Piston for High ROF

[isparkthela]

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:

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 , but I was also hoping to gain some knowledge on full steel toothed pistons. Are they your best option for high ROF setups?

[ILLusion]

Originally Posted by isparkthela

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 , 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!

[isparkthela]

Originally Posted by ILLusion

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!

[m102404]

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.

[Styrak]

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

[isparkthela]

Originally Posted by m102404

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.

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....

[m102404]

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.

[isparkthela]

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....

[Styrak]

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.

[isparkthela]

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!!!!

[ThunderCactus]

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

[m102404]

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.

[isparkthela]

Originally Posted by m102404

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!

[Eeyore]

Originally Posted by ILLusion

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!

Any thoughts on what qualifies as an insane ROF?

[m102404]

~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.