SpudFiles

Started working on my new mini hybrid today;



Churned out a very simple pvc back plug in a few minutes, wich is now epoxied in place.



somewhat sturdier than my previous effort
I want to shoot this from my shoulder, so I cant afford blowouts. I will put some bolts in it. According to my calculations this will take about 5000 N of force at an ideal 12x mix.

Chamber material is seamless steel pipe, 25 mm id, 2.5 mm wall thickness.
I still have to determine the chamber size...

HGDT says a 15 cm chamber will give 488 joules, vs 575 joules from a 20 cm chamber....
makes it harder to supress tough

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Nice planning on using a syringe or more complicated means of metering. You seem to be moving out of the realm of mini hybrids
Back plug looks good, I would trust it, then again I made a hybrid out of plastic...

Looks good, but what's that slot in the schrader? Won't it compromise sealing with the pump head?

SpudBlaster15 wrote:it should be fine at up to 10X or so.

*cough*

I would still put a couple of bolts in for good measure

HGDT says a 15 cm chamber will give 488 joules, vs 575 joules from a 20 cm chamber....
makes it harder to supress though

Depends what's most important, low noise and massive power are competing parameters, it's difficult to have both... but not impossible

What calibre is this anyway? With those dimensions a 0.22" will easily be supersonic at 12x, I assume though you're going for something bigger and heavier?

It's difficult to estimate the dimensions of that plug from the picture, but assuming a length of ~30mm and a tensile lap shear strength of 1KPSI for the epoxy, the joint should hold about 2.4KPSI. I would have went with more bonding area, but it should be fine at up to 10X or so.

The plug has a diameter of 25mm, and the bonding area is 25mm high.

planning on using a syringe or more complicated means of metering. You seem to be moving out of the realm of mini hybrids

Just syringe metering, cheap and reliable
It isn't clear to me where a mini hybrid turns into a normal sized one

Looks good, but what's that slot in the schrader? Won't it compromise sealing with the pump head?

It isn't a schrader, it's a dunlop valve.
I use it as it doesn't have a spring in it, and it doesn't leak air when disconnected.

Depends what's most important, low noise and massive power are competing parameters, it's difficult to have both... but not impossible

I'm going for the 20 cm chamber
Power is more important te me
I'm thinking of keep this unsurpressed until new year's eve, people don't pay very much attention to loud noises this time of year
especially not when they're my neighbours
I'm thinking of using a DWV pipe as the supressor housing, what size would be appropriate?
the barrel will be 1 meter long.

What calibre is this anyway? With those dimensions a 0.22" will easily be supersonic at 12x, I assume though you're going for something bigger and heavier?

I'm going for the largest one that fits
With a bit of luck it will be in the 16 mm range.

Labtecpower wrote:It isn't a schrader, it's a dunlop valve.
I use it as it doesn't have a spring in it, and it doesn't leak air when disconnected.

Ah, right.

I'm going for the 20 cm chamber
Power is more important te me

I'm thinking of using a DWV pipe as the supressor housing, what size would be appropriate?
the barrel will be 1 meter long.

As big as you can manage

You can easily have a 50-60mm tube and still have an attractive launcher:



Don't forget to be liberal with baffles and chambers.

I'm going for the largest one that fits
With a bit of luck it will be in the 16 mm range.

Can't argue with a bigger bore and since you can machine sabots easily, smaller projectiles or even shotgun rounds remain an option.

50 mm is what I was aiming for

I hope I can find some time to machine baffles and end caps for the supressor...
550 joules from a relatively small bore shoulder fired gun sounds like a lot of fun to me

I don't think I will spend my precious machining time on making sabots

Hmm.... how much are those PCB companies charging these days?

EDIT: and unsurprisingly, it doesn't work. I double checked my wiring, though, and I think the likely culprit is that I fried the power switching transistors with my 75-watt howitzer/soldering iron.

It was supposed to be a PWM circuit with a 12 and 3VDC output, but all I can measure at the emitters of the switching transistors is 0v.

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Mark;

post the schematic you used and the component side of that board.

As you wish:

mark;
I do see some problem areas.

What are you trying to achieve with this circuit design?
A DC motor control and 3 VDC charger?

Why such a high Astable frequency? 68KHz

What kind of motor?

It's basically just to provide two switched power sources without ohmic losses as involved with linear regulators. This is sort of a "proof of concept" circuit.

I suppose I could go lower with the frequency. 68kHz is just one of the "standard" 555 frequencies (made with a 1kohm, 10kohm, and 0.001uF capacitor).

The motor is brushless.

ITWOST, been working frantically on my semi-auto pneumatic rifle. had my barrel sealing valve working with a 100% seal, then i added a vent hole to fill the chamber so it would actually fire, and found out an epoxy job i did SUCKED so I i had to redo it... waiting for epoxy to cure.

Tomorrow I'm actually hoping to test it (free of epoxy leaks and just having to deal with thread leaks). After that there isn't much I can do until i get all the parts in the mail and my machined block from ramses.. But I can work on my dart design!

ITWOST, I just bought one of these.

Apparently somebody thought I would use that TSC gift card to quietly buy a new set of socket wrenches or something.

Only niggle is the 1-1/8" opening, but I can't really complain, as it already has a very redundant set of static seals pre-installed.

Why would you buy that