TRX4 Motor & Electronics

• Motor
• Turns - KV
• Speed controller
• BEC
• Servo (steering)
• Servos (shift servos)
• Radio control
• Bluetooth module
• Winch
• Limited-slip differentials
• Dual-rate module
• Overdrive / Underdrive
• Xerun Axe Combo
• Servo power supply
• Chargers
• Dischargers

Here is some information about the TRX4’s electronic components, its weaknesses, improvements and tuning options.

TRX4 Motor

The Traxxas® Titan 21T motor is a brushed motor. Driving underwater at full throttle for an entire journey is not really good for the motor’s ‘brushes’. Essentially, you’re creating a mini short circuit underwater (as we know, water conducts electricity) and the brushes will wear out (or burn out). Anyone wishing to convert their TRX-4 into a submarine should therefore opt for a brushless, waterproof motor.
However, you can also significantly boost performance with a different motor. This allows for smoother acceleration, greater torque and more responsive handling.

As speed isn’t really a factor when rock crawling, a motor with a higher ‘turn’ rating (the ‘turn’ rating determines a motor’s windings) makes sense here. The higher the ‘turn’ rating, the slower the motor spins, which results in 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. People who drive with 3S LiPo batteries in particular will notice a huge difference compared to the original 21T. These motors are also available in a hand-wound version, but in this case the speed controller will need to be replaced. Hand-wound motors require a higher current!
If a brushless motor is on your wish list, you’ll need to change the speed controller. The original Traxxas® speed controller isn’t designed for brushless motors. You can find information about the speed controller here.

When it comes to motors, however, the trend is clearly towards brushless and sensor-controlled models. In these, the speed controller is often integrated into the motor. A typical example is the Hobbywing Fusion, which is available in various versions.

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Differences between turns and KV

Time and again, you come across the question of just how fast this brushless motor actually spins compared to my standard brushed motor. Brushed motors are specified in turns; the lower this value, the faster these motors spin. With brushless motors, it’s the other way round: the higher the KV value, the faster the motor spins.
The values given here always refer to a 1-volt input voltage with no load on the motor. This means that a 2300KV brushless system rotates at 2300 rpm at a 1-volt input voltage. On a 2S LiPo battery, this equates to 2,300 rpm × 7.4 volts = 17,020 rpm. On a 3S battery, it is 2,300 rpm × 11.1 = 25,530 rpm.

Then there is the question of torque in brushless systems. It is often claimed that a 1800KV motor has more torque than a 2300KV motor. Unfortunately, this is not true. The 2300KV motor simply requires more current to generate the same torque, but conversely, it spins faster at the same voltage.

There are figures here so that you can compare the two.

Number of turns (T) in a brush motor	Revolutions per minute (rpm)*
* Revolutions at 1 volt without load These figures can vary considerably depending on the manufacturer and are therefore only approximate values intended to give a general idea.
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

So we can answer the question about our original Traxxas® motor as follows. With the 1800 brushless system, the motor runs more slowly than the Titan 21T; with the 2300, we’re roughly the same speed.
There’s no one-size-fits-all answer as to which is better; some people even run 2700s or even faster motors. As I never really drive my crawler at high speeds, a brushless system with a lower KV rating is definitely recommended, but as always, it’s a matter of personal preference.

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TRX4 Controller

The Traxxas® speed controller can be programmed via the remote control and, strangely enough, does not come set to Crawl mode by default. This mode is number 5 and should be reprogrammed after purchase using the button on the speed controller. You’ll find detailed instructions on how to change this in the user manual.
The Traxxas® speed controller has an output current of 1 ampere at the BEC, which is perfectly adequate for a standard vehicle. However, anyone fitting a winch, an additional servo, etc., should consider replacing it. The 1 ampere at 6 volts for the winch isn’t really much, and a fault is likely in the long run.
The best-known ESC is probably the Hobbywing WP-1080-brushed. This ESC delivers 6 volts and 3 amps via the BEC, with a peak current of up to 6 amps. Nothing stands in the way of some crawling fun. If you want to run a brushless motor, combos such as the Hobbywing Xerun Axe are a very good choice (Click here for the test report). These motor-and-ESC combinations are available in various KV ratings of 1200, 1800 and 2300 KV. On the motor side, the ESCs deliver 60A continuous current and 360A peak current. The BEC outputs 6 amps at 6 volts (R2 version). Please do not forget to programme the ESCs to 6 volts, otherwise the differential servos and the gear servo will be damaged. The ones from Traxxas® are designed for 6 volts!

