Modded Gearbox Sounds Like Blender

Discussion in 'Gun Building, Modifications & Repairs' started by Adrian_Grey, Dec 14, 2017.

  1. Adrian_Grey

    Adrian_Grey New Member

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    I've made my first attempt at upgrading my G&G GR15 raider to have better trigger time. For the sake of this post, here are the relevant parts:

    SHS 13:1 gears |

    Magic Box 30K High Torque motor (Long-axis) |

    Modify 8mm ceramic ball bearing bushings |

    Modify shims |

    All other parts are stock G&G

    My biggest conundrum has been in the gears and shimming them properly. I shimmed them to the point where there was very little play (maybe 0.1-0.05mm if I could guess it), going from bevel to spur to sector. I shimmed each gear relative to the next. When I put the gears in all together, and screw the gearbox shut, they spin freely no matter what side I turn the gearbox.

    When I installed the motor and trigger, and plugged in a battery, the gears sounded like junk. I've looked up Youtube videos of how a good shim job should sound, and a guy who did a similar test setup got his to sound like a power drill. Mine sound like a blender.

    Here's the video for reference:
    And here's mine:

    I've tried shimming certain gears more loosely or tightly, and they only produce a variation of this blender sound. They don't make it go away. This sound occurs even when I install the anti-reversal latch and push the cutoff lever out of the way.

    Does anyone have any good suggestions? I've been at this for several days trying to figure out what is wrong with this gearbox, and I've done a ton of research on teching/troubleshooting, but I haven't encountered a problem like this. I want to figure out what's wrong with the setup and get everything running perfectly before I reassemble the whole gun.
     
  2. Adrian_Grey

    Adrian_Grey New Member

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    I've looked up probably 3 different videos on shimming, and decided to follow the bevel-spur-sector method.
     

  3. Adrian_Grey

    Adrian_Grey New Member

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    I've also shimmed this previously and it put too much strain on the wires/battery (making them overheat) so I took it apart to loosen the shim job.
     
  4. Hangtight

    Hangtight Well-Known Member

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    Have you shimmed the bevel to the motor pinion once you've established the correct pinion height?
    0.05-0.1mm float is way too tight for bearings.
    What battery and spring? Because if you're trying to run that motor and gear combination on 11.1v then it'll be trying to do around 35rps. With a stock piston and anything under a M130 spring the piston won't be able to complete it's forward travel before the sector gear comes round again. Pre engagement, nasty noise, broken stuff....
     
  5. Adrian_Grey

    Adrian_Grey New Member

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    The battery is a JAG Arms 9.6V (don't know the amps). The spring is the stock spring that comes with a G&G GR15 Raider (the metal version). I also changed the piston to an "SHS steel teeth high speed lightened piston". I also corrected for AoE using sorbopads and a bit of manual filing.
     
  6. Hangtight

    Hangtight Well-Known Member

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    Do you know what fps the stock spring gives? And did you check the piston slides freely in the gearbox shell when it's screwed together? The SHS pistons can be tight in some gearboxes.
     
  7. Adrian_Grey

    Adrian_Grey New Member

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    According to the website, the GR15 raider (CQB version) has an FPS of 335-350. I've put the SHS piston into the gearbox and screwed it down, and the piston actually has a decent amount of wiggle room.
     
  8. Hangtight

    Hangtight Well-Known Member

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    It sounds like the stock spring is probably an M100. Even using the SHS piston you probably have a safe rate of fire off around 28-29rps before you get premature engagement. With the 9.6v battery your set up is trying to do just the wrong side of safe.
    Is it mostly OK on semi auto and then sounds terrible on full auto?
     
  9. Adrian_Grey

    Adrian_Grey New Member

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    I'm not sure what a good sound is supposed to be. When I fully assembled the gun before, the gun was a bit finicky on semi but fairly consistent on full auto. Does that mean I need a different battery/spring?
    During that test, the battery and wires were overheating, which I'm told is due to overshimming, so now I'm back to square one making sure I get the shim job right this time.
    I'm only starting with the gears, motor, trigger and battery installed, to make sure the gears sound right before I put everything back together.
     
