High Speed Gears Stripping Pistons

[Bar1975]

how do i upload pics here? it's asking for a URL.. do i need to host them somewhere first?

[Spike]

Host your images on photobucket or facebook or something. Copy the URL of the picture (Right click, copy image url) and then past them here with the format [img]www.whateveryourpictureis.something[/img ] without the space

[MaciekA]

Friends don't let friends use photobucket. Join the 21st century and get a Dropbox or CloudApp account.

[Bar1975]

ok.. got with the 21st century

The black piston below is the first set up with high speed motor. This didn't last much more than 100 shots on semi and full auto (full auto streams for a few of seconds)

The first two teeth were removed for AOE.

Note the cracked off pick up tooth and the stripped teeth. Looks like the sector was engaging those later teeth first as the piston was on it's way back?




The second piston (white) is the second set up. High Torque motor (both set ups used 9.6V battery) AOE was corrected but after several hundred shots (semi and full auto streams for a few seconds) i started to hear a different sound and felt something was happening. I stopped and opened the gearbox to find this.



Harder to see but note the shredding of the same teeth as the piston above. The pick up tooth was still in tact but probably not for long. This piston was not swiss cheesed either.. the black one was. (this may not have happened if Swiss cheesed)

At the end of the day the damage to both is similar enough to point to the same cause. If it's per-engagement then it will continue to happen to any new piston i place in here.

Recommendations so far have been to increase the string strength so I'll grab an M120 as i don't want to have to replace the motor with anything higher than the 120. I'll pick up a new nylon fiber piston and do the same AOE and swiss cheesing mods.

My question remains around short stroking this new set up? Will short stroking guarantee a fix for this issue? If i start without this i could end up stripping the new piston so it makes sense to remove a tooth or two just to cover all possible angles here?

[Bar1975]

arghh.. why didn't the pics show up in the thread? i can view the shared pics when pasting the link into a browser.. but not when pasted into these editor...

anyways... below are the links to the pics

First Set Up Piston: https://www.dropbox.com/s/eiua8n4lny99uar/black.JPG

Second Set up Piston:: https://www.dropbox.com/s/gl92zp757gzwl2a/photo.JPG

[wind_comm]

I feel like it might be overzealous AOE correction. I don't _completely_ remove the 2nd and 3rd tooth, just reduce the height till they clear the pickup tooth. (generally about 90% of the 2nd and 50% of the 3rd)

it seems you may have to shave the 4th tooth as well.

the picture of the black piston is basically too much stress on the pickup from not engaging the 3rd tooth to relieve the stress. the wear is probably incedental, or at least overspin.

[Bar1975]

interesting thought.. most AOE mod videos i see instruct to shave them down all the way (some do recommend not entirely shaving the 3rd tooth but my sector gear teeth generally always hit that 3rd tooth so I've gotten into a habit of taking it all the way off)

Moving forward I'll make sure to try and preserve some amount of tooth in all teeth when correcting AOE. It makes sense that it would be less stress to have something to dig into.

It should be noted that both pistons when set up were showing no signs of teeth wear but as soon as the high speed gears got a hold of them the wear started. So no doubt it's related to the new gears somehow.

[Chiba]

Originally Posted by Bar1975

interesting thought.. most AOE mod videos i see instruct to shave them down all the way (some do recommend not entirely shaving the 3rd tooth but my sector gear teeth generally always hit that 3rd tooth so I've gotten into a habit of taking it all the way off)

Moving forward I'll make sure to try and preserve some amount of tooth in all teeth when correcting AOE. It makes sense that it would be less stress to have something to dig into.

It should be noted that both pistons when set up were showing no signs of teeth wear but as soon as the high speed gears got a hold of them the wear started. So no doubt it's related to the new gears somehow.

Just remember than all parts wear out. It's just how long it takes before it becomes apparent. In your case, the high ROF is revealing the issue very early.

Agree that for the black piston, the pickup tooth was weak and it was pulled off.

And agree you might have been overcorrecting the AOE too much. Got any pics of the piston and gearsets together?

[MaciekA]

So we know that you either have an AoE problem or a PE problem. It doesn't matter which problem it is because you want to build your system to prevent both.

Either way, you want several things to be true when the sector gear pickup tooth comes back around for another whack at the bat:

• The sector pickup tooth must meet your piston pickup tooth at a nice angle. You may think the angle is good but it can be deceiving depending on the shape of the tooth (rounding) and where the piston sits when the sorbothane or neoprene (or whatever padding) on your cylinder head "settles" under the pressure of the piston head and the spring.
• Your piston pickup tooth must be strong enough to handle the stress at a high RoF. It is much greater than when at a low RoF, especially with a torque motor and especially with a LiPo.
• Your piston must be returning home faster than your sector gear comes around again. Have you checked that your piston moves freely and is not experiencing any binding? Take the spring and spring guide and gears out and seal the system up and see if your piston can freely fall up and down the entire range of motion without any help from your hand. If not, you have a slow piston with some friction or binding.

