Best Waterproof Servo for TRX4 Sport Under $50
For a TRX-4 Sport, the INJORA INJS235 and Power HD LW-25MG are two sub-$50 steering servo options worth comparing, provided their fitment and waterproofing claims check out. On the Sportโs 6V supply, both are rated at roughly 23 to 25 kg-cm, more than double the 9 kg-cm of the stock Traxxas 2075X. The DSServo DS3218 costs less, but its specs are looser and its waterproofing is the sellerโs word.
Is the Stock TRX4 Sport Servo Worth Replacing?
The Sport ships with the Traxxas 2075X, which Traxxas describes as a waterproof metal-gear digital servo. It puts out 125 oz-in (9 kg-cm) at 6V with a 0.17 second transit time. Traxxas also lists the Sport with direct steering and no servo saver, so every hit on the front wheels goes straight to the servo and horn.
Since the stock servo already has metal gears and a waterproof case, the main reason to upgrade is to get more steering torque. Traxxasโs own upgrade guide points TRX-4 owners with big, sticky tires toward its 400 oz-in brushless servo, which sold for about $100 at one retailer I found. That is double the budget here.
| Servo | Torque at 6V | Torque at higher voltage | Voltage range | Rough price |
|---|---|---|---|---|
| Traxxas 2075X (stock) | 125 oz-in (9 kg-cm) | n/a | 6V | n/a |
| INJORA INJS235 | 347 oz-in (25 kg-cm) | 486 oz-in (35 kg-cm) at 8.4V | 4.8โ8.4V | about $30โ$35 |
| Power HD LW-25MG | 319 oz-in (23 kg-cm) | 347 oz-in (25 kg-cm) at 7.4V | 6.0โ8.4V | about $40 |
| DSServo DS3218 | sold as 20 kg-cm class | n/a | 4.8โ6.8V | about $15โ$20 |
Prices change by seller, so check the listing before buying.
Three Waterproof Servos Under $50
INJORA INJS235
The INJS235 is a brushless servo that servodatabase lists at 347 oz-in at 6V and 486 oz-in at 8.4V. On the Sportโs 6V output you get about 25 kg-cm, not the 35 on the box. A marketplace listing gives a 4.8โ8.4V range, a 180ยฐ range, and a 300 mm lead.
INJORA sells several servos with โ35KGโ in the name. Some are 270ยฐ versions, and at least one is a 360ยฐ continuous-rotation servo meant for winches. Look for the INJS235 model number in the listing, because a continuous-rotation servo will not steer the truck.
Power HD LW-25MG
Power HD rates the LW-25MG at 23 kg-cm at 6V and 25 kg-cm at 7.4V, with a 6.0โ8.4V input range. It has an aluminum case, copper and aluminum gears, and two ball bearings. Power HD says the 36 cm lead was made to suit TRX-4 wiring.
It is slightly more expensive than the INJORA, with listings around $40 at the time of writing. One buyer review on eBay mentions the horn sitting close to the Panhard bar on a TRX-4, so check that clearance after you mount it.
DSServo DS3218
The DS3218 is the cheapest of the three, at about $15 for the DSServo listing. It has a 25T horn spline, a 4.8โ6.8V range, and comes with a 25T adjustable metal arm. The voltage limit means it cannot take a 7.4V supply from an external BEC.
The waterproof claim comes from sellers, and no independent water testing turned up in the sources I looked at. Sellers also tend to quote torque at the top of the voltage range, which the Sportโs 6V output will not reach.
Does the Sportโs 6V BEC Limit These Servos?
The XL-5 HV in the Sport has a 6.0V, 1A BEC, and the same output also powers the receiver. The 6V torque figures in the table are the ones you will get with the stock setup. The 7.4V and 8.4V figures need an external BEC set to that voltage.
None of the three listings gives a stall current, so the spec sheets cannot show whether a 1A BEC keeps up when the wheels bind on a rock. Traxxasโs own notes for its 400 oz-in servo say it works on the TRX-4 with the High-Voltage BEC Kit #2262 and the #8247X metal servo horn. Forum posts from TRX-4 owners also bring up aftermarket BECs for the same worry. Neither Traxxas nor the makers of these three servos say a BEC is required for them, but a BEC is a cautious addition if you plan to run 7.4V or more.
Do You Need a Metal Servo Horn?
The stock servo uses a 25T spline, and Hot Racingโs aluminum horn for the TRX-4 is sold for 25-spline standard-size servos. The Power HD listing says its package includes plastic 25T arms. Direct steering with a servo that has more than twice the torque puts a lot of load on the horn, so a metal 25T horn is worth buying along with the servo. Listings run from about $5 for a machined aluminum horn to around $13 for the Traxxas 8247X.
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Installing the New Servo and Centering It
- Unplug the battery and turn the truck off.
- Take off the horn and steering link, then unscrew the old servo from its mount.
- Bolt the new servo into the mount and plug it into the steering channel on the receiver (channel 1).
- Turn on the transmitter and the truck with the horn still off, so the servo moves to its center position with the steering trim at zero.
- Press the horn on so the wheels point straight, reconnect the link, and tighten the horn screw. A small drop of blue threadlocker on that screw can keep it from backing out.
- Turn the wheels lock to lock by hand and by radio. If the linkage binds at full lock, reduce the steering travel on the transmitter or move the horn one tooth.
If the lead on the new servo does not reach the receiver, a servo extension cable will solve it. The INJORA lead is listed at 300 mm and the Power HD at 360 mm.
The spec sheets cannot say how any of these servos will behave on the Sportโs 1A BEC when a tire jams against a rock. If the receiver resets or the steering stutters at full lock after the swap, the BEC is the first place Iโd look, and that is the point where the Traxxas HV BEC kit or a third-party one starts to look worth the money.