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TRX4 External BEC

Anyone who needs a higher voltage than the 6 volts provided by the Traxxas® ESC, or more current than the 1 ampere supplied by Traxxas®, will eventually find themselves asking: do I need an external BEC?
There’s always a BEC built into the speed controller. With Traxxas®, the speed controller’s built-in BEC delivers 6 volts and 1 ampere. This isn’t enough to power the winch. Even if you need more than 6 volts, the power provided by Traxxas® simply isn’t sufficient.
If you have a different ESC (e.g. the TRX4 ESC), you’ll definitely have more current available. However, if you want more than the 6 volts – which is the maximum for Traxxas® servos – you’ll need to fit an external BEC. A widely used BEC is the Castle – CC Bec 10A, with a maximum voltage of 25V.

However, fitting it isn’t as simple as just clipping it onto this or that cable. A little experience with electronics, a soldering iron and knowledge of RC receivers are essential. So here’s a request! If you don’t have the basic knowledge, please don’t attempt this – the vehicle could well go up in flames.

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TRX4 servos

Following some initial problems with the servo, these appear to have been resolved and complete failure no longer occurs.
However, the holding force is particularly high, and anyone who does more than just ‘go for a spin’ with their crawler should consider upgrading to a significantly more powerful model.

Important note:
The Traxxas® 2075/2075X steering servos were not particularly reliable in the early years, but the widespread criticism seems to have contributed to the servos in the latest series being significantly less prone to faults. Tip:
It is essential to limit the steering servo’s travel, either via the BT module or, more elaborately, via the programming button.

It’s important that the servo is waterproof – after all, nobody wants to end up with an aquarium inside their servo after crossing the next stream. The Power-HD Digital Servo LW-20MG offers excellent value for money, delivering plenty of power – 20kg of holding force at 6.6 volts is an impressive figure. With the Power HD LW-25MG model, the manufacturer has clearly recognised the frustration felt by many TRX drivers and developed a servo that, with 23.0 kg at 6.0 volts, not only offers ample power but is, of course, waterproof. What’s more, the servo comes with a cable long enough to reach back into the receiver housing without the need for an extension.
The choice is vast, and it’s almost impossible to list everything here. The 20 kg servo was the first one I fitted back then; this was followed by the HD25, several of which are still working perfectly in my vehicles. However, some cars are fitted with significantly more powerful

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TRX4 switch servos

The TRX’s gear-driven servos operate at 6.0 volts. According to the Traxxas® data sheet, the TRX2065 is not designed for 7.4 volts either.
Furthermore, the original servos are fitted with a rather delicate gearbox. If you wish to replace the servo with one featuring a metal gearbox, there are various options available.

With the 2065X, Traxxas® offers a replacement with a metal gearbox at a rather steep price of around 45 euros. Anyone who finds that too much, or who doesn’t really trust Traxxas® servos anyway, should have a look round the accessories market. The companies HD Power (TR4) and Savöx (SH-0265MG) offer powerful servos with metal gearboxes at a reasonable price in their ranges.

However, anyone wishing to run their receiver on 7.4 volts (not the Traxxas® one, of course) will need a different servo anyway. HD Power offers the TR 4 Servo. According to the data sheet, this is rated for 7.4 volts, has a metal gearbox and is, of course, waterproof.
JX (PDI-HV1151MG) also offers a servo rated at 8.4 volts, which can even engage the differential locks with a force of 4.2 kg.
With gear-type servos, please pay attention to the cable outlet on the servo; to ensure it fits through the differential servo mount, it should point downwards.

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Wireless remote control

The Traxxas® TQi remote control is supplied as standard with the vehicles. It offers 4/5 channels, trim for the 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 which is pre-programmed for cruise control at the time of purchase, and two buttons for Menu and Set. The ‘Set’ button is used, for example, to save the speed setting for cruise control and, of course, to configure the levers and steering wheel for throttle/brake/reverse and steering.
The other functions of these two buttons (Menu and Set) should be consulted in the user manual. It is quite comprehensive.

