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TRX4 Motor & Electronics

Here is information about the electronic components of the TRX4, the weak points, improvements or tuning.

TRX4 motor

TRX4-Motor The Traxxas® Titan 21T motor is a brushed motor. Running completely underwater in full throttle mode is not really beneficial to the "brushes" of the motor. Basically, you build a mini short circuit underwater (water conducts as we all know) and the brushes wear out (burn). If you want to turn your TRX-4 into a submarine, you should buy a brushless waterproof motor.
But also the performance can be increased with a different motor. Smoother starting, more torque and also more sensitive driving are possible here.

Brushed Since crawling is not really about speed, a motor with a higher turn value (the turn value determines the windings of a motor) makes sense. If the turn value is higher, the motor turns slower which brings better throttle response and more torque. A very good motor, if you want more torque, would be for example: the Tekin Rock Crawler Brushed Motor 45T. Especially people who drive with 3S-Lipos will notice a gigantic difference to the original 21T. These motors are also available in a hand wound version, but then the controller must be replaced. Hand wound motors require a higher current!
If a brushless motor (brushless) is on the wish list, a change of the controller is necessary. The original one from Traxxas® is not designed for brushless motors. Information about the controller can be found here.

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Turns vs KV differences

Again and again you read the question how fast does this brushless motor turn compared to my standard brushed motor. Brush motors are specified in turns, the lower this value the faster these motors turn. With brushless motors it is the other way around, the higher the KV value the faster the motor turns.
The values given here always refer to 1Volt input voltage without load on the motor. This means that a 2300KV brushless system will turn 2300rpm at 1Volt input voltage. On a 2S Lipo this means 2300rpm x 7.4 volts = 17020rpm. With a 3S 2300U/min x 11,1 = 25530 rpm.

In addition now the torque comes with the Brushlesssystemen. Here there is always the statement, the motor with 1800KV has more torque than the one with 2300KV. Unfortunately this statement is not true. The 2300 motor simply needs more current to build up the same torque, but conversely turns faster at the same voltage.

There are values here so that you can compare the whole thing somewhat.

Turn count (T) Brushed motor
Rotations per minute (rpm)*
* Rotations at 1Volt voltage without load
 The whole thing can vary greatly depending on the manufacturer and are therefore only approximate values that should clarify the whole something. 
13,5 Turns 3300 U/min KV
17,5 Turns 2200 U/min KV
21,5 Turns 1800 U/min KV
35 Turns 1450 U/min KV
55 Turns 980 U/min KV
Gerät bitte im Querformat nutzen!

So we can answer the question about our original Traxxas® motor as follows. With the 1800 brushless system the motor turns slower than the Titan 21T, with the 2300 we are about the same speed.
Which is better can't be answered across the board, some also run 2700's or even faster. If I am actually never fast with my crawler, then a brushless system with less KV is certainly recommended, but as always that is a matter of taste.

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Regler01 The Traxxas® controller is programmable via the remote control and is strangely not delivered in crawl mode. This mode would be the No.5 and should be reprogrammed after purchase via the button on the controller. The exact description how to change this can be found in the manual.
The Traxxas® controller has an output current of 1 Ampere at the BEC, which is perfectly sufficient for the normal vehicle. But if you add a winch, another servo etc., you should think about a change. The 1 amp at 6 volts for the winch is not really much and a defect is likely in the long run.
The best known controller is probably the Hobbywing WP-1080-brushed. This controller offers 3 amps of current at the BEC 6 volts and up to 6 amps as peak power. Nothing stands in the way of crawling fun. If you want to run a brushless motor, combos like the Hobbywing Xerun Axe are a very good choice (Click here for the review). These combinations of motor and controller are available in different KV strengths of 1200, 1800 and 2300 KV. The controllers output 60A continuous and 360A short load on the motor side. At the BEC they give 6 amps at 6 volts (version R2). Please do not forget to program the controllers for 6 volts otherwise the differential servos and the gear servo will suffer servo death. The ones from Traxxas® are for 6 volts!

