Passive and Active Breaking mosfets?

[laurence]

Hi, already got a thread up about mosfets atm but need to clarify this,

What is the difference between an:

-Active breaking mosfet
-Passive mosfet
-And an AirFET

Just wondering how they differ from each other?
thanks

[Bachelarius]

Re: Passive and Active Breaking mosfets?

- Passive braking -
Read up on the (lack of) difference between a motor and a generator. I.e. a motor can be used to generate a current. When a trigger is released, a passive braking mosfet creates a short between the 2 contacts on a motor, which then uses the current generated by the motor to try and drive the motor in the opposite direction - thus braking. Simple.

- Active braking - actually very very rare, if non-existant. Requires a processor to do the braking intelligently by reversing the current to a motor, allowing for a much gentler braking. HOWEVER most active braking fets you see on the market, advertised as an active braking 'fet is in fact just a passive-braker. Active-braking was a name given to the original mosfets with the shorting-when-off trick, described above. It's just an old name which stuck from the very first prototypes, even if it is a little inaccurate.

When it comes to the market, unless there is a micro-processor there, Active Braking = Passive Braking. The names are interchangeable

- AirFET - Just a mosfet brand name. Comes in a braking and non-braking flavour. Read the articles and explanations he writes about the above, he describes it well, but I think he is the only guy out there which actually uses the term 'passive braking' haha!


It should be noted though, if you do not need the braking feature (and Midas has already proved that you don't with his non-braked 50rps build), DO NOT BUY AN AB FET! It's a lazy hack which leads to excessive motor heat and damage and can be avoided through the use of a heavier spring and short stroking. If you happen to use a gearbox with those horrible Ares-style micro switch things, you should not use an AB fet full stop, it causes serious damage to the motor and mosfet due to a dirty signal that the switch creates. The shock from the piston impact causes switch bouncing and very rapid On-BRAKE!-On-BRAKE!-On... effect, which heats both the 'fet and motor up by a lot.

[laurence]

Re: Passive and Active Breaking mosfets?

Ahhh okay, its just im building a semi auto DMR and removing the AR latch and so want to get rid of any sloppiness or overspin i might get, thanks very much for the info tho, helped a lot.

[Bachelarius]

Re: Passive and Active Breaking mosfets?

Why exactly are you removing the ARL?

Before you respond, have a careful read of this: http://www.airsoftcanada.com/showthread.php?t=25310
And this: http://eagle6.co.uk/beta/reviews/how...t-off-timming/

[laurence]

Re: Passive and Active Breaking mosfets?

Thanks, quickly, im just wondering, if i were still to get an passive breaking mosfet, how much would it damage the motor? As the gears and motor wouldnt really be getting up to any real speed and so how much would the PB mosfet damage the motor?
thanks

[laurence]

Re: Passive and Active Breaking mosfets?

Also, i want to remove the ARL as i dont want the gears to be pulled back halfway when i run low on battery and then not have the juice to return them again, i understand the role of the cut-off lever, its just i am disabling full auto so wont be able to just switch it back.

Would you just recommend i get a standard mosfet and stick with an 11.1?
thanks

[Bachelarius]

Re: Passive and Active Breaking mosfets?

Basically with braking, every time you release the trigger, the motor sparks. This leads to heat and crap build up. Heat will start to weaken the motor's winding/wiring whereas the crap buildup will raise the overall internal resistance over time. If you can avoid using it, do. But I do not see any gain in removing the ARL. You will get better results with a large spring, short stroked down and a large battery to give the gearset some more speed/momentum to bump the gearset past the Lockup point.

A Neo Motor will also provide faster spin-down than a regular ferrous one. The Tienlys and I think the X High Techs also both have improved airflow to help with heat, but you need a vented grip as well, to take advantage of it.

[laurence]

Re: Passive and Active Breaking mosfets?

This is for an M14 DMR, i will be using an 11.1 lipo and was thinking of using an Element Ultra torque which is a decent clone of the Systema magnum and pretty cheap, its only pulling an m130 spring, and will now be getting an SHS steel cut off lever for it too, the gun isnt gonna get massive amounts of use.
The reason i wanna remove the AR latch is because i dont actually need it if im going semi-only and also i dont want the gun to lock up, as if i do to a trigger pull too short, then i dont want it to lock up and instead the gears will come back to resting position. I want breaking mosfet as i want that snappiness and sharpness with the shot. Dont really wanna shortstroke my gears as they are steel guarder ones and i dont have acess to a dremel/grinding thing. Its just semi-only gun...

[laurence]

Re: Passive and Active Breaking mosfets?

Im just wondering how much extra wear my motor will get on semi auto in my m14 with a 7.4 or 11.1 lipo, been looking at this AB mosfet here: Gate GDS-4004 - AB MosFet with active braking

[Bachelarius]

Re: Passive and Active Breaking mosfets?

No clue on that mosfet, have a google around.

And the answer for the damage to expect is some. It completely depends on a motor. It's not life-threatening either way. Plenty of rifles have this feature installed and I am sure that plenty more will have as well. I'd personally avoid it and find other ways of dealing with it, but then again I'm a bit anal about these things and I would not ever remove an ARL either :/ Far too much can go wrong if you do in my eyes.

You just can't completely control a gearbox without either an ARL or using a micro-controller with cycle completion (e.g. the black talon Chimeras that are about to hit the market, I think PsyphyerVII is planning on including V7 compatibility, but that one's a waiting game)

[laurence]

Re: Passive and Active Breaking mosfets?

Okay, well atm, i think i might just see how it is with just a neew cut-off lever and better motor
thanks for the advice and info man