CYMA P90 full upgrade - Finished... For now...

[Asomodai]

Maybe it’s a quirk of a P90 box??‍

Well, come Christmas day I may have some time to install the new motor and see what happens. Going to change the connections to deans so I can use my lipo's as well. 

If it still doesn't work then I am going to have to go the whole hog and short stroke it. I really didn't want to have to do it, but considering how many new things I have had to do and learn in the past few days, this cant be much more of a stretch (he says)

 

[Prisce]

Short stroking is one thing that hasn’t appealed to me yet, it’s on the list of projects. 

DSG’d, try to get that magical 70RPS figure, short-stroke, Swiss cheesed piston, in an M4 pistol. 

Trouble is, I doubt I’d ever use it. I don’t use full auto at all, just want to build it to say I have.

 

[Iceni]

The air-nozzle finishing up in random places is nothing to do with a badly built box.

It's a combination of 2 things.

Mosfet without active braking, And a gearbox running a ROF that is closing in on the 2 shots on semi value.

Most ETU systems are also AB mosfet systems. It's nothing to do with been a microswitch, it's all about that active braking circuit that stops the over-spin. AB without an AR latch allows the box to roll backwards to settle as well. So the gearbox will always settle in the most neutral position.

I have a gearbox that will break the 2 shots on semi with a fully charged 7.4v lipo. I haven't bothered to correct it as after a few bursts it settles. If it didn't settle I'd switch to an AB mosfet. The air nozzle can end up anywhere in the cycle and it does 3 shots when out of a gun without a BB load!!!

It's caused because of the energy in the motor and gears. Heavy gears take longer to spin up, but also retain more energy and take longer to come to rest. More piston weight will actually help stop it, As the weight puts load onto the spinning gears with the spring. Reducing gear weight is a double edged sword. You get faster spin up time, and faster arrest time, but the whole system is less efficient on auto putting more drain on the battery.

The advantage of running close to the 2 shots on semi value is the gearbox acts more and more like a pre-cock system the closer you are to the 2nd shot. The over-spin in effect has partially drawn the piston and spring and has a much shorter distance to move. It's another reason my gearbox that breaks the 2 shot semi has been left untouched, because once you are into the flat discharge part of the battery the gun has instant trigger response, Then pre-cocks, Rather than cycling into a shot.

The disadvantage of this is I have to release the spring after a days play, to ensure it's sat at the correct position for storage. Otherwise my springs loose power at an alarming rate. I do this by shooting an 8.4v nimh that is close to discharged to just roll the gearbox over.


It's the same reason they lighten flywheels in racing cars. A lighter flywheel lets the engine gain and loose RPM much faster. So you have less time between gear changes and have more available power band per gear change. The disadvantage is fuel economy and it's easier to stall, as you have less potential energy saved as inertia on the flywheel.

 

[Asomodai]

The air-nozzle finishing up in random places is nothing to do with a badly built box.

It's a combination of 2 things.

Mosfet without active braking, And a gearbox running a ROF that is closing in on the 2 shots on semi value.

Most ETU systems are also AB mosfet systems. It's nothing to do with been a microswitch, it's all about that active braking circuit that stops the over-spin. AB without an AR latch allows the box to roll backwards to settle as well. So the gearbox will always settle in the most neutral position.

I have a gearbox that will break the 2 shots on semi with a fully charged 7.4v lipo. I haven't bothered to correct it as after a few bursts it settles. If it didn't settle I'd switch to an AB mosfet. The air nozzle can end up anywhere in the cycle and it does 3 shots when out of a gun without a BB load!!!

It's caused because of the energy in the motor and gears. Heavy gears take longer to spin up, but also retain more energy and take longer to come to rest. More piston weight will actually help stop it, As the weight puts load onto the spinning gears with the spring. Reducing gear weight is a double edged sword. You get faster spin up time, and faster arrest time, but the whole system is less efficient on auto putting more drain on the battery.