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TRX4 External BEC

BEC If you need more voltage than the 6 volts from the Traxxas® controller or more current than the 1 amp Traxxas® provides, you will eventually have to deal with the question: Do I need an external BEC?
There is always a BEC built into the ESC. With the Traxxas®, the controller with the built-in BEC provides 6 volts and 1 amp. For the drive of the Winch too little. Even if you need more than 6 volts, the power of Traxxas® is not enough. If you have a different controller (compare TRX4 controller) you have more current available in any case. But if you want more than the 6 volts that are maximum for the servos of Traxxas®, the installation of an external BEC is necessary. A widely used BEC is the one from Castle - CC Bec 10A with a maximum voltage of 25V.

The installation is here but not easy times, I now clamp this to this or that cable. A little experience with the handling of electronics, a soldering iron and knowledge of RC receivers are important. Therefore, a request! if there is no basic knowledge, please keep your hands off, the vehicle can also times burst into flames.

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TRX4 Servo

2075X Yes, the servo of the TRX4. Certainly the weak point in a really very good car. I think you can really talk about the failure of the original servo is very likely. Some don't even make it past the first day. Of course, it can last forever, but the experience of many TRX4 drivers is probably more negative.
Suddenly the servo stops working and says goodbye without a comprehensible reason. What to do now? Of course you get a new servo within the warranty, but how long will this then do its job.

Important notice:
The steering servos of the type 2075/2075X from Traxxas®® were not very stable in the first years, but the general criticism has probably contributed to the fact that the servos of the last series work much less sensitive to interference.
The steering servo must be limited in the stop, either via the BT module or more complex via the programming button.

The solution:
It is best to replace the servo directly with a much better one. The original from Traxxas® has 9kg actuating force, but there are also some that offer much more and above all last longer.

hdpower It is important that the servo is waterproof, no one wants to create an aquarium in the servo after the next stream crossing. The Power-HD Digital Servo LW-20MG offers for good money a very good servo with power full, 20kg actuating force at 6.6 volts are already a really great value.
Power HD has now expanded the range to include a special servo for TRX-4 drivers. With the Model Power HD LW-25MG one has probably recognized the despair of many TRX drivers and developed a servo that with 23.0kg at 6.0 volts not only offers sufficient power and is of course waterproof. No, the servo also has the corresponding long cable to get back into the receiver housing without extension. Also TSP has with the servo T53 DHS a servo which is supplied with a suitable long cable34cm length and with 24kg performs its service very well. According to the manufacturer, these servos can also be driven directly up to 8.4 volts.
And if you already remove the, also change the servo horn in one with, one of metal is much more stable and also does not shear off even the small teeth.

For those who want even more, there is the TSP Servo T81 BHMW 45Kg IP67. It probably costs a lot more, but has everything made of steel inside. The workmanship is beyond reproach, but so is the price.
Who exchanges the Traxxas® servo should think of a servo extension of at least 10cm. The servos from Traxxas® have longer cables. So to get back into the receiver housing an extension is necessary.

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TRX4 shift servos

The shifting servos from the TRX run on 6.0 volts. According to the Traxxas® data sheet, the TRX2065 is also not designed for 7.4 volts. In addition, the original servos are equipped with a quite sensitive gear. If you want to change the servo for one with metal gears, you have several options.

Traxxas® offers with the 2065X a replacement with metal gearbox at a quite proud price of about 45,- Euro. If this is too much or you don't really trust the Traxxas®servos, you can look around in the aftermarket. The companies HD Power (TR4), JX (PDI-1151MG) and Savöx (SH-0265MG) offer potent servos with metal gears for a reasonable price.

But if you want to run your receiver on 7.4 volts (not the one from Traxxas®, of course), you need another servo anyway. From the company HD Power there is the TR 4 servo. According to the data sheet, this is approved for 7.4 volts, has a metal gearbox and is of course waterproof.
Also JX (PDI-HV1151MG) offers a servo with 8,4 Volt which can switch the locks with 4,2 KG.
With the shifting servos please pay attention to the cable outlet on the servo, this should, so that it fits through the holder of the differential servos, go down.

