extending gearbox life - semi or auto

[old_and_slow]

Thoughts at 0045am - My way of thinking is that semi auto places less stress on gearbox components than full auto and following on that if a gun was only fired semi auto the gearbox would last longer than on on full auto.

Is this the case or does it not matter are the stress levels equal

[plainlazy44]

Re: extending gearbox life - semi or auto

I think its the other way around actually. As far as the gears are concerned, the initial torque is higher than that needed to maintain the gearbox running, therefore the highest stresses in the gears is when the motor begins to spin, ie semi causes more wear. Also the anti-reversal latch is used less during full auto firing, i think? Wear on the piston is the same regardless.

[old_and_slow]

Re: extending gearbox life - semi or auto

hmm - you could be right, you know, regarding the start up stresses on the gears.

Piston wear will be the same however a piston used on semi auto will last, time wise, longer due to it not rattling up and down the cylinder 20 times a second on full auto.

[[email protected]]

Re: extending gearbox life - semi or auto

If you dont have a mosfet fited a lot of semi-auto firing will cause your trigger contacts to burn out quicker-it will also wear the cut off lever and as plainlazy suggested the initial startup causes more wear to gear train particularily if using high voltage/mah batteries. Short bursts and proper battery size are recommended.Also be wary of excessive dry firing.

[seansamurai1]

Re: extending gearbox life - semi or auto

If Ive been told the truth then this is what I was told by a gunsmith. AEGs are designed to be full auto and thus work more efficiently in full auto.

[wires]

Re: extending gearbox life - semi or auto

As sean said, full auto is kinder to the gearbox

[plainlazy44]

Re: extending gearbox life - semi or auto

hmm - you could be right, you know, regarding the start up stresses on the gears.

Piston wear will be the same however a piston used on semi auto will last, time wise, longer due to it not rattling up and down the cylinder 20 times a second on full auto.

Time-wise yes the gearbox will last longer if used only on semi, but to look at the difference properly it'd have to be tested on the same number of cycles/number of rounds fired.

I've checked my machine design notes and it is true about the initial stresses being higher, it increases the oveload factor in the stress equations.

As someone's said above, the trigger contacts are prone to early failure, usually before the gears i'd hope :s

[old_and_slow]

Re: extending gearbox life - semi or auto

Time-wise yes the gearbox will last longer if used only on semi, but to look at the difference properly it'd have to be tested on the same number of cycles/number of rounds fired.

Indeed.

I've checked my machine design notes and it is true about the initial stresses being higher, it increases the oveload factor in the stress equations.

As someone's said above, the trigger contacts are prone to early failure, usually before the gears i'd hope :s

So, I assume a set of high torque gears are needed?

[plainlazy44]

Re: extending gearbox life - semi or auto

Best way to reduce bending and contact stresses would be a set of helicals. The tooth shape on them means the meshing is less abrupt.

I'm no gearbox tech though, just an engineering student. Without seeing the maths/fatigue analysis i can't tell you whether the helicals are worth the investment.

[seansamurai1]

Re: extending gearbox life - semi or auto

You need good bushings for helicals due to the sideways force. Most of the wear is start stop motion on the gears, the cutoff lever and high current draw through the wiring, contacts and motor, this also affects battery life quite heavily. All of this comes from semi auto usage.