GTA
All Springer/NP/PCP Air Gun Discussion General => European/Asian Air Gun Gates => Czech & Russian Air Guns => Topic started by: subscriber on January 15, 2019, 12:33:20 AM
-
EDIT: If you are in a hurry to see the objective motion study , click link below to take you directly there:https://www.gatewaytoairguns.org/GTA/index.php?topic=153475.msg155689447#msg155689447 (https://www.gatewaytoairguns.org/GTA/index.php?topic=153475.msg155689447#msg155689447)
A few days ago I had my 46M apart to increase its compression (velocity); by adjusting the piston "TDC".
Then, I took a bunch of pictures and measurements of the cocking linkages. While I tried to accurately capture all the functional dimensions, I did take some licence with the aspects that are somewhat arbitrary; such as the cocking handle shape.
In order to understand the dynamics of this brilliant mechanism, I thought I would "quickly" model it in Solidworks. About two days into it, and this is what I have - below.
For clarity, parts that would clutter the design were left out. In fact, I simplified (?) the design, and eliminated the need for two of the parts - explained further down.
Another EDIT: The "guide" parts I left out of the design, do help to stabilize the compression tube, where it is cut into a "U" all the way to the front. The barrel band clamps the tube down onto the internal "guides", and so improves the system integrity. Thinking another way; the parts would not exist, if they had no value. However, they are not critical to enable our understanding of the linkage dynamics...
Baikal IZH MP-46M SSP pistol:
(https://www.pyramydair.com/images/zoomed/IZH-46M-Match-Pistol_IZH46M_pistol_zm.jpg)
(https://www.pyramydair.com/images/zoomed/IZH46M_6_zm.jpg)
-
Opening the charging handle to draw in a full charge of air.
Note that the pump handle makes contact at its outer surface against the forward intermediate connecting rod (not the one hinged at the piston). In this phase of operation, the friction reducing rollers are idle and are not in contact with the rear side of the pump handle.
In my model, both the opening and closing surfaces of the pump handle are in contact when the full opening stroke is reached. The actual piston has two extra parts that the hinge pins pass through that regulate the full open handle position. These parts also determine the degree of over-center of the piston connecting rod.
I have taken licence by simplifying the design; and "throwing out" the two extra parts: There is a U-notch in the forward intermediate link that acts as a positive stop to determine the connecting rod over-center resting state.
-
Closing the pump handle to pressurize the valve.
Image number 12 in the previous post is the actual starting point for the charging (closing) stroke. It is also the end of the opening stroke. The actual pistol has a little travel between these states. It also has a vent hole in the top of the cylinder that determines the 100 mm effective stroke length...
Note that the contact has shifted to the friction reducing rollers at the hinge point of the intermediate slider linkage...
Also, not that the piston connecting rod goes over center by one degree, or about 2 mm at the anti-friction roller surfaces.
-
Actual forward intermediate connecting rod, showing friction reducing rollers.
Note piston dangling off to lower left, via actual connecting rod. Two connecting rods are hinged together with a rivet; that also captures anti-friction rollers.
-
If I understand correctly how this works.... a simple scissors pumping mechanism like a Crosman 13XX would have the forward-most link rod extended past where the rear link lever connects to it as the pump arm.... This mechanism uses a changing leverage system, via the roller, to increase the mechanical advantage during the latter stages of the stroke....
Bob
-
Yes, Bob; the key is more variable leverage than a simple toggle provides.
The slider drastically speeds up the piston travel early in the stroke while air pressure is low, while then also providing the leverage to make the last part of the stroke easy. Also, does not slam shut at full stroke, as the force does not drop off a cliff, as with Crosman et al linkages.
I will grab some specific dimensions later (probably tomorrow), but the Baikal's sliding lever changes the length of the short end of the lever by more than 3:1; over and above the sine wave motion typical of toggles. Of course, what counts is the length of the long side, over the length of the short side; and the angles and effective force components acting at any given instant.
