Thursday, 19 March 2015

A New Battery Will Make Me Go "ROF ROF ROF!"

Last weekend was the first game since ages, and I got to run around with both the new MP5K PDW as well as the G36C with its M4 magwell. To make it really short and sweet: Everything went extremely well. Mostly anyway.

M4 magwell

In one very stressful situation I didn't quite manage to slap in a new M4 mag as quickly as I would have hoped, but I put that solely on the newness of it all. Later on it went pretty much as well as I'd expect. Once you get the "reverse AK" reload down, it's definitely quicker than some rifles (the AUG for example). No feed issues whatsoever through 400ish BBs from several magazines.

First slide the back end in, then twist forward while pushing up. The magwell bevel will guide the magazine in perfectly.


The MP5K performed very nicely, and the lightness of it made it a real joy to use. Very quick to pop out of cover and hose someone down. One of only two gripes came up after a rather lengthy episode of running around, when my goggles developed a nice film of moisture on their upper edge, exactly on the spot where you'd need to look through to be able to aim down the very low-sitting iron sights that I was using at the time. This is easy to alleviate with a scope mount and a holo or reflex sight, which will change your head position to a more upright one when aiming.

It does look slightly comical with the sight. The distance from the top of the sight to the bottom of the mag is only slightly less than the overall length of the gun with the stock folded.

The other problem I ran into was with trigger lag, or more accurately the time it took the motor to cycle the action. At one point, I was intending to quickly pop out of cover, shoot one single well aimed shot and take cover again. As more seasoned players are surely aware, the default NiMH batteries that come with guns aren't all that great powerwise. I peeked over the edge of cover, tapped the trigger and only heard the motor spin for a bit, but not enough, so no shot was fired. I had to slink back into cover as I was immediately spotted and had no time to shoot again. Obviously what happened was that the motor had wound the spring back a ways, but not quite enough to make the sector gear release the piston.

To treat the trigger lag issue, a better battery with more amperage is the obvious first choice. It's easy and quick to do, and has worked on my other two AEGs very nicely.

As I have been toying with the idea of upping the rate of fire on the MP5K anyway, I thought I'd devise a little test to go through the batteries I currently have, possibly finding a good, ROF-upping battery replacement that way.

Battery testing

I set up the chronograph (UFC Pro), loaded up some mags and went to work. The batteries used, in addition to the stock 8.4V NiMH that came with the gun, were the following:

  • VB Power 7.4V LiPo (2200 mAh, 20-40C)
  • Flame 9.9V LiFe (1500 mAh, 15C)
  • Turnigy 11.1V LiPo (1800 mAh, 20-40C)

All batteries were charged fully before starting. They all have their stock mini-Tamiya connectors at this time. I have gold-plated Deans connectors already on order, and will repeat this test once they arrive and I have them installed. That should give some hard data on what kind of effect (if any) the connector has on the system's efficiency.

I listed the batteries and their respective rates of fire (ROF) of in both rounds per minute and rounds per second on the table below.

Battery ROF(rpm) ROF(rps)
8.4V NiMH 750 12.5
7.4V LiPo 857 14.3
9.9V LiFe 1000 16.7
11.1V LiPo 1500 25

One interesting point of note is that the lower voltage LiPo outperforms the higher voltage NiMH by a fair margin. According to my understanding, this is simply due to the fact that the NiMH battery basically gives out too little power for the motor to turn effectively.

With all the Lithium batteries, it was practically impossible to get the gun to half-cycle, so any new battery should at least fix the non-firing situation I encountered while playing.

As for upgrading the gun, I would like to reach a ROF roughly around 20 rps (1200 rpm). Of course, with my luck, that lies directly in between the LiFe and the the high voltage LiPo. The latter would empty the 90 round midcaps in 3,6 seconds of full auto. Yes, I'm sure it would be fun for a while, but the internals would likely break somewhere (at least the trigger contacts would suffer without a MOSFET), and I'd be out of BBs really quickly.

I'd be lying if I said that during the test I wasn't even slightly worried something would go wrong with the 11.1V LiPo, especially since the spring in the MP5K only gives out about 1 Joule and the gearbox is completely stock. With no angle of engagement correction and a fairly low powered spring, I was definitely expecting some sort of premature engagement. No sign of that, though, during the 40ish rounds I put through the gun with the high voltage LiPo. I'm sure something would break in the long run, though.

Furthermore, finding an 11.1V stick LiPo that would fit in the gun might also prove somewhat problematic. I am pretty fond of the LiPo batteries in general, though, so I'll most likely replace the stock battery with a 7.4V LiPo when the time comes. Apart from that, I'm not entirely sure at this point which way to go about reaching the 20 rps mark. High speed gears, a new motor to turn them, something else? I'm open to all suggestions.


  1. 14:1 Gears could be tried for a higher RPS, a friend has a JG G3 and he put a lightweight piston in which help marginally, increased his rps by 1.. hehe. other than that, high speed gears, shimming and possibly a high speed motor would do the job.

    1. Yeah. Higher speed gears, and I'm actually thinking high torque motor. They have very snappy response (I have the SHS High Torque in the AUG and it's brilliant), so there would be very little trigger lag. Shimming naturally, and I have a light weight piston lying around that I could use. Perhaps a slightly springier spring might also come in handy to avoid any premature engagement issues.

    2. ive ordered a 16:1 Gearset for my Cyma M14 EBR ( i'd post a picture of it but im unsure if i can here ) . i meant high torque motor, from what i have read online high speed motors arent too great. ive also heard that " Swiss cheesing" the gears and piston give a better rate of fire too. i am in the UK ( Northern ireland ) so am limited to 328 Fps on .2g bb's.