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Hydraulic recoil buffer

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Hydraulic recoil buffer

Unread postAuthor: wdr0 » Fri Apr 28, 2017 8:22 pm

Hey, so I'm planning to do more work on my large hybrid cannon in the fall and my current idea in a line of ever revolving plans is to fit it with a hydraulic recoil system. I have two questions related to this. The first being in general about the recoil forces, with my 4" bore and 1200 psi pressure generated my thoughts are that the most force the mount could ever receive would just be that pressure across the surface area so around 15,000 lbs? Is this an errenous or over simplified line of thought?

My other question is related to the hydraulic aspect. The general principle is have the recoil force extend a hydraulic cylinder forcing oil into a tank and compressing gas to absorb the energy, the oil then is allowed to slowly drain back into the cylinder. What I am unsure about is if the tank will need to have a membrane to avoid the nitrogen from dissolving into the oil. At the volumes I need hydraulic acumulators are excessively expensive and if I could use a plain tank would that would be ideal. I think with my system the resting pressure would be less than 500 psi, and the peak pressure around 1500. I'm have no idea of the rate nitrogen would dissolve into the oil at these pressures, don't know if anyone here dose either?


Thanks
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Re: Hydraulic recoil buffer

Unread postAuthor: jackssmirkingrevenge » Fri Apr 28, 2017 10:45 pm

The first being in general about the recoil forces, with my 4" bore and 1200 psi pressure generated my thoughts are that the most force the mount could ever receive would just be that pressure across the surface area so around 15,000 lbs? Is this an errenous or over simplified line of thought?


First of all, let's briefly smile about the fact that the only word you misspelled was "erroneous" ;)

Recoil force applies Newton's third law. You need to know the weight and velocity of your projectile, as well as the weight of your launcher. Technically, we need to count the propellant gas as well, but we'll ignore it for the sake of simplicity.

Your launcher will attempt to move at the following velocity:

V launcher = [projectile velocity x projectile weight] / launcher weight

I think a hydraulic buffer would be a little overkill. What about a gas strut?
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Re: Hydraulic recoil buffer

Unread postAuthor: wdr0 » Sat Apr 29, 2017 10:08 am

I had initially considered gas struts, however from what I could find it would seem they are ill suited as there is not enough restriction on the return so they move back into position too quickly.

As for the specifics of the launcher the current estimated weight is 600lbs with a velocity of 1060 fps when firing a 10lb projectile. So I am getting 17.7 ish for the recoil velocity based on the method you provided? Regrettably I have not much exposure to physics so roughly understand the principles but not how to get the information I need

Also, I am unsure and still debate if I should even bother with the recoil system, I have a trailer frame that I can put it on which would make the total weight close to 1,100 lbs at which point I'd think it may only roll a couple feet which would be fine.
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Re: Hydraulic recoil buffer

Unread postAuthor: D_Hall » Sun Apr 30, 2017 5:40 pm

wdr0 wrote:the most force the mount could ever receive would just be that pressure across the surface area so around 15,000 lbs?

Correct. Depending on how you do your valving and such you may never actually see this much, but it does provide an upper bound on recoil force.

My other question is related to the hydraulic aspect. The general principle is have the recoil force extend a hydraulic cylinder forcing oil into a tank and compressing gas to absorb the energy, the oil then is allowed to slowly drain back into the cylinder. What I am unsure about is if the tank will need to have a membrane to avoid the nitrogen from dissolving into the oil. At the volumes I need hydraulic acumulators are excessively expensive and if I could use a plain tank would that would be ideal. I think with my system the resting pressure would be less than 500 psi, and the peak pressure around 1500. I'm have no idea of the rate nitrogen would dissolve into the oil at these pressures, don't know if anyone here dose either?

You can probably get away with a normal tank. For that matter, you can probably get away without your 500 psi resting pressure. You'd obviously get more travel without it, but for what you're doing ambient would work.


With all that said.... Why reinvent the wheel? Go buy a couple of automotive shock absorbers and be done with it. Note that at the office we have a 30 mm gun with a Mann breach and that's all we use.... automotive shock absorbers. Available in sizes from Smart Car to Semi truck, surely one will do what you need and for a lot less effort (probably less money too).
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Re: Hydraulic recoil buffer

Unread postAuthor: wdr0 » Sun Apr 30, 2017 8:04 pm

well, initially I was thinking on using shock absorbers. But then I had seen elsewhere(I can't recall right now), that they would not have enough restriction on the return stroke and would move forward just as fast as they retract. Although Since you have had success with them I'm inclined to go that route. I'm not sure how I'd best go about sizing though? As a starting point as earlier mentioned I think most loads I fire would be around 10lbs, so I think that is what I'll design for. It also seems the struts are sold more by what vehicle they fit without actual useful specs for this purpous..
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