In part one (How to Upgrade and Maintain Your Airsoft Replica), we examined the compression chain components, which was the easy part. Now we dive into Drive Train Components. Here things can get a little complex as rarely can you upgrade just one item without having to strengthen others as well. This section will be broken down into two parts: Mechanical and Electrical.
The “Art” of Airsoft Tech’ing is in finding the right balance or combination of parts that work reliably and consistently to achieve your desired FPS and RPMs. Increase one area and you have to sacrifice in another or reinforce it to be able to withstand the addition stresses. The best gearboxes are developed through an evolution of trial and error. Just having thrown together the most expensive parts does not guarantee a successful AEG. If you can afford it, the easiest way to do this is by buying a complete upgraded gearbox from a reputable manufacture that has done all this work for you. Even then, it helps to understand what they put inside.
At this point you’ll need to align yourself to one of four camps; High Speed (CQB), High Power (Woodland), the Holy Grail of Airsoft tech’ing, the “Oh My God, there are a HUNDRED BBs coming at me from the next county” High RPM/FPS. The first two are reasonablely attainable on a budget; the third would be for bragging rights as Echo1s Minigun might be cheaper. The forth, and more common, is finding a happy medium of a decent rate of fire and adequate FPS for the style of game play you enjoy.
Obviously everything is held together within the Gearbox, so it stands to reason that your gearbox should be stronger than your strongest component. The weakest area on most gearboxes is the front framework that surrounds the cylinder head, Version 2 gearboxes are notorious for this, and it is also the one area that gets the most abuse. As the piston slams forward, that energy is transfer from it through the cylinder head into the gearbox; in essence pushing the front end away from the rear till, eventually, it will snap off. Now multiply that by the RPM of your set up and then again by the FPS of the spring and you end up with a very big number indeed! It boils down to a lot of trauma it has to endure. This is also why having a metal piston head and metal cylinder head without any form of bumper between them is a bad thing. Most Stock Gearboxes can handle a M110 Spring and still have a reasonable life span; some high end AEGs will survive a M120 Spring for 100,000 BBs. After that you are rolling the dice to see if your AEG will survive the day. The point is to bear in mind the quality and durability of your Gearbox when choosing your upgrade spring. Being one of the more pricier upgrades, it pays to do some research on the box you are thinking on getting. Don’t rely on just the Manufacturers and Venders claims. Reinforced and Radialized (meaning there are no sharp 90* cuts in the cylinder opening hole) are two key words to look for. Bushing size comes into play here too, but that will be covered further on.
The first thing everyone wants to upgrade is the Main Spring. Yes, it is a quick and easy way to increase FPS, but it comes at a price. The Main Spring is the driving force that everything else in your gearbox revolves around. The stiffer the spring, the more pressure is exerted on the rest of the components, mainly the gears and piston, but also the bushings, piston & cylinder head, and the front of the gearbox share in absorbing that pressure. Even the motor and battery, which now have to work harder, have their lifespan shortened. With ANY spring upgrade, you’ll need to replace any plastic bushing with metal ones. Up the anti to a M110 – M130 spring, you’ll need to replace any casted pot-metal gears, and the piston needs to be reinforced. Your RPMs will suffer at this point without a stronger motor, and your stock battery might not have a strong enough charge to full compress the spring, leading to gearbox lock-up. Over that, you’ll need to build a gearbox from the ground up. Yes, you can fit a M150 in your pot-metal Chinese AEG and run a $15 11.1v Lipo battery on it, just don’t expect it to last very long.