For reference, my MP5K runs an M130 spring, a type 2-ish cylinder, 3/16" sorbothane pad, 13:1 gears, neo motor, SHS lightened 15 tooth piston, stock ~90mm barrel. High RoF and 380fps. No PE, no problems with the pickup.

My advice:

• Try an M120 spring.
• Review AoE and PE.
• Check that your piston is as free of friction as possible. Make sure to seal your gearbox completely with screws when testing. Keep the cylinder in there too. Then do the same test WITH your gears in there just to make sure you're not getting piston/gear binding. Test everything you can logically think of possibly going wrong before destroying any more pistons, you'll be surprised what you can find.
• Consider a piston with some balls - shs 15 tooth (nylon, all metal teeth rack), lonex red (glass-reinforced nylon, mostly metal teeth), etc. Don't install a fancy piston until you have worked out any other latent kinks in your system. After installing a fancy piston, re-test for binding and friction (without gear, then with gears) again to make sure you're not about to kill another piston.
• If you are using Deans/XT60 and a MOSFET and LiPos, consider doing your tests with a small and weak LiPo rather than a strong one. I use a little 650mAh LiPo for initial gearbox tests so that I don't completely destroy a piston if there's any surprise binding or friction -- that way I simply get some lockup or heat and can keep reviewing until perfect.

BTW, the way I post my dropbox pics is to go to the dropbox UI and "copy public URL"

[nstahl.19]

+1^ Man you should be a gun doctor! Personally I've used a ton of your advice on ASC.

[lurkingknight]

forum ate my post yesterday, but AoE correction is not about making the sector pickup meet the piston pickup at 12:00. It's about creating the situation where the two meet with as much surface area contact as possible. Your final resting place could be 12:00 but that depends on the gearbox shell and all other components as tolerances are all slightly different. Too much of an angle can drive the angled tooth of the sector into the face of the pickup that will eventually shear the back of the piston off. At least in my mind's eye.

Also I agree with wind_comm that you may need to leave more of the 2nd and 3rd teeth on while just completely removing the 1st normal tooth. You just want enough room for the sector to clear the rack. I run m110s in my guns and have not seen any sort of wear that would indicate the setup won't work.

Also you mentioned polycarb pistons in your other thread. POLYCARB IS CLEAR it's a material that's meant to take object to object impact force on a single vector. It does very poorly when you start twisting and pulling at it. It does not resist shear forces well. While the pickup tooth is a point of contact, the rest of the piston body is subjected to shear force where the pickup meets the body. It will crack or tear.

What you want is a polymide piston, this material is often mislabeled as polycarb, but CARB IS CLEAR. mide is not. That's how you tell the difference. This is just me repeating info from someone who knows the material better. I myself only use nylon fiber pistons with metal racks. Nylon fiber is reinforced with fibers much in the same way that fiberglass or carbon fiber works in principle, or in the construction world, you have rebar in concrete and fiber reinforced concrete.

[MADDOG]

Originally Posted by lurkingknight

forum ate my post yesterday, but AoE correction is not about making the sector pickup meet the piston pickup at 12:00. It's about creating the situation where the two meet with as much surface area contact as possible. Your final resting place could be 12:00 but that depends on the gearbox shell and all other components as tolerances are all slightly different. Too much of an angle can drive the angled tooth of the sector into the face of the pickup that will eventually shear the back of the piston off. At least in my mind's eye.

Also I agree with wind_comm that you may need to leave more of the 2nd and 3rd teeth on while just completely removing the 1st normal tooth. You just want enough room for the sector to clear the rack. I run m110s in my guns and have not seen any sort of wear that would indicate the setup won't work.

Also you mentioned polycarb pistons in your other thread. POLYCARB IS CLEAR it's a material that's meant to take object to object impact force on a single vector. It does very poorly when you start twisting and pulling at it. It does not resist shear forces well. While the pickup tooth is a point of contact, the rest of the piston body is subjected to shear force where the pickup meets the body. It will crack or tear.

What you want is a polymide piston, this material is often mislabeled as polycarb, but CARB IS CLEAR. mide is not. That's how you tell the difference. This is just me repeating info from someone who knows the material better. I myself only use nylon fiber pistons with metal racks. Nylon fiber is reinforced with fibers much in the same way that fiberglass or carbon fiber works in principle, or in the construction world, you have rebar in concrete and fiber reinforced concrete.

This is why the lonex red pistons work so well, they are fibre reinforced and I have not stripped one yet. They are worth the investment. I have these running with 13.1 ratio gears with no modification except a Sorbo for AOE correction and even that is not at a 12 o'clock position it is still almost half way to the 1. The piston itself still looks like new very minimal wear and easily has had a full year plus of gaming on it, and for me that is a significant amount of rounds down range. In excess of 10,000 bb's at least if I count up the number of bags I bought last year.

