Featured Upgrading an APS UAR / GB V3 / motor and gears

Discussion in 'Gun Building, Modifications & Repairs' started by charger_gti, Oct 11, 2021.

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  1. charger_gti

    charger_gti New Member

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    Hello everyone

    Long time reader of this forum, desperation made me register. Already read most of the sticky topics.

    I don't have a lot of experience modifying AEG but I wanted to upgrade my least capable gun, the APS UAR.

    I already have (not installed) a jefftron leviathan V3, SHS 13:1 gears and a Guarder ITU motor (18tpa I believe).

    In Portugal we have a fps limit of around 370fps with 0,2g BBs. I use 7,4v batteries 25-50c discharge

    I want to improve trigger response and achieve a ROF of 20 to 25rps. No more than that.

    My problem is that I do not know what to expect in the following situations regarding PME:

    1. Just changing the motor and keeping the stock gears (18:1) with jefftron leviathan v3

    2. Changing both the motor and gears with jefftron leviathan v3

    Wanted to avoid having to short stroke it.

    Thank you all for the help.
     
  2. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    We need more details.

    Which spring are you using? M110?

    You will not PME on such a low ROF with a M110.
     

  3. charger_gti

    charger_gti New Member

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    No. M100 to keep it legal in Portugal. Besides that I only have with me.at the moment sp90 and sp100 springs
     
  4. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    SP90 is more like M1005 and SP100 is more like M115.

    So is your spring made by Guarder?

    If not are you using a soft spring or a hard spring? With soft springs your FPS is going to continually drop until it settles weeks later.
     
  5. charger_gti

    charger_gti New Member

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    The spring is the stock one on the APS UAR around 360fps

    With this spring, 13:1 gears and the Guarder ITU motor I won't have PME?
     
  6. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    Not on a 2S lipo
     
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  7. charger_gti

    charger_gti New Member

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    Thank you! Will try it on the next few days!
     
  8. Ben3721

    Ben3721 Well-Known Member

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    That all sounds right in the ballpark of your goals without any pme.

    Now if you threw in a 3 cell lipo youd have the chance of piston pme.


    I tend to short stroke and use a heavier spring to fight overspin, not so much pme.
     
  9. charger_gti

    charger_gti New Member

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    I am also concerned about that. But, in you opinion, with my modifications, should I expect any overspin?
     
  10. Ben3721

    Ben3721 Well-Known Member

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    You'd have to test and find out. No reason to short stroke unless you need to. It's less efficient and harder on the motor to short stroke.
     
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  11. OutlawAirsoft

    OutlawAirsoft Active Member

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    Your planned build isn't exactly high stress, so throw it together and see if it works. A high stress (insane FPS or ROF) that has problems like pme can absolutely shred your piston and or other parts.
     
  12. Ben3721

    Ben3721 Well-Known Member

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    I've only once encountered true pme, it was a ported 35rps setup on a m90 spring when I was new brand to teching.

    That day I learned what pme was. Luckily I was using a plastic piston.

    If you really really want to know if your having pme on a short stroked setup leave 1 extra tooth on the piston and color it with a marker. Then run the build for a weekend and check to see if the marker is worn at all.

    Pme damages all kinds of parts. A plastic tooth piston looses teeth, a metal rack piston can rip the rack out, gears can break a tooth, the arl latch can be hit so hard it damages then arl holes... All are a lovely sound. Pme can be heard quite easily. If your gun sounds like a blender with marbles then it's probably best to stop using it.
    But a clean even sticotto thump is what you want to hear.
     
  13. charger_gti

    charger_gti New Member

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    Thank you all for the help. Trust me, I have asked in a lot of places and read all the different things you can imagine.

    From "you will destroy your gun if you only change the motor to the Guarder ITU", passing "no problems, you can even run it with an 11,1v and 12:1 gears" ending in "short stroke 3 teeth with that setup".

    In the end it's only a APS UAR. Easy to change/replace.
     
  14. Ben3721

    Ben3721 Well-Known Member

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    It's also not really a big stress these days to break a piston or gearset. Especially if you know how to swap them.

    Nice shs/gmt gears are 20 bucks and a shs steel rack piston is like 8 bucks.

    The 12:1 gears have a meshing flaw between the spur and thin 10 tooth bevels (used to be thick long 9 tooth bevel teeth) causing more slack than should be accepted.

    13:1 mesh a lot better. If you do short stroke them, two off the release and one off the pickup. Paired with a sp120 spring youd get near your goal with a snappier trigger, less overspin and 25-35rps depending on the motor/battery combo.

    13:1 gears are a really good ratio to work with, one can easily get 25 to 35 rps with pretty solid trigger response. If you stay closer to 25rps the motor will last much much longer.

    I maintain about a dozen aegs that see use every weekend. Most have 13:1 gearsets short stroked 3 on a sp120-130 spring with 18tpa to 22tpa motors. All are powered with 3s lipos and are mostly trigger response builds, but they do fire at about 25 to 35rps at near 400fps. The most common failures are stock bearings blowing and motor commutators wearing out over a year or two.

    My personal builds are typically pretty experimental and stupid fast.

    The better techs are able to actually get aegs to work long term, not just a short video after a rebuild.

    Welcome to the forum by the way.
     
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  15. charger_gti

    charger_gti New Member

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    Hello everyone

    Thank you for the help. So I installed the jefftron leviathan V3 in the APS UAR. Not that hard, had to file the gearbox a little to fit it correctly.

    Trigger response is greatly improved ( didn't change motor or gears).

    Problem: the selector switch plate is not like a normal V3 so I positioned the sticker in the wrong place. This means I only had semi. Will have to change its position.

    Also, the selector switch plate on the gearbox only functions with semi or full. Safe is done mechanically near the trigger. Took my a few minutes to see that :D

    Hope to correct it tomorrow.