-
Mathematical analysis of the measurement data presented by the images further down, led to this conclusion:
The Baikal MP-46M's pumping sliding follower generates force multiplication geometry, that very nearly follows the inverse of the air pressure build-up, that would occur when its 49 CC air is compressed into (an assumed) 0.5 CC residual volume.
In a word, it is brilliant!
Compare the curve shapes of the charts on the left with those on the right:
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=153475.0;attach=256855;image)
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=153475.0;attach=256859;image)
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=153475.0;attach=256825;image)
-
Someone was thinking clearly the day that was designed. nice.
-
Love all the diagrams. :-* Don't have any idea what they mean, but sure looks pretty. :-[ :-[ :-[ :-[ :-[ :-[
-Y
-
Beautiful diagrams. Really helps to visualize what is happening during operation of the pistol Had mine out last night at indoor silhouette - great pistols!
-
Subscrber,
Now that I've got new breech seals installed, the pistol seems to work well. However, when I extend the cocking lever, to almost full extension, I hear a noise that I can only describe as a "pfffft-zew." Is this normal? Or perhaps does it have additional problems?
-
Just a thought here. ;)
Maybe something to do with exposing the vent hole?
Mine doesn't make that sound.
-
John,
That is just the excess air spilling out of the vent hole, after the valve is closed. The valve is closed by going to "full cock" with the cocking lever. The purpose of this small air purge is to ensure that each charging stroke catches the same volume of air.
My pistol's vent hole is hidden on top of the compression cylinder, under the flat bar that actuates the valve. Earlier pistols had the vent hole underneath the cylinder; just ahead of the cocking linkage slot.
The vent hole's trailing edge is 100 mm from the rear end of the compression cylinder. That is what sets the effective stroke length; rather than the total distance the piston can move. Put another way: air compression starts as soon as the piston seal lip closes off the vent hole; while moving towards the breech end.
Depending on the speed with which I move my pistol's cocking lever back and forth, the wheezing sounds can be quite varied and quite loud. Now that I know what the sounds mean, I hardly notice them anymore. The sounds are different with the valve open, or closed.
-
John - Do you have the 46 or the 46M?
EDIT - Nevermind, I just re-read your other topic. In there you say you have the 46M.
-
So, I went to play with my 46M to see and hear, rather than just remember:
There is a buzzing noise right at the end of the cocking stroke, if I relax and re-extend the cocking lever, after completing the full forward stroke.
Probably air whistling in and out of the vent hole...
-
OK. So John quizzed me last night about this noise. I played with mine then to see if I could hear the sound he speaks of. At that time I was taking the cocking lever through it's full stroke and not hearing anything but the clicking of the breech release and the breech itself locking in it's fully up position.
Just now though, I manually freed the breech block and locked it up as though I were going to dry fire it. Leaving it in that upward locked position, I then moved the cocking handle to charge the chamber. Without all that mechanical noise, the pffft-zew noise is there.
All perfectly normal as far as I can tell. I just had never heard it before as that last method is not the way I charge my gun before shooting.
EDIT - I just repeated my test on my MP532 (same mechanism) and the noise is there as well. Really sounds like the piston is pulling air on the backstroke and that air is then being released through the vent hole, or more likely, the piston moving backward is creating a vacuum in the tube and air is rushing in through the vent hole once the piston seal has gone past it (forward).
-
Thank you gentlemen! One less thing to worry about. Now to see how to lightly lube it. And where.
-
John, now that you have new seals in it, be sure to store it with the breech block unlocked so as not to have them always compressed. Also put a very light smear of oil over them.
D.
-
John, now that you have new seals in it, be sure to store it with the breech block unlocked so as not to have them always compressed. Also put a very light smear of oil over them.
D.
Exactly. I had read that in another thread. Sound advice, thanks.
-
So, I have stretched this pistol design into a rifle concept, and modified it so that the barrel is the cocking lever, here: https://www.gatewaytoairguns.org/GTA/index.php?topic=153749.msg155692324#msg155692324 (https://www.gatewaytoairguns.org/GTA/index.php?topic=153749.msg155692324#msg155692324)