  10. Hangtight

    Hangtight Well-Known Member

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    That combination of components isn't going to work together. You could make the best job of shimming and actually make things worse because the low friction will mean it'll run faster, and that speed is the problem.
    Basically the sector gear is turning fast enough that it's getting round to pick up the piston before the piston has finished traveling forwards.
    You have two options. Either you can slow down the gears, or you can make the piston accelerate and travel faster.
    What's your field fps limit for full auto?
     
  11. Adrian_Grey

    Adrian_Grey New Member

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    I use different fields, but generally it's no higher than 350. The CQB field limit is 365 and the outdoor field's limit is 380-400.
     
  12. Specter4

    Specter4 Active Member

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    I recommend shimming too loosely to start and then increasing gradually starting with Pinion, then Sector, then Spur. I also shim my bevel a little looser to accomodate the pinion. It's a slightly different method that might be less precise but has never failed me in any of my high speed builds. It's also quicker and can determine if you have something like deformed gears causing this, a common problem with SHS due to the low QC and very difficult to figure out on your own without a good reference
     
    Last edited: Dec 17, 2017
  13. CommandoJoe

    CommandoJoe Member

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    I actually had this problem once because the motor was going in too deep (oh yes) into the gearbox, basically jammed into the bevel gear. Made a nasty sound, pretty close to that. Just thought I'd throw that out there

    EDIT: Forgot to add that the motor wasn't the wrong length or anything, it was brand new out of the box.
     
    Last edited: Dec 17, 2017
  14. Adrian_Grey

    Adrian_Grey New Member

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    Generally, how tightly do you shim the bevel gear to the pinion gear? I adjusted the motor height to the point where the pinion was flush with the bevel, and shimmed it to where the bevel had about 0.05-0.1mm of play. The problem before was that the gears were shimmed too tightly and that overstrained the motor/electrical system.
     
  15. Hangtight

    Hangtight Well-Known Member

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    Before you do the motor height, make sure that the grip doesn't touch the receiver when it's fixed to the gearbox. Otherwise it'll pull everything out of whack when you assemble. Then you get the pinion height so that it is fully engaged with the bevel, but no more. Then I shim the bevel in the gearbox to get about 0.1mm float. Now adjust the shims either side of the bevel so that with the motor in and everything snugged down you can just, and I mean just, easily move the bevel without moving the pinion. It's a tiny amount, but it means the pinion isn't jammed into the bevel, but the teeth are fully meshed.
     
  16. Hangtight

    Hangtight Well-Known Member

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    This explains it better.
     
  17. Hangtight

    Hangtight Well-Known Member

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    At least it would explain what I'd said better if my post hadn't disappeared!
    But this vid nails it. Just made sure that the grip doesn't touch the receiver before you start, so when you assemble nothing gets pulled out of whack.
     
  18. Adrian_Grey

    Adrian_Grey New Member

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    UPDATE:
    {{This is stuff I did two nights ago, and I have yet to apply the shimming changes mentioned by Hangtight}}
    I've loosened the shimming (supposedly ball bearings can't take too much pressure).
    With the gears installed and the gearbox screwed together, they sound like this:

    With the motor and trigger installed, with a 9.6V NiMH battery plugged in, they sound like this:


    With the whole gearbox assembled, the gun sounds like this:

    Look to my previous post on what parts are inside. I also installed an SHS high speed piston (steel teeth), with a stock G&G piston head.

    Even though I loosened the shims to the point where there was about 0.1-0.15mm of play with each gear, the wiring is still getting very hot. The battery got warmish-hot after prolonged semi-auto firing, and the motor got slightly warm. The heat seems to radiate from the motor and creep upwards to the battery. It was hottest at the tamiya connectors.

    I'm beginning to suspect it may be an issue with the wiring. When installing the motor one time, I accidentally jammed it in too hard and the teeth have left marks on the wire sleeve. I'm not sure if it's damaged the internal fibers, but now I think that may be the case.
     
  19. Specter4

    Specter4 Active Member

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    I just realized you're upgrading a combat machine. You're right for thinking its your wiring. Your motor is pulling a lot of amps, seemingly enough to cause a bottleneck of current within your system, the symptom being heat. I'd recommend a MOSFET while you're changing the wiring.