The advantage of running close to the 2 shots on semi value is the gearbox acts more and more like a pre-cock system the closer you are to the 2nd shot. The over-spin in effect has partially drawn the piston and spring and has a much shorter distance to move. It's another reason my gearbox that breaks the 2 shot semi has been left untouched, because once you are into the flat discharge part of the battery the gun has instant trigger response, Then pre-cocks, Rather than cycling into a shot.

The disadvantage of this is I have to release the spring after a days play, to ensure it's sat at the correct position for storage. Otherwise my springs loose power at an alarming rate. I do this by shooting an 8.4v nimh that is close to discharged to just roll the gearbox over.


It's the same reason they lighten flywheels in racing cars. A lighter flywheel lets the engine gain and loose RPM much faster. So you have less time between gear changes and have more available power band per gear change. The disadvantage is fuel economy and it's easier to stall, as you have less potential energy saved as inertia on the flywheel.

Thanks for posting! It actually puts me in mind of my F2000 which would always double fire on a fully charged 7.4v lipo. But would get better as the day goes on. Luckily the p90 isn't quite so close to the edge.

Does it matter if the piston ends up in a random place or is it a characteristic of the air nozzle in a random place?

My mosfets that I have spare are not active braking, but in my experience the gearbox likes to lock up on semi more with AB ones so I tend to stay away from them. 

I just installed the new neo high torque motor, on low charge it would cycle almost perfectly and the nozzle ends up mostly in the right place, once I fully charge it, it would act the same way as it did on the old motor. 

So I now need to make a decision, short stroke it and put an 120 inside and that might fix the issue, or leave it as it is. Unsure which way to go at the moment. It could potentially be a real BB hose if I wanted to on 11.1v. 

Cheers!

 

[Iceni]

Does it matter if the piston ends up in a random place or is it a characteristic of the air nozzle in a random place?

Only matters for storage. Most gearboxes without AB finish with some pre-cock. For storage you always want the most neutral position to preserve the spring.

As for the motor and RPS. I like to have at least 1 reliable gun. And by that I mean a gun that isn't pushing any boundaries. Slightly underpowered 330 fps, And low RPS 15 ish.

It gives me the best fall back and loaner gun. On a loan out it's not going to cost me significantly on ammo (I always supply it if loaning), And it's not going to break itself. 

If the gun settles in a position you are happy with and the ROF is playable then pushing for more isn't a priority, Especially if you already own a couple of high ROF guns. The lower fire rate for me at least gives me something else to work with in game, I tend to use semi more and play for kills rather than suppression.

 

 

[Skara]

I switched back to 7.4s on my 2 main guns for two reasons:

Less ammo consumption, meaning I don't dump a lonex 360bb mag in 4 seconds, keeping me in the fight for much longer than with 11.1 fastbois. Useful for tournaments, I don't have to worry about reloading mags mid game;

Less stress on the gearbox, they're both below 328 fps as per our law, but they're reliable, meaning I can hold the trigger knowing I won't fire my piston and spring along the bbs..

ARP on the other hand needs to run on 11.1s -.- until I swap the etu for a titan -.-

Oh, btw, a gun that always stops in the same place will sound nicer

 

[Asomodai]

Only matters for storage. Most gearboxes without AB finish with some pre-cock. For storage you always want the most neutral position to preserve the spring.

As for the motor and RPS. I like to have at least 1 reliable gun. And by that I mean a gun that isn't pushing any boundaries. Slightly underpowered 330 fps, And low RPS 15 ish.

It gives me the best fall back and loaner gun. On a loan out it's not going to cost me significantly on ammo (I always supply it if loaning), And it's not going to break itself. 

If the gun settles in a position you are happy with and the ROF is playable then pushing for more isn't a priority, Especially if you already own a couple of high ROF guns. The lower fire rate for me at least gives me something else to work with in game, I tend to use semi more and play for kills rather than suppression.

