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All of the products reviewed here have been bought with my own money and nobody pays me for the time I spend writing these articles.

If you find any of this stuff useful and/or would like to see RCModelReviews continue to publish material like this then please consider making a small donation towards the operation of the site.

 

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.

 

How do RC Servos Work?

THE BASICS OF RC SERVO OPERATION

RC servos come in an amazing range of sizes, speeds, strengths, weights, shapes colours and varieties but they all work on the same basic principles.

The job of an RC servo is to position its output arm to a position that exactly corresponds with the movement of the corresponding stick, switch or slider on the transmitter. What's more, it should do this as quickly as possible and provide a high level of accuracy regardless of the effects of aerodynamic loads or other factors.

Most servos, regardless of brand or type, consist of several main parts:

  • The mechanics. These are the gears and the case.
  • The motor. This provides the motive force to drive the output arm
  • The feedback pot. This allows the servo to measure the actual position of the output arm
  • The amplifier. This is the electronics that hook all those other bits together to make it work

Now let's take a look at those bits in more detail...

The Mechanics

Most RC servos have a plastic case, the top section of which contains a set of gears that can be either plastic or metal. The strength and rigidity of these mechanics play a significant role in determining the robustness and weight of the servo, with metal gears usually being significantly stronger (and heavier) than plastic.

The choice of gear material depends very much on the type and size of model in which the servo will be used. Generally speaking, plastic gears are only suited to models up to 5-6 lbs in weight.

Bearings

The output shaft and gear of a servo experiences significant side-loading during its operation and this means it needs some kind of support to stop it from moving out of mesh with the rest of the gears.

Cheap servos tend to simply rely on the plastic shaft rubbing against the plastic of the case and for small/slow models this isn't too much of a problem. These servos are often caleed 'bushed" and, because there has to be some clearance between the shaft and the case, usually demonstrate some side-to-side slop in the output shaft, which can appear as a degree of rocking up and down of the output arm.

However, precision and hi-torque servos really do benefit from the addition of a ball-bearing or two on the output shaft. This significantly reduces the friction, virtually eliminates wear and means there should be no slop at all in the output shaft.

Good servos have a single bearing (usually in the top of the case) while even better servos have two bearings -- one in the case and one at the bottom of the output shaft.

The Motor

There are basically three different types of motors used in model servos, the most common of which is a brushed motor with three or five-pole armature. The benefit of these motors is their low cost and robustness. The downside is that, because of their heavy iron armature, they tend to respond more slowly.

The second most common type is the coreless motor which, as the name suggests, does not have an iron-cored armature but instead has a lightweight plastic armature on which the field windings are formed. This has the advantage of being able to start and stop far more quickly (due to its low mass) and also produce more torque -- since the diameter of the windings is much greater than with a cored motor.

Because they cost more to manufacture, coreless motors are usually only found in expensive servos designed for very fast transit times (such as used on heli tailrotors).

The final motor type is the brushless variety being offered in just a few servo models from big-names like Futaba. The brushless motor can be designed to provide very high levels of torque and has no brushes to wear out. Servos with brushless motors are few and far-between right now though because of the costs involved.

Next Page: Pots and Amplifiers

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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?

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