MP7 Mosfet - some questions and help needed!

[dstbgre]

Hi guys

I have a TM MP7 in which I have installed all of the Nineball upgrades (damper piston head + cylinder head, polycarb piston, spring guide, cylinder, low friction bushings, 6.03mm barrel, enhanced spring) and, as expected, the stock battery just doesnt cut it. Its great with an 8.4 mini battery (tested using the nineball external battery kit) but I am not so keen on having an external battery if I can avoid it. As such I want to put in a mosfet and 7.4v lipo. However after trawling the net looking for information, as I have never installed a mosfet before, I seem to get so many different contridictions on what to use that I have no idea what is correct and what isnt. I was hoping someone on here would be able to clear up some of this!

Firstly active breaking or non-active breaking? I have seen posts on other forums stating that active breaking isnt good for prolonged semi. As I go to a semi only site I need something suitable for this purpose

Secondly will a 7.4v lipo provide either the same or higher current than a 8.4v nimh (I think it will just wanted to double check) and such be able to drive the upgraded spring?

Thirdly are there any prebuilt mosfets out there (available from the UK as I know about the infected one) that would be able to fit into an MP7 or would you recommend I build one? I can solder so I am happy to have a go besides it would be a good learning experience anyway.

Thanks guys!

[Genista]

Re: MP7 Mosfet - some questions and help needed!

Active breaking should be fine. The AB bit only loads both side of the motor with a +ve voltage.Some CPU controlled units apply a reverse current which can be quite harsh on the motor.

7.4v Lipo fully charged will give you around 9v (not 9.6v) which should be marginally more than an 8.4v mini. So, more voltage not current. That depends on other things including the C rating of the Lipo.

As for building your own, there are plenty of designs on the net and it's perfectly possible to DIY. I've built a few, but the key thing is to buy mosfets with the right power ratings (current and voltage) allowing for the high (ish) spikes that AEG's have. So I say go for it.

I have some pre-assembled AB mosfets which you can add your own cabling etc to if you fancy a middle option.

[No1_sonuk]

Re: MP7 Mosfet - some questions and help needed!

Active breaking should be fine. The AB bit only loads both side of the motor with a +ve voltage.Some CPU controlled units apply a reverse current which can be quite harsh on the motor.

Actually, all active breaking applies a reverse voltage. The difference is in how it's applied, and where it comes from.
The simplest active breaking shorts out the motor (that's what connecting both sides to +ve does).
Because the motor is turning, it acts like a generator, the "short" feeds the power back into itself. It slows down faster because the power it generates is in reverse to what would be needed to drive it in the direction it's turning. So it is effectively trying to drive itself backwards, making it slow down faster than if it was just disconnected.

[richardy]

Re: MP7 Mosfet - some questions and help needed!

in my opinion size is an issue in aeps...

infected armorys mosfets offer AEP sized mosfets... definatly worth a look with regards pre built ready to fit... as lets face it even though all of us can build mosfets most people simply dont have the time.

Lipo option, you can remove the end connector of your current 7,2v battery and soldier in on to a lipo pack 1000mah... and thus make a nice high powered pack for your mp7...

The trigger response even without a mosfet is GREATLY improved....

james see link below has done work on an mp7, the difference being hes also documented it with some articles, worth a read

http://www.apocalypsemeow.co.uk/

The eagle6 SMG lipo will be out soon, it will be pricey but ready to fit 7.4v 1000mah lipo with no mods what so ever... James had to mod our pistol AEP battery which fit but was a touch loose.

[Genista]

Re: MP7 Mosfet - some questions and help needed!

No1, I don't disagree in principal but the reality is that loading a motor and applying a reverse current from another power source are very different things. The later being more powerful and a more agressive way of doing things.

The back emf from the later would also be notably increased.

So the point about wear still stands.

[No1_sonuk]

Re: MP7 Mosfet - some questions and help needed!

No1, I don't disagree in principal but the reality is that loading a motor and applying a reverse current from another power source are very different things.

I was pointing out that your comment separating "The AB bit only loads both side of the motor with a +ve voltage" from applying a reverse voltage was incomplete.

The later being more powerful and a more agressive way of doing things.

Agreed. It also requires 4 MOSFETS in order to reverse the motor current (assuming an H-Bridge is used), rather than just 2 for the motor-shorting variety - 1 to switch on and off and 1 to short the motor.
I don't see the point in the h-bridge version myself - too complex, and twice as many MOSFETs to fail. It also takes up more space.

[richardy]

Re: MP7 Mosfet - some questions and help needed!

/richardy loses the ability to blink

[dstbgre]

Re: MP7 Mosfet - some questions and help needed!

Thanks for all the replys guys!
Genista thanks for correcting my info on LiPo - I misread a guide.
Firstly I think my head is going to explode with all the mosfet info however I will give AB a try and see what happens. I havent decided whether to buy one premade or whether to make it as I have a friend who works in an electronics who may be able to get me the components so I will give that a try first and, if not, then I will reconsider. From the guides I have seen I will get a P channel mosfet which can take 60v and 80a and an N channel one to go with it. Will this specification be ok for this application?

Richardy - thanks for the website I have taken a look and it looks good. I was particually interested in the conversion of the aep battery to an MP7 battery. I was having a look at the external battery adapter last night and I think im going to use that for the connector. When the other battery comes out though, assuming it fits into the mp7 with no mods, I will certainly be getting one (or several)