v2 semi locking

[CoWpLaGuEd]

Hello to everyone on the airsoft-forums ... forums ? ..

I'm troubleshooting an issue with my son's DMR. It's a budget build based on a new Cyma with a V2 gearbox (yes I know it's crap).
Now I'm aware of the locking issue with V2 gearboxes and over/under cycling, and ultimately this looks like it's caused by not fully pulling the trigger between shots. But it may be easier to come up with a technical fix than stop an adrenaline filled kid from smashing the trigger as quick as he can.

The gearbox is running a high torque motor and 16:1 gears, it's on a 3s LiPo via a 3034 mosfet. Modified selector plate to prevent full auto.

My assumption is that despite the lipo and high torque motor the 16:1 gears are not quick enough to help reduce the likelihood of the gearbox locking and with a M140 spring I'd be concerned about running it too fast without changing the gearbox housing to something a bit stronger.

So I've currently resigned myself to look for a solution to easily unlock it rather than prevent the lock happening.

I appear to have three options (or two and I've made one up that might not work)

1) make it more accessible to access the tip of the cutoff lever so it can be manually pushed into full auto.

2) allow access to the anti-reverse latch to allow it to spin back (don't like the sound of that one...)

3) (and this is the one I'm unsure of as I've not seen it suggested) add a small button to the mosfet to bypass the trigger and force it to cycle.

open to options if anyone has any words of wisdom. I've been thinking of weird  options like adding a small cap to the Mosfet (like you would to eliminate microswitch bounce) to make it fully cycle even if you did a short press.. but then that's just as likely to keep cycling after a full press and cause the same issues.

The key thing here really is keeping within his budget of about £0 ... so a £15 set of 13:1 gears might be ok but a £100 fancy mosfet is not.

 

[Adolf Hamster]

i take it the mosfet addition is something you've wired up yourself?

a common cause of semi lockups can be when a mosfet is applying an active brake effect to a build that doesn't need it, stopping the system too quickly before the cutoff lever has been properly disengaged.

However my electrical knowledge is limited to the simplicity of plain dc wiring and getting an off-the shelf product to do the magical silicone based shenanigans, so i can't say if your setup is doing that or not.

 

[concretesnail]

I'd suggest trying to steer clear of any easy to function full auto simply as a lot of sites have issue with dmr use if ts fairly simple to get it to cycle full auto.

I would suggest an electrical fix though, partly as it'll also prevent the human element of trigger spam.

Perun ab++ has dmr modes and fire rate limiters which enforce cycle times regardless of how fast poke the trigger.

Admittedly it's not a zero cost part but neither is it a £100, I think they are £40ish.

A good friend of mine has just fitted an ab++ into a picky rif and the performance and reliability change was astounding.

 

[CoWpLaGuEd]

Hi, yea it's a basic irlb3034 diy setup relying on the internal diode. So shouldn't be doing any active breaking, just stops the contacts arcing. I run them in my other guns.

I'd suggest trying to steer clear of any easy to function full auto simply as a lot of sites have issue with dmr use if ts fairly simple to get it to cycle full auto.

I would suggest an electrical fix though, partly as it'll also prevent the human element of trigger spam.

Perun ab++ has dmr modes and fire rate limiters which enforce cycle times regardless of how fast poke the trigger.

Admittedly it's not a zero cost part but neither is it a £100, I think they are £40ish.

A good friend of mine has just fitted an ab++ into a picky rif and the performance and reliability change was astounding.

Hmm yea seem to be about £45, I'll do some reading up, most of the other suggestions i'd seen were +£100. Thanks. Maybe if he does well in his exams ?

 

[Rogerborg]

a new Cyma with a V2 gearbox (yes I know it's crap)

Eh, airsoft, first world problems from third world pot metal.  Presumably you've radiused it?

stop an adrenaline filled kid from smashing the trigger as quick as he can

As a DMR owner, something that locks my box is other DMR owners whanging rounds downrange like No-full-auto-in-building-bro.  If he can't complete a trigger pull, how's he going to stick to one-in-the-air, a 2-second count, or whatever the local rule is?

add a small button to the mosfet to bypass the trigger and force it to cycle

Hmm, now that's an interesting suggestion.  Yes, I like that, especially if you're already building your own diodes.  As long as he's got the self control to not just mash the button until the magic smoke gets out, if the motor has properly stalled out and can't pull the spring.

 

[CoWpLaGuEd]

Presumably you've radiused it?

...or whatever the local rule is?

....as long as he's got the self control to not just mash the button until the magic smoke gets out, if the motor has properly stalled out and can't pull the spring.

I've not radiused it... I should have, but getting the shell back together with the spring I had was such a nightmare that that the plan is to swap to a better shell at a later date.

Local rules are a bit lapse, it would be good if they had a rule like that, I've been hit a few times by people with DMRs that they seem to be able to fire about as quick as full auto on semi.

If the button was on the MOSFET unit then you'd have to open the stock to get to it, so it's not like you could use it in game, and with a high torque motor and fairly gentle 16:1 gears it shouldn't struggle. I might give this a go as a trigger control training device. If that fails then maybe I'll buy a fancy MOSFET.

 

[Rogerborg]

Local rules are a bit lapse, it would be good if they had a rule like that, I've been hit a few times by people with DMRs that they seem to be able to fire about as quick as full auto on semi.

You're really playing at a site where they're fine with semi-auto trigger spamming anything up to 1.X Joules (1.1.3 < X < 2.5)?

Joking aside, that's not a site I'd be keen to play at. If they can't see the problem with that, I shudder to think what else they turn a blind eye to.

If the button was on the MOSFET unit then you'd have to open the stock to get to it, so it's not like you could use it in game, and with a high torque motor and fairly gentle 16:1 gears it shouldn't struggle. I might give this a go as a trigger control training device. If that fails then maybe I'll buy a fancy MOSFET.

Yup, that does sound like a pretty good solution.  I'm tempted to bodge up something similar myself.

 

[CoWpLaGuEd]

Ok, I think this will work. I've made a double switch from a miniature toggle switch and a microswitch. So you have to throw the toggle before you can press the switch. This should prevent any accidental firing (I will also fit a shield over the microswitch). I make all my MOSFETs modular so you can swap them out if there are any issues.

It works as expected, flick the switch, press the button and it cycles. I'll have to wait for it to lock again to fully test it, but this sure beats having to take the top reciever off any try and poke the cutoff lever with a screwdriver....

View attachment 84247

 

[Rogerborg]

View attachment 84247

That's a great job.  I was thinking more a couple of bare wires loosely wrapped in electrical tape.