Traxxas TRX-4 Brushless Conversion

Say you love your Traxxas TRX4 as much as we love ours (highly unlikely), what can you do to improve on what is already a fantastic package? Two words, more power! In this blog we look into the benefits of changing from a brushed to brushless power-train and show how you can go about upgrading the components on your TRX4.

Why convert my RC to brushless?

Some of the reasons users chose to upgrade to brushless power include:

• Power - size for size they offer more power
• Greater efficiency - leading to increased runtime from similar sized cells
• Control - a good speed controller will allow mapping to extract the most from your motor
• Weight - size for size they are often lighter
• Low maintenance (no brush replacement)
• Non-directional - Brushed motors often wear more in the reverse direction (note that Traxxas even fit a reverse turned motor for the TRX-4 specific drive-line setup)
• Bragging rights (seriously, we've had customers turn their nose up at brushed models before!)

It is worth noting that brushless motors do introduce the problem of cogging which can be an issue when driving an RC Crawler. The TRX-4's low ratio gearbox should help with this.

What will I need to convert my car to brushless?

The TRX-4, like many other models comes with a brushed motor and speed controller. You will need the following to convert:

• Waterproof Brushless Motor (with appropriate motor shaft diameter)
• Waterproof Brushless speed controlller (a must if you go puddle hopping like we do, less important if you just drift indoors)
• Various hex drivers (model dependant but in this case 2mm and 1.5mm) and some double sided tape
• Suitable LiPo battery

The last step on this list isn't always necessary, but is recommended to get the most from your upgrade. Ensure you select a battery that the correct plug for your speed controller, in our case we will be using the rectangular deans plug as we have plenty of cells on standby with this connector. We will be converting our TRX-4 to brushless and will be using a Absima Brushless Combo Set Thrust BL ECO to replace the current powertrain, other brushless combos are also available. It is not quite as advanced as the standard ESC but with its programable start mode, and configurable drag brake/brake force it should be suitable for use in the Defender.

Converting the Traxxas Defender to Brushless

In this blog we have documented how we opted to convert the model, but as ever it should not be considered as a guide and we cannot take responsibility for any damage you cause to your model (or yourself) by ignoring our warnings.. Just in-case  it isn't obvious, our first step was removing the body and the battery.

Brushless Motor Install

We opted to remove the battery cage to install the motor, this is not strictly required but it offers more access. There are four 2mm screws, two through the bottom and two attaching the sides to the metal chassis rails. From there we removed the three 2mm screws from the top of the motor cover. This motor cover actually holds the motor mount plate firmly vertical. To remove the motor you disconnect the power cables from the ESC and lift the unit straight up. The TRX-4 chassis uses a thick plastic motor mount that has 16 holes in it (paired and labelled A to H), offering multiple motor positions and from the factory ours came setup in position C. Remove the pinion gear from the motor shaft using a 1.5mm hex driver. Installing the motor will take some trial and error to ensure the gears line up. We started by rotating the pinion gear 180° over before installing it, to compensate for the shorter motor shaft length. The motor needs to be supported to ensure the motor mount stays vertical as you clamp down the motor cover plate. At this point it is worth test fitting the body to ensure it does not foul the motor or power cables.

Note : Gear mesh is important!

This part of the setup is often overlooked. You can get caught up  in upgrading your model and just throw the motor in without taking care to ensure it is installed accurately. Correct pinon/spur mesh should allow a small amount of play when rotating the . Also note that the gear alignment should be correct to ensure the teeth of the gears have the maximum contact area .This will avoid any binding that will put undue load on your drivetrain and will eventually strip your spur gear (ask me how I know this, or see below left). If you are having issues with stripping spur gears, it can be tempting to want to swap them out for more robust metal cogs; We tend to advise against this. Plastic  spur gears (whilst being noticeably quieter) can act as transmissions savers, taking the abuse that would otherwise get passed down to other weaker components.

Wiring in the new electronic speed controller

The XL-5HV speed controller is an excellent unit, but it isn't suited for use with our new motor. To remove it we unscrewed it from the chassis via the two 2mm hex screws from below. The lid of this is held on with three 2mm hex screws on the top, once removed the lid can be taken off, being careful not to lose the rubber seal gasket. The speed controller is plugged into the second channel of the receiver and can be unplugged. But to free the cable we also needed to remove the receiver box cable clamp, again another pair of 2mm hex screws on the top. We chased the three wire signal cable across the chassis to the receiver box. It heads between the two diff control servos and can be free'd from the hoop by removing the central 2mm hex screw between them. We then ran the new cable along the same path and replaced all the lids ensuring the seals were re-seated correctly to maximise the water resistance. Note the new remote power switch the Thrust ESC comes with. With its waterproof cover this could be mounted in a location still accessible with the top shell on, something the standard car lacks.

Installing the LiPo battery

For testing purposes we used a Absima 5000mAh 2S (7.4v) 30c LiPo battery with a deans plug, compatible with the new speed controller. For performance testing we also have a Gens Ace Tattu 1800mah 3S 75C LiPo Battery which we connected to an XT60/Deans adaptor (just for some quick runs as this is not advised for regular use). For comparison At 137x46x24mm the new cell fits nicely in the standard battery tray. If you are going for anything physically larger you will have have to modify the tray or remove it completely. We have seen several guides for expanding the depth of the battery tray by replacing the hardware and shimming the plastic latch up to clear thicker cells. There are also several aftermarket battery trays available that lower the cell's position in the chassis, reportedly improving the centre of gravity.

Configuring the speed controller

With the battery installed we stuck the chassis on a box, allowing the wheels to freespin whilst setting up the speed controller. Throttle range calibration is important to ensure your speed controller is getting the 100% range of the throttle trigger and not cutting off at say 80%. This was easily achieved by holding the set button and re-positioning the trigger whilst turning the switch on. The Absima A10 ECO has a relatively slim amount of configuration as can be seen from the programmable items chart below, but it should be enough for our needs.  We left most of the setup as standard (maintained the reverse function, left the drag brake off, left the low voltage cutoff as standard) but dropped the punch of the start mode to Level2 to avoid lunching the gears. We intend to experiment with the maximum brake force, potentially dropping down it to safeguard the transmission.

Brushless defender in Action

Initially we played it safe with the 2S battery but straight away you could see the difference. The truck had a lot more punch in acceleration and would perform small wheelies on grippy inclined tarmac. As you can see from the short clip below, at pace the truck will now casually defy gravity, skipping over the pump track berms and launching itself into the air on the steeper lips. With the 3S 11.1v  (75C) battery in the truck, it turned into a completely different beast. Giving it 'full beans' off the line will result in ridiculous wheelies even with the diffs locked. Even when already travelling at speed, pushing past 80% throttle would send the nose skyward and the tyres ballooning out from the rims as the big Defender cleared 23mph! Total disclosure, we did manage to break steering system powering into corners before we even got the 3S cell plugged in. The metal servo gear had lunched the splines on the servo horn and was just free spinning. Thankfully this was rectified with a cut down Absima metal servo horn; Perhaps we were a little foolish asking so much from a crawler steering system! We love our TRX-4 Land Rover Defender and will continue to tweak and modify it over the course of the year. Next on the agenda is fitting the official lighting kit and potentially a remote controlled winch.

RC Geeks - Huge Traxxas fans

We stock a large range of Traxxas electric models to suit any terrain or skill level. You can learn more or purchase the Traxxas TRX-4 Land Rover Defender in the three body colours Grey (as pictured) Green and Red on our webstore. Note that if you are intending to use the standard speed controller you will need a battery with the new Traxxas iD connector. Have you noticed any errors in this blog? Perhaps you have questions regarding the Traxxas Defender? Please leave your comments below!