock cord mounts. There are two flanges that stick up to attach the end caps to. Works great on BT-20 to BT-55 low power kits.

 

[hball55]

If you’re building an Eggtimer Apogee - like I will be when my order arrives - mounting it in the nose cone looks to be the simplest way to go.

That’s where I mount (nosecone) my magnetic apogee detectors, two coupler centering rings and a 38 or 54mm mmt tube. Still have to sand the CRs to get them to slide in smoothly. I don’t use all-thread with the MADs because it interferes with the electronics if the rods are too close. If I install the MAD in the coupler, I will use brass all-thread, but that can get expensive.