Practical AEG Upgrade
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More about EG-560, EG-700, EG-1000 and ICS Turbo 2000:
It is quite true that a properly shimmed mechbox can run perfectly fine with 7.2V. We upgraded a MP5 (we put in a spring which is almost one inch shorter but a little harder than the TM stock one) and have it driven by an EG1000 + a non-name branded 1800mah 7.2V battery and managed to achieve a consistent ROF of 24~26 at FPS of 298~302.
However, there is one exception - if you are using EG-560, the "7.2V test" will not give valid results. EG560 needs at least 8.4V to give reasonable performance. With proper power input, EG560 can produce ROF as great as that offered by EG1000.
EG1000 can give relatively high ROF even with low power input. However, it is also fairly easy to get over-heated. On stock gun using high mah (those with 2500mah or above) NIMH battery, stay at 7.2V in summer time - you don't want to cook your motor within an hour. .
The ICS Turbo 2000 motor is kinda on par with the EG700 in terms of performance. They are less likely to get over-heated and are therefore more 8.4V friendly on stock guns.
However, because of the different shape of the pinion gear, it is not recommended that you use Turbo 2000 on TM guns. Frankly, many parts from ICS are NOT truly TM compatible.
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7mm VS 6mm
In theory, a 7mm bushing due to its larger diameter allows the spreading of radial loads out on a slightly larger area of the mechbox shell. Simply put, it offers a relatively higher level of tolerance for radial and axial loads.
Going 7mm does not seem to be necessary unless you are using a very hard spring or that you want to use ball bearings in a high FPS setup.
Certain new AEG models from CA are 7mm based. TM and ICS seem to stick with 6mm as of the time of this writing.
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Spur gear breakage:
If your spur gear breaks, it is NOT necessarily due to poor shimming. If several teeth were broken together on the spur gear, chance is that the spring that you use is too hard (the impact generated on the gears is too high) or too soft (the gears run way too fast) for your configuration.
Sector gear breakage:
If two of the inner teeth on the sector gear break in a row, do whatever you can to minimize the gap between the spur gear and the replacement sector gear. One quick and easy way is to swap one or two shim washer(s) (depending on their thicknesses) from the bottom side of the sector gear to the top.
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Installing the variable-pitch spring:
As recommended by the manufacturer, the tighter coils are to be fitted to the rear of the mechbox (i.e. the side of the spring guide) for the best possible performance.
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Chronograph:
Oehler Research offers a really fancy (and expensive) Chronograph known as the Model 35 Proof Chronograph. It has a built-in printer included. Visit
http://www.oehler-research.com/ for more information.
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Why higher mah is better?
Higher mah means higher capacity AND ALSO the ability to sustain current draw at a higher rate. Effectively the motor can demand more from the battery at any given moment.
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Recommendation:
If you are to trim a M110/M120 spring, cut off some of the tighter coils.
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Beware of the suck-back problem:
Suck-back occurs when the piston retracts before the bullet has completely left the barrel. If you upgrade to a longer barrel without installing a matching cylinder, suck-back will occur (resulting in poorer FPS).
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HopUp:
According to the Bernoulli's principle, if a bullet is given a backspin an overpressure is formed under the bullet and an underpressure is formed on the top of the bullet. The bullet is therefore sucked up - this is why it can fly farther.
