Am I lacking the Juice?

[J4ck]

Fairly new at gun teching, decided to give it a shot on my Krytac LVOA S.

 

 

Currently running 13:1 gearset (The Prometheus wide use), full metal teeth piston, ASG U-22k (22tpa), with an M105 spring.

Battery wise - 1300mAH 25C 11.1v Lipos.

 

S/S two teeth of pickup, two teeth of piston. AOE corrected and well shimmed.

 

Getting a decent amount of over spin but not to the point of double feeding/misfeeds and decent compression.

 

Currently getting 22-24 RPS with around 1-1.05J output. 

 

In preparation for this build I was expecting nearer 30rps so just wondering where/why I fell short. My main guess is the output of my batteries just isn't enough, or too much resistance etc.

Was thinking of getting a slightly beefier battery and see, something with higher current. (40+ amps)

 

Is there any other flaws or problems that are obvious to you guys?...

Edited April 23, 2023 by J4ck

[LazzurusMan]

I'd say personally it's your motor. I use almost the same (not brands, but gear ratio etc) setup in my ares mutant, but I'm using an asg boost 30k, and hitting just short of 30rps.

Also, I know nothing about the Krytac LVOA S, does it have a mosfet fitted?

[J4ck]

37 minutes ago, LazzurusMan said:

Also, I know nothing about the Krytac LVOA S, does it have a mosfet fitted?

Yea it does, from what I've heard its a decent, but very basic mosfet + fuse.

 

It's just weird, on paper, it should be netting 31rps. Thanks 

 

 

[Skara]

Paper and reality are two different things.

 

I run a very similar setup in my King Arms PDW (ZCI 22tpa HT motor, SHS 13:1 short stroked by two and what appears to be a M100-ish spring) and I'm getting around 25 RPS on a 11.1v.

 

Regarding the battery, find out how many amps the motor needs and pick a battery that can provide them. Undersized batteries tend to commit sudoku quickly.

[Rogerborg]

47 minutes ago, Skara said:

Regarding the battery, find out how many amps the motor needs and pick a battery that can provide them.

 

Could be.  1.3Ah x 25C = 32.5A. That's 360W at 11.1V, or 240W at 7.4V.  I mean, motors do get toasty from waste heat, but I'd hope that at least 10% of that 360W (= 360 J/s) is making it out of the muzzle.

 

Worth a try though, more Ah and C is always better Ah and C.  I'm running 1.4Ah x 30C as fast as my mags can keep up.

 

 

 

47 minutes ago, Skara said:

Undersized batteries tend to commit sudoku quickly.

 

You just made up that wordle.

[J4ck]

7 hours ago, Skara said:

Regarding the battery, find out how many amps the motor needs and pick a battery that can provide them. Undersized batteries tend to commit sudoku quickly.

Searched online for specs on my motor but couldn't find a definitive answer, so I've got a multimeter coming tomorrow so I'll check resistance and work it out.

6 hours ago, Rogerborg said:

 

Could be.  1.3Ah x 25C = 32.5A. That's 360W at 11.1V, or 240W at 7.4V.  I mean, motors do get toasty from waste heat, but I'd hope that at least 10% of that 360W (= 360 J/s) is making it out of the muzzle.

Regarding the heat, motor stays very cool after firing it lots, if that helps ? 

 

Looking into a new battery in the mean time... Can a battery be *too* strong? Found these two and wasn't too sure if "A" was overkill.

 

A: 11.1V 2000 mAh 25/50C 

B: 11.1V 1450mAh 25C/50C

[Rogerborg]

48 minutes ago, J4ck said:

Can a battery be *too* strong?

 

Volts, yes. Some setups will be driven too hard with 11.1V - I tend to get double-shooting on semi without an active brake mosfet (other experiences are available).

 

Capacity and amps, no, go for it.  The battery will only supply what the motor is trying to draw. If it can't supply that much, then it'll heat up sharpish, and you really don't want that.

[ak2m4]

maybe also worth doing a sound rof check just to rule out any feed issues, helped me in the past.  always tricky issues.

[J4ck]

19 minutes ago, ak2m4 said:

maybe also worth doing a sound rof check just to rule out any feed issues, helped me in the past.  always tricky issues.

Yea that had crossed my mind too, sound check is showing as the same as IRL ROF.

 

Thanks though ❤️

[ak2m4]

as @Skara remarked, paper and reality can be very different due to all the little variables.  try a new battery, if you're hitting double-shots etc then maybe go up to a M110 spring.  chasing rof is a lot of fun 🙂

[J4ck]

Just checked resistance on my motor, its showing as 0.7-0.8 ohms. Meaning in theory it needs 12-16 amps...

 

My batteries should be outputting more than enough to supply the motor.

 

Unless this £10 multimeter from amazon is reading inaccurately....

 

  

7 hours ago, ak2m4 said:

as @Skara remarked, paper and reality can be very different due to all the little variables.  try a new battery, if you're hitting double-shots etc then maybe go up to a M110 spring.  chasing rof is a lot of fun 🙂

But yea I'm enjoying it to be honest, just a bit scary when I have no real base line for "good" or "bad"

 

Gets me questioning everything I've done, like my shimjob, still paranoid its awful!

 

Edited April 25, 2023 by J4ck

[LazzurusMan]

On 25/04/2023 at 17:58, J4ck said:

 

 

 But yea I'm enjoying it to be honest, just a bit scary when I have no real base line for "good" or "bad"

 

Gets me questioning everything I've done, like my shimjob, still paranoid its awful!

 

My ares mutant was stripped down and rebuilt from the ground up by myself and I know EXACTLY what you mean. Every time I pull the trigger I fully expect to shoot bits of the piston or gears at people.