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Radio remote control

Funke The Traxxas® TQi remote control comes standard with the vehicles. It offers 4/5 channels, trim for steering, a switch for first and second gear, a switch for engaging the differential locks (open - front locked - front and rear locked), a multifunction button that is assigned to cruise control at purchase, and two buttons for Menu and Set. The set button is used to store, for example: the speed in cruise control, and of course the lever and steering wheel for throttle/brake/reverse and the steering. The other functions of these two buttons (Menu and Set) should be read in the manual. This is quite extensive.

The supplied remote control has a wide range of functions, is really good and can be expanded with the Traxxas® Link Wireless, which is explained below.

Of course, there are alternatives to the Traxxas® spark.

  • Flysky FS GT3C*
    Very cheap remote control which can be converted to 8 channels with a hack - Some offer it for sale with 8 channels.
  • Flysky Noble up to 8 Channels
    Programmable to 10 channels via software update. Very nice and small radio for right- and left-handers with free routing of the channels to the switches.
    Currently available at Hobbyking in the UK.
  • Absima CR6P 6 Channels "my personal price-performance favorite".
    6 channels and a really interesting price with around 80, - leave little to be desired. All settings can be adjusted via a clear menu directly on the FB.
  • Spektrum DX6R
    6 channels and adjustable ergonomics leave hardly anything to be desired, channel mixer, etc. The haptics does not feel high quality. Suitable for right and left handers. approx. 500,-
  • Futaba T7PXR up to 7 Channels
    Up to 7 channels depending on the receiver, ergonomically adaptable to the user, suitable for right- and left-handers and an outstanding haptics. Professional FB at the very highest level, unfortunately also very expensive. approx. 600,-
  • Sanwa M174 Channels*
    Professional remote control system with 4 channels and touch screen on highest level. The price of the M17 is about 530,-.

*Not all then have the appropriate channels. So it may be that you then have to combine the locking of the differential, for example.


Absima CR6P I have the Absima CR6P and the Futaba T7PXR. The Absima is an extremely good radio remote control with 6 channels that leaves little to be desired for crawlers. It lies well in the hand and gives a very good feeling at the steering and throttle. Easy operation and an extremely good price are for me clearly the recommendation if you are looking for more channels, or but also no additional app like Traxxas® would like. Two different grips offer an individual adjustment to the hand size. The receivers are also available from most stores without any problems.

Futaba T7PXR Who a price of 600, - euros does not deter, who is looking for the absolute adaptation to their own needs, yes the Futaba T7PXR is recommended. 7 channels that you can route completely freely, ergonomics adjustment, extreme sensitivity and a touchscreen in smartphone size makes you rejoice. Especially interesting if you use the Futaba for short course racing or similar.

Flysky Noble With the Flysky Noble we have a quite inexpensive radio, over Hobbyking in UK the good piece for under 200, - to acquire. To use it for crawlers you should order an 8 channel or more receiver and install the latest firmware. Then you can change the Noble to 8 channels and more and route them freely. Thanks to Stefan A. for the info.

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TRX4 Bluetooth-Modul

Bluetooth Traxxas® has peppered its remote control and the receiver with a variety of programming options. To intervene here, there are two buttons on the remote control that can be used to access the programming interface. This is all of great advantage, but unfortunately also quite confusing. All menu items are indicated by a single LED that lights up and flashes in different colors. In addition, hardly anyone can remember all the functions via the remote control when it goes via the programming buttons.

If you want more comfort and clarity, the Traxxas® Link Wireless is the best choice. This is mounted in the remote control and then offers a visual insight into the menu items of the electronics via an app for smartphones. about sub-trim, steering stop or steering movement (linear or expotential), everything can be set here extremely clearly. You can also quickly change the multifunction knob to another function. The software is currently only available in English, when and if Traxxas® offers this in other languages is unfortunately not known. It is also possible to save settings as a set.

Software Update - Please read!
The first time the link module is connected to the vehicle, a software update is usually requested. This update takes about 10 minutes, regardless of a fast internet connection. First the software is loaded in 2 steps, then it is installed and verified in 2 steps. Please make sure that the connection between the devices is not interrupted during this time. If the installation is interrupted, you may have to send the transmitter with the link module to Traxxas®. A system crash cannot be repaired by resetting the transmitter.
Even after an update of the app via the Appstore, the software wants to have an update, so switch on briefly afterwards and check. Please make the software update in peace, it saves the trouble afterwards!

