After a few months of lightly tapping, it’s finally time to pound the drum about RC cars. Of course, there are countless styles of cars that you can get into. For now, I will focus on the type of cars that I recommended for beginners in the first article of this series: 2-wheel-drive, electric-powered, monster trucks.
Just like every other facet of RC, cars have benefited from recent advancements in radio, motor and battery technology. As I looked over my aging collection of well-used cars, I realized that none in my fleet reflected any of these modern advancements. So I took a two-pronged approach. I procured a new monster truck and I also modernized one of my older cars. Between this guide and a follow-up next week, I will cover my experiences with both projects.
The Case for RC Cars
I received my first RC car, a Kyosho Ultima, when I was in middle school. I really just wanted something to play with, but the Ultima turned out to be much more than a toy. Hobby-grade cars like the Ultima are meant to be worked on, and actually require some maintenance. As time went on, I found that I enjoyed wrenching on the car as much as driving it. It was also fascinating to make adjustments to the car and see how they affected its performance. That poor car endured countless modifications at my hand. Some ideas worked, but many didn’t. The Ultima always emerged relatively unscathed, and I got a little smarter each time. More than 25 years later, I still have most of the parts for that Ultima (in working order).
If a chemistry set is an ideal toy for aspiring chemists, then RC cars will cultivate the minds budding engineers.
If a chemistry set is an ideal toy for aspiring chemists, then RC cars will cultivate the minds budding engineers. Sure, they can teach you many lessons that carry over to full-size cars, but there is so much more. I learned about 2-stroke engines, electric motors, batteries, gearing, torque, and above all: the value of working with my hands. Countless times while working on space hardware in my professional career, I was able to apply a lesson learned from that Ultima. If, like me, you have a young tinkerer in your house, RC cars may be just the thing to let them explore relatively risk free.
Movin’ On Up
You may recall that I chose my recommended starter trucks (the Traxxas Stampede, ARRMA Granite and ECX Ruckus) because they are super tough and their big tires let them run just about anywhere. At the time, I did not have any experience with the Granite or the Ruckus, but I added them to the list because of their similarity to the Stampede. I am now the owner of a Ruckus and it has lived up to my expectations.
My motivation for getting a Ruckus was to have a truck that reflects current technology. Whereas all of my older cars and trucks use 75MHz radios, the Ruckus comes with a Spektrum brand 2.4GHz radio system. The previous article in this series talked about the advantages of 2.4GHz systems. Another modern feature in my Ruckus is a brushless motor. ECX offers versions of the Ruckus with either a brushed or brushless motor, but I was anxious to see the difference a brushless motor would make. I’ve used brushless motors in my airplanes for years, but this is my first car with one.
Brush-less is More
There are a few things in this world where not having a certain option is touted as a benefit. The first things that come to my mind are “seedless”, “strapless”, and of course, “brushless”. I’ll give a generic explanation of what brushes are and why omitting them is generally a good thing. For a more detailed explanation, Horizon Hobby has a very informative video on this topic.
Electric motors work by having a magnetic field (or several) with fixed polarity astride another magnetic field with alternating polarity. Working on the principle that opposite polarities attract and likes repel, the varying relationship between the two magnetic fields causes the motor shaft to spin. The fixed field is accomplished with simple magnets. The alternating field is created by passing electric current through coils of wire. By toggling the direction of the current in the coils (commutation), the polarity of the resulting magnetic field is also toggled.
In a brushed motor, commutation is a mechanical process. Voltage is provided to the motor through hard electrical contacts (the brushes) which are pushed by springs against a segmented contact (the commutator) on the spinning part of the motor (armature). As the commutator spins, the brushes contact different segments, which are wired to alternate the current in the coils. This process happens thousands of times per second.
Since commutation is self-contained, you do not need an external device to make brushed motors work. All you have to do is attach a DC energy source such as a battery, and the motor will spin. RC cars however, use an Electronic Speed Control (ESC) to regulate the input voltage to the motor and thus control how fast it spins. Think of an ESC as an electronic throttle.
A relatively powerful brushed motor might achieve efficiency values in the 50% range, while it is not uncommon for properly configured brushless motors to hover around 90% efficiency.
Brushless motors require specialized ESCs to operate. Here, commutation is an electronic process that is handled by the ESC. The motor itself is actually much simpler than a brushed motor because the brushes, springs and commutator are omitted. With those parts gone, we also lose a huge source of friction and electrical resistance…good riddance. The end result is that brushless motors are much more efficient than their brushed cousins.
A relatively powerful brushed motor might achieve efficiency values in the 50% range, while it is not uncommon for properly configured brushless motors to hover around 90% efficiency. For a given power source, going brushless could yield as much as 40% more output…that’s huge! That “bonus” energy could translate into more speed, quicker acceleration, and/or more run time.
Before we eat this presumed free lunch, let’s look at the drawbacks to brushless power. The most obvious difference is cost. In the case of the Ruckus, choosing the brushless option is a $120 upgrade over the base $170 truck…certainly a significant difference.
Another aspect to consider is that a brushless-powered truck may actually have too much power for beginners. Imagine learning to drive with a ’71 4-speed Hemi ‘Cuda. In fact, I was reluctant to allow my 11-year-old son to drive the Ruckus until he put in some time driving one of my slower cars. Right out of the box, the Ruckus was by far the fastest car in my inventory. While he quickly developed the skills to handle the Ruckus to my satisfaction, it still gets away from him at times. Being honest, it gets away from me on occasion! Of course, you can alter the gearing and the batteries to slow the truck down. However, if this will be your first truck, you probably are not yet confident making those types of changes.
