Rate of Fire Issues

Discussion in 'Gun Building, Modifications & Repairs' started by Spaceman7, Jan 11, 2016.

  1. Spaceman7

    Spaceman7 Member

    I have been heavily upgrading my Umarex Elite TAR-21 to make it competitive on the field. However, it is still severely lacking in the rate of fire department compared to similar builds. Troubleshooting this has been slightly irritating.

    Current Relevant Gearbox/Other Parts:
    • ZCI Hi Torque Motor (22 TPA)
    • Stock 18:1 Elite Force Steel gears
    • SHS Lightened (Swiss-Cheesed) poly piston/steel teeth
    • ZCI Polymer Piston Head
    • Stock Spring, seems to be a 110
    • Stock Microswitch Trigger System
    • OEM Cutoff Lever
    • Stock Cylinder
    • ZCI Aluminum Cylinder head with proper sorbo pad installation
    • Stock Tappet Plate
    • Stock 8mm Bushings, properly lubricated
    • Stock Metal QD Spring Guide
    • Nukefet with 16ga wiring, wired into the gun's original 18ga wiring
    • Rewired to Dean's

    Parts I am upgrading to after my next strip down:
    • ZCI 16:1 Gears
    • SHS V2 Tappet

    The battery I am using: 7.4v 1600mAh 20c LiPo.
    I have 11.1v batteries as well, however I would like to stick to a slightly slower rate of fire due to the proprietary gearbox now being the weakest part of my build, hence the 7.4v.

    Now the kicker.

    My TAR-21, with aforementioned upgrades, is shooting at a dismal 13-14 RPS. The trigger response is phenomenal, even though it has a very heavy pull, thanks to the High Torque motor. It fires at this speed with or without the blowback enabled, so it's not the weight of the bolt slowing it down.

    The same battery in my absolutely stock VFC HK416 (also wired to Deans, however this is pulling a much lighter spring as the stock one shoots about 340) pulls about 18-19 RPS. Mind you this is with a stock motor and their not-so-awesome self-shimming gears compared to a near perfect traditional shim job.

    I thought this may be due to the fact that the High Torque motor = Lower Speed, as compared to the balanced VFC stock motor, so I plugged the battery into a heavily upgraded G36 (about the same upgrades as the TAR) which contains an identical ZCI Hi Torque motor. It pulled about 20-22 RPS.

    Things I think may be the culprit:

    Stronger spring in the TAR compared to the 416, however I doubt this would pull down the rate of fire by 5 RPS, especially since the performance on the G36 with similar specs has a much better result.

    Length of the wire, as the wiring in the TAR probably adds up to about 3 feet for both the positive and negative sides, equalling a 6 foot circuit. However, this would only affect the trigger response, if it would have any effect at all, since electricity travels lightning fast (sorry, not sorry), and 6 feet (at a maximum) does not add a lot of resistance.

    Stock Wiring, my weakest suit in tech work is electrical-based. I am confident that my soldering job on the gun was above par, however I do not have much experience with it. The solder used from the manufacturer on the microswitch was not meltable by my soldering iron (450C hottest setting), so I was forced to wire the mosfet into the stock wiring, which is insulated 18ga. I do not know what conductor or insulation is used. Would the transition from 16ga at the battery to 18ga at the wiring to 16ga at the mosfet to 18ga at the microswitch cause an electric bottleneck with the 18ga (thinner wiring)? I have some 16ga wiring being shipped in my next order from the glorious Clandestine Airsoft, however I am waiting to re-do the wiring completely for when I can get different colored 16ga wiring for the negative side.

    Any help or insight to why the rate of fire is so terrible would be excellent. I can post pictures of my soldering job/wire set up if it would help with any consultation.
  2. Rushin

    Rushin Well-Known Member

    I'd switch the 18:1s out for 13:1s, that'll give you what you need.

  3. Spaceman7

    Spaceman7 Member

    I'll be switching to 16:1s this week. I find pre engagement to be much more serious on gears with a smaller ratio than the 16s, and I'm personally not a fan of removing teeth and risking the structural integrity of a gearset. Adding a stronger spring is not an option, as I'm already at the fps limit of my local fields. I'm just trying to figure out why the RPS on one gun is substantially lower than the RPS on a very similar internal build in a different gun.
  4. AirsoftRyan778

    AirsoftRyan778 Active Member

    You wont hit pme unless your piston is like 30 grams and you're using an m90
  5. Zaryk

    Zaryk Well-Known Member Supporting Member

    Poor quality wires could be part of your issue, I rarely see decent wires in a stock gun. Poor quality motor connector tabs or cheap high resistance fuses can also hurt your ROF. Also check for pinches and extreme bends in the wire as that causes unnecessary resistance. Another thing to check is motor height, if it's too tight it will slow you down.

