Terry walks us through an RC car upgrade, and discusses his choice of battery technology for RC cars. Surprisingly, Lithium Polymer batteries may not be the best bet for most users.

In my previous article, I talked about my experience with the ECX Ruckus monster truck and how it brought me back up to speed on current RC technology. One of the challenges that I faced with the Ruckus was that I thought it was too fast for my son to handle. He spent some time driving a slower car and soon had the skills necessary for the Ruckus. That gateway car was a Duratrax Evader BX buggy (which is no longer produced). It was a perfect starter car for him. It was slow enough to keep him out of too much trouble while he honed his driving reflexes. Yet, it was fast enough to get him excited about the hobby, challenge him on occasion, and satisfy the dirt-slinging ambitions of a pre-teen. Once he became comfortable with the Ruckus, however, it was clear that we needed another fast vehicle to keep both of us entertained.

The modified Evader is slightly smaller than the Ruckus, but its performance is on par. Both are powerful and fast.

The simplest route would have been to install a more powerful brushed motor and a new set of high-traction tires on the Evader. After briefly considering that option, I decided to modernize the buggy completely. I added ball bearings, a 2.4GHz radio, a brushless motor system and a quasi-monster truck makeover. Let's walk through that upgrade.

Many RC cars include bronze bushings on their moving parts rather than ball bearings. They work okay for beginners, but they eventually wear down and the tolerances between moving parts get loose. Then things get sloppy, noisy, and draggy. Upgrading to ball bearings reduces quite a bit of friction, but also maintains the same tolerances throughout the life of the car. I purchased a set of ball bearings for the Evader and guided my son through the steps to install them.

Ball bearings reduce friction between rotating parts, but they also maintain consistent tolerances over time. The bushings included with many starter cars eventually become sloppy and wear out.

To install the bearings, we had to disassemble the whole transmission. This was a good opportunity for my son to get a look inside the gearbox and get a feel for what it does and how it works. There are also bearings for the rear axles and front wheels. It probably took less about an hour to do the whole thing.

The radio that came with the Evader worked just fine. However, I wanted not only a 2.4 GHz radio, but something with more adjustability to help control the power I expected out of the souped-up Evader. I ended up with a Futaba 4PLS 4-channel radio system. What a radio! I’ll cover its range of features in the upcoming computer radio overview. But I can say that this is by far the nicest surface radio I’ve ever owned and probably the last one I’ll ever need.

I removed the receiver that was in the car and replaced it with the Futaba receiver. It is held in place with adhesive-backed Velcro. The Evader has a flexible tube that is mounted vertically to elevate the receiver antenna. Since the antenna on the 2.4GHz receiver is considerably shorter than the antenna on the stock 27MHz receiver, I shortened this tube accordingly.

I upgraded the Evader’s stock radio with a Futaba 4PLS 4-channel radio. It is a 2.4GHz radio with built-in telemetry features.

Duratrax sells a brushless upgrade kit that is intended for 2-wheel drive buggies and trucks. Since motor mounts are pretty much universal across all hobby grade cars, this was a bolt-in replacement. I removed the stock motor and ESC from the car and the brushless components filled in the empty space. As with the receiver, the ESC is held in place with Velcro.

The only remaining step was to remove the pinion gear from the old motor and add it to the new one. The motor position is adjustable to accommodate different gears and to allow adjustment of the gear mesh between the pinion and its mating spur gear. I set the mesh by sandwiching a strip of paper between the gears.

Inserting a piece of paper between the gears is an effective way to set the proper mesh when installing a motor. In this photo, I am installing a Duratrax brushless motor on the Evader. Note the small setscrew on the pinion gear…they strip easily.

Sometimes it is necessary to change gearing when you change motors because of each motor’s specific performance characteristics. However, I was confident that the stock gearing would not overstress the brushless motor. The only question that remained in my mind was whether the stock transmission gears would hold up to the added power of the new motor. So far, they are working fine.

At this point, it is worth pointing out the value of having quality tools when working on RC cars. Many times (as with pinion gears) you will need to remove small setscrews (typically 3mm) that have been tightened as much as possible. Trying to remove these setscrews with a hex wrench (aka Allen wrench) that is the wrong size or even slightly worn will very likely strip the drive cup of the setscrew. Then you are in for some real frustration! So keep metric and standard wrenches on hand and toss them when they start to become worn. Ball-end hex wrenches wear out and strip screws easily, so I generally avoid them.

This photo illustrates the overall layout of the Evader after being modified to a brushless-powered truck.

It is also a good idea to have a few Japanese Industrial Standard (JIS) screwdrivers on hand. Many RC cars use JIS screws. They look much like Phillips screws, but the drive cups are slightly different. Using a Phillips screwdriver on JIS screws will cause premature wear on the drive cups and eventually strip them. Phillips screws, however, are quite tolerant of using JIS drivers. JIS tools tend to be rather expensive, but they are a worthwhile investment.

