DIY cycle completion mosfet?

[kjones734]

Am I missing something? What is the need for a timed lenght for the shot? Why not just us the cutoff lever thats already standard in the gearbox that already completes a full cycle on semi? If your not looking for features like burst fire then a strait up mosfet would be good. All adding a mosfet does is directs the current through the mosfet instead of your trigger contacts so you dont burn them up. So what am I missing that you want to have a timed cycle involved?

[zephurah]

The idea is that when the trigger is only slightly pulled, that the gearbox would automatically cycle all of the way through. If you just have a mosfet, it doesn't do the job of cycle completion. The idea with the timer is that it bypasses the trigger contacts and sends a continuous signal to the inline mosfet past the initial trigger pull. This way the mosfet would send energy to the motor even after the trigger is released. This would be done with a small potientiometer on the timer.

Edit: DigiKey is confusing, can't find the timer i'm looking for. RIP. I'm sure you can see what i'm talking about, but the more that I try and make a schematic, the more that I see that this isn't as plausible as it seems. It for sure would work, but to make a pcb, buy all of the really small parts and somehow mount them all inside a gearbox shell is really awkward. Probably easier to just get an 11.1 and shim your gears.

Edit2: If anyone actually wants to do this, PM me and i'll send the schematic and parts list.

[T6e9a]

Surely theres gotta be a way to do it without a potentiometer.

I already have micro switches i stocked up for this sort of project. Im sure with some hot/super glue and a little bit of wiring, it could be possible to fit it in the contacts area.

All I really need is to figure out what electrical components combined with 2 mechanical switches can accomplish the task.

I'll shoot you a PM anyways and see if i can't make sense of the schematic and try that way anyways.

[Snarf]

Let us know how it goes. I'm also interested in trying this out, but I won't be able to until the summer.

[walkera994]

Use active braking MOSFETs. The way AB MOSFETs work is by having two separate MOSFETs setup in a half bridge configuration (you can Google this or request I add more detail). When there is no input (trigger not pulled), the motor is braking. When there is input, the motor is shooting. The brake does not "reverse the polarity" as I've seen on other forums. All it does is short the motor terminals together. When the motor is spinning and no power is supplied to it, it becomes a generator. All you're doing is dissipating this energy electrically instead of mechanical. AB has negligible effects on your motor. AB is a method used in the automotive industry for sunroof motor, window lift motors, windshield wiper motors, and more. The brake will take effect when the cutoff lever disconnects your trigger contacts and stop your motor pretty close to the end of the cycle. 

As far as pulling the trigger a little bit to get one shot, I would simply modify the trigger assembly to lower trigger distance.
EDIT:
The reason why there isn't "cycle completion" on stock guns, upgraded guns, or guns without AB MOSFETs is because of the moment of inertia of the motor armature, shaft, and gear. It actually causes overshoot, especially if you're using a low powered spring, high powered motor (neo), or high power battery (>9.6V). Undercycling does not happen because the cutoff lever is mechanically switched by the sector gear.