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

Alternatives:
Of course, there are also alternatives to the Traxxas® radio.

• Flysky Noble NB4
  Can be programmed to 10 channels via a software update. A very attractive, compact remote control for both right- and left-handed users, with flexible channel mapping to the switches. Price in Germany around 240. This remote control is also available in other versions.
• Spektrum DX6R
  The Spektrum DX6R, with its 6 channels and adjustable ergonomic design, leaves little to be desired – channel mixers and so on. It doesn’t feel particularly high-quality to the touch. Suitable for both right- and left-handers. Approx. 500,-
• Futaba T7PXR / Futaba T10PX
  A high-end remote control with up to 10 channels and extremely fast transmission – perhaps a bit over the top for a crawler. However, anyone who also drives very fast vehicles will certainly find this a very good choice. Prices range from 400 to 660 euros.
• Sanwa M17 4 channels*
  Professionelles Fernsteuersystem auf höchstem Niveau mit 4 Kanälen und Touchscreen auf allerhöchstem Niveau. Der Preis der M17 liegt bei etwa 530,-
• Flysky Noble Pro
  Up to 18 channels on a pistol-style control unit, freely routable switches and push-buttons, customisable colour touchscreen display, suitable for both right- and left-handed users. Price around 500,-

*Not everyone will have the right channels. So it may be that, for example, you’ll have to combine the differential locks.

Recommendations:

The Flysky Noble NB4 is a fairly affordable radio control system that comes with one or two 4-channel/8-channel receivers. The Noble is available to buy from Speedshop 24 in Germany. If you wish to use it for crawlers, you should carry out a firmware update to enable up to 10 channels and order the appropriate receiver (FGr8B for 8 channels) or (FTr10 for 10 channels).
You can then configure the Noble for up to 10 channels and route them as required.

If a price tag of 600 euros doesn’t put you off, and if you’re looking for a controller that can be fully tailored to your own needs, then the Futaba T7PXR comes highly recommended. With 7 channels that can be routed entirely as you wish, ergonomic customisation, extreme responsiveness and a smartphone-sized touchscreen, it’s certainly something to get excited about. S-Bus servos, gyros and similar components can be programmed directly on the Futaba. This is particularly useful if you’re using the Futaba T7PXR for drifters, flat-track racers, short-course racing or similar applications.

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TRX4 Bluetooth module

Traxxas® has packed its remote control and receiver with a wide range of programming options. To access these, there are two buttons on the remote control that allow you to enter the programming interface. Whilst this is all very useful, it is, unfortunately, also rather confusing. All menu items are indicated by a single LED that lights up and flashes in different colours. Furthermore, it’s unlikely that anyone could remember all the functions on the remote control when accessing them via the programming buttons.

If you’re looking for greater convenience and clarity, the Traxxas® Link Wireless is the ideal choice. It is fitted into the remote control and, via a smartphone app, provides a visual overview of the electronics’ menu options. Everything can be adjusted extremely clearly here, including sub-trim, steering stop and steering movement (linear or exponential). You can also quickly reassign the multifunction button to a different function. The software is currently only available in English; unfortunately, it is not known when or if Traxxas® will offer it in other languages. It is also possible to save settings as a preset.

Software Update – Please read!
When connecting the Link Module to the vehicle for the first time, a software update is usually required. This update takes around 10 minutes, regardless of how fast your internet connection is. First, the software is downloaded in two stages, then installed and verified in two further stages. Please ensure that the connection between the devices is not lost during this time. If the installation is interrupted, you may have to send the transmitter and the Link Module back to Traxxas®. A system crash cannot be resolved by resetting the transmitter.
Even after updating the app via the App Store, the software will still require an update, so please switch it on briefly afterwards to check. Please take your time when carrying out the software update – it will save you a lot of hassle later on!

