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I Love Electricity

Lithium Polymer Powered Brushless E-Maxx



The Traxxas E-Maxx is a great machine…a 4 wheel drive, dual motor, 14.4 volt electric monster truck. Because it is electric, it’s quiet, high-torque and cheap to run. As I’m into mechanical devices and electrical tinkering, this is the perfect R/C vehicle for me to experiment on. I’m a basher and started is project mainly because I like to modify things.

NiCd is OK…NiMH is GOOD…Lithium Polymer RULES!:

Let me start by offering a little warning…LiPo batteries can be very dangerous if not charged properly or are abused. Therefore, if you decide to convert to LiPo, you MUST get a special LiPo charger such as the AstroFlight 109 (The SuperBrain 969 is not a proper LiPo charger). Second, over-drawing the packs could result in a fire…therefore an automotive type auto-reset circuit breaker should be used…or at least a fuse that will cook before the packs are overloaded. Also, the stock EVX WILL NOT handle 24 volts…you need a new ESC like the Victor 883 for brushed or Warrior 9920 for brushless to get away with this.

How do I get away with LiPos in my Maxx? Simple…I’m using two PolyQuest 11.1v, 4400mah LiPo packs wired in series for ~24 nominal volts. Safety always comes first, so I have a 30amp circuit breaker to prevent LiPo fires should the rotor get locked. It is also important that LiPos are not over discharged, so I installed this battery alarm. Motors become much more efficient at higher voltages…that’s why Traxxas went 14.4v instead of the usual 7.2v systems. By going to 24v, the efficiency increases even more because for the same power, amps go down (Ohm’s Law).

Major benefits of the LiPo batteries include:

A 45+ minute bashing runtime! And that 45 minutes is very conservative, with mostly full throttle up and down a 35 degree hill!

With the brushless setup, I can literally peel out and lay rubber on pavement!

The truck is much more stable as well, cornering on a dime at high speed due to less battery weight.

Continuous donuts are effortless in 1st and 2nd gear…in forward and reverse!

Discharging is a thing of the past

The only downside? LiPos take a long time to charge. Thankfully, the AstroFlight 109 can charge 1-9 cells, so I can charge the 6s pack in one shot…it takes about 1 hour 10 minutes to charge. The batteries don’t even get warm while charging…It may take a bit to charge, but I’ll never have to “discharge” again. You’d need 3 or 4 sets of NiMH to get the same runtime, so overall charging time isn’t much different.

FM Radio:

The stock E-Maxx comes with a 3 channel AM radio, with the third channel set to shift from low to high gear. The transmitter is a standard pistol-type with the shift button mounted as a rocker switch activated by the thumb. I personally prefer stick style radios, probably because I started with this type and am very comfortable with it. Additionally, I’m not too fond of AM radios because of interference problems. Therefore, I’ve replaced the stock radio system with an Airtronics FM system. I have one radio configured for 75MHz surface use and multiple receivers, so that I can use the same radio on all my bots and R/C vehicles. I dropped one of these 4 channel FM receivers into the E-Maxx with the left stick configured for throttle and right stick configured for steering as one normally would. I placed the shift channel onto the left and right movement of the left stick, which I removed the spring from so it doesn’t bounce back to neutral.

The FM system is less prone to glitching…think of AM radio verses FM radio reception. The FM system is also more powerful, which allowed me to run the antenna horizontally along the underside of the chassis…granted, I lose some range, but still have more than the stock setup…and I did it to get rid of the unsightly antenna sticking out of the body! Look at the overview pics at the top of this page to see the difference.

Servos & Suspenstion:

I quickly replaced the shift servo with a high speed one so that when I shift, there is even less of a delay between gears. I plan to replace the steering servo with an even higher torque one in the future. I replaced the stock plastic shocks with purple anodized aluminum shocks. The difference in fluidity is very noticable and greatly improves handling. I also replaced the plastic bumpers with aluminum ones from Duratrax.

Speed Controller:

The original Traxxas EVX ESC is a good unit…but it only works on brushed motors and would fry on 24 volts. To run brushless, I needed a new one. The Warrior 9920 is designed for up to 20 nimh cells or 6 LiPo cells. It costs a whopping $200 but this is a state of the art motor controller!

Tires:

The stock tires use a chevron tread. While they provide good traction, they caused a lot of steering wobble at high speed. I solved this by buying afew other sets of tires for various terrain. Shown are Proline’s “Big-Joe” tires and rims. These tires have an aggressive tread but still permit be to keep going straight even at top speed. The Big-joe tires are about an inch high and an inch wider than the stock tires, allowing more rubber to hit the pavement. I also bought sets of Proline’s “Road Rage” tires and Hot Bodies’ “Death Grip” tires.

Shocks and Gearing:

Motor:

The Lehner Basic XL 1600 is a brushless motor designed to take a beating! Solid aluminum construction means that it is very durable. The 1600 works very well on 24 volts, and in a perfect world would reach 38,400 RPM! This quality motor will set you back $150.

Fun in the dark:

The PolyMaxx is fun in the dark with the addition of a few LEDs.