The Quest for a better TM MP7A1...

[onizuka-gto]

Well, it's done.   

 

http://home.comcast.net/~gpochini-geico/mp7.wav

 

I haven't managed to do any photos yet, but the conversion itself is simple.  You'll need:

 

1.  pair dean's connectors/heat shrinks

2.  2 pcs low resistance wires, approx 4.5"

3.  soldering iron

4.  capability of disassembling the mp7

 

All that needs to be done is to wire up the dean's connector to the two new battery leads, disassemble the gun, and solder them directly to the battery connector inside the foregrip.

 

Note:  With the switch assembly in your hand, looking at the face of the battery socket, the positive contacts are on the left.  Negative is on the right. 

 

I soldered the leads to the top contacts on the switch assembly, with the wires at close to a 90 degree vertical angle.  This was done so that the wires were as out-of-the-way as possible and so they'd run along the top of the battery compartment to the front.

 

If you decide to move away from lipo or what have you, you can always disassemble, reheat the solder and pop the wires off the terminals.  Once that's done you will be able to use the stock battery again.  There is no permanent modification to your gun.

 

The biggest issue I had was that of space within the battery compartment.  I removed the little sliding lever inside the front of the battery compartment and had to fiddle with making the pigtail, battery, wires and dean's connectors fit inside the compartment.  It was snug, but it's not a big deal. 

 

Because space is at a premium, you may want to make the pigtail on your lipo pack as short as you're comfortable making it.  Mine is about 2" long, which really is an inch TOO long.  Also, because of the tight quarters, BE SURE YOUR WIRING AND DEAN'S CONNECTORS ARE ALL PROPERLY INSULATED.  You do NOT want to short anything inside the compartment because you're wadding up wires to cram inside there. 

 

As you'll hear from the .wav file, the rate of fire is better than stock, even if only a bit better.  I didn't do semi shots on the recording, but there is noticeably less 'wind-up' time before the piston is released, which was my main goal.  Add to that another 300 mah and I'm very pleased with the results.

 

Here's the Eflite pack I bought.  I got it for 26 bucks locally and walked out the door with it, but ordering online is obviously a convenient alternative.  I'm just impatient. 

 

http://www.redrockethobbies.com/E_Flite_7_..._p/eflb0990.htm

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Thanks Wudjak!!!

 

Just a question, is there any higher voltage li-po that could also fit the mp7?

 

It'll be nice to know, because that website you gave me is actually in my history logs while i was looking for compatible Li-po but i discarded that webby because it didn't tell me the dimensions of the batteries, so i couldn't really know what batteries would fit where...

 

[bullzebub]

since each cell is real small , you could probably fit a 3 cell in there ... but that would give you 11.1V! i think that is a bit much for the puny mp7! :-P

[Wupjak]

The little guy battery was the smallest of those that i could hold in my hand at the RC/hobby shop. I suppose there are 3 cells, but you'll run into space constraints because of the added length and wiring space.

[pingpong]

No. There is no space for six or more full AA cells. We can't use less than six cells either, we need six cells to get 7.2v at least. Capacity is no substitute for voltage.

 

1.2v per cell (in series) x 6 cells = 7.2v.

 

1.2v x 7 = 8.4v.

 

1.2v x 4 = 4.8v

 

See?

 

Also, we could build a simple 7.2v replacement pack with the CPB750 cells of course, but we'd need the custom connector for it. Anyway the point of this exercise is to get more voltage.

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why not use li-ion cells?

 

i believe they are.. 3.7 volts 600 mah each..

 

so using.. 4 li-ion cells.. 2 x peries.. which make.. 2x 7.4v 600mahpack (ull get 8.2-3 volts when fully charged for awhile). put the to packs together in paralell form. which will give you a cell pack of 7.4v 1200 mah. which i believe is A LOT since li-ion gives a more powerful discharge rate compared to nicd or nimh...

