Random question about motor efficiency

Discussion in 'Gun Building, Modifications & Repairs' started by Jerichow, Jul 31, 2015.

  1. Jerichow

    Jerichow Member

    199
    0
    Lakeville
    So I'm working on a friend's M4 doing a rebuild because the stock gearbox was @#$%. It's rebuilt as such:

    Matrix Zombie Killer 8mm Gearbox Base
    Modify 8mm Steel Bearings
    Stock 18:1 Gears
    ZCI Torque Motor w/pinion from the original motor to match the bevel
    NukeFet w/24a Resetting Fuse - Deans XT's
    SHS M110 w/Bearing Spring Guide
    Stock Piston(Aoe/Glued, Lightened) w/SHS orange piston head - no bearing.
    Batteries are:
    - Turnigy Nanotech 2000Mah 15c 11.1v
    - G&P 1600Mah Small Type NiMh

    So my question is this - with a ZCI Torque motor with the 22TPA armature - I'm actually running into an odd issue(I think). The gears are shimmed well, I get 10+ rotations with a light flick of the sector gear with the shell screwed shut and it was shimmed bevel to pinion. Each gear has about .05mm of play so I know they're not too tightly shimmed. With a fully charged 11.1v, I get overspin issues causing it to cycle twice per trigger pull, and on the 9.6v the trigger response is all but instant, so the motor is clearly not struggling.

    Yet the batteries I'm running it on are dropping voltage quickly, including a brand new Turnigy NanoTech 11.1v 2000Mah 15c cell. It's got a 30A discharge, and that should be fine for a setup like this, but after a handful of bursts and a bit of semi auto, the fuse gets quite warm, even the mosfet starts to barely warm up, and the LiPo dips low enough to cause my battery sensor plugged into the JST port to go red and beep at me.

    I've heard about motors running around the 50% max speed mark achieve maximum efficiency(Mostly the discussions about Lonex motors). So I was wondering, could it be that my motor is running a setup that is too light for it, and is somehow running inefficiently and drawing too much power because of that? Or am I missing the point entirely, and should be using a slower battery so that it operates closer to the 50% of max speed mark?
     
  2. Raven1st

    Raven1st Well-Known Member

    5,521
    444
    San Ramon valley
    Is the 15c burst discharge rating? If it is that is low for a battery.

    Ideally you want a battery that can output 40-60% more than your system draws to make it easy on the battery.
    Your setup looks like it draws 50 Amps upon startup, so your battery is most likely struggling to power the setup.
     

  3. Jerichow

    Jerichow Member

    199
    0
    Lakeville
    I use this battery.

    25c Burst w/2000Mah will be 50A, and the gun is rarely ever used in semi-auto only. I cycled it close to 1000 times(testing and then running 3 190rd midcaps through it) and only used up about 440mah.
     
  4. Raven1st

    Raven1st Well-Known Member

    5,521
    444
    San Ramon valley
    The over-spin you are experiencing can be caused by a sticky shuttle or weak main spring.

    The trigger shuttle may not be disconnecting when it needs to, or moving slowly, which leads to a prolonged cycle and more over-spin. This can be solved by smoothing the movement of the shuttle, shortening the shuttle return spring and, if needed, trimming down the top of the trigger to make it easier to disconnect the shuttle.

    The main spring may not have enough resistance on the gears to slow down the cycling. This, and PME, is why high-speed builds use very strong springs.
    I recommend you look at the trigger mech before you mess with the spring.

    The battery looks like it is not powerful enough.
    I ran the numbers again following Zard's guide and it looks like you pull 58 Amps on startup. This means your current battery pack is holding you back a little bit and is being pushed to the limit which is terrible on the battery. That explains the voltage alarm going off.

    The fuse and Mosfet getting warm is caused by resistance in the wiring.
    I can't really help you with that other than saying 'Make sure your connections are solid'.