Lastly, having so much power available can be hard on the vehicle. Beginners are going to crash into things. Having more power just means that they crash into them faster. Yes, the Ruckus and similar trucks are surprisingly tough, but there is a practical limit. And let’s not overlook the toughness of the things they may crash into (mailboxes, fenders, ankles, etc.).
To sum up the “brushed vs. brushless” argument, I’ll say that brushless is the better long-term investment. You’ll just need to be more diligent until you can handle the extra power with confidence. However, don’t feel that brushed motor vehicles are dogs. Until recently, cars with brushed motors were all I knew and I rarely felt that I needed more power. If you can’t have fun with a monster truck running a brushed motor, you probably should consider a different hobby.
Examining the Ruckus
The Ruckus is a pre-built truck, so it arrived in a sizeable box. All I had to do was install four AA batteries into the Spektrum transmitter and charge the truck’s battery with the included charger. The battery that comes with the Ruckus is a 7-cell, 2400mAh Nickel Metal-Hydride (NiMH) pack. The included charger plugs into an AC outlet and has a single button to operate it--easy! With a fixed charge rate of 2 amps (2000mA), it theoretically would take 72 minutes to charge a fully depleted pack (2400mAh/2000mA = 1.2 hour = 72 minutes). There are other factors that affect the actual charge time, but 72 minutes is a good ballpark estimate.
Like most RC cars, the Ruckus includes a polycarbonate (Lexan) body that is attached to the car with nylon posts and small body clips (aka hitch pins, hair pins, or R-clips). The body adds style to a car, but it also provides a great deal of protection. Polycarbonate is incredibly tough stuff, so think of the body as a sacrificial shield for the expensive guts within. With the body removed, you can see the inner workings of the truck. The plastic chassis has a channel in the middle for the battery. A T-shaped plastic strap covers the battery to keep it in place.
Probably the first things you’ll notice with the body removed are the long suspension arms and big oil-filled shocks. This long-travel suspension system (along with the big tires) is what makes monster trucks so versatile. They can run over or into just about anything without much damage
Looking behind the front wheels, you can see the steering mechanism. A servo operates the system of levers to articulate the steering. Most of the servo is hidden under the grey cover in the chassis, which protects it from the elements. The radio receiver is also in this compartment. You may notice that one of the steering arms is spring-loaded. This helps protect the gears inside of the servo from being damaged by sudden jolts to the front wheels.
Moving further back in the chassis, the brushless ESC is mounted above the battery compartment. Notice that there are three sets of wires coming from the ESC. One small gauge, 3-conductor wire leads up to the receiver. Three larger wires connect the ESC to the motor. The final pair of wires connects the battery to the ESC. Like most modern ESCs, the Tazer included with the Ruckus features a Battery Eliminator Circuit (BEC). This allows the main battery to power both the motor and the radio gear (which operates on only 5-6 volts).
At the rear of the Ruckus, is the red anodized brushless motor, which is bolted to the transmission. The output of the transmission is a set of universal drive shafts that reach out to the rear wheels. As you push the suspension up and down, you can see how the drive shafts telescope in and out to accommodate this movement. In many ways, this system is probably more complex and capable than the drive system on your full-size car. Then again, your full-size car isn’t meant to tear across open fields at full throttle and jump off of ramps three times its height.
Hidden inside of the transmission is a differential. Just as with full-size cars, the point of a differential is to allow the left and right wheels to turn at different speeds…as when going around a turn. It is a vital piece of hardware. The Ruckus includes a gear-type differential, which effectively sends all of the motor’s power to the wheel with the least traction. Most full-size cars also have gear differentials. Did you ever notice how most tracks left on the street by burnouts are just one streak instead of two? A gear differential is the reason why.
Having power to just one wheel may sound like a bad thing, but it usually isn’t…at least not with backyard bashers. Let’s say you take a corner too hard and the truck tips up on two wheels. The rear tire that came off of the ground is now getting all of the power while the tire on the ground is coasting. This is just like letting off of the throttle and will usually prevent the truck from getting into an even worse attitude (although flips and roll-overs are to be expected…and enjoyed).
Race cars will typically have a ball differential instead of a gear differential. A ball differential is equivalent to a limited-slip differential in full-size cars. The main difference being that you can adjust the tension in the differential so that it distributes the power more evenly between the right and left…even if there is a difference in traction. Maybe Marisa Tomei can explain it better. After all, she earned an Oscar for explaining differentials.
With the higher efficiency of the brushless motor, I was getting seven or eight minutes of hard running from each charge.
When I first drove the Ruckus, I was startled by several things. First of all was the speed. It is considerably faster than any monster truck I’ve seen with a stock brushed motor. I was also surprised by how well it coasts. Without the drag of brushes on a commutator acting as a brake, the Ruckus goes surprisingly far after you let off of the throttle. The ESC provides electronic brakes (and reverse) if you need to stop in a hurry. The last big thing I noticed was how long it ran. I’ve had fast cars with brushed motors before, but the cost of that speed is run time. With the higher efficiency of the brushless motor, I was getting seven or eight minutes of hard running from each charge. Higher capacity batteries (more mAh ) are readily available and would stretch the run time even greater.
The tires that come with the ruckus are a compromise between on-road and off-road traction. They do really well on my paved street (often sending pebbles zooming in all directions) and they hook up reasonably well on the hard-packed dirt fields around my neighborhood. All in all, I’m comfortable taking it just about anywhere.
Between me and my son, we’ve jumped, cartwheeled, rolled, skidded, and generally abused the Ruckus. We haven’t broken any parts yet, but I’m sure that day will come. When it does, that will be a chance for us to fix it together. Having the Ruckus and being able to share it with my son has reignited my excitement for monster trucks.
This guide will continue next week. In the next post, I will talk about the older RC car that I recently modernized. I will also discuss battery options and why I prefer the types of batteries that I use.
Photos courtesy Terry Dunn