Traxxas®app2 Bluetooth Traxxas®app1

Explanations in the Garage - Channel Setup section:

  • Steering:
    Subtrim of the steering center position and limitation for left and right separately.
  • Throttle:
    Subtrim of the throttle control, setting of the max. speed and the braking power. (If the braking power is reduced here, the reversing speed also changes)
  • Channel 3-5: Here the servos can be reversed:
    Channel 3: 1/2 Gear
    Channel 4: Front differential lock
    Channel 5: Rear differential lock

Explanations in Home - Drive Effects:

  • TSM Assistance:
    I think this is complete nonsense for a crawler. This is more interesting for fast vehicles.
  • Steering Sensitivity:
    Set the sensitivity of the steering (Expotential).
  • Throttle Sensitivity:
    Set the sensitivity of the throttle (Expotential).
  • Steering:
    Set the end points of the steering (both sides are equally limited).
  • Breaking:
    Adjustment of the braking power between 0 and 100%.
  • Throttle Trim:
    Adjustment of the throttle trim
  • Cruise Control:
    Setting for cruise control
  • By activating the round button to the right of the sliders, you put the function on the multifunction button of the remote control.

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TRX4 Winch

Winch There is probably not the best winch, widespread and popular are the "Warn" Winches. These are excellent replicas of the real models and have a very large scale factor. They are offered by RC4WD in different designs. One has here an exceptional position, because it is really very powerful and can easily pull over 10KG from the ground upwards.
But also for the somewhat smaller built Winches there is a deflection system with which it is possible to increase the tractive force.
The large RC4WD 1/10 Warn 8274 is really a real monster. Further there are the RC4WD 1/10 Mini Warn and the RC4WD 1/10 Warn. Which one you want to install now is up to your own taste and space. All have a high current and should not be connected directly to the original Traxxas® controller. For this, please read the explanations about the controller and the BEC!

Winch To control everything from a distance, of course, a remote control. RC4WD offers the Warn Wireless Remote/Receiver Winch Controller to match your Winches. With this you can control everything perfectly.
Once again, the remote control for the light system is not suitable for the Winch, the very high current would destroy the light remote control.

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Diff1 The instructions do not apply to the TRX4 Sport because it has permanently locked differentials and you can not control them individually via the remote control.
What is always asked, you can not change the order in which the differentials are locked. Traxxas® has decided that you can use the toggle switch on top of the remote control first the front differential and then the rear additionally locked. Both individually and independently allows the supplied remote control so not. Not everyone wants but this order, many want first rear then front. So you still have the full steering, but already locked the rear axle.

Sure, you can do it. First you should swap channels 4 and 5 in the receiver box. Channel 4 controls the servo for the front lock, 5 the one for the rear. But since one of the two servos works in reverse, you have to switch both channels. This can be changed with the Traxxas® Link Wireless. Here you change the channels 4 and 5 in the Garage / Channel Setup area.

Channel 4 is set from Reversed to Normal and Channel 5 from Normal to Reversed. Then the rear differential is locked in switch position 1 and the rear and front differential in position 2.

Diff2 Diff3 Diff4

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Dual rate module

Dualrate Modul For all those who simply lack a channel (4-channel remote control) or drivers who actually always have either the differentials open or both closed, there is the possibility with a dual-rate module, which is available from the company Simprop, over a channel to drive 2 servos that also work in opposite directions.
The module is switched to the appropriate channel and then both servos are plugged into the dual rate module. The second servo is then switched to reverse via a switch on the side and a small potentiometer is used to adjust the travel of the servo on the module.
The price of the module is just under 20 euros.

The whole thing requires some time until you have set the second counter-rotating servo, but then the whole thing works very well. The part is really extremely small and still fits in the receiver box.

The module has an operating voltage of 4.8 - 6.0 volts. Who operates it with 7.4 volts does this of course at your own risk!

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Overdrive / Underdrive

Overdrive1 Overdrive refers to the technical property that the front axle turns faster than the rear axle.
During the conversion, the ring gear and bevel gear in the differential are replaced. With overdrive, the front axle rotates through the conversion (3.09/2.75)-1 = 12.36% faster than the rear axle.