Test Drive

After the bearings, new radio and new motor were installed, the Evader looked pretty much like it did before. It was, in fact, a very different machine. My son and I test drove it and found that it was now much faster-nearly as fast as the Ruckus. However, the upgraded Evader had a strong tendency to spin out at every turn. There are numerous suspension adjustments that can be made to fine-tune steering response, but I think tires are the best place to start attacking traction problems.

I was still using the Evader’s stock knobby tires which were several years old. Although they didn’t look very worn, they had hardened over time. Just as with full-size cars, soft tires are sticky tires. So, I set out to find some new tires that would be softer and also have a tread pattern that would work reasonably well on dirt or paved surfaces.

The Duratrax Evader BX served as an ideal starter car for my son. It was fast enough to hold his interest, but tame enough that he could control it. Best of all, it readily accepted upgrades to improve its performance.

Tires are typically glued to the wheels, so I couldn’t just pull the old tires off of the stock wheels (not easily anyway). I had to look for new wheels and tires for the Evader. I can’t even begin to tell you how many choices there are when it comes to wheels and tires. They are made to suit any application you can think of. You can even get paddle tires to run your car in loose sand or skim it across open water! For a 1/10 scale buggy like the Evader, you can expect to spend at least $40-$50 on a full set of tires.

As I was searching for tires on the Tower Hobbies website (where I bought the Evader), I came across a set of four all-terrain tires for just $10.99. These tires are stock equipment on the Evader EXT 2.4, a not-so-distant cousin of my Evader BX. I also found the matching wheel set for only $9.99. Just glancing at photos of the EXT 2.4, I could see that it shares the same core components as my BX. With the allure of a cheap set of tires, I ordered the EXT wheels and tires with the assumption that I could use them on my BX. For the most part, I was right. I did have to install longer front axles and steering knuckles from the EXT to make the front tires work. But even with those added parts, I was ahead of the game cost-wise.

Although cost was a deciding factor, the main reason I wanted the tires from the Evader EXT was to make my Evader a little bit more versatile. The larger front and rear tires would give better footing on grass and rough ground than the smaller buggy tires (which are better suited to well-groomed dirt racetracks). Even with the bigger tires, I could have kept the original buggy body on the Evader. Keeping that form-fitting cover in place would help keep out a lot of the detritus that inevitably permeates into all parts of the car. The only problem is that it would have looked a little odd (oh vanity!).

I found a prepainted monster truck body on sale for about $20 (a very good deal), so I picked that up as well. Because this body wasn’t specifically made for the Evader or any of its variants, I knew that I would have to find my own way to mount it to the car. I bought an EXT front body mount and I was able to fit it on the BX with a homemade adapter plate made from a scrap circuit board. The rear of the body is held in place with Velcro.

I adapted the front body mount from the Evader EXT by fabricating a simple adapter plate from scrap circuit board.

When I was done, my Evader was a hybrid of the BX buggy and EXT 2.4 truck models. After installing the larger rear tires (which is equivalent to changing gears), it now keeps pace with the Ruckus. The softer tires also alleviated much of the spin-out problem. I plan to tweak it further with suspension adjustments.

The Evader upgrade was a very straightforward project and just a hint of the customization that is possible with RC cars. My goal was also to illustrate that older cars need not be discarded. In many cases, they can be upgraded to take advantage of new technology. My son and I now have a pair of cars with similar performance that we can enjoy together on the street or down at the park.

The completed truck conversion of the Evader BX looks very different from the original buggy style. This radical change only required a few component swaps. Such adaptability is common in the RC car world.

Battery Choices

Batteries have progressed a long way during the past decade--a very long way. Lithium-Polymer (LiPo) batteries matured to the point where they can finally handle the extremely high discharge rates that hobbyists demand. These batteries are not only lighter, but they have much higher energy densities than Nickel-Cadmium (NiCad) and Nickel Metal Hydride (NiMH) cells. Along with brushless motors, LiPo batteries are responsible for making ridiculous performance available to the RC car masses. Cars with out-of-the-box speeds of 50+ mph are not uncommon, with some cars being capable of more than 100mph!

The performance advantages of LiPo technology come with a tradeoff--they are intolerant of abuse and mishandling.

With all of the performance available using LiPo batteries, you may be surprised that I’m going to suggest that you ignore them for now. The performance advantages of LiPo technology come with a tradeoff. LiPos are intolerant of abuse and mishandling. The consequences of a scorned LiPo may be as slight as a premature death for the battery pack. A more severe reaction would be fire. Yes, cars (RC and full-scale) and homes have burned to the ground because an angry LiPo caught spewed flames.

