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Old 11-01-2013, 12:13 PM   #46
Chuuken
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Re: Trigger Mechanism Design Rules

Hey Popgun Pete,

I was thinking about a comment you made in another thread about "circle analysis", and I was about to PM you to ask about it... Then I found this thread! I'm replying just to bump this back into the public eye!

I am finishing up my first gun build right now. I've basically recreated a mechanism used by Rene Potvin. I have tested it in situ, and it appears to be functional and sound, but I am looking forward to seeing how it looks when given the "circle test" treatment!

Thanks again, Popgun Pete, for being such a wealth of knowledge.


Mike W

Last edited by Chuuken; 11-01-2013 at 12:13 PM. Reason: spacing
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Old 11-02-2013, 02:29 PM   #47
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Re: Trigger Mechanism Design Rules

Quote:
Originally Posted by Chuuken View Post
Hey Popgun Pete,

I was thinking about a comment you made in another thread about "circle analysis", and I was about to PM you to ask about it... Then I found this thread! I'm replying just to bump this back into the public eye!

I am finishing up my first gun build right now. I've basically recreated a mechanism used by Rene Potvin. I have tested it in situ, and it appears to be functional and sound, but I am looking forward to seeing how it looks when given the "circle test" treatment!

Thanks again, Popgun Pete, for being such a wealth of knowledge.


Mike W
Any photos of your mechanism, or a drawing?
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Old 11-02-2013, 05:10 PM   #48
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Re: Trigger Mechanism Design Rules

Pete, Have you ever seen one of these in your hands? I've never seen one out of a gun and pulled these pics off of a tutorial made by the USA Distributor for C4 on how to clean a C4 Mech. I can't really figure out the circles here.
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Old 11-02-2013, 07:15 PM   #49
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Re: Trigger Mechanism Design Rules

I remember looking at the same "C4" tutorial, but I have never laid my hands on one. The design is a reverse mech with a rocking tooth formed by the short bar mounted between pivoting side plates that straddle either side of the multiple plate sear lever arm. The rear pivot pin for the sear lever is very high up and located directly behind the sear tooth, so the torque on the sear lever is very low with the gun cocked and bands loaded, but is enough to turn the sear lever when you pull the trigger. In fact the round tooth is probably what makes the sear lever turn as the tooth is in a sense "angled", same principle as the Prodanovich "balanced sear" mechanism. Without a band load the mechanism will not release, you have to pull the spear out by hand as the sear lever is biased upwards by its spring, but that will be overridden by the band pull when the trigger moves out from under the sear lever's forward tip which is a small metal roller. This is a momentary release action trigger mechanism, the sear lever always sits on the top of the trigger unless you pull the trigger, so to push the spear tail into the sear box the round bar sear tooth is rocked back on the sear lever arm and the spear tail slides in over the top of it until the separate spring action acting on the pivoting side plates pushes the tooth back up into the space created by the spear tail notch. The round bar that forms the sear tooth has a counterpart on the bottom that binds on the sear lever arm underneath and checks the rotation of the side plates when the spear tail is pulled forwards by the band load and is held ready for the shot.

Very well made and no doubt expensive to make, which is what you would expect for the money, although the lever arms are rather short and are no doubt a consequence of stuffing the trigger mechanism into a very small space. Those small lengths are made up for by the "balanced sear" action, just as they are in the Prodanovich mechanism. Later reverse mech guns have made use of the cocking stock to lengthen the sear lever arm by extending the sear box even further back in the gun, however if the mechanism does the job then there is no need to make it any longer than necessary, plus it adds to the weight.

I will check out the photos and see if one lends itself to a "circle analysis" drawing. Attached is a diagram that shows how a torque is produced by the round tooth if my estimate of where the spear tail notch acts on the tooth is correct (thin red line parallel to the spear).
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Old 11-02-2013, 08:28 PM   #50
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Re: Trigger Mechanism Design Rules

I'll need to read that again a few times, but, in short.. You're awesome.

C4.. I can never figure out what exactly they have done. But I wish I could.
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Old 11-02-2013, 09:41 PM   #51
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Re: Trigger Mechanism Design Rules

Well here is the best that I can do with the photos I have, but should be close enough. Pretty neat design, more so when you think about what it does in such a small space.