 

the only thing is... iono if itll fit inside the gun. each sell is an AA size

 

soo. wanna try that static? =D

 

 

EDIT: OR you can use recharable 123a size li-ion =D

[Wupjak]

BAD WUPJAK! I forgot to post the photo of the project. Please note that, after this photo was taken, I had to resolder the wires. This was because they stuck straight out into the battery compartment and didn't allow the battery to move to the rear as much as it needed to. When I resoldered them, the wires pointed to the top of the photo, or 'up' inside the battery compartment. That allowed the battery pack to slide closer to the rear of the compartment so that I could cram the wiring into the remaining space. Even so, it's a tight fit.

 

Also note that there is 1" or more of wiring between the lipo battery and the dean's connector that doesn't need to be there. In fact, it adds to the clutter in the battery compartment. I'll probably lop that off and redo that connector this weekend.

 

As I believe I noted previously, the copper tab on the right side of the switch is the positive side. You'll see that I sharpie'd that side for illustrative purposes. Yes, the wires are both yellow. Thank you.

 

[onizuka-gto]

why does the li-po have two sets of wires?

 

[Wupjak]

the shorter lead is a cell voltage balance testing lead, iirc. lipos get cranky (read: blow up) when the voltage cell to cell is imbalanced.

 

BTW I just used Audacity to graph that .wav I uploaded to count the number of rounds per second on LiPo. I came up with 12-13.

[Xaccers]

I used to run my CA36 M100 off of a 7.4v 2000mAh 2C li-pol as it was the biggest battery I could fit in the foregrip without getting a custom.

RoF was slightly below that of a 8.4v NiMH/NiCd, but not much (I'm not running with a 11.1v Li-Pol in a battery box) so 7.4v inside a MP7 should be perfect.

 

Incidently though, the only li-pol chargers I've found run from a 12v power supply only, no mains, so I had to also buy a mains to 12v power supply.

 

I'd also cover the copper contacts and solder joints and any bare wires with electrical tape, the last thing you want is a short!

[Wupjak]

Ran my MP7 at OP: White Noise yesterday without a chance to use it in a cqb setting.

 

Sadly, the little LiPo pack must have taken some sort of nasty jolt inside the battery cabinet and the pack started to swell.

 

After an honest evaluation, the stock battery really does well enough at turning the little motor over. Trigger response is the weak point of this gun but perhaps an external torch such as that available for the G18/93R will overcome that while maintaining the ease of use of the stock batteries.

 

In the end, I did the LiPo conversion to be able to say that I did it. I am fortunate in having a bit of disposable income dedicated to testing and evaluating fun projects. This conversion, while producing some very positive, tangible gains, is dubiously worthwhile. This is especially true when considering the maintenance/delicacy of the battery packs compared with the stock battery (carrying a spare battery really is a better alternative if you find yourself using the MP7 much at all).

 

I undid my pigtail just now and restored my MP7 to stock. Since I rarely if ever use my sidearm, it'll be good enough.

[bukkake]

Heya,

I maybe going to buy MP7 from WGC, and that serial number plate kind of disturbs me. Can it be removed just by removing the two bodypins and sliding out? Im not so familiar with gun internals so I wouldt go and open it .

 

First post ;P.

[Scotchy829]

Heya,

I maybe going to buy MP7 from WGC, and that serial number plate kind of disturbs me. Can it be removed just by removing the two bodypins and sliding out? Im not so familiar with gun internals so I wouldt go and open it .

 

First post ;P.

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Nice name

 

And yes, the serial number plate is removeable after taking out the twin pins and sliding off the stock.

[jaeger0416]

So, has anyone tried perhaps building a 7.2v 1400mah cell with the new IB mini cells?

[staticzero]

Why? 2/3A cells are too large to fit in the MP7. Might as well use an 8.4v IB1400 pack if you're going to have to mount it externally.

 

For those wondering what's up with my custom pack plans the dang cells are still out of stock, hopefully they'll come in soon.

[Scotchy829]

For those wondering what's up with my custom pack plans the dang cells are still out of stock, hopefully they'll come in soon.