 

I am unsure how I can make the sure that it would be in a mostly neutral position unless I take apart the gun everytime I use it. The Air Nozzle finishes in a random position to the piston. So even if the nozzle is all the way forward it is actually a little more likely that the piston is all the way back. I do own some high ROF guns already. 

I switched back to 7.4s on my 2 main guns for two reasons:

Less ammo consumption, meaning I don't dump a lonex 360bb mag in 4 seconds, keeping me in the fight for much longer than with 11.1 fastbois. Useful for tournaments, I don't have to worry about reloading mags mid game;

Less stress on the gearbox, they're both below 328 fps as per our law, but they're reliable, meaning I can hold the trigger knowing I won't fire my piston and spring along the bbs..

ARP on the other hand needs to run on 11.1s -.- until I swap the etu for a titan -.-

Oh, btw, a gun that always stops in the same place will sound nicer

I am with you on this. I do worry that my midcaps wouldn't feed going so fast on 11.1v as well. But I would like the piston and nozzle in the right place... I am undecided. 

However in the meantime I have tackled the other big part of the build, electrics!

I had some fun with this. I only had a diagram for the P90 that would take into account if I had a single trigger contact on the mosfet. However mine had two contacts. I initially set it up for the positive motor wire to go to the full auto trigger loom and the trigger contact on the mosfet as well as the motor output on the mosfet to the same auto trigger contact loom. When connected up it just went straight into full auto. Went back to the drawing board and realised I just had to feed the trigger contact loom to the trigger contact part of the mosfet and the motor and battery straight from the mosfet. Easy when you think about it, but things were getting complicated because of the oddness of the V6 gearbox. 

It was really difficult to wire up the dual stage trigger with 16AWG wire as it was so thick, but just about managed it, I couldn't connect the trigger loom to the trigger contacts on the mosfet as the mosfet solder patch was far too small for 16AWG. I could have just gotten away with the original wiring as its just triggers but we live and learn!

I did overstretch the return trigger spring by accident... It doesn't seem to affect much, but I might want to source another if I can. 

I forgot to buy some wire crimps so I had to bite the bullet and solder directly to the motor which was pretty difficult because of the magnetism and the small area of contact. 

Here it is with a 30C 7.4V lipo in storage mode. This is also with the new SLD Neo motor. 

I did try a 11.1v and it broke straight through the double fire barrier on single shot. Ridiculous ROF! 

I also installed the Laylax extended Mag catch. Was it worth the money? Probably not, but will be damn useful for mag changes with gloves on! 

View attachment 41008

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I have three  choices.

Leave it as is and finish up the project.

Open it back up put in the M120 and short stroke it by a couple of teeth and use 7.4V and take the ROF hit from what it currently achieves.

Or go with 11.1 and hope for the best. Thoughts?

I do need to re-chrono it since putting in the new M100, I have a feeling it might be slightly too hot as it is. 

View attachment 41006

Whilst I was at it, I extended my ARX160 wires and installed a Deans connector. 

View attachment 41007

 

[Asomodai]

Hard to see but because of the screws on the SLD motor, I was not able adjust motor height low enough. Had to get the dremel out and eat away at the gearbox. Gearbox sounds much better now!

View attachment 41011

 

[Asomodai]

Just tried what I thought was a heavier M120 spring but still getting the piston and air nozzle in random places. Either the Spring is only an M100 or/and I really need an AB mosfet or/and something else is wrong. Will chrono tomorrow to check the FPS. The spring is much shorter then the others I have, though feels a little stiffer. 

 

[Asomodai]

I have just tried it with an M120 spring, FPS is 404 FPS. Unfortunately the piston and nozzle still end up in random places. Could there be an underlying issue here? Would short stroking it help?

Or do I need to settle on an AB Mosfet instead?

 

[Asomodai]

I put it all together again with the hot M100 spring and got around 370FPS, then with the M90 got just over 330FPS with a variance of around 4 FPS, hopefully this should settle down. If I replace the TM AUG HC barrel with a tightbore this will probably come up to 350 should I choose to. I am really impressed with the compression of the guarder parts as regardless of what spring I put into it, the resultant FPS was always at the top range of what the spring should be able to do. 

