Occasional double-shot on semi?

[SSPKali]

I have recently fitted some 13:1 Solink helical gears to my M733 build. Everything else stayed the same - warhead motor (mid speed one?) 7.4v via a Perun AB++ Totally flawless with the SHS 13:1 gears but a bit noisy, hence the helicals.

 

Now it has started double tapping every 20-40 shots. Tried turning off precocking, turning on “sniper delay” or using AB to no avail.

 

Stripped it down the check trigger trolly and cut off lever - apart from a little greasy gunk I dug out all working fine and shimming spot on.

 

Took one tooth off the pick up side to drop power a smidge (right on site limits with an M95!) and it is still doing it.

 

Any ideas?

[Galvatron]

It may be worth recalibrating your trigger.

[Colin Allen]

6 hours ago, Galvatron said:

It may be worth recalibrating your trigger.

The Perun AB++ uses a traditional trigger switch.

Edited 14 hours ago by Colin Allen

[agors]

it means everything is butter smooth in the gearbox, so well done lol.

 

up the spring and short stroke the sector to meet fps. what barrel and bb weight do you use? 

[Skara]

Does the sector gear properly activate the cut-off lever? Is there enough contact?

Edited 13 hours ago by Skara

[Rogerborg]

2 hours ago, agors said:

up the spring and short stroke the sector to meet fps. 

 

I'd be minded to agree, except that active braking isn't sorting it.  Is there anything sorcerous about brushless motors that might be in play there?

[agors]

I mean, brushless motors have loads of torque and the setup is not great to start with.

there's lots of torque and lots of inertia due to the low ratio Gearset. 

 

I really don't get why people use 7.4v with 13.1 gears.

just use 11.1 and 18:1 gears. same semi time and way less strain on the Gearset and motor (building torque with gears, NOT with motor!)

 

but again, if changing gears and battery is not a possibility then yeah the only solution is to short stroke and use a heavier spring.

 

at some point based on BBs used and barrel length the cylinder to barrel volume ratio will be affected so short stroking won't be the best solution

[Skara]

3 minutes ago, agors said:

at some point based on BBs used and barrel length the cylinder to barrel volume ratio will be affected so short stroking won't be the best solution

We're talking silly long barrels though, 400mm +

Your average 360mm-and-below barreled AEG can take some short stroking. My 7" SSG is short stroked by 4 teeth and I'm pretty sure I can knock five more off without worrying in the slightest about running into voluming issues.

[agors]

well yes because your barrel on a 7inch is only 20cm or so. definitely you're nowhere near that situation but that's a terrible comparison lol. 

 

if the OP has a 363mm+ barrel and using .32 or heavier bbs with -5 on sector then definitely it is to be considered. 

 

in any case case that is a corner case, without knowing OP setup it's difficult to help;

 

independently it is a terrible setup (7.4v+13.1+brushless) IMO. 

[SSPKali]

Thanks all, I am running a 300mm x 6.01mm barrel and 0.28g BBs. 

 

Cut off lever is working fine and being tripped by the sector gear.

 

I am starting to think I will sell the Warhead motor and fit an XT or SHS one as this is only a back up gun and spends more time being used as a test bench than actual use 😁

[Fatboy40]

3 hours ago, Rogerborg said:

 

I'd be minded to agree, except that active braking isn't sorting it.  Is there anything sorcerous about brushless motors that might be in play there?

 

They really don't like active braking, they can stutter etc., and pretty much handle stopping themselves using their own circuitry / speed controller.

 

As the Perun AB++ is an inline MOSFET, it's not an optical controller, it's not smart enough to monitor the cycle of the sector gear. I'd bet an "optical controller" would immediately resolve this, telling the motor to stop at exactly the right time to prevent overspin.

 

I'd try a slower / brushed motor first if one's available, and if all is then good consider your options.

[Zarrin]

I'll occasionally get these kind of issues in a build I throw together. There are two things I can usually do to get the system running smoothly.

- what I usually do to correct it is try different switch blocks (the part of the switch assembly with the single contact that pushes into the two leaf plate contacts) The little molded L shape groove that engages with the end of the cut off lever can come in quite different shapes and thickness from switch block to switch block. Finding one that works well with your setup can help - note that over time that molded piece can get worn down and squished resulting in slipping and sliding that could just cause the effect you are talking about of a double shot - after all it is a very abrupt mechanical / kinetic flick that occurs when the switch block is pushed out of the channel. 

- The other side of the same problem is the cut off lever - It's possible that your new sector gear does not bump the cut off lever quite as consistently as your old gears resulting in a slightly tamer (though usually efficient enough) tug on the switch block, resulting in that 'good enough' engagement but just bad enough to give you issues once every 20-40 shots.

@ak2m4 posted on FB not too long ago about some precisely machined switch blocks with a nice big square contact - as someone who still has old school switch assemblies in all but one of my AEGs, that's the kind of thing I would love to get my hands on 😅

I'm guessing if you put something like that in your M733 it might well sort you out.

Edited 4 hours ago by Zarrin

[agors]

2 hours ago, SSPKali said:

Thanks all, I am running a 300mm x 6.01mm barrel and 0.28g BBs. 

 

Cut off lever is working fine and being tripped by the sector gear.

 

I am starting to think I will sell the Warhead motor and fit an XT or SHS one as this is only a back up gun and spends more time being used as a test bench than actual use 😁

man don't do it. brushless are in every way superior to brushed. 

if anything remove those 13.1 and use 18.1 +11.1!