Gear ratio comparison:
- Underdrive with a 10Z pinion and 35Z ring gear has a ratio of 3.50:1
- Standard with an 11Z pinion and 34Z ring gear has a ratio of 3.09:1
- Overdrive with a 12Z pinion and 33Z ring gear has a ratio of 2.75:1

Overdrive front axle: 12.36% faster
Underdrive rear axle: 13,26% slower
Over,- and Underdrive: 27,27% difference between front and rear axle

The clear advantage is the increased climbing ability (the vehicle pulls itself up the hill over the front axle) and the reduced turning circle of the vehicle. But, where there are advantages there are always disadvantages, the load on the drivetrains increase significantly, the rear tires are basically ground behind.
For drivers who really use the car the way you're supposed to, you climb with your car and don't abuse it for full throttle bashing, or thinks the top speed on a crawler can never be high enough, who can think about such a conversion.

The underdrive is then the same conversion only in the rear of the car, the rear axle is thus made slower. Effect is basically the same. With the underdrive, the speed of the rear axle changes by 13.26%, so it turns 13.26% slower. For the Traxxas® you can buy the overdrive as well as the underdrive. If you then mount both at the same time you have over 27% speed difference between front and rear axle. Both at the same time I would not recommend, the load that results here (3.50/2.75)-1= 27.2% is then already extreme.

Overdrive as well as underdrive is really only for people who use their vehicle in extreme terrain, the material wear increases clearly because we brace the drive unit in itself. Whoever converts this should also be aware that there will be follow-up costs (eg cardan shafts and drive axle), which does not improve if you build them out of steel. This simply transfers the load to the next part (shift unit at the differential, etc.).

The overdrive and underdrive use hardened pinions and ring gears. So when rebuilding, you should change the remaining pinion and ring gear front or rear with. So the part number Traxxas® 8279R also order.

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Xerun Axe Combo

Xerun Widely used is now the Xerun Axe Combo. Unfortunately, there are also videos on the net with which you disassemble the receiver and - or the differential / switch servos. The Xerun Axe Combo must be set to 6 volts, not 7.4 volts. You can check this via the HobbyWing app before connecting to the receiver.
The plug of the combo is unfortunately completely equipped with black cables. Unfortunately, the plug is also sometimes incorrectly plugged into the receiver. The connector is labeled - / + / S. If you look at the receiver and the connectors are on the left side of the receiver, then the connector with the L must be on the right. Otherwise just look at another connector, you can see the contact from one side, the one from the Xerun please plug in exactly the same way.
More information can be found in the Hobbywing menu and a driving report on Xerun Axe Combo can be found here.

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Servo power supply

In general, the question always comes up, I want to install a servo with 30kg. That's all well and good. The first problem, however, is that the original receiver is only operated with 6 volts, more is not possible, for example, because of the Traxxas® switch servos. Then the current output is not very potent at 1 amp. So if I want to use a servo with tens of kilos of power I need more voltage (volts) and more current (amps). To realize this, there are several ways of which 2 are shown here.

Option 1 - Direct power supply:

direktstrom We only use 2S lipos and do not use 3S lipos. Here we can make a direct power supply to the servo. This means that the servo is directly supplied with power from the battery. The plus and minus pole are directly connected to the battery. Here a high voltage servo that can handle at least 8.4 volts is essential. 2S Lipos have in the fully charged state to the 8.4 volts, so the servo must also tolerate. Important here would be that the negative pole must be connected to the battery and also to the receiver. Who does not want to ping out or can crimp new connectors, should help themselves with a Y-cable.

Option 2 - external BEC:

externesbec We drive 3S Lipos or use both types. Here we need an external BEC, e.g. the Castle Creation BEC. This is programmed to the appropriate voltage, eg 7.4 or 8.4 volts. The servo gets the direct power supply from the Castle BEC, independent of the voltage of the battery. Important here, the negative pole must be connected to the Castle BEC and also to the receiver. If you don't want to ping out or crimp new connectors, you should help yourself with a Y-cable.

Who is not familiar with this and also a drawing as above does not really say what, keep your hands off it! In a short circuit is otherwise the Lipo in flames and the car burns you off!

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