Piston for High ROF
 

I just recently got a computerized MOSFET switch from Extreme-Fire and it drastically increased my rate of fire. After toying with it for 2 minutes my piston looked like this:
http://i864.photobucket.com/albums/a...h/DSC_0118.jpg
One feature of this MOSFET is that it allows the user to adjust the motor speed in either direction. In the future, I will definitely be turning it down a notch :D , but I was also hoping to gain some knowledge on full steel toothed pistons. Are they your best option for high ROF setups?

Your best option is to actually create a properly balanced setup. A proper setup can handle polycarbonate or nylon pistons just fine.

If you provide an exact part list of your setup (include battery type, motor, spring, gear set, etc) and we might be able to help diagnose your problem.

Further to that, you may consider short-stroking if you really wish to have insanity rate of fire!

I actually don't want a high ROF setup. By installing the MOSFET I was hoping to gain active motor braking and added trigger response. I knew the rate of fire would also be increased, just not to that extent. Before the MOSFET, the gun shot right around 18-20 RPS and like I was saying....the MOSFET can be programmed to adjust motor speed. So, hopefully I can dial it down to around 20 RPS.

As for the gun it is a G&P m4
Battery: 9.6v Elite 2000 4/5A cells
Motor: Stock, G&P m120
Gear set: Due to the known problem of the axles failing on G&P gears, I had to replace them with some "China" gears set.
Spring: Stock....was shooting between 350-370 FPS w/.2
Bushings: Stock, 8mm ball bearing
Everything is pretty much stock except for the swapped out gear set.

Thanks for the help!

Personally...I'd rather toast a piston if something was off than to mangle a gear set. i.e. sacrifice the poly/nylon piston if there's a crash

I'd double check your Angle Of Engagement (AOE).

Did you go for a normal, high torque or high speed gear set?

On your next setup...you might consider "dumbing" it down a bit with a 8.4v mini battery first, just to double check that everything is working right before you goose it with a higher voltage battery.

**edit**
Also...strongly consider completely removing the second tooth of the replacement piston (in your pic the second from the right). It won't affect the strength of the piston nor significantly affect the ability for the sector gear to pull the piston...and it will hedge your setup so that the first tooth of the sector clears the piston teeth to engage at the beginning of the pull stroke.

WOW that piston is COMPLETELY stripped, every tooth.
Don't think I've seen that before...

Yea, I had no idea how things were going to work out so I am not too upset that a JG piston lost it's life.

The gear set is "standard" ratio.

I am still learning my way around a gear box and as seen in my picture, the wear pattern on the piston teeth seems like the sector was catching the piston on the high side (towards the bottom of the picture). But to keep adequate spacing between the sector and spur gear....I didn't think I had an option.

Is that what you mean by AOE? The engagement angle where the sector catches the piston?

In the future, I will be sure to test with an 8.4.... :)

The AOE (search for that term and the fully spelled out words on this site, it's been covered a couple of times with pics and stuff) is the engagement of the contact surface of sector gear and the first tooth of the piston.

It's not really adjustable, but it needs to be right. It's dependant on the overall length of the piston body and the piston head...as it sits tight against the cylinder head...while it's in the mechbox shell. Different manufacturers will have slightly different specs and this can lead to some pretty screwy combos if you mix and match brands. These oddball setups can result in the first tooth of the piston being positioned either too far forward or too far back for the sector gear to pick it up cleanly.

If the sector gear tooth comes around too soon (i.e. the motor/gear ratio/battery combo is causing the gear to spin so fast that the piston hasn't come fully forward yet) then it's likely that the first tooth (and subsequent ones) will impact rather than engage the teeth of the piston....mangling them.

If the engagement is too much off the other way, the flat of the sector tooth will engage the edge of the piston tooth, putting excess stress on the tooth...which will wear, compromising its strength.

Regardless of your motor, battery, spring, gear ratio combo....you want the AOE to be good regardless if you're in semi or full auto.

Simplified...
Stiffer spring = piston returns forward faster and is in position to be picked up correctly by the sector gear again
High V battery = motor will typically spin faster = sector gear comes around faster
High speed motor = sector gear spins faster
High speed gear set = sector gear spins faster
High torque gear set = sector gear spins slower, but with more power

As you change one thing...you might start to push other items out of wack.

One of the most reliable ways to see that it's done right is to set everything up...shoot the gun a bit...and then disassemble again to see what the wear patterns are.