[wind_comm]

Originally Posted by lurkingknight

forum ate my post yesterday, but AoE correction is not about making the sector pickup meet the piston pickup at 12:00. It's about creating the situation where the two meet with as much surface area contact as possible. Your final resting place could be 12:00 but that depends on the gearbox shell and all other components as tolerances are all slightly different. Too much of an angle can drive the angled tooth of the sector into the face of the pickup that will eventually shear the back of the piston off. At least in my mind's eye.

Also I agree with wind_comm that you may need to leave more of the 2nd and 3rd teeth on while just completely removing the 1st normal tooth. You just want enough room for the sector to clear the rack. I run m110s in my guns and have not seen any sort of wear that would indicate the setup won't work.

Also you mentioned polycarb pistons in your other thread. POLYCARB IS CLEAR it's a material that's meant to take object to object impact force on a single vector. It does very poorly when you start twisting and pulling at it. It does not resist shear forces well. While the pickup tooth is a point of contact, the rest of the piston body is subjected to shear force where the pickup meets the body. It will crack or tear.

What you want is a polymide piston, this material is often mislabeled as polycarb, but CARB IS CLEAR. mide is not. That's how you tell the difference. This is just me repeating info from someone who knows the material better. I myself only use nylon fiber pistons with metal racks. Nylon fiber is reinforced with fibers much in the same way that fiberglass or carbon fiber works in principle, or in the construction world, you have rebar in concrete and fiber reinforced concrete.

well actually, I don't even completely remove the 1st normal tooth (I call it the 2nd tooth btw) I take it down to where it clears the pickup, and if the sector gear doesn't like it, it'll just wear itself down harmlessly.

also, the 3rd tooth at 50% height generally clears for me, and if it doesn't it'll wear down harmlessly.

use polycarb in your bullet-resistant windows and hockey rink glass. until we find something better, glass-fibre reinforced nylon is where it's at.

also, Lonex reds are AMAZING, but REALLY REALLY need to be lightened. A LOT.
also, if you have the luxury of going to a local store to inspect your potential new SHS piston in person, DO IT. even if it is $20 in person rather than $8.50 from HK. they're great pistons, but have quite a few issues, so an inspection beforehand is priceless. (also you get to chill at an airsoft store for a while. usually motivation enough.)

as far as AoE correction, I generally don't even go for 12:00. after factoring sorbo compression, I shoot for flush tooth-to-tooth contact. for some pistons/sectors, it's quite a ways away from 12:00. do keep in mind that I'm a crazy idiot who has a 1/4" sorbo pad AND the stock cylinder head pad on top. still doesn't reach 12:00. =D

[Stealth]

Originally Posted by MADDOG

This is why the lonex red pistons work so well, they are fibre reinforced and I have not stripped one yet. They are worth the investment. I have these running with 13.1 ratio gears with no modification except a Sorbo for AOE correction and even that is not at a 12 o'clock position it is still almost half way to the 1. The piston itself still looks like new very minimal wear and easily has had a full year plus of gaming on it, and for me that is a significant amount of rounds down range. In excess of 10,000 bb's at least if I count up the number of bags I bought last year.

Heh, so that's why you haven't bought another. I should tell Lonex to make them weaker. =P

[lurkingknight]

Originally Posted by wind_comm

well actually, I don't even completely remove the 1st normal tooth (I call it the 2nd tooth btw) I take it down to where it clears the pickup, and if the sector gear doesn't like it, it'll just wear itself down harmlessly.

also, the 3rd tooth at 50% height generally clears for me, and if it doesn't it'll wear down harmlessly.

use polycarb in your bullet-resistant windows and hockey rink glass. until we find something better, glass-fibre reinforced nylon is where it's at.

also, Lonex reds are AMAZING, but REALLY REALLY need to be lightened. A LOT.
also, if you have the luxury of going to a local store to inspect your potential new SHS piston in person, DO IT. even if it is $20 in person rather than $8.50 from HK. they're great pistons, but have quite a few issues, so an inspection beforehand is priceless. (also you get to chill at an airsoft store for a while. usually motivation enough.)

as far as AoE correction, I generally don't even go for 12:00. after factoring sorbo compression, I shoot for flush tooth-to-tooth contact. for some pistons/sectors, it's quite a ways away from 12:00. do keep in mind that I'm a crazy idiot who has a 1/4" sorbo pad AND the stock cylinder head pad on top. still doesn't reach 12:00. =D

I can't remember if I have 1/4" or 3/16 for sorbo, but on both my p90 and g36 it's right on top of the original rubber pad on the cylinder head. So I've got way more than just the sorbo :P