The ins and outs of chassis materials
The chassis is one of the most important parts of your RC car; it's the backbone to which all other parts attach in one way or another. The material that makes up the chassis can literally make or break it, so choosing the right material for what you are doing is critical. The most common materials on modern RC cars are molded plastic, molded fiber-reinforced plastic, aluminum and woven carbon fiber. Each of these materials has their own strengths and weaknesses, so it is important to choose the right one for each application. A few of the important considerations are stiffness, weight, durability, cost and of course, availability.
WHY CHASSIS FLEX EFFECTS BALANCE
There is a lot of buzz in the RC world about tuned flex chassis, so it is important to know how chassis flex effects the car's handling. The front to rear suspension stiffness, along with chassis flex, determines how weight is distributed to each tire during cornering. The suspension stiffness is dependent on the springs, shocks, sway bars and suspension geometry. If the front stiffness is greater than the rear, the front will lose grip first and the car will have under steer and vice versa. This weight transfer effect is what allows us to tune the corner balance of our cars. If the chassis is too flexible, it will twist and the weight will not transfer to the tires predictably. The amount of twist will change as the cornering loads go up, so the car will handle differently during high speed cornering than it will during low speed cornering, which could be desirable in certain situations. The downside to chassis flex is that suspension adjustments become less effective than with a stiff chassis. So changing the spring rate one step with a stiff chassis, might require a two step change with a softer chassis.
Plastic-molded chassis like this one for the Team Associated SC10 are soft and allow for some chassis flex. They are also less expensive than the rest offered.
Injection-molded plastic is durable and inexpensive to manufacture, so it is the material of choice for most RTR kits. Since it is injection molded, complex shapes can be designed, which cuts down on the part count of the kit. Chassis are often tub shaped with ribs for extra stiffness, but require the most material to provide durability because of its low strength. In general, plastic chassis are the softest and allow the most flex, but are the most cost effective.
MOLDED FIBER-REINFORCED PLASTIC
By looking at this chassis, you'd never know that it's fiber-reinforced. This Team Associated T4 chassis is a lightweight and stiff option, but it can be brittle in the cold.
Fiber-reinforced plastic has strands of fiberglass or carbon fiber mixed in with the plastic resin. This material looks very similar to ordinary plastic because it can be injection molded into the same shapes; however, it is much stronger, lighter and stiffer. It is usually seen as an upgrade to plastic; however, there are times when you want the chassis to have some flex. Even though fiber-reinforced plastic is stronger than regular plastic, it will not bend as far without breaking. Low temperatures make the problem even worse because it will make the material brittle, so take that into consideration when using this type of chassis during the winter months.
Aluminum plate chassis are most common and can help dissipate heat from nitro engines. This Team Associated RC8.2 chassis has pockets machined out to reduce weight.
Aluminum is another popular chassis material due to its durability and rigidity. It is lightweight compared to other metals, however, it is still heavier than plastic or carbon fiber. Aluminum is not very expensive in sheet form, but machined chassis and chassis components can be more costly. The finish of machined aluminum is attractive, and it can be anodized different colors for a sharp-looking package. Pockets can be machined into key areas to help reduce weight and add some chassis flex. Aluminum can act as a heat sink so it is usually the material of choice for nitro cars; however, it is too heavy for most electric applications.
Stiffer is not always better in the RC world. A stiff chassis gives you more control over suspension adjustments and will react quicker whereas a soft chassis will be slower to react and less responsive to changes and driver inputs. However, a softer chassis is more forgiving to drive. By reacting a little slower, a chassis with some flex can be easier to control. This can help lap times and can be more fun for bashing.
WOVEN CARBON FIBER
Carbon-fiber plate chassis are very common on touring cars and some 4WD off-road buggies like the Team Associated B44.1. They can be tuned by adding or removing screws from the bottom and top plates.
Woven carbon fiber is composed of layers of carbon fabric mixed with epoxy resin. It is light and stiff which makes it a popular choice for racing. It can be molded into complex shapes, but most carbon-fiber RC chassis are cut out of a flat sheet. Carbon-fiber chassis are often composed of two layers connected by aluminum standoffs. This design is often used on touring cars and some pan cars. Double-decker chassis designs allow the stiffness to be tuned by adding or removing screws in the top plate. The disadvantages of a carbon-fiber chassis are cost and durability. A carbon-fiber chassis will not stand up well against a crash, particularly if one of the edges is impacted. This tends to cause the laminated layers to separate, which can sometimes be hard to detect.
A little flex can also be helpful when driving on a rough track. When the tire hits a high speed bump, the oil in the shock will try to pack up which hurts grip. A chassis with a little bit of flex will let the chassis absorb those high-speed bumps but still be firm enough to be responsive to steering input and setup changes. In general, a stiffer chassis works better for smooth, high-traction tracks, and softer chassis works better on rough tracks and may still be all right for less technical tracks. In the end, it comes down to driver preference.
There are many aftermarket chassis available, so understanding the differences between materials used to create them can save you from buying something that doesn't work well for your application. As new materials and production techniques become available, so will RC products. If you research what materials are used and their properties, you will be sure to stay ahead of the game.