Explanations in the Home – Drive Effects section:

• Steering / Lenkung:
  Steering sub-trim: centre position and left/right limit adjustments are separate.
• Throttle / Gas:
  Throttle sub-trim, adjustment of maximum speed and braking power. (If the braking power is reduced here, the reverse speed will also change)
• Channel 3-5 / Kanal 3-5: The servos can be reversed here:
  Channel 3: 1st/2nd gear
  Channel 4: Front differential lock
  Channel 5: Rear differential lock
  

Erklärungen im Bereich Home - Drive Effects:

• TSM Assistance / TSM Assistent:
  I think this is complete nonsense for a crawler. It’s more relevant for fast vehicles.
• Steering Sensitivity / Lenkempfindlichkeit:
  Adjust the steering sensitivity (exponent) (Expotential)
• Throttle Sensitivity / Gasempfindlichkeit:
  Adjust the throttle sensitivity (exponent)
• Steering / Lenkung:
  Adjust the steering end points (both sides are limited equally)
• Breaking / Bremse:
  Adjust the braking power between 0 and 100%
• Throttle Trim / Gas Trimmung:
  Adjust the throttle trim
• Cruise Control / Tempomat:
  Cruise control settings
By pressing the round button to the right of the sliders, you assign the function to the multifunction button on the remote control.

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TRX4 Cable Winch

There is probably no single ‘best’ winch, but ‘Warn’ winches are widespread and popular. These are excellent replicas of their real-life counterparts and have a very high level of scale detail. They are available from RC4WD in various designs. One model stands out in particular, as it is exceptionally powerful and can easily pull over 10 kg off the ground.
However, even for the slightly smaller winches, there is a pulley system that makes it possible to increase the pulling force.
The large RC4WD 1/10 Warn 8274 is a real workhorse. There is also the RC4WD 1/10 Mini Warn and the RC4WD 1/10 Warn. Which one you choose to fit depends on your personal preference and the space available.
However, they all draw a high current and should not be connected directly to the original Traxxas® speed controller. Please read the explanations regarding the speed controller and the BEC!

To control everything remotely, a remote control is, of course, the ideal solution. RC4WD offers the Warn Wireless Remote/Receiver Winch Controller, which is compatible with your winches. This allows you to control everything perfectly.
Please note once again that the remote control for the lighting system is not suitable for the winch; the very high current would damage the lighting remote control.

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Sperrdifferenziale

These instructions do not apply to the TRX4 Sport, as this model has permanently locked differentials and these cannot be controlled individually via the remote control.
A question that comes up time and again is whether it is possible to change the order in which the differentials are locked. Traxxas® has decided that the toggle switch on top of the remote control first locks the front differential and then the rear one as well. The supplied remote control does not allow both to be locked individually and independently. However, not everyone wants this order; many prefer to lock the rear first and then the front. This way, you still have full steering capability, but the rear axle is already locked.

Of course, this can be done. First, you need to swap channels 4 and 5 on the receiver box. Channel 4 controls the servo for the front differential lock, whilst channel 5 controls the one for the rear. However, as one of the two servos operates in reverse, you now need to switch both channels. You can change this using the Traxxas® Link Wireless. Here, in the Garage / Channel Setup section, you can change channels 4 and 5.

Channel 4 is set from ‘Reversed’ to ‘Normal’ and channel 5 from ‘Normal’ to ‘Reversed’. Afterwards, switch position 1 locks the rear differential, whilst position 2 locks both the rear and front differentials.

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Dual-rate module

For anyone who simply lacks a channel (4-channel remote control) or for drivers who generally always have either the differentials open or both closed, there is the option of using a Dualrate Modul – available from Simprop – to operate two servos via a single channel, which also operate in opposite directions.
The module is switched to the appropriate channel, and then both servos are plugged into the dual-rate module. A switch on the side is then used to set the second servo to reverse, and a small potentiometer is used to adjust the servo’s travel on the module.
The module costs just under 20 euros.

It takes a bit of time to get the second, counter-rotating servo set up properly, but once that’s done, the whole thing works very well. The unit is really extremely small and still fits inside the receiver box.

The module has an operating voltage of 4.8–6.0 volts. Anyone running it at 7.4 volts does so at their own risk, of course!

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Overdrive / Underdrive

Overdrive refers to the technical characteristic whereby the front axle rotates faster than the rear axle. During the conversion, pinion and bevel gearthe pinion in the differential are replaced.
With overdrive, the front axle rotates (3.09/2.75)-1 = 12.36 per cent faster than the rear axle as a result of the conversion.