While you are at it, if you find a plastic Spring Guide in your gearbox, replace it with a metal one, if you can, go with a ball bearing version, as this reduces stress on the spring by letting it flex smoother. The main problem with plastic spring guides is that they crack and shatter in a relatively short time, and if a chunk of plastic falls into the gears, it could cause further, more serious damage, like stripping a gear or piston, or at the very lest, jamming up the gun. So this upgrade doesn’t directly improve performance (though a ball bearing version will increase spring compression a bit) it does improve reliability
There is a wide variety of Pistons available out there to choose from, made from equally wide variety of materials, each one is designed for a slightly different application. Terms like ‘Half-tooth or Full-tooth’, ‘Bi-metal’, ‘Short-stroked’ and ‘Poly-this’ and ‘Nylon-that’, just seem to muddy the situation even more. There is no one super piston out there that can do everything. So where to start, the teeth on the bottom of the piston engage the corresponding teeth of the sector gear to compress the spring, when the sector gear teeth run out, the piston is free to move forward and wait till the sector gear has completed its revolution and picks up the first tooth of the piston again. This is the basic operation of the gearbox. Now as long as the sector gear teeth that engage the spur gear are lower than the teeth that engage the piston, any Full-tooth piston will work. However, with High-Torque-Up gears, these teeth (the spur and piston teeth on the sector gear) are almost the same size which would cause the sector-spur teeth to engage or interfere with the piston teeth and jam up the gearbox at the very least. This is where the ‘Half-tooth’ piston comes into play, it only has a portion of the teeth molded in that is directly over the piston teeth of the spur gear, thus allowing higher gear ratios to produce more torque to compress stiffer springs. Needless to say, Half-tooth Pistons are most beneficial to high FPS set-ups, and Full-tooth Pistons are high speed and general purpose. While sticking on the subject of teeth, the ‘Hybrid’ and ‘Bi-metal’ pistons come into play. These pistons have a body made of one material and an insert with the teeth made of another material, typically out of steel, called the rack. On pistons designed for mild upgrades or high speed, this rack might just be the last few teeth where the piston sustains the highest pressure of a fully compressed spring. For a little more strength all the teeth will be metal. Short-stroke Pistons have a few teeth removed, thus reducing the distance the piston retracts and the amount of compression imparted on the spring. These are typically used with vented cylinders (where the piston doesn’t need to come all the way back to get a full “breath” of air to fill it) and high speed set ups, due to the quicker response time. The piston body is made out either a synthetic polycarbonate or nylon material, or an aluminum alloy material. Synthetic is lighter (RPM) and alloys are stronger (FPS). A good compromise for a general purpose set-up would be a polycarbonate piston with a full metal rack of teeth. Your piston is probably the one item you don’t want to go cheap on, it is the hardest working part in the gearbox.
All most as diverse as pistons, Gears come in various ratios to suit your needs. Picture a 10-speed bicycle, by moving the derailer, you select two gears for the chain to ride on, give you a wide range of ratios to choose from. 1st gear gives you the torque to start off with, but sacrifices acceleration and top speed to do this. 10th gear gives you the fastest speeds, but would require a huge amount of power to get going from a standstill. Where as 5th gear is a good compromise of torque, acceleration and top speed. Same thing with the Gear Sets that are available in High Speed Ratios, Standard Ratios, Torque Ratios, and Super Torque Ratios. Choose your gears in conjunction with your motor to compress your spring at your target RPM or FPS. Every combination is a trade-off of between RPMs and FPS. For example, using a standard motor with high speed gears (or a high speed motor with standard gears) will increase speed, but at the cost of how stiff of a spring it can compress. Likewise, that same motor with torque gears (or a torque motor with standard gears) will handle a M130 spring, but at a slower rate of fire. Now to compensate for what was lost, you can increase the voltage of your battery, but you have to ensure that the rest of the electrical circuit can handle the addition amperage draw, more on that later. Another big feature found on gears is the orientation of the teeth that mesh between the gears themselves, namely standard straight cut and helical cut. The main benefit of helical gears over standard gears is an increase in contact surface between the teeth themselves. This means the pressure exerted by the spring is spread out over a larger area and thus it can stand stiffer springs and are more reliable. The trade-off seems to be slightly nosier gears.
With a high speed set-up or when feeding issues are encountered, a Sector Gear Delay Clip is a good upgrade to improve feeding reliability. This little piece slips over the tappet plate post on the sector gear and increases the duration the tappet plate remains in the rearward position to permit the BB to rise into the hop-up unit.
A final word on gears and pistons, try to get them from the same manufacture. This is to ensure all the teeth are of the same pitch, and will mesh together nice and smoothly. This will also go a long way towards quieting the noise of the gearbox.
