M120 Build...help please!

[grimreefer]

Originally Posted by BeAcH

i would suggest that you run a 10.8 volt battery or lipo for that set-up, as this set up is the same as mine and a 10.8v is perfect, good rate of fire.

This is going to be semi-only. Trigger response is still important though. I'll have to see how it is with my 9.6v crane battery and the Guarder Infinite Torque up motor.

Originally Posted by m102404

What M4 body are you running it in? My last build with a KA M4 body wouldn't work right until I swapped all the internals into a Systema mechbox shell.

I'm testing out PP Torque Up gears...they're running really well so far. Smooth and quiet. Triggermaster III mosfet, 11.1v battery, PP Hard piston, random ventilated piston head. Guarder Infinite motor.

Trigger response is very good (attribute to motor/battery).

Don't ruin your build by compromising on the mechbox shell...

Best of luck,

Tys

I believe the body is Hurricane. Is the Trigger Master going to be beneficial in my semi-only setup?

[m102404]

Semi-auto causes the most amount of arcing per shot with the switch assembly vs. full auto. That leads to burning out your switch assembly.

"Big" batteries provide a lot of power, which in a normal setup travels through the switch assembly, and with arcing will contribute to burning out your switch assembly. Big benefit to a big batteries is really quick trigger response. With a 11.1v LiPo...the shot is very close to immediate when the trigger is pulled.

Depending on your gearing ratio, battery, motor, spring power, shimming, etc...your piston will come to rest somewhere between fully forward and most of the way back. Sort of "pre-cocking" the piston...but really unreliable. With repeated semi shots...the stopping point should be the same shot to shot. On one setup I had, the piston was consistently coming to rest about 80% of the way back after each semi-auto shot. In full auto, with pretty much any AEG, the piston rest position will be completely random.

A mosfet senses a very low voltage across the switch assembly and then "dumps" power to the motor (probably not the exact proper electrical way to describe it). The current/voltage that the motor needs, doesn't go through the switch...it's fed directly from the Mosfet chip. So, regardless of how many shots in semi/otherwise...your switch assembly will basically last for ever.

A mosfet with active breaking essentially senses when the switch assembly is disconnected by the cutoff lever and "freezes" the motor to stop the gears from rotating further. This will result in a consistent/predictable shot to shot trigger/lag time...and when storing your AEG, a couple of shots with active breaking will result in the piston being left as far forward as possible and thus not storing the spring in a compressed state (which will kill off its power).

Computerized mosfets (i.e. triggermaster III) have additional features such as, semi auto only, 3rd burst, speed up/slow down motor, etc....

Hope that helps,

Tys

[ujiro]

I don't know if I like the idea of the active breaking though.. All I can see it to be is essentially running current through the motor but in the reverse direction, effectively stopping it from continuing to turn the gears from the momentum. Sounds like it could cause premature wear, making things go from full speed to a dead stop in an instant.

[ILLusion]

That's exactly what it does, and is the same technique employed by the Systema PTW and Revolution gearboxes.

[ujiro]

But can that really be healthy for the gearbox? It would be like driving in your car and then slamming it into reverse to come to a stop at 100kph.

[ILLusion]

Originally Posted by ujiro

But can that really be healthy for the gearbox? It would be like driving in your car and then slamming it into reverse to come to a stop at 100kph.

Why wouldn't it? Active braking just assists the gearbox in its natural state.

Over-rotation is caused by the motor itself. The piston assembly is so light weight that the kinetic energy it is loading on to the gear train would be minimal at best. Combined with the fact that the NATURAL STATE of the piston is actually FORWARD due to the spring bearing weight on it, its natural state would be assisting the motor, rather than being neutral or negative.

It's one thing for a gearing setup to go in to a full reverse to stop a light piston from traveling rearward when it's naturally trying to go forward. It's another for it to stop a 2000 pound vehicle traveling at 100km/h that has a natural state that has a neutral impact on the geartrain.

With the automobile analogy, if you release power from the motor or geartrain, the vehicle will not immediately stop in its spot nor return to some resting spot. Whereas in a gearbox, if you released the power from the motor (let's say you even manage to completely yank it out of the gearbox at the end of the cycle or during over rotation), the natural state for the piston is still to return forward and stop there - it won't continue to over-rotate.

Again, over rotation is caused by the motor. If you get the motor to stop it, then over-rotation will not occur, especially if the piston is naturally trying to rest forward due to the spring weighing on it.