Gear ratio comparison:
- Underdrive with a 10-tooth pinion and 35-tooth ring gear has a ratio of 3.50:1
- Standard with an 11-tooth pinion and 34-tooth 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

Changes:
Overdrive front axle: 12.36% faster
Underdrive rear axle: 13.26% slower
Overdrive and Underdrive: 27.27% difference between front and rear axles

The clear advantage is the improved climbing ability (the vehicle pulls itself up the hill via the front axle) and the vehicle’s reduced turning circle. However, where there are advantages, there are also disadvantages: the strain on the drivetrains increases significantly, and the rear tyres are essentially just being dragged along.
Drivers who really use the car as it’s intended – climbing with their vehicle rather than misusing it for full-throttle bashing, or who don’t believe a crawler’s top speed can ever be high enough – might want to consider this sort of modification.

The Underdrive is essentially the same modification, but applied to the rear of the car; in other words, it slows down the rear axle. The effect is essentially the same. With the Underdrive, the speed of the rear axle changes by 13.26 per cent, meaning it rotates 13.26 per cent more slowly. Both the Overdrive and the Underdrive are available for the Traxxas®. If you fit both at the same time, you end up with a speed difference of over 27 per cent between the front and rear axles. I wouldn’t recommend fitting both at the same time, as the resulting load (3.50/2.75) – 1 = 27.2 per cent is quite extreme.

Overdrive, just like underdrive, is really only intended for people who use their vehicles in extreme off-road conditions; wear and tear on components clearly increases as we put stress on the drive unit itself. So anyone fitting this conversion should be aware that there will be associated costs (e.g. propeller shafts and drive axle), which are not reduced even if these are made of steel. This simply shifts the load to the next component (the differential’s gear unit, etc.).

The Overdrive and Underdrive use hardened pinions and ring gears. So, if you’re carrying out a conversion, you should also replace the remaining pinion and ring gear at the front or rear. In other words, be sure to order item number Traxxas® 8279R as well.

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Xerun Axe Combo

The Xerun Axe Combo is now widely used. Unfortunately, there are also videos online showing how to dismantle the receiver and/or the differential/gear 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 it to the receiver.
Unfortunately, the Combo’s connector is fitted entirely with black cables. Regrettably, the connector is sometimes inserted incorrectly into the receiver. The connector is labelled with - / + / S. If you’re looking at the receiver and the terminals are on the left-hand side, then the terminal marked with an L must face to the right. Alternatively, simply look at another connector – you can see the contacts from one side here – and please plug the Xerun connector in exactly the same way. You can find further information in the Hobbywing menu, and a test drive report on the Xerun Axe Combo is available here.

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Servo power supply

People often ask: ‘I want to fit a servo with a 30kg holding force.’ That’s all well and good. The first problem, however, is that the original receiver only operates at 6 volts; you can’t go any higher, for example because of the Traxxas® switching servos. Furthermore, the current output of 1 ampere isn’t particularly powerful. So, if I want to use a servo with tens of kilograms of holding force, I need more voltage (volts) and more current (amps). There are several ways to achieve this, two of which are shown here.

Option 1 – Direct power supply:

We only use 2S LiPo batteries and do not use 3S LiPo batteries. In this case, we can set up a direct power supply to the servo. This means that the servo is powered directly from the battery. The positive and negative terminals are connected directly to the battery. A high-voltage servo capable of withstanding at least 8.4 volts is essential here. Fully charged 2S LiPo batteries have a voltage of around 8.4 volts, so the servo must be able to handle this. It is also important to ensure that the negative terminal is connected to both the battery and the receiver. If you don’t want to use jumper wires or are unable to crimp new connectors, you should use a Y-cable.

Option 2 – external BEC:

We use 3S LiPo batteries or a combination of both types. Here, we need an external BEC, e.g. the Castle Creation BEC. This is programmed to the appropriate voltage, e.g. 7.4 or 8.4 volts. The servo now receives its power directly from the Castle BEC, regardless of the voltage supplied by the battery. It’s also important here that the negative terminal is connected to the Castle BEC and also to the receiver. If you don’t want to use a jumper or are unable to crimp new connectors, you should use a Y-cable.

