Reducing ROF - Big dillema here.
 

Well, ad many may know, I've had for years a big piston stripping problem on my M249, mainly due to the fact that I'm pushing the machine too hard for high-ROF.

My first config was HighSpeed Motor, Highspeed Gears and 12 volts battery, on stock spring, result, 5 stripped pistons.

After that, I switched to a high power spring (PDI150% IIRC), 4 stripped pistons.

After that I tamed down the battery to 9.6Volts, result, 3 stripped pistons.

After that, I totally rebuilt the gearbox with a Super Torque-Up motor (RPM slightly lower than HighSpeed), Hi-Speed gears, same PDI150% spring and a Prometheus piston which, I was told, was supposidely unstrippable. All that ran by a 9.6V battery. Result... yeah, you guessed it, a stripped Prometheus piston. But at least, the gun worked for a while before sending the piston to hell.

Now the big dillema, what do I do to to reduce the ROF to a sane level...

First step, stronger spring. Higher force required should slow down the mechanism along with increasing the piston return speed. Would that be enough...

If not, i guess the second step would be to switch to regular ratio gears, or to make the battery 8.4V, what would be the best bet, that I don't know, hence my question...

Any comments will be appreciated.

Low voltage battery sounds like the solution you need. Putting in a stronger spring will increase piston loading and accellerate piston death.

How many shots are you getting per piston?

Are they stripping in the same place? If the first teeth are dying first, I suspect there may be something wrong with the initial piston alignment. It may be starting a bit too far forward or rearwards so you get even heavier wear on the first few teeth.

Sounds like you are experiencing the very common piston stripping that happens to the CA M249 when you adjust for too much hop up. Rips the tail end of the piston off. Should use a 9.6V. If too high still, either lower mAh battery or 8.4V battery.

EDIT: You said for years, I assume this isn't the CA M249 is it? Top 249 maybe?

Yes, it is a TOP M249.

The first 12 pistons (all Guarder polycarb) were stripped running with the original mechbox with the ANGS piston conversion kit. All pistons had their first tooth ripped off the piston. The number of shots per piston would go from as little as Zero to 500.

The last one that was stripped (Prometheus) was part of a PGC V3MAX gearbox fitted with V2 internals. That piston had ALL it's plastic teeth grinded flat, except the first one. Number of shots would approach the 1300-1400

The actual battery is a 9.6V 3900mAh

keeping in mind, hispeed gears are designed for stock springs. its not recommended that you use hispeed gears with power upgrades.

Yeah, high speed gears sound like the first thing that should go in the setup.

A Flat or Torque Up gear set will lower your RoF (torque up isnt really necessary for these springs, but it'll work too). Spring can stay as is, as MadMax pointed out, stiffer springs wear stuff out faster. Maybe even go to a 8.4v pack and a 140% spring, and tightbore inner barrel.

I 2nd MadMax's recommendation for an 8.4v pack.

If you're too cheap to replace your 9.6V battery with a 8.4V, you can always add a section of cheap wiring to your electrical circuit.

Buy some crappy Tamiya connectors and cheap speaker wires and connect them in series to your existing wiring. The cheap connectors and wires will form a high resistance to slow your ROF.

If the ROF is still not slow enough, use the entire 8ft roll of shitty wiring!

Couldn't you just pop in a variable resistor?

It would be pretty cool, because then you could actually change your ROF.

Have to be a pretty high wattage pot in that case, like a wire wound one. For the amount of current drawn by the motor, it'll burn out most pots unless they are rated to handle that kind of power.

It WOULD be cool though!

Agreed. most pots are rated for 3 or 5Amperes

Ok, I've modded my 9.6V to 8.4V, I'll keep the spring-gears-motor setup the same, and a metal piston taken from a G&G M4 is on the way (BTW, I've never heard of these pistons, it's true that during my time off from airsoft, I've quite missed the G&P and G&G boat, so I know very little about them and what they're made of).

I can only hope this'll work more than 6 hours...
I'll keep you guys posted, to thank you for your great help.

Best regards,
PoFF

Take a look at the DeepFire full-rack TN pistons. Unlike the the Prometheus piston with half plastic/half metal teeth, the DeepFire has ALL metal teeth...even the first tooth.

http://img.redwolfairsoft.com/upload...mg/cpp06-l.jpg

Thanks for the heads up Skruface, I never seen those in WGC, maybe time to check redwolf more often.

As promised an update,

- Piston replaced by an aluminium piston taken from a G&P M4 gearbox, slightly heavier than its plastic counterpart. Hopefully it'll prove much tougher than it's plastic counterparts.
- Battery changed, now it's a 8.4V made from Sub-C GoldPeak 4300mAh Ni-MH, rated 30 amps cyclic, 60 amps peak.
- Everything else was left the way it was. STU Motor, HS Gears, 150% spring. But I rewired the gearbox with 12AWG wiring.

Result, the ROF is still fast as hell, slightly down from what it originaly was, but not really noticeable, maybe 3 or so rounds per second less. So far so good, I've been running extensive dryfiring and the piston still seems to be in good shape. Combat testing will be done this sunday.

*Crossing fingers*

well the HS gears won't help your situation if you want to reduce ROF. A high capacity battery can supply high current without much voltage drop so your motor will crank out the torque required to spin HS ratio gears.

ouch, HS gears and an aluminum piston....
considering the polycarbonate pistons are just as strong, if not stronger then the aluminum pistons, and considering the aluminum pistons are prone to problems...

high speed gears are not designed to be used in anything over a stock gun.

Standard ratio gears
8.4v
polycarb piston