    The three gearboxes you mentioned are of totally different designs. I have seen one gearbox run good on a certain brand part and another gearbox run like crap with the same part. This is due to each manufacturer having their own standards for acceptable tolerance deviations.

    Not sure if this stuff is something you already checked, or if it even helps at all, but I thought I would throw my two cents in.
  6. TheInfidel23

    TheInfidel23 Resident Derp Supporting Member

    Your gear ratio is your biggest enemy here.

    Go to 13:1. You won't even get close to PME with an SHS piston. Go ahead and disable the blowback, if you are truly worried about reliability of the shell.

    I have this gun, it gets up and kicks just like any other gun. My setup uses an identical ZCI 22 tpa motor, 13:1 gears, and an SHS piston. I get around 20 ish on a 7.4v 2200 mah battery.
  7. Dannyboyextreme

    Dannyboyextreme Active Member

    Why did you wire the nukefet into the stock wires?? The entire guns wiring should be replaced
  8. Spaceman7

    Spaceman7 Member

    Will consider trying a set of 13s on my next order. I can throw the 16s in my scar when I get it back I suppose. I also forgot to mention that my first shot in semi-auto is always a two shot burst. Every shot after that is functional semi-auto until i reset the spring again. This started only after switching to the High Torque motor. Is this a form of PME? Should I see my doctor? In all seriousness the cutoff is intact and functional. This happens with both a 7.4v and a 11.1v.

    The max temp of my soldering iron was not enough to remove the old wire harness. The connectors on the microswitch actually began to warp at that temperature even though the solder wouldn't budge.

    I will be doing another attempt on the wiring when I do my next order and will replace motor tabs with new ones as well. The wiring has no fuse. There are little clips that run the length of the gun that hold the wiring out of the way of the bolt and below view through the exhaust vents but they just put pressure on the shrink wrap. However, the wiring is looped and lightly zip tied near the mosfet to maintain the length of the wires in a much more organized way.

    The motor is actually at the loosest setting as the armature is fairly long for a short type motor. I also lost the little bump pad that the screw pushes into so it doesn't touch the motor directly so it was convenient it didn't need height adjustment. Any ideas on where to get a new bump pad as well? I thought about just cutting a neopad up and using it.

    I didn't take into account error and deviation, but I know Echo 1 doesn't have the greatest quality gearbox shells on their entry level guns, maybe just the set up of the bullpup's gearbox is also contributory.

    EDIT: I am also trying to maintain the gun's ability to quickly meet my other field's indoor fps limit, which would require me swapping out the spring for an m90/m95. Would I experience pre engagement with 13:1s on this setup with an m95? If so I may just stick to 16:1s and run an 11.1v instead.
    Last edited: Jan 11, 2016
  9. TheInfidel23

    TheInfidel23 Resident Derp Supporting Member

    A 7.4 will be fine and better in the long run, just use that and 13:1's with your desired spring.

    When I rewired my gun, I left the internal wiring and only did the long run to the front. The gearbox routing is scary at best, so I just left it.

    Replace that spacer for the motor cage immediately. If I'm remembering correctly, the grub screw for motor height will now be pushing straight I to the motor arm, which may be sapping power. Find it, or make a new one from sheet metal, or something solid.
  10. Spaceman7

    Spaceman7 Member

    I'm going to leave the wiring in for now until I can get some more electrical supplies. I imagine there may be some bottlenecking due to the 18/16ga combination.

    I stripped the gun apart tonight to put in the 16:1s just to try and noticed I hadn't shimmed the bevel high enough and was making odd contact with the pinion gear, I didn't feel like reshimming tonight so I'll update tomorrow when everything is put back together.

    I also managed to find my motor spacer buried in the bottom of my airsoft toolbox, smart thinking that the little screw may have been sapping power since it was directly touching the motor arm.

    Also finally managed to get my g36 completely reassembled. It was my first gun and has been out of commission for the last 7 years. Every time I went to reassemble, more 10 year old pieces of pot metal would snap. Nothing in the gun is stock now besides the GB shell. Too late to test for noise reasons so looking forward to tomorrow to get both the TAR and g36 in excellent order.