Note also that the timing will change very slightly if you're shooting blanks vs. shooting BBs.

Search the site for AOE...the pics are very helpful.

I searched around this site and didn't find any good topics about AOE. Unless I just missed it, which is very possible.

I am beginning to think the piston was completely flattened due to something I did. Mechbox.com says to adjust the tappet plate catch on the sector gear to the "1 O'Clock" position to set the timing. I was unsure about this step....

There's no "timing" in a gearbox. It tell you to set it to the 1 o'clock position so that the gear does not engage the piston until the first cycle. Otherwise if you have the wrong geartooth in the wrong position on the piston and close up the mechbox and fire it....bad news.

That just ensures the first tooth contacts the first position on the piston when you fire it the first time.

Great! I think I got it now :)

AOE reference found on another site: http://baguioairsoftgroup.forumotion...ment-t2724.htm

One last thing..any decent piston recommendations?

Thanks alot everyone! Top notch for sure!!!!

Double torque gears are actually really good for high ROF setups, and my prometheus piston handles 1258rpm no problem, just my box mag has trouble keeping up lol

see airsoftmechanics.com for lots of good info on trick setups (and the original designer of the extreme-fire mosfets is Gandalf on that forum). Caution...the info on it is very detailed/technical at times...it'll make your brain bleed...

I've had good luck with Modify Polycarbonate full tooth pistons. The supercore piston is supposed to be very good as well.

Yes, I have spent a lot of time trying to decipher that info. I highly recommend Extreme-Fire. Superb quality control & customer service.

Thanks again everyone!

Any thoughts on what qualifies as an insane ROF?

~35 rps (2100rpm) is freaky
~40 rps (2400rpm) is outright scary...to hold, let alone get hit with

Highest I did was ~32rps (somewhere in the 1800-1900rpm range) and that was retardedly fast, IMO. Fun though...with the right lighting it looked like silly string coming out of the gun.

Stuff doesn't last for long at those speeds....

Al had a vented piston with front and back teeth missing and a double sector setup that ran off a big lipo brick...M170 spring just to get it shooting 350-ish...freaking nuts.

Pwauahahahahah oh my, sorry. Looks exactly like my JG piston after putting a LiPo in it. Had to have it swapped out with the metal tooth one.

So my M4 shooting 28 bps with a 9.6V is just about in the "freaky" catagory.

I don't know why anyone uses any other piston than the deepfire all-titanium tooth.
It's bloody indestructible.
I've been running them in both my high fps/rof guns for 3 years and they show practically no wear. I've installed them in several other guns too and they've never crapped out.
Some people used to say that the bodies had cracked but I have never found that.

With high rof, you'll probably need to shave the second tooth as m10204 mentioned

One very important thing. Make sure you're using at least a 340 fps spring at over 25bps. Much slower than that and the piston won't get back fast enough.

The first thing that I see with your setup, is that you have too strong of a spring for a standard ratio gear set, which is amplified by the higher voltage battery. Either tune down the spring OR get a torque up gear set.

You're experiencing what's called "overdrive", where energy is built up in the motor when cranking a heavy spring.

Spring upgrade trouble occurs when a considerable amount of accumulated energy is forced through the motor to overcome the increased tension caused by the upgraded spring. The greater the spring tension, as well as higher the gear ratio so will the energy accumulated become greater. This accumulated energy is released right after the Sector Gear releases the Piston, and in a standard torque ratio gear set, the energy is expended and forces the gears to spin way faster than expected. This is the overdrive. The gear ends up spinning so fast, that the teeth end up slamming in to the piston tooth rack as it's coming back in to battery.

Two opposing forces this great usually doesn't end in something good, and something will have to give. In this case, it was your piston teeth that took the brunt of the force.

If you must maintain the velocity provided by that spring, your best bet is to torque up the gear set so that less strain is applied to the motor. The less strain that's applied to the motor, the less likely you'll experience overdrive, and you'll reduce your current load as well (for greater battery life.)

Consider, a real P90 shoots 900rpm, which is 15rps.

An M4 is 700-950rpm.

That all definitely makes sense Illusion. I got 50,000 rounds out of that gun before the axles sheared off of the sector and spur gears....which also damaged the original piston. I could be wrong, but aren't stock G&P gears standard ratio? If I was experiencing "overdrive" with this stock setup, should I have been able to get 50K rounds?

What happened here was a combination of a very powerful MOSFET, poor AOE, miss matched replacement parts, and what you described.