[Adolf Hamster]

that really does sound like the typical precocking tuning adjustment.

 

mosfets like the ab++/warfet run on timers, so essentially they wait for the cutoff lever to trip then add X milliseconds more runtime to the motor (which is what you set when you tune them).

 

if the delay is slightly too long, what can happen is the cycle settles in a different position each shot until that goldilocks position where it runs enough to fire twice. if your box has a window for viewing the piston you can test if this is happening by seeing how far back the piston stops each time, the behavior i'm describing it'll settle slightly further back with each shot until the double fire when it settles further forward and the process repeats.

 

having ab off with precocking can make things a bit more chaotic as motor overrun will happen naturally and can vary from just about everything you can think of (shimming tightness, motor, spring, piston tightness, hell even the grease viscousity or how warm the box is), indeed having too little overrun (typically active braking without precocking) is what give trigger lockups when the system stops too quickly. typically i'd advise ab and precocking together although if you're being conservative with how much precocking is going on it's probably ok to not have ab. you don't usually want ab without precocking unless it's a speediboi build that suffers double fires without it.

 

if you had the precocking really dialled in then i can absolutely see you going from perfection to just barely too long a delay just from a gear swap even if they're the same nominal ratio and shaving a tooth would absolutely do it.

 

sniper delay/dmr mode is just a rate of fire limiter, its only effect is to stop you firing a second shot if you spam faster than it's been told to allow, so shouldn't be affecting this.

 

that said, none of the above explains why it's happening with precocking turned off, but hopefully i've adequately explained why i'd want to be double/triple checking that it is definately off before testing for the behaviour. the other test is to change the amount of precocking, increasing it should make the doubles happen more frequently, reducing it should cure the issue.

[SSPKali]

1 hour ago, Adolf Hamster said:

that really does sound like the typical precocking tuning adjustment.

 

mosfets like the ab++/warfet run on timers, so essentially they wait for the cutoff lever to trip then add X milliseconds more runtime to the motor (which is what you set when you tune them).

 

if the delay is slightly too long, what can happen is the cycle settles in a different position each shot until that goldilocks position where it runs enough to fire twice. if your box has a window for viewing the piston you can test if this is happening by seeing how far back the piston stops each time, the behavior i'm describing it'll settle slightly further back with each shot until the double fire when it settles further forward and the process repeats.

 

having ab off with precocking can make things a bit more chaotic as motor overrun will happen naturally and can vary from just about everything you can think of (shimming tightness, motor, spring, piston tightness, hell even the grease viscousity or how warm the box is), indeed having too little overrun (typically active braking without precocking) is what give trigger lockups when the system stops too quickly. typically i'd advise ab and precocking together although if you're being conservative with how much precocking is going on it's probably ok to not have ab. you don't usually want ab without precocking unless it's a speediboi build that suffers double fires without it.

 

if you had the precocking really dialled in then i can absolutely see you going from perfection to just barely too long a delay just from a gear swap even if they're the same nominal ratio and shaving a tooth would absolutely do it.

 

sniper delay/dmr mode is just a rate of fire limiter, its only effect is to stop you firing a second shot if you spam faster than it's been told to allow, so shouldn't be affecting this.

 

that said, none of the above explains why it's happening with precocking turned off, but hopefully i've adequately explained why i'd want to be double/triple checking that it is definately off before testing for the behaviour. the other test is to change the amount of precocking, increasing it should make the doubles happen more frequently, reducing it should cure the issue.

Thanks for the extensive advice!

 

pre-cocking and AB are off and it rarely does it, turning on pre-cocking increases the occurrence. Not tried PC and AB together…I was under the impression that the AB++ couldn’t have both “on” at once (even if the LEDs said they were both enabled, only one was working?)

Having run it without the upper receiver on I can see the piston sitting further back each shot until at some points it double shoots. 

 

Just given it another test and it was good as gold! Bloody typical! Will still throw an old motor in just to see. Might try a new cut off lever and / or trigger contacts if that fails. It might be down to the cut off nub on the spur gear being a hair different and messing things up.

 

UPDATE: Just tried with PC on 1 / AB on 2 to 3. Still double tapping.

 

No PC and AB on 1 and no double tapping… but the occasional failure to cycle (sad whiring noise!)

 

Just fired 150 times with everything OFF and it didn’t skip a beat! I love transient issues! 
 

Thanks for all the suggestions, will keep in mind if it starts playing up again.

Edited 2 hours ago by SSPKali

[Adolf Hamster]

Hmm, looking at the ab++ manual you're right they do state ab settings are irrelevant whilst precocking is enabled.

 

Which would imply they're either using an amount, or having none and you just factor in the overrun when dialling it in (ie total precock=intentional overrun+natural overrun).

 

It getting worse with precocking enabled sounds like its naturally double spinning, in which case active brake would be the solution.

 

They mention they have different strengths, which would ordinarily lead to the suggestion that dialling it up would be the next step.

 

The big caveat is i dont know if the warhead would react in the normal way and just do its own thing.

 

Cutoff tweaks might help, the perun is flying blind all it knows is are the contacts open or closed, so if the col is mechanically engaging earlier/later that will change the timing. I remember the old ascu2 i had fun with the col not lifting enough to actually trigger the switch on the mosfet ended up going to the local brick and mortar and rummaging through their box of levers till i found one that worked.