Mini 4WD is any miniature model within the mini scale of between 1/20 (1:20) to 1/48 (1:48) Scale (ratio). From 1980 to 2018, the term is popularized predominantly (99%) by a 1/32 (1:32) scaled, AA battery powered plastic model race car without remote control. All four (4) wheels are direct-drive, thus “4WD” for 4-wheel drive, as opposed to “AWD” or All-wheel drive. This particular type of Mini 4WD uses horizontal side rollers to guide the vehicle along the vertical walls of the un-banked track for steering, providing speeds from 14 to 65 km/H (9 to 40 mph) on the track. At scale, (multiplied by 32), 1:1 speed represents 126 to 2,080 km/H or 288 to 1,280 mph.
Mini 4WD Design
In a standard 4WD design, the separate four wheels are allowed to rotate at different speeds through the use of differentials. This is important for cornering to eliminate binding. In a Mini 4WD, this is not a standard design and is only achieved through optional one-way wheel sets. Thus, the standard Mini 4WD utilizes a direct drive to all 4 wheels even around corners. Chassis’ are designed to hold the motor and batteries in differing arrangements. There are sideways motors positioned in the rear. There are sideways motors positions in the front. There are in-line motors positioned in the middle. Rear and Front position motor designs position batteries side by side in the front or rear of the motor placement. Middle position motor designs position the batteries straddling either side of the motor. Rear and front position motor designs utilize a propeller rod extending from the main motor gear box that drives both the front and rear axles. Middle position motor design powers both the front and back wheels through separate gear boxes eliminating the need for such a propeller rod.
Chassis’ are designed with front bumpers, optional side and rear bumpers designed to hold guide rollers that interact with the track’s 58mm high walls.
The body is designed from hard plastic or soft, transparent Polycarbonate, known by the trademarked names Lexan, for special or limited editions, which attaches with a catch-type lock at the back of the car, distinguishes one model from another.
There are three specifications that characterize all motors: RPM, torque, and power-consumption. RPM is the speed the motor provides, and the torque its strength. Higher the RPM means higher maximum speed ; Higher torque gives more acceleration and allows the car to better withstand the difficulties of climbing slope or running through turns.
The motor is one of the important components a mini 4WD racer need to make the car move, There are two types of motors: single-shaft or double-shaft motors.
Different types of gears have different ratios of rotation of the motor and the wheel, and they include (3.5:1), (3:7:1), (4:1), (4.2:1), (5:1), and “Special” (ratio varies but are usually 6.4:1). The higher the ratio, the better the acceleration rate and torque; the lower the ratio, the better the maximum speed.
Tires and Wheels
It is recommended that, among the different wheels available, the compatible ones must maintain the same size as those from the assembly packet. The smaller the diameter of the wheel, the more stable it is, as the car’s center of gravity is lowered. Although one can easily assume that a larger wheel suits a faster car the best, this is not at all the case. Large wheels are for cars with high gear ratio (i.e. “5:1”) and weak motor; small wheels are for cars with low gear ratio and strong motor. Wider wheels allow for more stability but suffer from friction, and thus, the loss of speed;thinner wheels are intended for speed, but the car could be susceptible to flipping off the track.
There are four types of different wheels: normal plastic, one-way, aluminum, and lock-nut. Normal plastic wheels are fine, but they are not adequate for really fast cars. They become loose after disconnecting them from the axle several times. Additionally, they create drag when the car going through turns as the axle locks the two wheels at same speed, since the outer wheel must cover more distance than the inner wheel (relatively to the turn of the course). One-way wheels allow either side to roll faster than the other when turning, and minimize the speed loss in turns. Aluminum wheels are very light, sturdy, and best for speed. Some aluminum wheels have preventive measures against loosening with the axle. However, lock-nut wheels are the best in preventing the cars from losing the wheels during a run.
There are four types of tires: rubber, sponge, reston, and semi-pneumatic. Rubber tires come as standard with the Mini 4WD, and, although it has good grip, it is heavy and is susceptible to slipping on wet surfaces. The alternate solution to the rubber tire are the reston or sponge tires, which are very light, have good grip, and are better suited for rainy days. Yet, these get dirty easily, and they tend to exhaust the motor.
Bumpers are usually found at the opposite ends of the mini 4WD. Upgrading the bumper becomes a necessity as the mini 4WD is modified to run faster than what the stock kit usually runs. The faster the car, the more the car needs down force to counter the decrease in stability. The stock chassis+bumper combination does have a tendency to bend, causing the rollers to run at angles and may make the mini 4WD fly off the course. Aluminum, fiberglass, or carbon fiber plates are usually installed as after-market upgrades to prevent this from occurring. Another possible upgrade are the screws that keep the rollers to the bumper. Only Tamiya offers aluminum plates as upgrades.
Most after-market upgrade plates are usually wider than the stock bumper, and they facilitate the installation of “side extension” plates that make the front profile of the mini 4WD even wider.
Roller is the wheel that rests on either end of the mini car’s bumper and glides against the wall of the course. This allows the car to change direction and maintain stability. Conventional roller will do fine on a car with average speed, but, on a much faster car, aluminum or ball-bearing rollers must be purchased to acquire additional downforce and stability. These rollers do not tilt in angle as the conventional plastic rollers, and, therefore, have better chance in preventing the car from flinging off the course. Ball-bearing rollers have small metal balls around the internal ring, on which the roller spins, in order to minimize friction. Some rollers consist of two rollers on a pole -one at the base and other at the top-, so that they may offer the best stability. There are three types of roller arrangements. The first one is in which all rollers are same-sized, and this is for straight courses. The second arrangement, in which larger rollers are stationed in the front, is less stable when running through corners but minimizes speed losses; the third arrangement, in which smaller rollers are put in the front, is more stable when running through corners but the car is more susceptible to speed losses as it pushes into the wall.