Academic discussion: Maximum Spring vs Motor TPA

[Pseudotectonic]

This is not meant to be a definitive graph but just a snapshot of my current understanding for peer review/critique, if anyone wants to share data that can prove or disprove otherwise that'd be great, cheers

 

 

 

 

[Adolf Hamster]

As a sterilised "one motor manufacturer, one spring manufacturer, one gun built by one good tech and tested with one brand/weight of bb's" chart it certainly has the expected form.

 

Of course there will be complications:

 

-A taller gear ratio will move the curve to the right, likewise a shorter gear ratio will move it to the left

-Short stroking (with the appropriate increase in spring strength) will shrink the pme zone

-a higher voltage battery will move the curve to the right, lower to the left

-a heavier piston setup will expand the pme zone

-any sub optimal build that adds friction will move the curve to the left

 

Heavier ammo is a curious one, intuitively it should expand the pme zone although by how much isnt something i could comment on, it could well be insignificant.

 

As for individual motors, well a strong neo motor in good order isn't going to be placed in the same spot as a knackered ferrite motor even if they have the same nominal tpa.

 

All that said, its still a useful illustrative tool for where the ballpark is.

[Sewdhull]

I'm not sure how a heavier BB affects gearbox speed or what the mechanism would be to make that happen. 

 

 

[Adolf Hamster]

2 hours ago, Sewdhull said:

I'm not sure how a heavier BB affects gearbox speed or what the mechanism would be to make that happen. 

 

It doesnt affect how fast the motor is spinning, but the back pressure would resist the piston more, slowing it down.

 

Same idea as a heavier piston, as your rof limit before you get pme is dictated by how long it takes the piston to be in the proper position to be picked up again.

 

But as i said i'm not sure just how significant that effect would be, it may well be negligible

[Lozart]

12 minutes ago, Adolf Hamster said:

But as i said i'm not sure just how significant that effect would be, it may well be negligible

 

Compared to all the other variables you mentioned and indeed airsoft tolerances, I'd say it would make three parts of fuck all difference. Technical term, that is.

[Leo Greer]

For some reason the photo graph won't load for me.

 

While I can't offer any specifics without looking at the graph, I can add some general knowledge:

 

PME is governed by all aspects of mechanical resistance, including those not often discussed. For example, a stickier lube/grease in your cylinder creates more friction between your piston o-ring and the cylinder, lowering the PME threshold. Heavier BBs will do this also, as they create more mechanical resistance. This is because a heavier a BB requires more energy to accelerate, hence why air volume ratios are very important. The more mechanical energy the BB requires to move forward, the more pressurized air builds up behind it before it breaks over the hop nub, the more resistance is applied to the piston's forward path.

 

The curve is actually quite steep--a build could have no PME on .20g but suffer mild PME using .25g and heavy PME with .30g-.32g. This is far more prevalent in DSGs, where the cycle is shorter, the timing is stricter, and the piston is moving faster (resistance increase on an exponential curve relative to velocity).

 

Hop packings also affect PME threshold. An off-spec hop packing can be slightly too tight, causing more resistance and lower the threshold. Off-spec BBs do the same thing.

 

You can raise the PME threshold by using a cylinder with a smaller effective volume (porting farther forwards). This allows the piston more time to gain momentum before experiencing air mechanical resistance, effectively increasing piston speed, which increases air pressure, increasing FPS in some cases and increasing efficiency/consistency.

 

A wider inner barrel and wider nozzle will also raise the PME threshold.

 

The same applies for the drivetrain side of things--a more efficient electrical setup with less resistance leads to a faster rate of fire which leads to a lower PME threshold for a certain setup, irrelevant to gear ratio, spring weight, etc. So, ironically, a better setup here leads to a lower PME threshold. This goes for how thick your grease is, how well the gears are shimmed (truly bad shimming where extra resistance is caused, not just noisy shimming), and other factors like gear meshing.

 

Contrary to popular belief, polishing your gearbox around the gears to reduce resistance does nothing. It's actually really silly, since the gears should never contact anything but themselves, the piston teeth, and the bushings/bearings.

 

 

Edited November 2, 2023 by Leo Greer

[Adolf Hamster]

37 minutes ago, Leo Greer said:

Contrary to popular belief, polishing your gearbox around the gears to reduce resistance does nothing. It's actually really silly, since the gears should never contact anything but themselves, the piston teeth, and the bushings/bearings.

 

Thats a thing people beleive?

 

Wait, its airsoft i shouldnt be surprised.....

[Pseudotectonic]

If the image doesn't load for any reason here is a direct link to imgur

 

https://i.imgur.com/gFEvWkO.png

 

On the subject of polishing, I wonder if anyone has gone so far as to polishing the gears and piston teeth with metal polish like autosol or something so it improves the meshing characteristics

[Leo Greer]

People used to do it a lot when finish quality was worse, but nowadays it's pretty irrelevant, as gear finishes are already smooth, and as they wear in they tend to polish themselves, especially on soft aftermarket gears like SHS. Harder gears like Siegetek and even really hard stock gears like Krytac don't do this as much.

 

1 hour ago, Adolf Hamster said:

 

Thats a thing people beleive?

 

Wait, its airsoft i shouldnt be surprised.....

 

Yeah.... yeah.... In a lot of ways, American airsofters are even dumber than the variants y'all have over there.

 

34 minutes ago, Pseudotectonic said:

If the image doesn't load for any reason here is a direct link to imgur

 

https://i.imgur.com/gFEvWkO.png

 

 

Unfortunately my computer won't open the Imgur link either... It's probably my content blockers disliking both for various reasons.

Edited November 1, 2023 by Leo Greer

[Sewdhull]

These types of motors tend to be less efficient with more windings, electrically speaking.

Low tpa motors need more current to produce the same power and will have more losses and get hotter.

Lower currents are better if you can match a motor with gearing to get what you are after.

 

 

 

[Lozart]

21 hours ago, Adolf Hamster said:

 

Thats a thing people beleive?

 

Wait, its airsoft i shouldnt be surprised.....

 

 

We live in a world where people think that polishing the pins on the mains plug of their HiFi makes it sound better.

 

Nothing surprises me any more.

[Cannonfodder]

21 hours ago, Adolf Hamster said:

 

Thats a thing people beleive?

Considering there's people who believe vaccines cause autism and the earth is flat then I'm not surprised. In short, people are dumb

[Colin Allen]

1 hour ago, Cannonfodder said:

Considering there's people who believe vaccines cause autism and the earth is flat then I'm not surprised. In short, people are dumb

People are idiots!  Surely everyone knows that the earth is a tetrahedron.

[Adolf Hamster]

1 hour ago, Lozart said:

We live in a world where people think that polishing the pins on the mains plug of their HiFi makes it sound better.

 

1 hour ago, Cannonfodder said:

Considering there's people who believe vaccines cause autism and the earth is flat.

 

And depressingly it seems easy access to verifiable information was not the cure 

 

[Lozart]

10 minutes ago, Adolf Hamster said:

 

 

And depressingly it seems easy access to verifiable information was not the cure 

 

 

 

You can't fix stupid.

[Cannonfodder]

16 minutes ago, Lozart said:

 

You can't fix stupid.

But you can muffle it with duct tape