Bushings and Ball Bearing, while doing the same thing, serve different purposes. Bushings are solid pieces of metal with a hole in the middle to support the axle of the gears. Their ‘solidness’ is what counters the lateral forces produced by high power springs and motors, making them good candidates for a high FPS set up. Meaning, as well as being turned in circles around their axle, gears are being pushed front and back by the motor and main spring. This puts an uneven strain on the bushing and will wallow out the hole in an oval fashion. So the harder the metal and the better the lube, the longer the bushing will last. Stainless Steel is harder than Brass which is harder than most aluminums, additionally, there are oil impregnated steel, also called ‘Oilless Bushings’ and hardened hybrid metals. All metal bushings are better than the nylon ones that still come in some cheaper budget AEGs. Since it is the small center hole that wears out in the bushing, it doesn’t matter if it is a 6mm, 7mm, or a 16mm bushing, that little hole in the center is always the same size. What does matter is that the bushing sits in the gearbox as tight as possible, preferable requiring a small mallet to tap them in place, and that they sit square in the hole. Any slack in the gearbox hole will let the bushing move around and wear it out, thus requiring a new gearbox. Where Bushings fail is when they are used in a high speed set-up, as the increased speed produces increase friction which generates increased heat, and this heat de-tempers the metal bushings, softening the metal, and leads to premature failure.
Ball-Bearing, by comparison, are complex and delicate components, designed to reduce the rotational friction created by the gear axle spinning in the bushing. It does this by trapping small steel balls between two raceways that act as ‘wheels’. These small balls are also the Achilles Heal of the Ball Bearing Bushing. When selecting Ball Bearing Bushings, bigger is better, not just overall size, but as the size of the balls themselves. The same lateral forces mentioned before, are pressing down on the balls, causing them to wear out, and when one of them fails the whole bushing fails. So a 9mm Ball Bearing Bushing should have balls that are noticeablely larger than a 6mm Ball Bearing Bushing. I have seen cases where a manufacture has used the same size ball in all their bushings from 6mm to 10mm. Having thicker raceways doesn’t serve any purpose, and they only do it to save on manufacturing costs. The same installing guidelines apply to these as well. With the reduce friction letting the gears spin faster, Ball Bearing Bushing are great for a high speed rig built around a M100/M110 spring, though the larger Ball Bearing Bushings will support up to a M130 spring reliablely. Where they fail is when a heavy spring is used with a Ball Bearing Bushing with small balls causing them to wear prematurely, and when they fail, they throw the gear out of alignment which can lead to further more serious damages.
Like gears there are 3 basic types of Motors available; High-Speed, Standard, and High Torque. There are a few pricier options that advertise Torque and Speed, but I haven’t seen enough reviews to form an opinion on them yet. If you have the cash to spare, then go for it and let me know how they work out. The harder your motor works, the more amperage it draws, so a quality high capacitance battery will be needed to provide juice for it. One of the biggest differences between the brands is the build quality, which is pretty hard to determine just by looking at them. I do two tests to get an inclination of the quality of the motor. First I’ll try to slide the armature back and forth with in the can, if there is very little play, the manufacture has taken the time to properly shim it and hopefully has spent the same effort on the rest of the motor. Second, I’ll twist the motor to gauge the magnet strength, the stronger the magnet the more torque the motor will produce. However this can be misleading as to the quality of them. Cheaper man-made magnets, while initially strong will lose there magnetism quicker, especially when repeatedly heated up by high loads. High-Speeds Motors get the speed from the windings of the armature and the timing set into the bell. To test these, hook a battery straight to the motor and listen to sound it makes, the higher the whine, the faster the RPM. Other qualities to look for are cooling fins on the end bell, components that are screwed in, as opposed to press fitted, and heavy gauge brush wire that has lugs on them to attach them to the motor, as opposed to the ones with thinner wire that is just trapped between the brush hood and the brush spring. A word of caution on motors, motors do not like excessive heat, which is a sign of it working too hard. Heat weakens the magnetic charge of synthetic magnets and can burn the lacquer insulation off the wire windings of the armature. Both will kill or severely reduce the effectiveness of that motor. If this becomes an issue, either reduce the spring or increase the torque of the gears.
Getting into the electrical side of the equation, it’s all about reducing resistance. The more juice that can get to the motor, the better it will run. The less energy lost to heat and arcing, the longer your battery will last.