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Keep us updated please

[R1200RT]

I can't remember where I saw it, but isn't it possible to use the TM Pro Light for extra power - or am I just being thick?

[Nebulus]

Sorry for inconvenience.

Still looking for experience 'bout fitting this spring http://www.wgcshop.com/pcart/shopper.php?itm=NB-PT-G18CFPS inside MP7 gearbox.

Does it improve FPS rate?

How about the reliability of stock gears set ?

Thanks in advance for the invaluable information!

[famman47]

Will we soon be able to contact Cheapbatterypacks.com and ask for the "Staticzero pattern" custom mp7 replacement battery?

[squeakyL]

Well, I'm on the verge of getting a 6x double stick of CBP 750s not to increase voltage, but simply to make charging easier, since I like NIMHs much better.

Doe anyone have any idea of how easy/hard it is to get the connector off the mp7 stock nicd and onto a double stick?

[maelstrom]

for anyone wondering a thunder power 7.2V 1320 pack does not fit internally. Just got a mp7 and though i could stick it in but the guides for the battery pusher block it.

[unxconformed]

I have a solution that may work, its something I did for a R/C helicopter at one time.

 

You take a 3s lipo battery (3 cell) and you regulate the voltage to whatever you require with a home built regulator. In my helicopter I couldn't go over around 9.6v otherwise it could fry the electronics. What I did was have my dad (electronics master) make me a regulator to keep the voltage at a steady 8.4v. This worked really well.

 

I don't have a mp7 yet, but I am sure I could fit my 3s pack in there. It has a 30amp continuous discharge rating and is 1500mah. I could easily regulate it to 9.6v or 8.4v. The only issue I can see is if I can fit the regulator in with the battery. It shouldn't be so hard because the regulator components are actually very small.

 

One thing about lipo's is that when you charge say a 2 cell pack, it doesn't charge up to only 7.2v or whatever, it actually charges up to more like 8.7 or so volts. You can tell that the battery is almost dead, when the voltage gets to around 7.2v. Its lame in my helicopter because as the voltage changes, the helicopter performs differently. But I would imagine that a 2 cell pack should work good for most people.

 

As far as saftey, I have tons of lipo's laying around the house, They are pretty tough unless you discharge them too fast and hard, or charge them way to fast. If you put more than the recommended amp flow in while charging, you can have one catch fire. I use them in R/C stuff, and they take crashes pretty well.

 

Anyways, hope that helps, I may get a mp7 in a month or so and try this out.

[maelstrom]

most of the lipo's i've dealt with are 34mm wide, a little too wide to fit, if i could find a 32mm wide and 10-12mm deep cell it would be great but most reputable cell makers that i've seen only make them 34mm wide.

[Sh0ty]

Maybe I'm just wierd, but everytime I see Lipo in this thread, I think of the procedure. (surgical) "woohoo! Lipo here I come!" -onizuka-gto

 

lol, you don't look that fat.

 

-Sh0ty

 

EDIT: Spooling (it's 12:00 AM over here)

[unxconformed]

the pack I had in question is 30mm wide, but it is 25mm thick. It is also 100mm long. The pack was built to space the individual lipos apart for airflow, so it could be made to be about 15 -20mm thick. It can also be shorted down to maybe 90mm in length. It is rated at 30 amp discharge.

 

Does anyone know what the amp draw on the mp7 is?

 

My problem I encoutered is if I wanted to regulate the 11.1v down to say 9.6 for the mp7 and still have the capability to draw 30 amps, the regulator would be too large to fit in the gun with the battery. If the amp draw is lower, I may be able to build a regulator that would fit in with it.

[bepo]

I was reading airsoft forums last night and one of the things that was sugested to greatly increase your trigger response and ROF was MOSFET's. there's a huge guide here: http://www.airsoftmechanics.com/guides.php?aid=14&page=9

 

It fits perfectly with your project and the results show a good 14% increase in ROF

[Wege]

ok.. so.. something that increases a ROF from (plucks figure from air) 700rpm, to 775odd RPM.. how is that a noticeably good thing?