[Speedbird_666]

14 minutes ago, LazzurusMan said:

Every time I pull the trigger I fully expect to shoot bits of the piston or gears at people.

 

Had similar feelings when I first rebuilt and shimmed a gun (circa  2006ish) - but once you've rebuilt a few guns from the ground up, you learn pretty quickly whether things will go bang or not.

 

Pretty much every gun I buy now gets disassembled into it's constituent parts and rebuilt - warranties be damned.

 

On 25/04/2023 at 17:58, J4ck said:

 

My batteries should be outputting more than enough to supply the motor.

 

Voltage sag is an issue with Airsoft batteries as they are amongst the lowest quality when it comes to hobby LiPO packs - internal resistance is pretty high on a new Airsoft pack, so much so that RC guys would bin them as 'end of life' for their RC Quads/Planes/Helis etc.

 

Don't believe the C or capacity ratings either. 

 

For example - I have 3-year old Turnigy 1300mah 25C Lipos intended for RC that completely outperform both Vapextech 1300mAh 25C Airsoft packs I bought last month - both in capacity and ultimately ROF. 

 

 

 

[Rogerborg]

4 hours ago, Speedbird_666 said:

internal resistance is pretty high on a new Airsoft pack, so much so that RC guys would bin them as 'end of life' for their RC Quads/Planes/Helis etc

 

Yup, one of the very few pieces of actually worthwhile content I've seen in a Failbook group is an RC guy measuring the internal resistance of a bunch of batteries sold for airsoft versus some sold for RC use - all of the airsoft packs had much higher resistance, even freshly unpacked.

 

It seems that they've found a ready market for QC fails and Friday Cells, because "they all do that, mate".

[Lozart]

7 minutes ago, Rogerborg said:

 

Yup, one of the very few pieces of actually worthwhile content I've seen in a Failbook group is an RC guy measuring the internal resistance of a bunch of batteries sold for airsoft versus some sold for RC use - all of the airsoft packs had much higher resistance, even freshly unpacked.

 

It seems that they've found a ready market for QC fails and Friday Cells, because "they all do that, mate".

 

AND they have the brass neck to charge MORE for them too! Cunts.

[J4ck]

Just threw a titan 2 into my gun yesterday, everything seems to be running okay to me....

 

The titan app is registering 40-45rps though.... Chrono and sound tests come up 25! Any Ideas why it might be so inaccurate?

 

Peak Current : 70A

Avg. Semi Current: 31A 

Avg. Full Current 13.8A

RMS Power Semi 800W

RMS Power Auto 337W

RMS Power Peak 1700W (?!?!)

 

Might have a look into measuring resistances as well...

[Rogerborg]

Is there a reason why you want more than 25rps?  I mean, it's fun to go brrrt, but it's of fairly limited practical use in airsoft (unless your intention is to make a viral video that impresses Sklyaar on Reddit, but makes everyone else shake their heads sadly).

[J4ck]

Nah not really any reason, just enjoying learning to tinker around with my gun, so thought it would be a good target to aim for.

 

I don't think I'll put anymore money in to the gun for now. I'm happy where its at. Was just worried I had really fucked up somewhere.

 

I *think* I've done a good enough job. Just hard to tell

Edited April 28, 2023 by J4ck

[Rogerborg]

1 hour ago, J4ck said:

just enjoying learning to tinker around with my gun

 

There is no more noble cause.  I'd call it a win and move on, airsoft is more of an art than a science.

[Leo Greer]

By the numbers, your RPS is correct.

 

24,000 / 60 / 13 (approximate ratio, not actual) = optimal cycle speed. That means the speed the motor should turn the gears if the gears weighed nothing and the spring had no resistance. Optimal speed is about 30 RPS.

 

However, the gears do weigh something and the spring does provide resistance. This means we have to factor in a final variable: efficiency. If you're getting 25 RPS, and assuming your motor is exactly 24K (most motors can be off by up to 1K, and some are far worse), that means that you're at 81% efficiency. This could be better in a gun as low powered as this, but it's fairly respectable, and indicates that you probably don't have any huge issues.

 

That being said, here are some caveats:

 

Motors can perform at "high efficiency" on paper but still be heating up overly fast due to bad shimming or whatnot. The motor can be strained but still put out full RPS.

 

Motors can be badly off-spec in terms of speed. For example, it's well documented that the ASG 30K Boost is actually 35K in practice, similar to the 16TPA 35K Tienly GT. This can lead to issues with inexperienced techs who have a faster-than-it-should-be motor on their hands.

[J4ck]

34 minutes ago, Leo Greer said:

By the numbers, your RPS is correct.

 

24,000 / 60 / 13 (approximate ratio, not actual) = optimal cycle speed. That means the speed the motor should turn the gears if the gears weighed nothing and the spring had no resistance. Optimal speed is about 30 RPS.

 

However, the gears do weigh something and the spring does provide resistance. This means we have to factor in a final variable: efficiency. If you're getting 25 RPS, and assuming your motor is exactly 24K (most motors can be off by up to 1K, and some are far worse), that means that you're at 81% efficiency. This could be better in a gun as low powered as this, but it's fairly respectable, and indicates that you probably don't have any huge issues.

 

That being said, here are some caveats:

 

Motors can perform at "high efficiency" on paper but still be heating up overly fast due to bad shimming or whatnot. The motor can be strained but still put out full RPS.

 

Motors can be badly off-spec in terms of speed. For example, it's well documented that the ASG 30K Boost is actually 35K in practice, similar to the 16TPA 35K Tienly GT. This can lead to issues with inexperienced techs who have a faster-than-it-should-be motor on their hands.

Appreciate the reply, gives me confidence.

 

Took it out over the weekend and performed really well, super happy with the build. and NOTHING broke!!