The Trigger Switch is just a mechanical device that closes a pair of contacts to complete an electrical circuit, in this case one between your battery and your motor. Some Trigger Switches even have a secondary set of contact that is closed by the selector plate as well. All these contact points create resistance to the flow of energy. If the amperage draw of the motor is high enough the electricity will even arc across the contacts and cut holes in them, eventually ‘burning them out’. MOSFETS really help out here, but we’ll get to that in a moment. For a good switch, look to the size and thickness of the metals used. Wider contacts reduce resistance and thicker copper counters the effects of arcing. On a related note, arcing also leave a carbon build up on the contacts, which also increases resistance. If they haven’t burned a hole through the metal, this build up of carbon can be removed with super-fine grit sand paper.
The Wiring is the artery that the electricity flows through. The thicker the wire and the more conductive the metal, the less resistance it generates. Most low end AEGs come with 20 AWG (American Wire Gauge) or poor 18 AWG copper wire. This is adequate to get the job done, but it produces a lot of resistance, even with the stock motor. By upgrading the motor, gears, or spring, you increase the amperage draw on the electrical circuit, and the stock wire can’t effectively keep up. By upgrading to lower resistance wire, you increase the flow of electricity to match the needs of your motor. For mild upgrades, 18 AWG Silver Wire is adequate. Silver is more conductive than copper, but not as good as gold. For harder working set-up, 16 AWG is commonplace. The composition of the wire also makes a difference; a single solid conductor (the metal part itself) has the least resistance, but is very stiff and hard to form. Next is the finely stranded (a lot hair sized wires twisted tightly together) conductor, which has a lot of flexibility and low resistance. The last choice is the regular stranded (6-10 thicker wires twisted loosely together), typical of stock AEGs. Of the three, the second is the most common choice. Most up grade switches come with 18AWG Silver Wire, but if you are good at soldering, the wire by itself is also readily available to improve your existing switch or fuse harness.
FOR THE LOVE OF AIRSOFT, DON’T REMOVE THE FUSE!! The Fuse is there to protect the rest of the electrical circuit, and it’s much easier on the wallet to replace a $1 Fuse (if that much) than buying a new $50 battery because something shorted out. While it is true that the Fuse and Fuse Holder do generate additional points of resistance, this is a small price to pay for the protection it provides. If space is an issue, you can replace the bulky Glass Tube type Fuse Holder with a more compact Mini Spade type Fuse from any automotive store. The main advantage to the Glass type Fuse is that they are available in ‘Slow Blow or Delayed Blow’ version which ignore the normal sudden spike produced in the initial nanoseconds of pulling the trigger. The ‘Quick Blow’ may pop even when there is nothing wrong. Stock AEGs mostly use 15 amp fuses, whereas upgraded motors might need 20 amp or even 25 amp ones.
The basic function of a MOSFET is to divert the high amperage current away from the switch by sending it directly to the motor. It does this by sending a low amperage current to the switch to act as a signal source to tell the MOSFET when to close the circuit to the motor. It acts like a solid state relay that protects the trigger switch from burning out. A MOSFET by itself does not replace the need for a fuse. There is a wide range of MOSFETs available, many with addition feature like active braking (which reverses the polarity going to the motor to stop it), and burst fire (by programming how long the circuit remains energized per trigger pull). Additional features might include a thermal breaker (similar to a fuse, but it resets itself once the link has cooled off), a mini spade fuse or a low voltage indicator (great for li-poly battery use). Installing a MOSFET requires rewiring the trigger switch, so some soldering skills are needed. There is only one MOSFET Unit out there that I know of that is completely ready to be dropped into your gearbox, that comes with a replacement trigger switch ready to be installed.
There is no debating that Deans Connectors are vastly superior to the traditional Tamiya Connectors. Their wide gold plated pins are soldered on to the wire, which produces considerably less resistance than Tamiya’s small crimped on pins and do not bend out of shape. Additionally, Deans bodies are more heat resistant and won’t melt as easily as the Tamiya. They as more compact in size, and while they do not lock together like Tamiya does, the spring tension inside the female Deans connector is more than adequate to keep the connection together while the battery is in your AEG.
Well there you have it, your whole gearbox explained to you in basic laymen terms. I sincerely hope this gives you, the beginner Airsofter, some of the basic knowledge to make informed decisions about upgrading your prized AEG. At the very least, it should point you in the right direction. So see you out there on the field, play safe, play smart, and have fun!
By Don Bransford – Don’s Tech Tip Corner