I am just going to keep it as is! It seems to feed with no issues. Had a quick cheeky shot out back and the hop unit appears to be overactive at max setting so begs well for lower settings. I went quite a bit overbudget because of picking some wrong parts and deciding to get a better motor. 

RPS is a bit slower slower then my AUG high cycle. The Chrono says about 26 RPS, but it sounds much less to me, more like 19RPS. What do you guys think?

https://www.youtube.com/watch?v=bunSqAnbdaI

So here she is! Not much to look at externally. But its all going off inside! 

I have learnt a hell of a lot for my first true gearbox build. Nothing is ever so simple. The V6 gearbox is much simpler to open and close then on a V3 box. Reversal latch is easier to keep in place, the electrics and trigger being outside the gearbox makes it much easier to reassemble as well. There are a few things I would do slightly differently next time (16:1 gears, better tappet plate). But for now all is well! 

I haven't decided whether to do a full upgrade on my JG Mp5 yet. I may just hand it over to the experts as this has taken up a lot of time. I think the V2 box would be a bit of a challenge as well. 

View attachment 41034

 

[Iceni]

I think that huge delayer chip is what's throwing you off.

With a stock delayer chip the gearbox would probably look normal.

I'll edit up an image when I get chance to show you. But in essence the chip is throwing you off because you are are not accounting for the size of it. I'll give you a clue, the chip will pull back your tappet plate almost fully Before the sector engages the piston.

 

 

[Asomodai]

I think that huge delayer chip is what's throwing you off.

With a stock delayer chip the gearbox would probably look normal.

I'll edit up an image when I get chance to show you. But in essence the chip is throwing you off because you are are not accounting for the size of it. I'll give you a clue, the chip will pull back your tappet plate almost fully Before the sector engages the piston.

 

Sorry in what way? Is that what is causing the piston and tappet plate to end up at random points? I do have another more traditional plastic one. But seems almost as big. 

 

[Iceni]

It'll need an image to explain, so you'll have to wait, the missus want to go shopping! I promise I will get back to you with an explanation.

 

 

[jcheeseright]

My precision measuring tool tells me it's 26rps but my ear says 19rps, so I'll ignore the tool.  

 

[Asomodai]

It'll need an image to explain, so you'll have to wait, the missus want to go shopping! I promise I will get back to you with an explanation.

 

No problem. Its more because I have just assembled the whole thing and started putting away my workstation. If I need to put in a different delayer chip I need to stop what I am doing

Cheers for your advice so far though! I really appreciate it!

My precision measuring tool tells me it's 26rps but my ear says 19rps, so I'll ignore the tool.  

Not necessarily ignoring it, but what I am hearing is more like ~20RPS. But I get your point. 

 

[Iceni]

No problem. Its more because I have just assembled the whole thing and started putting away my workstation. If I need to put in a different delayer chip I need to stop what I am doing

No the chip is fine, It's just interacting for a longer period than normal. The length of the outer edge is what interacts. You are seeing the tappet plate and air nozzle been pulled back earlier and for longer over standard.

It boils down to the sector interaction with the piston, When that happens the tip of the chip is already going to be at 10 O'clock so the tappet plate will appear to be almost fully back. So there is no spot where the gearbox is totally neutral with that chip. For the sector to engage and stop the cycle you will already see tappet retraction every time.

 

[Asomodai]

No the chip is fine, It's just interacting for a longer period than normal. The length of the outer edge is what interacts. You are seeing the tappet plate and air nozzle been pulled back earlier and for longer over standard.

It boils down to the sector interaction with the piston, When that happens the tip of the chip is already going to be at 10 O'clock so the tappet plate will appear to be almost fully back. So there is no spot where the gearbox is totally neutral with that chip. For the sector to engage and stop the cycle you will already see tappet retraction every time.