If you’re not familiar with this and even a diagram like the one above doesn’t really mean much to you, stay well away from it! Otherwise, a short circuit will set the LiPo alight and the car will burn down!

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Chargers

The question of which charger is any good comes up just as often as the question of which tyres are best. There’s no one-size-fits-all answer here either. Everyone has different requirements when it comes to such a device and may want to charge just one battery or several at once. Here, I’ll only be discussing devices designed for LiPo batteries, not those that use a USB port as a power source or have to be ordered online from somewhere in China. You know my view on local retailers.

A good charger should be easy for the user to understand, be capable of charging the connected LiPo batteries at a 1C charge rate (where 1C is the battery capacity) and balance them effectively.
ISDT K2 Air and ISDT K4 Duo are modern chargers offering plenty of power and app control, are extremely easy to use, and the menu is even in German. With charging outputs of 2x100 watts AC (2x500 watts DC) or 2x200 watts AC (2x600 watts DC), you’re always on the safe side. The fans operate at a moderate volume, so you can carry on working on your kit even whilst they’re running. Both chargers have two outputs, meaning two batteries can be charged at the same time. The ISDT units can also be powered by direct current via a mains adaptor, in which case the wattage output increases significantly.
SkyRC also offers the SkyRC D400, an extremely powerful charger with 2x200 watts AC, which also performs very reliably when discharging batteries (discharge power 2x36 watts) and is housed in a solid steel casing. A rock-solid charger that I’ve been using for several years now. The fans are, however, noisier than those on the ISDT units.

Anyone looking for something a bit smaller will soon realise that the choice here is endless. If you’re buying in-store, you can get advice; if you’re ordering online, you should know what you need beforehand. RC Plus offers the Cube 80 Duo Charger, with 2 x 80 watts, for 80 euros – it’s a really good option.

Generally speaking, a charger should be able to charge the battery at 1C (Formula: battery voltage x charging current = required watts), e.g. a 2S battery at 7.4 volts and 5000mAh (7.4 x 5 = 37 watts) or a 3S battery at 4500mAh (11.1 x 4.5 = 49.95 watts). So, if you only want to charge a single battery within these ranges, a 50-watt charger will suffice. However, if it’s just dad and son out and about, or even three family members, you should consider a dual charger straight away and use a unit with 2 x 80 watts or more.

Why don’t I recommend Traxxas®lader? Basically, they’re great for beginners – just pop the battery in and you’re sorted. However, they can only charge Traxxas® batteries, which are really overpriced. For anyone who feels very unsure about batteries, these chargers and their matching batteries are a safe and simple option.

I do not wish to go into detail here about high-end devices such as those from Junsi (all of which do not come with a power supply) or the ISDT X16. Model-makers planning to purchase these chargers do not need these explanations.

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Discharger

Wer öfters auch geladene Akkus wieder mit nach Hause bringt oder die Restladung oft im höheren Bereich hat, der kann sich mal über ein Entladegerät Gedanken machen. Diese können einen Akku mit bis zu 35Ampere innerhalb kurzer Zeit leer saugen und auf eine vorher eingestellte Endspannung bringen. Hier gibt es zB.: den ISDT FD-200 25A oder den SkyRC BD250 35A. Der ISDT FD200 ist, wie man es von der Firma kennt App gesteuert und kann über fertige, von einem selber erstellte Presets, bedient werden oder auch direkt am Gerät. Der SkyRC BD250 wird direkt am Gerät eingestellt, hat keine Presets dafür aber mit 35 Ampere mehr Leistung und ist auch leiser (deutlich grösserer Lüfter). Dafür ist der von SkyRC aber auch doppelt so gross. Beide Geräte arbeiten ohne zusätzlichen Netzanschluss und holen ihre benötigte Energie aus dem angeschlossenen Akku.

Anyone who keeps track of battery voltages in their head, or who uses very large LiPo batteries – for example, for bashing (4S and above) – is very well catered for with the SkyRC, but will need to keep adjusting the voltages they wish to achieve during discharge. This is all done via a large rotary dial and can be a bit fiddly from time to time. The ISDT has two buttons: one for the number of cells and the other for the discharge current. Alternatively, you can use your smartphone to pre-set the values for different batteries. Both devices can discharge LiPo batteries ranging from 2S to 8S.

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