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KA M4 Cut-off lever problem

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Old February 13th, 2013, 02:15   #1
rick_b16
 
Join Date: Nov 2012
KA M4 Cut-off lever problem

Has anyone had any similar problem? I recently did some upgrades to my gearbox i had noticed once i started using 11.1v battery in semi-auto my cut-off lever dont seem to catch the trigger mechanism very well and in often it will take 2-3 cycles before it will stop the motor. Or sometimes will even keep cycling as if it was in full auto. I tried to bend the cut off lever slightly to have a better catch to the trigger mechanism, it works slightly better but seems still as if its over spining and the cam on the gear is not catching the lever very well. But once i switch back to my 7.4v battery it works wonderfully.

Thanks for any advice

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Old February 13th, 2013, 02:35   #2
XZIVR
 
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Join Date: Mar 2011
Location: Calgary, AB
I feel like you probably didn't search too hard because that's a super common issue to happen with a higher voltage battery. The best solution is buy a mosfet with active braking.
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Old February 13th, 2013, 09:18   #3
lurkingknight
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Join Date: Jul 2011
Location: Ottawa
what spring and what motor are in the gun?

A few things come to mind that can cause this:

You probably have something called overspin. The battery has so much juice that it turns the motor so fast that the gears will keep spinning with residual energy from momentum, usually enough to do 2 maybe 3 cycles. This happens when you have a super powerful motor like a neodynium magnet motor and a weaker spring like a 90 or 100.

Your cutoff lever was already worn... there's a cam on the sector gear and a nub on the cutoff lever that grind together with every cycle.. the cutoff lever will wear before the sector... as it wears off it doesn't move as much, sometimes maybe not enough to reset the trigger.

Your trigger shuttle is being pinched too tightly by the gate prongs and requires 2-3 hits to reset. I've observed this usually is a problem combined with the cutoff lever wear.

From your description, you very likely have overspin. Active braking mosfets definitely help this, but your motor wear is increased... think of it like locking the brakes on your car but if you had magic tires that didn't slide on the ground... in motor terms, it's quite a violent shutdown of momentum. The polarity on the motor is reversed to stop the momentum.

The other option is Short stroking. Install a stiffer spring and remove teeth from the pickup side of the sector gear... If your target is around 300 fps, a 120 spring and 3 teeth will give you around 300. You will need a half metal rack or full metal rack piston to do this, if you do it with a non metal rack, you will strip the piston as you're releasing off a tooth in the middle, rather than the end, so the non metal teeth will give out eventually. This is usually an option for people with very powerful motors (neodynium) because the ease of which they pull stronger springs... I've read up to 190 springs are used in some instances. There's some added benefits to short stroking, such as correcting pre-engagement on super high speed/torque builds, you'll never engage the middle of the piston (what causes piston rack failure).
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Old February 13th, 2013, 11:22   #4
funkyboss
 
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Location: Montréal
I had an issue with KA M4 cutoff lever. It seemed unused but when I changed it with a brand new Modify, it worked well.
Try changing your cutoff lever, then install a mosfet.
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Old February 13th, 2013, 16:51   #5
wind_comm
 
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Join Date: Jul 2011
Location: Calgary/Vancouver
KA cutoff levers aren't very good. I had this exact issue. get a new/different one and it'll be fine.
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Old February 13th, 2013, 21:32   #6
rick_b16
 
Join Date: Nov 2012
sweet, Thanks for all the advice. I'll take u guys advice, i'll change the cut-off lever and install a ab mosfet. Keep you guys posted
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Old February 19th, 2013, 13:33   #7
rick_b16
 
Join Date: Nov 2012
changed the cut-off lever and installed an ascu mosfet works flawless now. thanks guys!
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