I get you now! 

Agreed, no need to open it back up. I really appreciate your advice with this build. You sir are a fountain of knowledge! 

The project for now is complete. We'll see how she performs on a game day, still waiting on my P90 midcaps to arrive!

 

[Iceni]

Right I have for you an image!

There we have 3 stages of Chip and sector engagement.


Stage 1 on the upper shows the 0 position for the chip (no engagement on tappet plate). You can see the sector gear is not on the piston teeth.. So it is going to keep spinning to stage 2.

Stage 2 on the upper shows the point at which the sector gear has engaged the piston. There is now load on the sector gear that should slow and stop the gearbox. You can see the chip has pulled the tappet plate almost fully back.

Stage 3 on the upper shows the point at which the chip has reset the tappet plate to a 0 position ready to fire. You can see this is right at the very end of the sector gear teeth. So you have maximum delay, and perhaps a problem if you want to reduce teeth on the sector or piston.

 

Lower (standard).

Stage 1 0 engagement on the tappet plate happens much later, and the sector is much closer to the piston teeth.

Stage 2 Engagement between the piston and the sector gear. The tappet plate is only just starting to move at this point, And still has several degrees more to turn before full retraction is achieved.

Stage 3 the tappet plate is fully released. Note there are still several teeth left on the piston before it is released.
 

Stage 2 in all instances will have some roll back and settle action on semi. Depending on the number of teeth on the bevel gear and ARL this distance may be larger or smaller. In a stock gearbox with standard gears the rollback is normally sufficient to allow the gearbox to return to stage 1 (no load on piston sector or tappet plate). A bevel gear with more ARL notches will not allow as much distance to fall back, The gears will be arrested sooner, leaving some load on the tappet plate or piston/sector.
 

Do you see now why I called the chip huge. It's got a very long holdback time that could cause problems if you short stroke the piston. Regular delay chips are much shorter on the release stage.

 

[Asomodai]

Right I have for you an image!



There we have 3 stages of Chip and sector engagement.


Stage 1 on the upper shows the 0 position for the chip (no engagement on tappet plate). You can see the sector gear is not on the piston teeth.. So it is going to keep spinning to stage 2.

Stage 2 on the upper shows the point at which the sector gear has engaged the piston. There is now load on the sector gear that should slow and stop the gearbox. You can see the chip has pulled the tappet plate almost fully back.

Stage 3 on the upper shows the point at which the chip has reset the tappet plate to a 0 position ready to fire. You can see this is right at the very end of the sector gear teeth. So you have maximum delay, and perhaps a problem if you want to reduce teeth on the sector or piston.

 

Lower (standard).

Stage 1 0 engagement on the tappet plate happens much later, and the sector is much closer to the piston teeth.

Stage 2 Engagement between the piston and the sector gear. The tappet plate is only just starting to move at this point, And still has several degrees more to turn before full retraction is achieved.

Stage 3 the tappet plate is fully released. Note there are still several teeth left on the piston before it is released.
 

Stage 2 in all instances will have some roll back and settle action on semi. Depending on the number of teeth on the bevel gear and ARL this distance may be larger or smaller. In a stock gearbox with standard gears the rollback is normally sufficient to allow the gearbox to return to stage 1 (no load on piston sector or tappet plate). A bevel gear with more ARL notches will not allow as much distance to fall back, The gears will be arrested sooner, leaving some load on the tappet plate or piston/sector.
 

Do you see now why I called the chip huge. It's got a very long holdback time that could cause problems if you short stroke the piston. Regular delay chips are much shorter on the release stage.

Very interesting explanation! 

So in its current state, the air nozzle does appear to fire as forward as it needs to, albeit in random positions, but if I short stroked, the Tappet wouldn't have enough time to push the Air nozzle fully forward before being pulled back again for the next round? Causing presumably less FPS and a compressed tappet spring? 

Thanks for this diagram mate! Very impressive.