Cyma Cm045 Highspeed Build Issues (Gate Nanohard)

[SSPKali]

Ok, I am a bit flummoxed. Having time on my hands I thought I would put some high speed gears and high torque motor into my AKS-74U and short stroke the piston to make it a snappy CQB gun.

 

Before I started tinkering all I had done to it was shim, replace the nasty blue air nozzle and hard wire in a Gate NanoHard MOSFET. It was putting out about 335fps +/-2fps and 18rps with an 11.1v stick battery.

 

Today the package from the great Peter at AK2M4 arrived so after lunch I stripped down the AK and started to fit the parts. The rack and sector gear were short stroked by 4 teeth (it has a very short barrel so no need for the volume) a Rocket M115 spring and the SHS High Torque motor fitted.

 

Now for the weird stuff, initially it was putting out about 280fps....but after 10 shots this started to drop and ended up around 110fps! I opened the gearbox again and added 8mm spacer to the back of the spring as a stop gap measure to see how it effected the fps. Now it will only occasionally fire, the MOSFET is bitching about "too much current" When I pull the trigger the green led on the MOSFET comes on and then fades out again, no movement from the motor. I guess it is sensing the trigger contacts but then cutting the power once the Amps get above a certain level (and before the motor turns over at all!)

 

Any ideas before I fit a new piston rack and re-fit all the old parts?!

[Adolf Hamster]

Make sure its not something like the piston jamming (either clamped in the case or smacking the spacer) and that everything is able to spin freely.

 

Otherwise, if you dont have ab enabled, it could have overrun and applied some precocking which is too much startup load for the motor?

 

Also this is a good lesson on why fuses or a mosfet with a cutoff are a good idea- better you find out this way than find out when something starts sizzling.

[SSPKali]

Just changed it back to 16:1 gears, std motor and M100 spring....still doing the same. Even with the motor cage off the GB when I pull the trigger the motor might click once but that is it...wondering if the MOSFET is borked?!

[Adolf Hamster]

hmm, if it's doing it with no load on the motor (assuming the motor spins freely) then it's either busted wiring causing a short, or the mosfet is dead.

[Skara]

Have you tried resetting it? There's a little plunger in the box that is used to reset the mosfet

[SSPKali]

So, an update: The "error flashes" were actually "11.1v battery" - totally user error. There were no lights in error mode, but I pressed and held the button to reset it anyway.

 

This seemed to let it cycle a couple of times then nothing. I checked the gear box for jammed tappets / pistons off the rails / random shims - nothing jammed and all moving really smoothly.

 

I rebuilt the gearbox without the cylinder / piston / spring or tappet just to check it span the gears on their own with zero resistance - exactly the same, couple of cycles then only a green LED when you pull the trigger.

 

I am going to fire off an email to Gate EU as this MOSFET is under a year old and not even skirmished yet.

 

Thanks for all the suggestions and lack of "obviously beyond help, sent it to me for a tenner" comments   

[Skara]

Are you using fully charged batteries?

[SSPKali]

10 minutes ago, Skara said:

Are you using fully charged batteries?

Yep, one of the first things I checked. Just had the shed wired for power and light so good excuse to test it  

[SSPKali]

Sooo that was a cursed build!

 

Gate MOSFET seems to be happy now, but the +ve "wire" on my 11.1v Li-Ion gave up because it was made from a thin piece of tin foil...and we all know what happens to that it you bend it 3 times  FPS were still all over the place and misfeeding every other shot. Then, for no reason, the piston jammed and the piston head gouged a chunk out of the cylinder....WHISKY TANGO FOXTROT?!!!

 

Luckily I popped an order into AK2M4 and had a new cylinder, piston head and 2x Cyma pistons waiting for me when I got home.

 

I rebuilt it all stock (including the dodgy blue air nozzle) and it ran fine at 330fps, consistent (+/-4fps) and no misfeeds using the old 7.4v LiPo from my M4.

 

I put in the SHS high torque motor and tested again. Quicker response and still feeding / good FPS.

 

I then swapped out the gears for SHS 16:1 short stroked 2 teeth, the other Cyma piston (again -2 teeth) and the o-ring nozzle. M115 spring gave me 345fps on average hopped for 0.28g

 

Super snappy in semi-auto, full auto is ok but I rarely use that. I think the feeding issue was due to the Strong Tappet Spring wasn't as strong as the stock one and 13:1 on 11.1v might have been taking the piss a bit 🤪

 

Safe to say I never want to take it apart again for at least 3 years (but if I do I will be damn quick at it!)

 

Edited March 23, 2021 by SSPKali