A profile photo with the levers laid on the outside of the sear case while sitting on their pivot pins would provide a better view if anyone wants to pull their C4 apart in the "interests of science".
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Old 11-02-2013, 10:15 PM   #52
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Re: Trigger Mechanism Design Rules

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Originally Posted by popgun pete View Post
Any photos of your mechanism, or a drawing?
Here she is, not exactly mechanically optimized, but the mechanism doesn't look like it'll be unsafe either, so we'll see how it feels in the water. This is a single band, 95cm gun.


https://www.dropbox.com/s/wx2fnjc1s39j6d6/mech.JPG
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Old 11-03-2013, 06:06 AM   #53
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Re: Trigger Mechanism Design Rules

Pete, what do you think about these one?
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Old 11-03-2013, 04:52 PM   #54
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Re: Trigger Mechanism Design Rules

Quote:
Originally Posted by Chuuken View Post
Here she is, not exactly mechanically optimized, but the mechanism doesn't look like it'll be unsafe either, so we'll see how it feels in the water. This is a single band, 95cm gun.


https://www.dropbox.com/s/wx2fnjc1s39j6d6/mech.JPG
This is basically an "Undersee" type mechanism as Denny Wells was the first to do it that way, as far as anyone knows. The green circle tells us that the sear lever arm could have been made longer, but if it does the job then it does not really matter with only a few bands on the gun.
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Old 11-03-2013, 05:15 PM   #55
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Re: Trigger Mechanism Design Rules

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Originally Posted by gspearguns View Post
Pete, what do you think about these one?
The long sear lever, reverse trigger mechanisms usually don't have a biasing spring on the sear lever, relying instead on the weight of the arm for it to flop down and stay there after the shot. As you load your gun right side up the lack of a spring is not a problem. The trigger needs a biasing spring and they usually are of the wire loop type with legs that fits around the trigger pivot pin. As the trigger does not have a catching step on its rear face the sear case here has one instead. The "circle analysis" diagram demonstrates that much of the gearing or leverage is in the sear lever. The tip of the sear lever will give a hit on the catching step, how much noise that makes on a long sear lever arm gun I do not know. Most reverse mechs have a catching step, including the "Sea Hornet/Biller" which are the first of this type mass produced for spearguns. As they stayed clear of curve matching they placed the sear lever tip forward of the top of the curve described by the top of the trigger. That way the trigger mechanism will not be driven backwards against the band pull. If the sear lever tip is behind the trigger pivot vertical as it is here then you have to curve match the parts (blue circle).

The relatch action needs to be considered, have you a photo of that? When the sear lever tip swings back up with spear tail insertion in the sear box mouth it has to reset the trigger to get back to the cam lock position.
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Last edited by popgun pete; 11-03-2013 at 05:37 PM. Reason: added "then"
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Old 11-04-2013, 04:00 PM   #56
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Re: Trigger Mechanism Design Rules

There seem to be a number of these long sear lever trigger mechanisms being offered in spearguns today, or as replacements for retrofit with some modification to the existing stock. The photo here is of the Bleutec "Raptor", mainly because I found more views of it. Note the staking of the pivot pins to stop the pivot pins falling out (or pulling the mechanism apart for that matter). You can see the biasing spring alongside the trigger. The catching step is on the rear of the trigger. Note that if a gun has a plastic trigger then receiving a whack from the sear lever tip may eventually bust it, so another pin is necessary in the sear case or housing to catch the front end of the sear lever. Personally I don't like load bearing plastic triggers. Made of the right stuff they can work, but if sub-contractors in far-off countries decide that some other cheaper plastic will do the same job, as far as they know (key words!), then they may substitute it in the interests of increased profit for them. The question is who is doing the quality assurance checking on a periodic basis by randomly sampling the product? Those further up the manufacturing chain may be oblivious of changes which may be undeclared, or unauthorized. Big brand names have a reputation to lose, so they keep a tight rein on their product. It all comes down to control and the ability to enforce product design and material specifications.
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Old 11-05-2013, 12:58 AM   #57
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Re: Trigger Mechanism Design Rules

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Originally Posted by popgun pete View Post
The long sear lever, reverse trigger mechanisms usually don't have a biasing spring on the sear lever, relying instead on the weight of the arm for it to flop down and stay there after the shot. As you load your gun right side up the lack of a spring is not a problem. The trigger needs a biasing spring and they usually are of the wire loop type with legs that fits around the trigger pivot pin. As the trigger does not have a catching step on its rear face the sear case here has one instead. The "circle analysis" diagram demonstrates that much of the gearing or leverage is in the sear lever. The tip of the sear lever will give a hit on the catching step, how much noise that makes on a long sear lever arm gun I do not know. Most reverse mechs have a catching step, including the "Sea Hornet/Biller" which are the first of this type mass produced for spearguns. As they stayed clear of curve matching they placed the sear lever tip forward of the top of the curve described by the top of the trigger. That way the trigger mechanism will not be driven backwards against the band pull. If the sear lever tip is behind the trigger pivot vertical as it is here then you have to curve match the parts (blue circle).

The relatch action needs to be considered, have you a photo of that? When the sear lever tip swings back up with spear tail insertion in the sear box mouth it has to reset the trigger to get back to the cam lock position.

