How to use an HV-servo with a 6V-radio

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As is often the case, these askJOHN articles come about because of a problem someone's having. A fairly common issue regards wanting to use a HV servo - like everything in our lineup - perhaps a DS930BLHV - with the stock Traxxas X-MAXX radio system (6V). Your hobby dealer offers a nice solution in the form a new radio system. This works because any aftermarket radio system designed in the last decade is optimized for high voltage servos. What this says about Traxxas is not our remit to comment.

In this brief article I'm going to share a trick for how to run a HV-servo with a separate high voltage power supply, specifically so as not to release the stock radio's magic smoke! All you need are two short extensions and the means to strip small gauge wires and solder them together.

This task is dead nuts easy, only costs a few bucks, and let's you enjoy the benefits of a super servo without the added expense of a new radio system because, in all honesty, the stock Traxxas radio may not be on the cutting edge but for most folks, works just fine.

What's the problem?

There are a couple of reasons you replace the servo in a TRX4 or X-MAXX. basically, they work a while and fail. Personally, being in the manufacturing game means our hat is off to Traxxas for what they give you for your money. No offense to anybody who believes otherwise, but an X-MAXX with radio and everything for $1000 is a gift. Something of a manufacturing miracle. That perceived shortcuts amongst some of the components develop after folks play with it a while can't be helped because if they built it for the aficionados, it would sell for twice the price.

Honestly, if you had to reach into your pocket to the tune of $2000 on the first whack, how many would get an X-MAXX? Not as many as at $1000, I assure you. Are you beginning to understand the problem? So what TRAXXAS seems to do (they don't consult with me so this is merely me reading between the lines based on what I observe), so what TRAXXAS do is put together a decent package for a great price.

The obvious result is this leaves room for the aftermarket to supply components for folks to pick and choose amongst (to get their rig to their desired state of tune). This is America and free choice is what it's all about!

Thing is, a chain is only as strong as the weakest link and while you can upgrade the steering servo, this reveals the next problem. The basic issue is this; the stock BEC doesn't produce have the cojones to run a powerful servo. It's kind of like having a garden hose with which to put out a house fire. Basically, a waste of time until the fire department shows up with real hoses. Once they connect to the exact same mains pressure as the garden hose, they can immediately bring enough water to bear to put out the blaze.

The EXACT same thing is happening with the stock BEC (a nearly free to build circuit added onto a speed control to supply juice to run the control electronics), e.g. power your system. When we speak of 6V vs 8.4V, and returning to the analogy of the firemen, it wouldn't matter to your efforts to put out the fire with a garden hose if mains pressure were 60psi vs 84psi because the basic problem is the 1/2" or maybe 5/8" diameter garden hose isn't big enough to deliver enough water. The fire department attack hose is 2-1/2" in diameter while a supply hose can be 5-6" in diameter. Big difference.

Same thing happens with your rig as the wires to supply the propulsion system are huge compared to the wires for the control electronics, are you grokking what I'm saying? Anyway, the issue with the Traxxas stock BEC is not so much the voltage, but how much amperage can it deliver?

Our servo runs on 6V, no problem, reduced output of course because physics, but it runs just fine. The issue with the stock BEC is amperage. It's a joke compared to what a real servo needs. In summary, your HV servo will operate on SV (6V is considered standard voltage, or SV, while 8.4V is considered high voltage, or HV and while all ProModeler will operate on SV, they are optimized for HV).

Put another way, yes, your new servo will work with your stock electronics, but just not very well. In short, you're not gonna see the power you paid for because the stock BEC doesn't deliver enough amperage. Capice?

Fortunately there's an easy fix . . . update the supply. One way is an aftermarket BEC. They're readily available, not too expensive, and a popular choice (we have them on the website). Unfortunately, if you connect a high voltage source to the stock radio, poof, you'll release the magic smoke. Alternatives involve buying a new pricey radio system (as you become the hobby shop's new favorite pigeon). But there's another way! We show you how to do what you need for less than $35 . . . battery included!

Best part is feeding the servo higher voltage and loads of current immediately brings your new servo to life because it can then give you all the torque and speed you paid. Note, one of our 2S packs is easily going to give you 20A of current as compared to the onboard BEC, which struggles to give you maybe 3A. So will any cheapo pack you buy online. What recommends our packs are things like multiple discharge connectors and our reliance on LiIon cells instead of LiPos because the steel shells they're made with are more durable.

Finally, the soldering involved in this job is exceedingly easy, too! Best part is, it either works, or doesn't - and if it fails in use - the risks are low compared to crashing a model airplane. Let's get started!

Note; in addition to an X-MAXX, this technique applies to crawlers like a TRX4, buggies, or pretty much 'any' vehicle of any brand, which is relying on a 6V BEC-circuit to operate the steering servo.


What do you need? Beyond a decent servo and a rig, you need either our 2S LiIon pack, or an aftermarket BEC of adequate capacity, plus two short servo extensions (as the source of material). Plus, a bit of heat shrink tubing to tidy things up (although you can use electrical tape if you don't care about aesthetics). That, and the usual accoutrements for soldering wires, e.g. a hobby knife to strip insulation, solder, plus a soldering iron (25W is easily adequate).

- An all 'rounder handy tool in the workshop is the tip of a #11 blade

So tool-wise, this means a hobby knife like an X-Acto with #11 blade unless you have wire strippers (the tip of a #11 is also handy for releasing the tangs holding the pins within the connectors and trimming insulation), plus a soldering iron with small tip.

This is gonna take you a maximum of five minutes from start to finish. Note, if you're going to be a lifer in this sport, buy a good soldering iron. Weller is a good brand. So let's get to it. Begin by cutting the wire extensions and wiring them together, like this. That's it. See, I told you it was easy!

- Remove the yellow signal wire of the extension connecting to the battery

A switch is a nice addition, we have them as does your local hobby shop. Or as an alternative, 'you' become the switch. Just order a spare connector or two, make the connection with them to the receiver before installing it so that it becomes very easy to make the battery connections to these short extensions (instead of hunting around for the port on the receiver once it's buried inside the model). Also, if you don't have enough free receiver ports, then get a y-harness from us. Confused? Read about how-to use it, here . . .

Double up, another use for a Y-harness!

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