Don’t think that LiPos are akin to live hand grenades - it’s not that severe. They do however require respect, diligence, and knowledge of their proper care and feeding. A common rookie mistake is leaving a battery plugged into your model and simply turning off the switch to deactivate it. If left overnight in this condition, housekeeping current demanded by the ESC could drain the battery below its safe discharge voltage…leaving you with an irreparable battery. As you get more familiar with the quirks of RC equipment, you may decide that you’re ready for the jump to LiPos. Then again, maybe you won’t. I have a workshop full of LiPo batteries that I use in my RC aircraft, but I still have not found a compelling reason to use them in my RC cars.

Here are examples of three different battery chemistries used in RC. The top battery is a 7-cell (8.4V nominal) 2400mAh NiMH pack. Below it is a 2-cell (7.4V nominal) 2100mAh LiPo battery. The bottom battery is a 2-cell (6.6V nominal) 2300mAh A123.

As the advancement of LiPo technology has stolen the RC spotlight for several years, NiMH batteries have quietly seen similar leaps in capability. For instance, the battery that came with my ECX Ruckus truck is a 7-cell NiMH with 2400mAh capacity. Other 7-cell NiMH packs are available in the same physical size (classified as Sub-C, as compared to AA, D, et al) but with more than 5000mAh capacity. Theoretically, such a battery would provide the same performance, but with more than twice the run time. The primary difference between the batteries is cost.

Whereas LiPos have some unintuitive requirements, NiMH cells can tolerate users with layman-level battery knowledge.

Of course, you can also do stupid things with NiMH batteries that would cause them to perish or catch fire. However, such things usually require malicious intent. Whereas LiPos have some unintuitive requirements, NiMH cells can tolerate users with layman-level battery knowledge. For that reason, I suggest that beginners start out with NiMH batteries. NiCad batteries are also a valid option, but they are not as prevalent as they once were.

The batteries that I most often use in my cars are called A123 cells. Specifically, their chemistry is Lithium-Nanophoshate (LiFePO4). A123 Systems is the company that brought this battery technology to market several years back. In short, A123 batteries are a compromise between the energy density of LiPo cells with the robustness of NiMH cells. There are other LiFe batteries on the market, but as I write this, only the A123 cells have the discharge rates needed for powering amp-hungry electric motors. Along with A123 cells, the other LiFe batteries are often used to power the onboard radio equipment for gas/nitro-powered cars and larger airplane models (where the required discharge rate is much, much lower).

A123 cells are my preferred battery type for RC cars. Here, we have a triad of different configurations: a side by side 2-cell pack (bottom), and end-to-end 2-cell pack (top left), and a factory-assembled 3-cell pyramid pack.

Most often, I use a 2-cell A123 pack in my cars. The fully charged voltage is 7.2v, which is roughly equivalent to a 6-cell NiMH battery. Each cylindrical cell is about the same diameter of a standard C-sise battery, but the A123 is roughly .6 inches longer. The original version of this cell has a 2300mAh capacity, but newer models (which I have not yet used) are 2500mAh. Compared to an average 6-cell 2500mAh NiMH battery, the 2-cell A123 has slightly less voltage and capacity, but only 45% of the mass (5.5oz vs. 12oz).

A123 batteries are a compromise between the energy density of LiPo cells with the robustness of NiMH cells.

Without getting mired in the discharge characteristics of the different cells, I will say that I detect very little difference performance-wise between the A123 and the stock NiMH in my Ruckus. If I didn’t know which battery was installed, I couldn’t tell the difference by driving. The only issue I run into with A123s is their form-factor. Side by side packs are often too wide to fit in stock battery compartments (the Evader is a notable exception). End to end packs have a small girth that may not mesh with the car’s battery retention method. I’ve always been able to figure out a workable solution with Velcro in strap form (Ruckus) and/or the adhesive-backed variety (Evader).

I think that I may be somewhat alone in my continued usage of A123 batteries. If you care to join me, you can buy factory assembled A123 packs from numerous vendors. Those of you comfortable with heavy soldering can save a few bucks by assembling your own packs from individual cells. In fact, most of my A123 packs were built with cells scavenged from certain DeWalt cordless drill batteries. Also note that A123 cells require specific chargers. Hooking one to a NiMH charger would be a bad idea. Many new RC chargers can handle multiple battery chemistries, including A123.

Coming Up

This concludes my RC car overview. I hope you now have a better idea of what is available off-the-shelf, as well as the potential for customization and experimentation. In reality, what I’ve shown here is a very narrow snapshot of the hobby. I’ll revisit the car topic periodically to touch on new developments or interesting projects. Next time, I'll assume the role of the Fun Police and take a critical look at Norm and Will’s testing of the DJI Phantom 2 Vision + quadrotor. They committed a few common rookie mistakes that are worth pointing out!