Technical Questions: Batteries + UMP 'competition series' internals

[kleinage]

Hi Folks, looking to dig a little deeper with a few items.

I'm returning to airsoft after a ten year hiatus. Never really got into it in the first place, got sucked into paintball instead, first with a basic electro marker, then into the wild and crazy experience of playing pump action paintball while surrounded by electros and speedballers. (My pump has a forgrip and folding stock, btw). Anyway, back to airsoft, got some techy questions.

My gun manual (Umarex UMP H&K branded 'competition series') recommends "an 8.4v 1400mah battery minimum." I wanted to figure out what equivalent 7.4 lipo would be, in terms of current, but I felt I did not have enough information. Researching a little further, I found that a 8.4v 1400mah NIMH battery should produce about 16.8amps at max capacity. (source: https://infectedairsoft.wordpress.co...teries-part-1/)

So I ordered a 8.4v 1600mah battery, and for kicks and giggles, a 9.6v 1600mah second batter with a c rating of 16, which if I calculated correctly, should give up to 25amps at max capacity, plenty to power any average AEG up to its full potential.

Now, I am concerned about wear and tear. So the question is, if I want longevity on my internals, should the 9.6v battery be just for those occasional rounds when I want a little more zing, or is it safe to be the daily driver? A little more info: given my current life circumstances I'm likely to normally only play once or twice a month a couple hours each time, or up to once a week MAX.

For this I need a little more technical information on the specs of the gun itself, which does not seem to be readily available. Anyone have knowledge of this, or know a way to get technical/repair manuals for guns for cheap?

First, it would be helpful to know the actually current the gun prefers. Are my borrowed calculations correct? ie. the gun needs at minimum 16.8amps to avoid problems? If so, what is the maximum recommended spec, ie the preferred current levels? (this will be useful info if I ever want to go Lipo, and to figure out how much I may be stressing the gun running this 9.6v battery). However, I also read that mini NIMH type airsoft batteries (the UMP uses a mini stick battery) do not operate at the max capacity of full size NIMH batteries. So theoretically my 9.6v stick could be performing closer to the optimal power for the gun (I suppose?) This, however, presumes the manufacturer did not design the gun around a lower power rating...(need more information).

Going deeper, does anyone know about the internals on the gun? Is the gearbox built well enough to handle the max power of the motor (given the 9.6v battery I picked up). I understand there are always trade-offs in terms of longevity when you start firing more ammo more rapidly- however I am most interested in trigger response, not ROF. In paintball I played pump, mostly, so I expect to be not much of a spray and pray type in airsoft either.

Finally, and more importantly, I know all good internals will still come to an end. Are repairs or upgrades so costly that it is worth worrying about it this much?

Thanks for any (thoughtful) posts. Very glad to have a newb question forum here.

[Styrak]

You can throw a 7.4v lipo or 9.6v NiMH in any gun and be just fine.

[Windows]

you're looking into it too much.

First recognize that max discharge ratings on batteries are max continuous ratings. Unless you're running an LMG, don't worry.

Second, realize that your current draw is a function of battery voltage and total resistance. The amount of power being supplied will vary with Chinese noodle wiring, fuses, inline connectors, bad solder joints, worn out brushes, cheap connectors, motor rpm, battery internal resistance etc.

Finally, realize that lithium type batteries typically have lower internal resistance than ni-cad, or ni-mh batteries. This means that for a given voltage, a lithium battery will output a higher current, and therefore power. Typically, most guns that will run on 8-9.6V ni-cad will also function just fine on 7.4V lithium.

As for what the gun prefers, it will depend on your setup. You need at least enough torque to drive the motor against the spring pressure. If you are getting pre-engagement and stripping pistons, you have too much.

[ThunderCactus]

If the motor only draws 12A, then it will draw 12A whether you have a 16A or 600A battery hooked up to it.
Any stock gun will run fine off a 7.4 lipo
If you want to run an 11.1, you'll need a mosfet at the very least to prevent your trigger contact from melting.

Most stock guns will be in the 12-18A range, so get a lipo that can do at least 20A.

Lots of tutorials on youtube on how to upgrade, or at the very least, disassemble and reassemble guns.
There's no real trick to being a guntech, you either have the mechanical aptitude or you don't. The videos help get your bearings when working on a mechbox, but not always on specific guns. Every AEG is basically the same, anyway.

One basic upgrade to do right away is the hop rubber, which is responsible for the majority of your range and accuracy.

Gears or piston are usually the first things to break. But you can replace those with SHS parts for like $50 and they'll handle 40rps.

Upgrades can be cheap or crazy expensive. Depends on what you want your gun to do.
If you're okay being in the 15-20rps range, and just want a bit more reliability, range and accuracy, then you could be down in the $100-$150 range.
If you want a crazy tweaker gun that people can't hear from 10ft away, shoots 250ft accurately, and cycles as fast as a gas rifle, then you could end up spending more money on upgrades than the gun is worth.

[cetane]

There's no real trick to being a guntech, you either have the mechanical aptitude or you don't.

Oh so very true for so much more than gun techs, for any techs..