Here are videos ...

http://www.youtube.com/watch?v=wfx8b...ature=youtu.be

http://www.youtube.com/watch?v=XDfYV...ature=youtu.be
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Old 11-05-2013, 08:19 PM   #58
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Re: Trigger Mechanism Design Rules

The reverse layout "Sea Hornet" mechanism keeps the trigger depressed after the shot, so the safety cannot be engaged until the mechanism is relatched as the safety cam will not turn with the front edge of the top part of the trigger still leaning on it. Both the trigger and sear lever have two distinct states, i.e. "cocked" and "discharged", unlike most other mechanisms where the trigger can swing back to the cocked position as it is free of the sear lever (except for perhaps a common coil spring connecting them) once the mechanism is discharged. The reason for this happening on the "Sea Hornet" mechanism is that the tip of the sear lever always stays on the same side of the connecting line that defines the mechanism's pivot pin spacing, so you get a second "cam lock" that holds the mechanism in the discharged state with the sear lever tip sitting on the catching step cut in the rear of the trigger. The very similar "Ultimate" speargun used this "two states" property to fit a safety interlock lever behind the trigger as it was kept out of the locked position until the mechanism was relatched. During the relatching sequence the sear lever tail has to push the trigger slightly backwards on most other mechanisms, so prematurely imprisoning the trigger on them with any safety device or interlock will stop the mechanism relatching and cause problems. While the "Sea Hornet", "AB Biller" and "Ultimate" spearguns all use "two state" reverse trigger mechanisms, only the "Ultimate" paired it with an interlock which required the trigger and interlock lever to be squeezed simultaneously in order to shoot the gun. It seemed a good idea, but the interlock spring was too strong and not easy to press with your middle finger on the lever that projected from the grip just under the trigger finger guard.

If on a long sear lever arm reverse mech you can keep the sear lever tip from passing to the other side of the line connecting the pivots then you can use the trigger to lock the sear lever in a second position where the trigger stays depressed after the shot and the subsequent relatch does not have to reverse the trigger from the fully rotated position which it will otherwise be sent to by its biasing spring.
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Old 11-07-2013, 07:49 PM   #59
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Re: Trigger Mechanism Design Rules

The "Ocean Rhino" has had a change of sear pivot pin position to improve the mechanism relatch as a greater input torque can now be applied to the sear lever. The vertical blue lines shown on the first attachment represent the "input" lever arms in each case, so you can see that the same push on the spear will produce more torque with the later mechanism. The change was to avoid the tendency of users to "slam dunk" the shaft into the sear box when all they need do is press on the shaft to reset the mechanism properly. The problem with the earlier version is the backing projection is not tall enough and only reaches half way up the diameter of the shaft with the sear lever in the discharged position. However if you give the shaft a slight twist as you press it in that better aligns the sear lever's short backing projection in the shaft's anti-rotation tail slot and that prevents the backing projection binding on the side walls or the base of the slot allowing the earlier mechanism to reset with just a firm push. The twist is very slight, just a flick of the wrist, but it works every time. Don't do it and the earlier mechanism seems to stick on occasion. The revised sear lever pivot pin position effectively makes the backing projection taller as basically the same sear lever sweeps through a greater angle than before so it fills more of the anti-rotation slot in terms of the height of the slot and thus aligns it from the start of pushing on the spear shaft for the relatch. A firm push should reset any trigger mechanism, even a multi-lever monster with high gearing. Slamming shafts into spearguns is asking for trouble as you effectively hammer the parts and the pivot pins in the frame, they are designed for sustained high loading, not impacts.

The "circle analysis" is updated in the second attachment. Note that the sear lever tip or tail now passes across the line drawn between the pivot pins so that the trigger is no longer held depressed after the shot. I mention this because it is another example of what I was referring to in the previous post, but for a regular trigger mechanism. Another example is the Scubapro "Panther" discussed earlier.
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Old 11-08-2013, 05:57 PM   #60
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Re: Trigger Mechanism Design Rules

I don't have an Omer "Cayman" to pull apart, but here is a manipulated photo to show what I think will be close to the "circle analysis". The trigger has a small roller in the top that bears on the curved tip of the sear lever. The knee bend in the front of the trigger may push on the housing creating a "frame lock" rather than a "cam lock", especially if the trigger stop position and thus trigger stroke to shoot is adjustable. The gray circle denotes where the sear lever probably hit a cross pin in the bottom of the housing before the mechanism received a cast metal trigger, there is a slight scallop under the sear lever just back from the tip to catch onto it. Belting the plastic trigger's catching step with the sear lever tip may have otherwise busted the trigger. I am pretty sure the plastic trigger relied on a smooth bearing surface rather than having a roller. On the relatch the sear lever tip has to get past the roller as it swings up to push the trigger forwards at the top and out of the way.

First time I saw a "Cayman" I thought that it was a toy gun that had somehow found its way onto the speargun rack in the store, dwarfed as it was by the spearguns sitting around it back then. Now there are many spearguns following this general layout for a eurogun with a high rear handle position.
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