This ad space is available now!

Your Reviewer

My Credentials
So who's doing this reviewing then?

Well I've been building and flying or driving radio controlled models for over 40 years and during that time I like to think I've built up a reasonable amount of knowledge.

I'm also a qualified electronics engineer who has worked in radio frequency, analog, digital systems and software for more than three decades. In fact I designed and built my first RC set back in 1969.

For the past nine years I've also been involved in the design and manufacture of some rather sophisticated engine technology and UAV flight control systems.

So, chances are I've been there, done that and have a huge pile of tee shirts to prove it.

Right now I'm heavily into 3D flying and enjoy all aspects of the RC hobby. I may be old but I don't feel it.

In the Pipeline

Here's just a little bit of what's to come on this site...

RC explained: Demystifying terms such as PCM, PPM dual conversion, single conversion, full-range etc., this feature will explain it all.

Cheap Chinese Engines: Just how good are those cheap Chinese glow and gas engines that sell for half the price of their "brand-name" equivalent? I put several to the test.

Build your own radio gear?: Back in the old days, building your own RC gear was not uncommon and now the arrival of 2.4GHz has made it practical again.

 

A DIY $8 Lithium Transmitter Battery (Part 3)

TESTING THE BATTERY

If you connect up your new battery pack and turn on the transmitter you should see something like this:

The transmitter should work as normal and the voltage display should read somewhere between 7.2 and 7.8 volts.

However, you will find that it beeps at regular intervals. That beeping is the low-voltage warning that is programmed to kick-in at 8.8V.

When an 8-cell AA pack reaches 8.8 volts it is very nearly dead flat. In such a situation, the low-voltage alarm would sound and warn you that it's time to land as quickly as you can to avoid losing control of the model.

But -- our 2-cell lithium battery only puts out about 7.4V most of the time so if we don't make another small change then it will beep all the damned time, even though it will continue to work just fine until the voltage drops down to about 6.5V.

So what can we do to stop that incessant beeping?

Well we could cut the wire to the tiny speaker -- but then we'd loose the timer beep and the other little noises that the transmitter is supposed to make.

The 8.8V warning level is built into the transmitter's software and can't easily be altered, so that leaves only one option... we have to fool the transmitter into thinking that it has more voltage than it really does.

Fortunately, this is a pretty simple thing to do and requires the addition of only a single 10-cent resistor to the circuit board.

Foiling The Transmitter's Low-voltage Alarm

In order to get at the circuit-board we must remove the back of the transmitter.

Before you remove any screws -- unplug your new battery! Also don't forget to remove the RF module if you have one installed.

Then undo the six phillips-head screws that hold the two halves of the transmitter together.

You can then lift the back off and position it out of the way like this.

Here is the main logic board from inside the 9X transmitter. You can ignore the grayed out bit, we're only interested in the bit that's colored in the above picture.

The board in the picture above has been removed from a transmitter but you can do this modification to your radio without removing the board or unplugging anything.

Here's a closer view. You'll notice I've circled a single component and labeled it as a 5.1Kohm resistor. In order to fool the transmitter into thinking it still has an 8-cell battery, we have to solder another resistor across this one.

If you've never worked with small electronic components and circuit-boards before you're probably screaming "no way, that's all way-too small for me!".

Well fortunately it's not as bad as you might think. We don't have to solder directly across the tiny resistor, we can solder to the copper tracks that it connects to.

To do this, we must first scrape off the solder-mask (that green paint) which covers the copper.

An important word of warning here: some of the components in your transmitter are sensitive to static electricity. If you have one, use an wrist-strap to earth yourself and use a conductive mat on which to work. If you don't have either of these things, Make sure you're not working on a carpeted floor and also avoid sitting on anything other than a plain wooden or metal stool. The friction of cotton clothing against plastic or nylon carpet/upholstery can generate very high voltages if you're not careful.

There are two places where you have to scratch away the green to expose the copper beneath. Use a sharp modelling knife but take care. In the picture above I've scraped the green off one position but it's not yet coated with solder.

In the above picture you can see that I've scraped and soldered the copper in both the places (circled) that we will be attaching our resistor.

You will almost certainly need to use a magnifier to identify these positions on your board and you will also need a soldering iron with a *very* fine point, plus some very thin rosin-cored solder. Don't use a big fat soldering iron and thick solder or you'll have problems.

If this bit looks too hard, you might want to find someone with decent eyesight and soldering skills to do it for you.

You need to tin the freshly scraped copper so that the resistor can be soldered in place so do this as quickly as possible and check afterwards that you haven't left any whiskers of solder that might short against neighboring components.

Use fresh solder and be quick -- those are the secrets here.

If your soldering iron is still hot then we can move on to the trickiest bit, installing the resistor.

If you found this information useful then please consider making a small donation towards the operation of this website.

Fresh Articles:

Privacy Policy

 

YouTube

 

Join the Forums!

Discussion Forums

 


The Blog

Updated: 20 Sep 2012
Here's a blog that will keep you informed just what's going on behind the scenes at RC Model Reviews and also tells you a little more about myself.

How compatible are 2.4GHz RC systems?

23 Mar 2010
How come there's no compatibility between different brands of transmitters and receivers? Why can't you use a cheap Chinese receiver with your Futaba FASST radio?

How to get a product reviewed here

4 Mar 2010
Since this has become a very frequently asked question, I've posted this simple guide to getting your product, or a product you're thinking of buying reviewed here at RCModelReviews

How servos work

Useful information on what's inside your servos and how they work.

The Good Oil

Important facts you should know about the oils that are used in our model engine fuels.

Heads-Up: 2.4GHz RC systems tested

How well do five different 2.4GHz systems stack up when hit by interference? The answers are here, with more to come.

Review: Bushnell's $80 Speed Gun

Yes it does work on model airplanes but there are some limitations involved with this bargain-basement radar speed gun.

Review: TowerPro MG995 servo

These are possibly the world's worst servos, find out exactly why you should avoid these boat-anchors at any cost.

Review: SK90

2.4GHz

It's cheap but can it really stack up against other glow engines in the .90 market? Find out in this review.

Review: iMax 9X 2.4GHz radio

How does this cheap 9-channel 2.4GHz radio system perform when compared to big-name systems that can cost two or three times as much? Have the Chinese finally developed a real contender with the iMax 9X?

2.4GHz Explained

Does all this 2.4GHz stuff have your head spinning? 2.4GHz

I've done my best to demystify the whole subject so if you feel like a bit of learning, this is the stuff for you!

Fix That Engine!

How can you tell when your engine needs new bearings? Who has the best prices and service on replacements? Just how do you change them? Get all that information and watch a great video tutorial anyone can follow.

Chinese Servos - How do they stack up?

Servos

The Chinese are now churning out a huge number of very reasonably priced no-name servos. But are they any good?

Baffled by batteries?

Batteries Nicad, NiMH, Li-Ion, LiPoly, LiFePO4, A123... the range of different battery types has never been greater. So how do they differ and what type should you be using?

Possibly useful: